ML13308A811

Review of Seismic Re-evaluation of Reactor Bldg & Balance of Plant Structures of San Onofre Nuclear Generating Station,Unit 1

ML13308A811
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Site:	San Onofre
Issue date:	09/30/1982
From:	Tsai N NCT ENGINEERING, INC.
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Enclosure 4 REVIEW OF SEISMIC REEVALUATION OF THE REACTOR BUILDING AND BALANCE OF PLANT STRUCTURES OF THE SAN ONOFRE NUCLEAR GENERATING STATION UNIT 1 prepared for Lawrence Livermore National Laboratory September, 1982 by N. C. Tsai NCT ENGINEERING, INC.

s3o50 MT. DALOBLVD P0.

BOx 937 LAFAYETTE. CA9ASA9 8212010036 821126 PDR ADOCK 05000206 PDR

CONTENTS

1.

INTRODUCTION 1-1

2.

REACTOR BUILDING STRUCTURES 2-1 2.1 Description of Structures 2-1 2.2 Seismic Analysis. Models 2-4 2.2.1 Containment Sphere Model 2-5 2.2.2 Reactor Building Model 2-7 2.2.3 Reduced Structure Model for NSSS Analysis 2-8 2.2.4 Effect of Sphere Enclosure Building 2-9 2.3 Method of Seismic Analysis 2-10 2.4 Structural Overturning 2-11 2.5 Structural Evaluation 2-11 2.5.1 Containment Sphere 2-11 2.5.2 Reactor Building 2-14 2.5.3 Concrete Foundation 2-16

3.

CIRCULATING WATER SYSTEM INTAKE STRUCTURE 3-1 3.1 Description of Structure 3-1 3.2 Analysis of Structure 3-1 3.3 Results of Seismic Reevaluation 3-3 3.4 Evaluation 3-3

4.

REACTOR AUXILIARY BUILDING 4-1 4.1 Description of Structure 4-1 4.2 Analysis of Structure 4-1 4.3 Results of Seismic Reevaluation 4-2 4.4 Evaluation 4-3

5.

VENTILATION EQUIPMENT BUILDING 5-1 5.1 Description of Structure 5-1 5.2 Analysis of Structure 5-1 5.3 Results of Seismic Reevaluation 5-2 5.4 Evaluation 5-2

6.

SEAWALL 6-1 6.1 Description of Structure 6-1 6.2 Analysis of Structure 6-1 6.3 Results of Seismic Reevaluation 6-2 6.4 Evaluation 6-2

7.

CONTROL AND ADMINISTRATION BUILDING 7-1 7.1 Description of Structure 7-1 7.2 Analysis of Structure 7-1

7.3 Results of Seismic Reevaluation 7-3 7.4.

Evaluation 7-4

8.

TURBINE BUILDING AND TURBINE GENERATOR PEDESTAL 8-1 8.1 Description of Structure 8-1 8.2 Analysis of Structure 8-2 8.3 Results of Seismic Reevaluation 8-4 8.4 Evaluation 8-9

9.

FIELD ERECTED TANKS AND BURIED PIPING 9-1 9.1 Method and Criteria for Reevaluation of Field Erected Tanks 9-1 9.2 Method for Reevaluation of Buried Piping 9-2

10.

GROUND MOTION TIME HISTORY AND IN-STRUCTURE RESPONSE SPECTRA 10-1 10.1 Ground Motion Time History 10-1 10.2 In-Structure Response Spectra 10-1

11.

SIGNIFICANCE OF UP TO TEN PERCENT DBE SPECTRUM EXCEEDANCE 11-1

12.

SUMMARY

AND CONCLUSIONS 12-1

13.

REFERENCES 13-1 Appendix A Questionnaire for the July, 1982 SONGS 1 Review Meeting A-1 Appendix B Resolutions to the Appendix A Questionnaire B-1 Appendix C Review Summary of the SEP Seismic Reevaluation Program Plan

1.

INTRODUCTION The San Onofre Nuclear Generating, Station Unit 1 (SONGS 1) was required by an August 4, 1980 letter- from the U.S. Nuclear Regulatory Commission (NRC) to perform a seismic reevaluation as part of the Systematic Evaluation, Program (SEP).

Earlier, the Southern California Edison Company (SCE) and the San Diego Gas & Electric Company (SDGE) had conducted a seismic reevaluation of the containment sphere, reactor building, reactor coolant system and concrete foundation at SONGS 1 for a postulated 2/3 g DBE seismic event (characterized by the Housner spectra) during normal operation.

Results of the investigation and the resultant modifications were previously reported in "

San Onofre Nuclear Generating Station Unit 1 Seismic Reevaluation and Modification," NRC Docket 50-206, April 29, 1977 (Ref. 1). Subsequent reviews by the,NRC staff and consultants identified several open items during a November 14, 1979 meeting (Ref. 2).

SCE addressed the open items in a written response to NRC on April 11, 1980 (Ref. 3).

Subsequently, SCE completed the seismic reevaluation of the balance of plant (BOP) structures which also included the computation of the in-structure response spectra.

The results were submitted to the NRC via the following correspondances:

o SCE letter to NRC, December 8, 1981 (Ref. 4) - Circulating water system intake structure, reactor auxiliary building, ventilation building, and seawall.

o SCE letter to NRC, February 9, 1982 (Ref.5) - Control and administration building.

o SCE letter to NRC, April 30, 1982 (Ref. 6) - Turbine building and turbine generator pedestal.

1 -1

0 o

SCE letter to NRC, April 30, 1982 (Ref. 18) - Methodology for field erected tanks.

o Reference 7 - Masonry walls.

o Reference 8 - Fuel storage building.

o SEC letter. to NRC, July 9, 1982 (Ref. 9) - Input DBE ground motion time histories and in-structure response spectra.

We have reviewed the information contained in Refs. 1 to 9 with respect to the seismic reevaluation of the (1),reactor building structures, (2) circulating water system intake structure, (3) reactor auxiliary building, (4) ventilation equipment building, (5) seawall, (6) control and administration building, (7) turbine building and turbine generator pedestal, (8) field erected tanks and buried piping, and (9) DBE input time histories and in-structure response spectra.

In addition to the above, we have reviewed the BOP structure seismic reevaluation program plan (Ref. 10). We have also conducted a limited review of the seismic reevaluation of the fuel storage building and.other BOP structure masonry walls although the NRC staff has the main responsibility for the complete review. All of the above mentioned structures are illustrated in the key plan, Figure 1.1.

The following documents formed the basis of our review:

NUREG/CR-0098 (Ref.11), the SSRT guideline for SEP soil-structure interaction review (Ref. 12), the Standard Review Plan (SRP), and the pertinent NRC regulatory guides.

The first two documents prevail wherever they contradict the SRP and the NRC regulatory guides.

This is to recognize the fact that the SONGS 1 plant was designed and built prior to the publication of the current design methodology and criteria. In addition, the seismic reevaluation is deemed adequate when it reasonably meets the intent of the above documents.

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SAN ONOFRE NUCLEAR GENERATION STATION UNIT 1 D0IESELCGENERATOR BUIL:DNRGATADMINISTRATION-j CONTROL BUILDING ENCLOSURE BUILDING F.W. HEATER PLATFORM CONTAINMENT r

SPHERE TiRBINE ORTH TURBINE PEDESTAL EXTENSION S1ALJ L

ELG FTTERINE Figre1.

Ky la0 o S0AnE PLnTfre UntOUSrutue VE1TILATION BUILOING FEXTENSN BUILDING REACTOR-AUXILIARY B UILD0ING

.IN...T.AKE.,

, -U SEAWALLL-,

Figure 1.1 Key Plan of San Onofre Unit 1 Structures 1 -3

0.

0 Our review of Refs. 1 to 9 with respect to the structure seismic reevaluation generated a series of questions, many of which were of clarification nature.

The questions, as shown in Appendix A, question groups 11 to IV, -were transmitted to SCE via an NRC letter dated June 30, 1982 (Ref. 13).

SCE -esponded to these questions during a meeting between the NRC staff and consultants and the SCE staff and consultants.

The review meeting was held in the Bechtel Norwalk office, California, from July 28 to 30, 1982.

Many questions were satisfactorily answered and hence considered closed during the meeting although NRC requested detailed written responses on some of the closed items.

NRC also requested written responses to those questions remaining open.

All questions on the fuel storage building were not discussed in the meeting, and were to 'be forwarded to the Structural Engineering Branch (SEB) of the NRC which is responsible for reviewing SCE's reevaluation of the fuel building. Appendix B summarizes the closed/open status of all questions listed in Appendix A, and identifies those closed questions for which SCE will submit written responses for NRC review.

In addition, Appendix B lists four additional questions which were not part of Appendix A, but were raised during the July, 1982 meeting.

Conclusions from our initial review of the seismic reevaluation methodology and acceptance criteria for the reactor building structures (as contained in Ref. 1) and for the BOP structures (Ref. 10) are summarized in Appendix C. The outstanding questions were forwarded to SCE via a January 19, 1982 NRC letter (Ref. 19), and SCE responded to the questions on April 12, 1982 (Ref. 20).

As a result of our review of Ref. 20, four items were identified as still outstanding (see Appendix A, question group I). They were forwarded to SCE via Ref. 13, for inclusion in the discussions during the July, 1982 review meeting. Appendix B identifies the open/close status of these four items as a result of the said review meeting.

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Subsequent to the July, 1982 review meeting, SCE submitted written responses to the items requested by the NRC, as identified in Appendix B.. They are the SCE letters to NRC dated August. 26 and September 45, 1982 (Refs. -21 and -26).

Sections 2 to 10 summarize our review of SCE's seismic reevaluation of the SONGS 1 plant structures,.in the following order: reactor building sturctures; circulating water system intake structure; auxiliary building; ventilation equipment building; seawall; control and administration building; turbine building and turbine generator pedestal; methodology for reevaluation of field erected tanks and buried piping; DBE input time histories and in-structure response spectra.

Each section gives a brief description of the structure, methodology and computer codes for the seismic analysis, stress results, codes, standards and specifications for stress evaluation, and any licensee proposed modifications resulting from the reevaluation. Safety margins from licensee's structural reevaluaton were. expressed as the ratio of the applicable allowable stress to the computed stress.

The ratio was designated by the licensee as the surplus margin for the reactor building structures, and as the safety factor for the BOP structures.

The adequacy for the seismic reevaluation of each structure is then assessed.

Section 12 presents the conclusions and a list of the open items from our review.

Note that the SEB of NRC has the main responsibility of reviewing the reevaluation of the fuel storage building and all masonry walls of the BOP structures, and the generation of the fuel building in-structure response spectra.

In addition, the adequacy of using the 0.67g Housner spectra as the DBE input for the seismic reevaluation program is not within the present scope of our review.

As stated in the November 16, 1981 NRC Safety Evaluation Report on the interim seismic adequacy of SONGS 1 (Ref. 14), the NRC staff expected to reach a final decision on the. SONGS 1 SEP spectra following the Atomic Safety and Licensing Board's Patial Initial Decision on 1 -5

SONGS 2 and 3 with respect to geology and seismology issues.

In an April 5, 1982 letter (Ref.

22), NRC indicated that the 0.67g Housner spectra are, in general, appropriate except for small exceedances by up to 10% in the period range from 0.07 to 0.25 second for the horizantal DBE spectra, and from 0.05 to 0.15 second for the vertical spectra. NRC confirmed the above as their final position via a September 16, 1982 letter to SCE (Ref.23). The license has assessed the effect of such small spectral exceedances on their previous seismic reevaluation of the SONGS 1 structures and in structures response spectra.

Their conclusions were presented in the attachment to their August 16, 1982 letter to the NRC (Ref. 24).

Our evaluation of Ref. 24 is discussed in Section 11 of the report.

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2.

REACTOR BUILDING STRUCTURES 2.1 Description of Structures Figures 2.1 and 2.2 show the general arrangement of the SONGS 1 containment sphere. and reactor building. The containment building is a 140' - diameter steel sphere, slightly thicker. than 1".

The upper portion is free standing, and is about 100' tall above the finished grade.

The lower portion is embedded in the concrete foundation.

The foundation is a spherical segment, the lowest point being about 40' deep in the ground.

Near the ground surface, the concrete foundation and steel sphere form a cavity about 6' deep, and 1'-2" to 2'-8" across from bottom to top.

The cavity is filled with sand to provide a transition stiffness from the free-standing portion of the sphere to the concrete-embedded portion.

Major containment penetrations include the equipment hatch, personnel lock, escape lock, steamlines and feedwater lines.

The steamline penetrations were not included in the study because their expansion-type connection prevents load transfer to the sphere.

The reactor building is a reinforced concrete structure, consisting of a primary shield wall, secondary shield wall, refueling canal, operating deck and three steam generator compartments.

The primary shield wall is a 5' - thick rectangular structure with inside dimension of 70' by 80'. It is supported by the foundation, and it supports the operating deck and steam generator compartments.

The refueling canal is supported at one end by the primary shield wall and at the other by the foundation.

The steam generator compartments provide 30" of shielding to the portions of the steam generators and pressurizer that extend above the operating deck.

2-1

CONTAINMENT STEAM SPHERE GENERATORS LOOPA PLANT PUMP NORTH (HIDDEN)

LOOP C LOOPI REACTOR BUILDING STRUCTURE Figure 2.1 San Onofre Unit 1 Reactor Building Structures 2 -2

ELEVATION

_120.00 CONTAINMENT SPERE

- 50.00 20.00 0.00 FOUNDATION

-- 20 MAT NOTE.

CG OF TOTAL STRUCTURE CG OF FOUNDATION CONCRETE CRADLE Figure 2.2 Elevation View of SONGS 1 Reactor Building Structures 2-3

The foundation of the SONGS 1 reactor building is a concrete mat in the shape of a spherical segment.

The foundation mat rests on the containment shell, which in turn is supported by a concrete cradle.

Anchorage of the mat to the cradle is provided by the fuel transfer tube.

See Fig. 2.2 for the concrete cradle -and the foundation mat.

The above mentioned structures were originally designed using the Housner Spectra with 0.25 g and 0.50 g horizontal acceleration for the Operating Basis Earthquake (OBE) and the Design Basis Earthquake (DBE), respectively.

A reinforced concrete sphere enclosure building was added to the plant around 1976 as a result of the Sphere Enclosure Project.

The building houses the containment sphere, and is cylindrical with a conical roof.

It was designed for a seismic input equivalent to the 2/3g San Onofre Units 2 and 3 Design Basis Earthquake, which is the modified Newmark and Hall spectra.

The Sphere Enclosure Project was approved by the NRC in Amendment No. 25 to Provisional Operating License No. DPR-13 (Ref. 15).

Although the concrete enclosure building need not be included in the seismic reevaluation, it produces through soil coupling with the containment and reactor building.

Such effect was partially addressed by the licensee in Ref. 3.

2.2 Seismic Analysis Models This topic includes three issues, i.e., the structure modeling, structure damping, and soil-structure interaction modeling.

In the seismic reevaluation of the structures, two different seismic analysis models were used. The first one, called the containment sphere model, is for the seismic analysis and stress evaluation of the containment sphere and concrete foundation.

The second one is the reactor building model, which 2 -4

was used in the seismic analysis and stress evaluation of the reactor building.

In addition, a reduced containment and reactor building model was used in the nuclear steam supply system (NSSS) reevaluation.

They are seperately discussed below.

2.2.1 Containment Sphere Model (a) Discussion -

The containment sphere model is an axisymmetric finite element model, including both the structure and soil-structure interaction.

The containment sphere and reactor building are represented by shell elements.

The concrete foundation and subgrade are represented by solid elements, and the NSSS by several lumped masses.

The solid elements representing the subgrade are massless, and this is equivalent to using frequency-independent soil springs in the impedence method for soil-structure interaction modeling.

The soil properties corresponding to an effective dynamic shear modulus of G=4100 ksf were adopted for the soil elements in the model.

The licensee judged this to be the best estimate value assuming a probable range of soil strain levels of 0.02% to 0.2% for the 0.67 g DBE and a probable range of soil confining pressure of 3 to 6 ksf.

At the upper bound confining pressure of 6 ksf, the G value varied from 4100 ksf to 8000 ksf, and the corresponding structure rocking mode frequency varied from 3.7 to 5.0 Hz.

The damping was specified as 4% of critical per mode for the combined soil-structure model.

This simple way of specifying the damping was chosen so as to facilitate the application of the response spectrum method of. analysis to the model using the Bechtel version of the ASHSD code.

2-5

(b) Evaluation -

The containment sphere model appears sufficient for modeling the structure and soil-structure interaction. Our initial review indicated a concern on whether there is sufficient number of elements representing the sand filled transition zone to accurately determine the local bending -stress in the shell (Question II(5), Appendix A).

It then became a closed item during the July, 1982 meeting, but SCE was requested to provide a written response.

The massless soil elements are equivalent to using frequency-independent soil springs in the impedence method of modeling soil-structure interaction, and the effect of the embedment and the spherical shape of soil-structure contact surface can be accurately accounted for.

The subgrade soil profile is nearly uniform to a considerable depth, which justifies neglecting the frequency dependency in the soil springs.

The simple way of specifying the damping, i.e., 4% per mode for the soil structure interaction model, appears to be conservative.

NUREG/CR-0098 (Ref. 11) allows the use of 5% to 7% damping for welded steel and 7% to 10%

damping for reinforced concrete when the DBE stress level is at or just below yield. The damping associated with soil-structure interaction was estimated to be 10% for rocking, 12% for horizontal translation and 18% for vertical translation (Table 3.7.1.1 of Ref. 1).

We had a concern on the soil property variability, as stated in Question II(1) of Appendix A. It was an open item from the July, 1982 review meeting, and SCE provided a response on September 15, 1982 (Ref. 26).

The response stated that the average soil strain of 0.2%, which led to the selection of the soil shear modulus of G=4100 ksf assuming a 6 ksf overburden pressure, was determined from a one-dimension response analysis of the site subjected to the 2-6

DBE time history ground motion. Based on this average soil strain,, the licensee indicated that a +30% variation in the soil strain,. and consequently a +10%

variation in the soil shear modulus, would be appropriate., The frequency shift resulting from the +10% variation in. soil-shear modulus wo.uld-then be about +5%

which, when. combined on a square-root-of-sum-of-squares (SRSS) basis with estimated frequency shifts due to structural mass distribution (5%), soil-structure interaction methodology (5%), and other uncertainties (5%), produced a probable overall frequency shift of +10%.

Due to the fact the soil conditions at SONGS 1 site are very uniform and have been extensively tested and studied, we believe that SCE's estimates of the variations in both soil shear modulus (10%) and overall soil-structure interaction frequency (10%) appear to be sufficient.

Hence, the broadening of in-structure response spectra by +15% would also be sufficient.

Our remaining concern is that it is not clear to us whether strain dependent soil properties were considered in the aforementioned one-dimensional response analysis of the site soil, such as by using computer code SHAKE.

2.2.2 Reactor Building Model (a)

Discussion -

The reactor building model includes a finite element model for the reactor building consisting of triangular plate elements, an 8-mass stick model for the containment sphere, some simplified stick models for the NSSS and its supports, and a set of six frequency-independent soil springs attached to a foundation node that is located at the center of gravity (C.G.) of the concrete foundation.

The foundation node is rigidly connected to the reactor building finite element model with multi-point constraints.

2 -7

The soil spring stiffnesses were determined from the analysis results of the axisymmetric containment sphere model, after several trial and error iterations, in an attempt to match the axisymmetric analysis results as closely as possible for the soil-structure interaction modes.

The soil spring values were provided in the licensee's response to Open Item No. 6 (Ref. 3).

The reactor building model was analyzed by the Bechtel SAP 1.9 computer code which allows the specification of separate damping values for individual structure materials and for soil-structure interaction.

The following damping values were used:

Reactor Building - 5%

Containment - 4 %

Soil Horizontal Translation -

12 %

Soil Rocking - 10%

Soil Vertical Translation -

18%

The impedance damping values were determined from field tests of concrete slabs that were intended for providing soil-structure interaction parameters for the seismic design of San Onofre Units 2 and 3.

(b)

Evaluation - The damping values and structure modeling appear sufficient.

The modeling of soil-structure interaction with impedance soil springs attached to the foundation C.G. node is also sufficient.

In Question 11(3) of Appendix A, we requested clarification on how the impedance soil springs were determined from the trial and error interation because it would be difficult to correlate or match the modes between the containment sphere model and reactor building 2-8

model; we also questioned why the horizontal translation spring. (KH=6.4x10 9 lb/in) was two orders of magnitude-larger than the vertical translation spring (KV-5.4xlO7 lb/in). This item was considered closed during the July, 1982 review meeting; however, SCE was requested to follow up with, detailed documentation and to assess the effect of the relatively large horizontal soil spring on components located at low elevations (e.g.,. RPV).

Concern was expressed previously on the soil property variation in the containment sphere model.

This same concern applies to the reactor building model.

SCE's August 26, 1982 response (Ref.21), however, has closed this latter concern.

2.2.3 Reduced Structure Model for NSSS Analysis (a)

Discussion -

For the NSSS reevaluation, the lumped mass containment model and a reduced reactor building were used.

The reduced reactor building model contains 24 degrees of freedom at six nodal locations which are sufficiently rigid to preclude local flexibility from influencing the low frequency range.

A frequency comparison with the detailed reactor building model was made to verify the validity of the reduced model.

The structure damping was represented with the Rayleigh damping.

The soil structure interaction was represented with the same soil springs that were developed for the detailed reactor building model, except that the horizontal soil springs were assumed infinitely stiff.

(b)

Evaluation - The reduced reactor building model appears sufficient for the reevaluation of the NSSS.

Concern on the soil property variation, as expressed 2 -9

0 I,

previously for the containment sphere and reactor building models, also applies here.

In addition, during the July, 1982 review meeting SCE was requested to submit documentation to substantiate the validity of restraining the horizontal soil-structure interaction degrees of freedom in tTie reduced structure model.

SCE's August 26, 1982 response (Ref. 21) then resolved this concern.

2.2.4 Effect of Sphere Enclosure Building (a)

Discussion - The reinforced concrete enclosure building was not included in the reevaluation because its design was initiated at the time when the reevaluation of the containment sphere and reactor building was near completion.

However, the licensee investigated the effect of the enclosure building on the response of the reactor building due to the through-soil coupling.

In Ref.. 3 the licensee showed that the through-soil coupling effect reduced the response at the primary shield, the operating deck, and the foundation.

(b)

Evaluation - Based on the information provided in Ref. 3, we find that the reactor building model, which is uncoupled from the sphere enclosure building, is sufficient as far as the evaluation of the reactor building is concerned.

The same conclusion, however, may not be applicable to the evaluation of the containment sphere and in-structure response spectra.

This concern gave rise to Question II(2) in Appendix A. SCE's August 26, 1982 response (Ref. 21) did not satisfactorily address our concern with the in-structure response spectra, i.e.,

the effect of through-soil coupling from the sphere enclosure building on the frequency shift of the spectral peaks.

2 -

10

2.3 Method of Seismic Analysis (a)

Discussion - The spectral response method was used for the analysis of both the containment sphere and the reactor building models.

The analysis of the containment sphere model was done using the Bechtel ASHSD code.

A 4%

damping per mode was specified for' the-model.

The analysis of the reactor building model was-done using the Bechtel SAP 1.9 code.

The modal damping was determined from the individual damping values specified for the structures and the soil-structure impedances, using the strain energy technique.

The results are shown in Table 3.7.2-3 of Ref. 1.

Separate horizontal and vertical analysis were performed.

In the analysis for each individual. direction, the square-root-of-sum-of-squares (SRSS) method was used to combine the modal responses.

The applicable results from the three components of earthquake were then combined using the SRSS method.

To substantiate the validity of the SRSS combination for the responses from the three earthquake components, the licensee compared the results with those from a time history analysis of the model in which the three ground motion components were input simultaneously.

Table 3.7.2-12 of Ref. 1 shows the comparison of the stress resultants at several critically stressed elements.

In general, the comparison is favorable.

(b)

Evaluation - The spectral response method of analysis as used in the seismic stress response calculations is sufficient. The combination of the responses to the three earthquake components by the SRSS method also appears acceptable.

Question II(4) in Appendix A questioned the discrepancy between the modal 2 -

11

damping values shown in Table 3.7.2-3 of Ref. 1 and those presented in the November 14, 1979 meeting (Ref. 2). The licensee provided a clarification during the July, 1982 review meeting.

2.4 Structural Overturning (a)

Discussion - Because of the very low elevation of the C.G. of the entire containment and reactor building, the licensee stated that overturning of the structure due to earthquake is unlikely.

They also checked the soil bearing pressure due to the structure dead weight and DBE overturning moment, arid found the soil pressure within limits established for the site.

(b)

Evaluation - The overturning and soil bearing pressure evaluation appears sufficient.

2.5 Structural Evaluation 2.5.1 Containment Sphere (a)

Discussion - The steel containment vessel was originally designed to the requirements of ASME B&PV code Section I,.1963 Edition (draft and code cases).

The containment shell material was supplied to a specification equivalent to the current ASME Specification SA-516, Grade 70 plate material.

For the present evaluation, primary membrane and bending stress values due to the DBE and normal operating loads were compared with corresponding stress limits for metal containment components of Subsection NE of Section III of ASME B&PV code.

2 -

12

Normal operating loads as defined by the licensee included the internal pressure due to a Design Basis Accident (P=49.4 psig), dead weight (D),- and feedwater piping loads on the containment due to differential thermal and seismic movement. It must be recognized that the Desigh Basis Accident pressure is not a normal operating load. Stresses due to the aforementioned loads were computed with the same containment. sphere model previously used in the seismic analysis.

Primary membrane and bending stresses were evaluated at several critical locations, including:

o Basic shell away from discontinuities and penetrations; o

Shell-base junction; o Shell in vicinity of equipment hatch and personnel lock; o

Main feedwater penetration.

The primary plus secondary stress intensity was also evaluated at the shell-base junction.

Loads considered in the evaluation were dead weight, internal design pressure (49.4 psig) and seismic load due to the DBE or an OBE (Operating Basis Earthquake).

The OBE ground motion was specified as one third of the corresponding DBE ground motion.

At the main feedwater penetration, the feedwater pipe load was also included in accordance with current code rules for metal containment.

This pipe load is due to differential thermal and seismic movement.

2 -

13

Stresses calculated from the load combinations were then compared with the applicable stress intensity allowables as specified in the ASME B&PV Code Section M, Summary 1972 Addenda (P. 25, Note 2), and Section V, Appendix P(P. 322).

The allowable stress intensity, Sm,was established from test data on the minimum ultimate tensile strength of the material in the containment sphere.

It, was equal to 21,600 psi.

A surplus margin was defined as the ratio of the allowable stress to the actual stress. It denotes the level of safety margin built into the original design as measured by current standards.

As shown in Table 3.8.2-3 of Ref. 1, the minimum surplus margin under the combination of DBE and normal operation loads was 1.05 and 1.19 for the primary membrane (at shell-basement juncture) and the primary membrane plus primary bending (at equipment hatch) stress condition, respectively.

At the base juncture, the primary plus secondary stress intensity was found to be within the allowable intensity, 3Sm.

Table 3.8.2-4 of Ref. 1 shows the evaluation for the critical compressive membrane stress.

A surplus margin of 1.08 resulted for the longitudinal compressive stress near the shell-base juncture.

In addition to the above, the containment shell was also evaluated for the combination of OBE and normal operation loads.

The minimum safety margin was similar to that for the DBE case.

(b)

Evaluation - In general, computation of the stress resultant from the containment sphere model appears appropriate.

The stress intensities for the DBE combined with normal operating loads and design accident pressure were 2 -

14

evaluated based on applicable section of the ASME Code that was current during the seismic reevaluation program.

Surplus margins-at the critically stressed locations all exceeded 1.0, indicating that the original design also meets current design standards.

We have previously identified four areas of concern, as stated in Questions 11 (6) to 11 (9) in Appendix A.. First, it was not clear how the feedwater pipe load at the penetration was determined and what its magnitude was.

Second, it was not clear how the local shell stresses at all major penetrations were computed because, apparently, the axisymmetric shell model could not account for such local stress evaluation.

Third, the licensee did not address the potential of buckling of the shell near the shell-base juncture where large hoop compressive stress could develop due to the thermal loads.

Finally, we need a clarification on the magnitude of the internal pressure that was used in evaluating the compressive membrane stress as shown in Table 3.8.2-4 of Ref. 1. The text of Ref. 1 appears to suggest that the 49.4 psi accident pressure was used.throughout the stress evaluation of the shell, which would be unconservative for computing the compressive stress.

Items 11(7) to 11(9) became closed as a result of the July, 1982 review meeting, and item 11(6) was satisfactorily resolved by SCE's August 26, 1982 Response (Ref. 21).

3.5.2 Reactor Building (a)

Discussion -

The stress analysis of the reactor building model incorporated the NSSS component support modifications which were necessary to upgrade the reactor coolant system (RCS) to withstand the DBE seismic loads.

The support modifications are briefly described in Ref. 1, Section 3.8.3.1.1.

2 -

15

Loads considered in the stress. evaluation included normal operation loads (dead weight, live load) and DBE seismic load.

Ppessure and temperature loads were judged to have negligible effect.

For the evaluation of the reinforced concrete structures, the stress criteria for ultimate strength design, as defined in ACI-318-71, was used, except for bond, anchorage and minimum steel requirements.

For these requirements, ACI 318-63 was used because this was the applicable code at the time of construction.

The load factors in applying the ACI ultimate strength design criteria were all taken to be unity, and hence the load combination became:

U=Dead Weight + Live Load + DBE where U is the applicable required section strength.

For the NSSS supports, the stress criteria from the ASME B&PV Code,Section III, Subsection NF, were used.

The NSSS supports were evaluated for the primary load combination of DBE plus pressure plus dead weight.

For structural steel not covered by ASME Code, Section M, the following load combination was considered:

0.9Y=Dead Load + Live Load + DBE where Y is the section strength required based on the plastic design method as described in the 1971 edition of AISC Specification for Design, Fabrication, and Errection of Structural Steel for Buildings.

2 -

16

The stress analysis of the reactor building model was performed for the various loading conditions using the Bechtel SAP 1.9 Code..

The reinforced concrete structure was most critically stressed on the south secondary shield wall near the two lower-corners.

The minimum-surplus margin was 1.14 in concrete shear (see Table 3.8.3-2 in Ref. 1).

The results of the stress evaluations for the NSSS component supports and support anchorages are summarized in Ref. 1, Table 3.9.1.5-2 and 3.9.1.5-3, respectively.

Loading applied to the anchorages was that determined from the component support analysis and transmitted to the concrete structure. Ultimate strength analysis was performed for the concrete, and working stress analysis was performed for the structural steel.

Minimum surplus margins were 1.12 for the component supports (the RCP lateral supports and structural support frame) and 1.1 for the support anchorages.

(b)

Evaluation -

The stress evaluation for the reinforced concrete structure appears sufficient.

Concrete shear was the governing stress, and the minimum surplus margin was 1.14.

Sufficiency of the stress evaluation for the NSSS supports and support anchorages, on the other hand, is conditional upon the sufficiency of the NSSS stress analysis, which is not within the present scope of evaluation.

2.5.3 Concrete Foundation (a)

Discussions - The loads, load combinations, and applicable codes and standards that were considered in the stress evaluation of the concrete foundation were identical to those applied to the reactor building concrete structures.

The 2 -

17

stress resultants were computed from the containment sphere model, using the ASHSD program.

Tensile stresses in the foundation were asumed to be resisted only by reinforcing. The maximum stress occurred at the primary shield - base juncture, where a minimum surplus margin of 1.07 was determined for the reinforcing steel.

Potential foundation sliding was evaluated by examining the bearing and shear stresses in the subgrade soil that were calculated from a finite element analysis. These stresses were sufficiently small compared to the allowables, thus precluding sliding.

It was also reasoned that slippage of the building along the spherical surface of the shell with respect to the concrete cradle was very unlikely.

(b)

Evaluation - The evaluation of the concrete foundation for stresses and potential of sliding and slippage appears to be adequate.

2 -

18

3.

CIRCULATING WATER SYSTEM INTAKE STRUCTURE 3.1 Description of Structure The intake structure is an embedded reinforced concrete. structure that houses the. major components, of the circulating water system, the safety related salt water cooling pumps, and the tsunami gates. The 12' reinforced concrete intake pipe transitions to a double reinforced concrete box culvert with two pump chambers.

The top slab of the pump chambers forms the slab base of the pumpwell.

The pumpwell has a 22' 9" high peripheral retaining wall.

The discharge tunnel is a 10' 8" square single reinforced concrete box culvert which transitions to the 12' reinforced concrete discharge pipe.

The intake structure foundation is a reinforced concrete slab, 3' 4" thick and 136' 3.5" long with a varying width, bearing directly on the San Mateo formation.

3.2 Analysis of Structure The intake structure is rigid, essentially completely embedded, and weighs about 65% of the weight of the displaced soil. For these reasons, the licensee assumed that soil-structure interaction is negligible and the response of the structure closely tracks the free field ground motion.

Under such circumstances, the governing seismic loads on the external peripheral walls and base slabs were the dynamic earth pressures (active or passive) and, where applicable, the hydrodynamic pressures.

The governing seismic loads on the internal cross walls and floor slabs were the inertial loads due to the appropriate peak ground acceleration (ah=0.67g, a=o.44g) and, where applicable, the hydrodynamic loads; dynamic amplification was not considered because, according to 3-1

the licensee, the fundamental frequencies of the internal walls and slabs were in the unamplified region of the input response spectrum.

Thus, no dynamic analysis of the intake structure was performed.

According to Ref. 16, which forms part of the SONGS 1 balance of plant structure seismic reevaluation criteria depicted in Ref. 10, two thirds of the maximum peak DBE ground accelerations were used in computing both the active dynamic earth pressures and hydrodynamic pressures, while 70% of the maximum peak DBE ground accelerations was used in computing the passive dynamic earth pressures.

The simultaneous effects of the three components of the DBE were considered in the structural analysis.

This was done by combining 100% of the effect due to motion in one particular direction and 40% of the effects due to motions in the remaining two directions.

In the stress analysis, the individual walls and slabs were modelled as beams or plates depending on whether the reinforcements are essenially one-way or two-way construction.

End conditions of the beams and plates were hinges, fixed ends, partial restraints, depending on the structural arrangements.

The partial restraints were achieved by applying the allowable moments of the adjoining structural elements to the edges of the beam or plate model under consideration.

The intake and discharge culverts below elevation (-)7' 9" were treated differently.

They were modelled as box frames and analyzed by moment distribution method.

3-2

3.3 Results of Seismic Reevaluation The analysis results due to the combination of normal 6peration loads and, DBE seismic loads were, compared with the allowable limits-specified in the balance of plant structure seismic reevaluation criteria (Ref. 10).

The criteria allowed a maximum ductility ratio of 3.0 for bending moment when the allowable elastic moment was exceeded.. However, no ductility ratio exceeding 1.0 was allowed for shear.

As a result of the reevaluation, the licensee concluded that all structural components comprising the circulating water system intake structure met the reevaluation criteria requirements with the exception of the north, south, and east pumpwell walls.

The maximum moment ductility ratio computed in both the north and south pumpwell walls, was 9.7, which exceeded the 3.0 limit.

For the east pumpwell wall, the allowable shear in the wall support beam was exceeded. The licensee identified certain conceptual modifications to these walls.

3.4 Evaluation In general, the methodology and results for the seismic reevaluation of the intake structure are adequate. Our initial review resulted in four questions, i.e., Questions Al to A4 in Appendix A.

Questions Al and A4 became closed items, and Question A2, regarding the analysis of the intake and discharge culverts, and Question A3, regarding the application of partial edge restraints to the wall and slab analyses, remained open as a result of the July, 1982 review meeting.

However, SCE's August 26, 1982 response (Ref. 21) satisfactorily addressed the concerns in Questions A2 and A3.

3-3

4.

REACTOR AUXILIARY BUILDING 4.1 Description of Structure Except for the northeast corner, the reactor auxiliary building is a single story, embedded, reinforced concrete structure.

The plan dimensions are about 134' by 60'.

The northeast corner includes an additional story having several roof levels. It is above grade, and is constructed of masonry walls, reinforced concrete walls and slabs,. and structural steel floor and roof framing.

The building foundation is a stepped reinforced concrete mat, 2' 4" thick, bearing directly on the San Mateo formation.

4.2 Analysis of Structure Because the majority of the structure is fully embedded and weighs about 62%

of the displaced soil, soil-structure interaction was considered negligible.

For the reinforced concrete structure below grade, the analysis methods were similar to those adopted in the intake structure analysis.

The differences were:

(a) Hydrostatic and hydrodynamic loads were not applicable to the auxiliary building, and (b) the computed inertial loads for the internal walls were conservatively increased by 50% although, according to the licensee, the fundamental frequencies of such walls were in the unamplified region of the 7% damping DBE response spectrum.

The masonry walls, located above grade, were analyzed inelastically for out-of plane loadings; in addition, they were checked for flexural, shear and sliding modes of failure due to in-plane loadings.

The methodologies and criteria for evaluating the 4-1

masonry walls were described in Ref. 7, and are not within the present scope of our review.

Other structural components such as masonry wall connections, roof diaphragms, etc., were analyzed utilizing the calculated reactions from the inelastic analysis of the masonry walls due to out-of-plane loadings.

They were also evaluated for combined effect of in-plane and out-of-plane loadings.

4.3 Results of Seismic Reevaluation The reactor auxiliary building was found sufficient for the combined DBE and noramal operating loads in accordance with the balance of plant structure reevaluation criteria.

For the connections of masonry walls to the concrete diaphragm slab and to the metal roof decking, the computed forces exceeded the UBC criteria. The licensee proposed some conceptual modifications to these connections.

Meanwhile, they reasoned that the connections would not fail due to the occurrence of a DBE because:

o The UBC criteria corresponds to working stress limits; o

The computed forces in the connection of masonry wall to concrete diaphragm slab exceeded the UBC allowable by less than 20%; and o

The computed forces in the connection of masonry wall to metal roof decking were shown to be within the computed ultimate connection capacities in both tension and shear.

4-2

4.4 Evaluation The seismic reevaluation of all structural elements of the auxiliary building, except for the masonry walls that were not within the scon of our review, appears sufficient. Our initial review raised two questions that were of the clarification nature.

They are the Questions B1 and B2 listed in Appendix A. Both became closed items during the July, 1982 review meeting, upon the clarifications provided by the licensee.

See Appendix B for the resolutions.

4-3

5.

VENTILATION EQUIPMENT BUILDING 5.1 Description of Structure The ventilation equipment building is a single story structure with a roof of steel decking supported by structural steel roof framing.

The roof framing is supported by peripheral, reinforced concrete block walls.

The structure is approximately 44' by 21' in plan, and 20' high.

The concrete block walls are supported by a 1'6" wide, 8" thick continuously reinforced concrete footing.

5.2 Analysis of Structure Seismic analysis was performed for the east-west and vertical directions.

The plan dimension of the building in the north-south direction is about twice that in the east-west direction, and hence a north-south direction seismic analysis was considered not necessary. Lumped mass stick models were developed for the east-west and vertical seismic analyses.

Soil-structure interaction was accounted for by incorporating appropriate stiffness parameters. The seismic responses were computed from the BSAP code using the response spectrum method.

In addition, in-structure response spectra were developed for the evaluation of the building roof beams, roof decking, and associated connections.

Soil bearing pressure was computed by combining the dead load, seismic overturning moment effect and 40% of the vertical earthquake effect.

The worst condition was found to be when the full east-west seismic component was combined with 4096 of the north-south seismic component.

5-1

5.3 Results of Seismic Reevaluation Reevaluation of the masonry walls was reported in Ref. 7. All structural elements other than the masonry walls were found to have satisfied t-he balance of plant structure seismic reevaluation criteria.

The only exceptions were the 3/4" roof ledger bolts on the east-west walls and the beam end insert plate bolts to the north-south walls, and conceptual modifications were identified. The licensee concluded, however, the ultimate capacity of the connection bolts would be substantially greater than the UBC working stress limits and hence safety functions of the structure would not be impaired due to the occurance of a DBE.

5.4 Evaluation Reevaluation of the masonry walls are not within the scope of our present review.

Reevaluation of all other structural elements generally appears sufficient.

Our initial review generated four questions.

They are the Questions 111 (1),

I (4), III (5) and Cl listed in Appendix A. Question III (1) concerned with the soil property and its variability that were included in the soil-structure interaction analysis. Question III (4) concerned with the variation of the modulus of elasticity of masonry walls with frequency that was considered in developing the equivalent linear model for the masonry walls. Question n (5) concerned with the simplified representation of the structural elements when evaluating the out-of-plane loads in the masonry walls.

Finally, Question Cl requested clarification on whether a north-south seismic analysis of the ventilation equipment building was actually performed.

Questions 111 (4), 11 (5) and C1 became closed items during the July, 1982 review meeting.

Refer to Appendix B for the resolutions.

In their September 15, 1982 letter (Ref. 26), the licensee provided a written response to Question M (1).

Conclusion from our evaluation of this response is similar to that 5 -2

previously discussed in Subsection 2.2.1 for the reactor building structures.

That is, we believe licensee's estimated variation of the overall soil-structure interaction frequency, +13.5% in this case, to be sufficient; however, it is not clear to us whether strain dependent soil proproperties were used in the one-dimensional response analysis of the site. In addition, it is not clear to us what soil shear modulus was used in the soil-structure interaction analysis of the ventilation equipment building. Ref. 26 implied that G=4100 ksf was used, the same value previously used in the reactor building structure analysis.

If this is-the case, we need a clarification because the confining pressure is a parameter for selecting the soil property (see Fig. 3.7.2-19, Ref. 1), and the confining soil pressure beneath the ventilating equipment building is most probably different from that with the reactor building structures.

5 -3

6.

SEAWALL 6.1 Description of Structure The seawall is a cantilevered steel sheetpile wall ihich extends along the western boundary of the site. The sheetpiles are regular carbon grade steel. MZ-27 shapes having a minimum yield stress of 38,500 psi.

They are protected with a 2.5" gunite coating extending to elevation (+)4' on the seaward side, and to an elevation 1' below finished grade on the plant side.

The top and bottom elevations of the wall are (+)28' and

(-)8', respectively.

The finished grade adjacent to the plant side of the wall varies from elevation (+) 14.5? to (+)17.0'.

The top of the newly constructed beach walkway on the seaward side of the wall is at elevation (+)14'.

During construction of the beach walkway, horizontal and vertical gravel drains were installed on the seaward side of the wall below the water table to assist in relieving pore pressure buildup in the soil after a seismic event.

6.2 Analysis of Structure The seawall was analyzed employing equivalent static analysis methods for the DBE and the site specific tsunami.

The site specific tsunami was specified in Section 2.4.6 of the SONGS 2 & 3 FSAR (Ref. 17).

The DBE and tsunami were taken to be sequential, non-stimultaneous events with respect to their load effects on the seawall.

For the DBE, 70% of the peak ground accelerations was used as the average effective accelerations for the reevaluation of the seawall.

A force equilibrium procedure was used in the analysis similar to Colomb's wedge analysis in which the critical angle of the wedge was determined to obtain the maximum pressure on the wall.

Soil parameters corresponding to seismic and post-seismic 6 -1

conditions were used for the seismic and tsunami analysis, respectively.

Under the DBE, active soil pressures were determined using the DBE-as the basis for an equivalent static loading.

Passive soil pressures were based on a beach elevation of (+)14' MLLW corresponding to the top of the beach walkway.

The wall was then analyzed for the tsunami loadings.

The hydrostatic loads included the extreme high tide, the tsunami wave, and a storm surge, all assumed to occur simultaneously to produce a maximum still water elevation of (+)15.6' MLLW.

Hydrodynamic loading on the seawall included a 7' breaking wave superimposed on the maximum still water elevation.

6.3 Results of Seismic Reevaluation The safety factor for stability was found to be 3.8 and 5.3 for the DBE and tsunamic events, respectively. The maximum bending stress induced in the steel sheetpile was also found to be well within the allowable.

6.4 Evaluation The reevaluation of the seawall appears to have satisfied the balance of plant structure seismic reevaluation criteria, with the exception that it is not clear to us how the equivalent static analysis of the cantilevered (above finished grade) portion of the seawall was performed.

Ref. 4 appears to imply that 70% of the peak ground acceleration was used in the equivalent static analysis of both the embedded and cantilevered portions of the structure.

We request a clarification on this concern; however, the reevaluation results indicated a large surplus margin of about 5.7 in 6 -2

bending and 3.8 in stability, and we believe that the seawall will be stable against the postulated DBE and tsunami loads.

6 -3

7.

CONTROL AND ADMINISTRATION BUILDING 7.1 Description of Structure The control and. administration building is a 3-story reinforced concrete structure with a single-story administration office building attached to the east side.

The 3 story portion of the building has only a partial second floor slab because structural steel framing (without a slab) is used to support electrical raceways at this floor level in the 4KV switchgear room. The north and west walls of the building are 2'10" thick, and the remainder of the structural walls vary from 8" to 13" in thickness.

Overall dimensions of the building are approximately 110' wide, 140' long, and 36' high.

The structure is slightly embedded with grade level varying from elevation (+)14' to (+)19'9".

The foundation consists of reinforced concrete wall footings as well as individual column footings.

The wall footing width varies from 1'8" to 8'10", and their thickness varies from 1' to 2'. Column footings vary in width from 2' to 6'6", and their thickness varies from 1' to 1'6".

7.2 Analysis of Structure The analysis was essentially done using a three dimensional finite element model.

The model included all reinforced concrete, structural steel, masonry walls, and foundaton stiffness and damping.

The foundation stiffness and damping were specified at every foundation nodal point to account for soil-structure interaction.

Beam elements and membrane elements were used to represent the equivalent linear out-of-plane and in-plane properties of the masonry walls, respectively.

The 7-1

beam elements were given very small in-plane stiffness while their out-of-plane properties were represented by equivalent cracked section moment of inertia and shear area.

Their mass density and Poisson's ratio were computed based on the equivalent solid thickness of the masonry blocks.

The properties of the membrane elements that represented the in-plane characteristics of the masonry walls were established such that the elements would resist the resulting in-plane and normal stresses due to applied loads.

Represented by plate elements, the reinforced concrete slabs and walls were given orthotropic or isotropic material properties depending on whether their principal reinforcements were in one or two directions.

For the orthotropic plate elements, the moduli of elasticity and Poisson's ratios in the two directions were proportional to the respective cracked section moments of inertia.

The reinforced concrete and the structural steel beams and columns were represented by beam elements in the finite element model.

The steel truss members in the building were modeled as truss elements.

A response spectrum analysis of the finite element model was performed using the Bechtel BSAP code.

The BSAP code computed the soil-structure composite modal damping values ranging from 7.03% to 23.3% of critical but a maximum composite modal damping value of 20% was used in the analysis.

The seismic responses were then used to evaluate the various structural components.

A time history analysis of the finite element model was also performed to generate floor response spectra necessary for the reevaluation of subsystems.

The Bechtel BSAP code was used for the time history analysis, and the floor response 7 - 2

spectra were calculated using the Bechtel SPECTRA code.

The input free field motion was a 20-second synthetic time history that was developed in accordance with-the provisions of the Standard Review Plan (SRP), Subsection 3.7.1.

The equivalent static analysis method was used for the reevaluation of various structural elements-of the control and administration building.

The applicable floor response spectra were used to determine the equivalent acceleration coefficient in the analysis.

All static loads were included in the static analysis.

The finite element model was utilized in the static load analysis.

7.3 Results of Seismic Reevaluation For the reevaluation, the control and administration building was divided into critical and non-critical portions.

The critical portions included the three-story reinforced concrete structure comprised of the control room and 4KV switchgear room and the southern end of the building which houses the safety related station batteries and security batteries. The non-critical portion consists of a single-story administration office building located on the east side of the control and administration building.

For the evaluation of the in-plane shear stresses in reinforced concrete walls the allowable from Section 11.10.5 of ACI 318-77 was used.

The shear strength due to the reinforcement was accounted.for, however, when necessary.

For the critical portions of the building, the maximum computed moments and shears were found to be within the allowables except for certain reinforced concrete 7 -3

walls,. slabs, and beams.

For the concrete walls, the maximum computed flexure ductility ratio was 2.29 which occurred in the east control room wall WC-C-d.

The maximum computed flexure ductility ratio was less than 2.0 for the reinforced concrete slabs, and less than 3.0 for the reinforced concrete beams.

Thus the critical portions were found to satisfy the balance of plant structure reevaluation criteria.

Reevaluation of the non-critical portions indicated that the administration office building also met the corresponding reevaluation criteria. In this reevaluation, additional capacity in the plastic mode of behavior of structural steel was relied upon for three steel columns and one beam connection.

7.4 Evaluation Reevaluation of the masonry walls are not within the scope of our present review.

Reevaluation of the various structural elements other than the masonry walls appears sufficient, and no modifications appear necessary. Our initial review, however, generated Questions InI (1) to M (5) plus Questions Dl and D2, as listed in Appendix A. All these questions became closed items during the July, 1982 review meeting, except for Questions M (1) and M (2).

Question n (1) concerned with the soil property and its variability included in the soil-structure interaction analysis, and Question M (2) concerned with the method for computing the soil damping ratio at each foundation node where soil spring was used.

SCE's September 15, 1982 response (Ref. 26) satisfactorily resolved our concerns in Question III (2), but not M (1).

The two concerns with Ref. 26 we previously identified with the ventilation equipment building (Section 5.4) are also applicable here.

Besides, we need quantitative justification of SCE's judgment that the influence of backfill conditions on the soil stiffness parameters at the various foundations of the control/administration building would be insignificant.

Table A-6 of 7 - 4

Ref. 26 shows that the reduction factors to the soil spring parameters at some 13 foundations resulting from the backfill conditions were from 0.60 to 0.77, which appear to be significant.

During the July,.1982 meeting SCE was also requested to provide clarification of the calculations for the concrete expansion anchors that connect the steel beams to masonry walls, and to provide a sketch of a typical anchor (Additional Question No.

1, Appendix B).

SCE's August 26, 1982 response (Ref. 21) provided the requested information which indicated that the existing anchors possess a safety factor of 4.4 and 1.8 against shear and pullout failures, respectively.

While the 1.8 margin against pullout was low compared to the 4 to 5 margin required by the NRC seismic related Bulletin IE 79-02, the licensee reasoned that such requirement is not directly applicable to this case because IE 79-02 is intended for, pipe supports and because the type of vibratory motions experienced by pipes and supports is not directly related to what was under consideration.

We find this reasoning too ambiguous to preclude the expansion anchors under question from the requirement of the IE 79-02 safety margin against pullout failure, and request that the licensee provide further justification.

7-5

8.

TURBINE BUILDING AND TURBINE GENERATOR PEDESTAL 8.1 Description of Structures The turbine building consists of four individual structure systems surrounding the concrete turbine pedestal.

They are the turbine building north and south extensions and the east and west heater platforms.

The licensee is currently converting the four turbine building steel platforms from moment resisting frames to moment resisting braced frames by adding seismic bracings.

The north extension is a one-story structural steel frame building with two bays in each direction and a mezzanine. It has an 8.5" thick prestressed concrete roof deck and a steel grating platform at the mezzanine elevation.

A 1.5"? wide expansion joint was provided at, the juncture between the extension and the turbine generator pedestal.

The south extension is a one-story steel frame building.

It has an 8.5? thick prestressed concrete roof deck and a 1.5"? wide expansion joint between the extension and the turbine generator pedestal.

The west heater platform is a one-story steel frame with 2 bays in the EW and 6 bays in the NS direction.

The platform supports an 8.5? thick prestressed concrete roof deck.

The east platform is similar to the west heater platform with one fewer bay north of Column line E.

The results of analysis reported in Ref. 6 were based on the addition of 6 new braces to the north extension, 14 braces to the west heater platform, 15 braces to the east heater platform, and 8 braces to the south extension.

The installation of all new braces was scheduled to be completed by the end of November, 1982.

8 -1

The turbine generator pedestal is a reinforced concrete space frame supported by a 5' thick mat foundation.

It consists of haunched columns at the four corners and three haunched intermediate walls.

The operating deck consists of an 8' thick center section that supports the turbine generator.

The top of the deck is at elevation 42'.

A large steel structure weighing about 120 tons, the gantry crane travels back and forth from the south extension, over the turbine pedestal deck to the north extension.

The top of the rail is at elevation 42'6".

The turbine building foundation consists of individual and combined footings. Two columns from each of the four extensions are founded on the pedestal basemat, and in north extension one column has its foundation cast monolithically with the spent fuel pool wall. Foundation modifications are being installed to accomodate the increased uplift loads at locations where new bracings are postulated.

There are peripheral masonry walls in the four extensions.

They are supported on continuous spread footings. Except for the masonry wall in the north extension that is cantilevered from the foundation, all masonry walls are connected to the steel framing with out-of-plane only lateral support at the deck level.

8.2 Analysis of Structures The turbine building complex was evaluated utilizing a 3D finite element model.

It included the four turbine building extensions in conjunction with the turbine generator pedestal, gantry cranes and a lumped mass representation of the spent fuel pool. There were plate elements representing the prestressed concrete decks, pedestal deck and pedestal shear wall; beam elements representing the structural steel columns and girders, 8-2

reinforced concrete columns and beams, gantry crane, spent fuel pool and out-of-plane properties of the masonry walls; truss elements representing diagonal bracings; spring elements representing soil media; direct liniks representing, the out-of-plane only connections between masonry walls and steel framing at the roof deck level; rigid links representing the pedestal basemat, the rigid connections. of the steel columns to the pedestal basemat, and the rigidity of the massive concrete connections throughout the turbine pedestal.

The masonry walls were represented by a grillage of beams having equivalent linear elastic properties, based on an independent non-linear analysis of the walls., This assured that out-of-plane reaction of the walls was properly transmitted to the steel framing.

Soil-structure interaction effects were considered by representing the soil media by soil springs attached to the column footings and the pedestal basemat.

The response spectrum analysis of the finite element model was performed using the Bechtel BSAP code.

The computed composite model damping values for the soil structure system ranged from 4.0% to 50.8%, but a maximum value of 20% was used in the analysis.

The response spectrum analysis generated moments, shears and forces for the various elements comprising the finite element model.

For the seismic reevaluation of the various structural subsystems and components, in-structure response spectra were first developed from a time history analysis of the 3D finite element model.

The structural elements were then evaluated utilizing the equivalent static analysis method.

8-3

Static stresses due to dead loads and live loads were determined by performing static analysis of the finite element model.

8.3 Results of Seismic Reevaluation Unless otherwise specified, the reevaluation was based on the balance of plant seismic reevaluation criteria.

In general, the basis for criteria governing the stresses within the elastic range was current day code requiremnts.

In the structural evaluation of steel beam-columns, biaxial bending of the members along with their axial loads was considered.

When calculated stresses were in the inelastic range, a plastic interaction equation taking into account biaxial bending and axial load was used to evaluate the ultimate strength of the beam-columns.

This interaction equation is Equation (4-1) as shown in the text of Ref. 6, and was accepted by the Structural Stability Research Council's Guide to Stability Design Criteria for Metal Structures, 3rd Edition (Ref. 18) and the latest Canadian Standards Association Code, "Steel Structures for Buildings - Limit States Design."

In the evaluation of concrete strutural members, an increase of the original compressive strength of the concrete by up to 50% was used.

Results of the seismic reevaluation are summarized below:

(a)

North Extension - Six new braces are being installed in the north extension.

Introduction of the new braces along with the required foundation modifications significantly stiffens the structure.

The braces had a safety factor of 1.34 to 1.51.

8 -4

All girders were found to be within allowable stress limits, with a safety factor of 1.05 to 1.80 in bending.. The crane rail girders had a safety factor of about 1.5.

For the mezzanine, all beams were within allowable stress limits except for beam NEM B4 which had a safety factor of 0.80. The licensee will strengthen this. beam by adding, cover plates.

The evaluation for the eight column-girder moment connections indicated that connection A-7 had a safety factor of less than 1.0 for beam-web shear stress and hence will be modified by adding a web doubler plate.

All bolted connections had a safety factor in shear ranging from 1.64 to 4.24.

In the column evaluation, column B-6 was found overstressed for the near-grade portion and flange coyer plates will be added.

The anchorage at column D-6 had a stress of 124 ksi and will be strengthened by installing rock bolts directly into the pedestal mat.

All column base plates were found adequate.

The existing foundations in the north extension have been modified to withstand the increased uplift due to DBE loads.

The modifications were designed to ensure the allowable soil bearing pressures and footing stresses were not exceeded; the resultant safety factors were 3.85 and 2.5, respectively.

(b)

West Heater Platform - There are 14 new braces in this structure.

They had a safety factor of 1.67 to 3.68.

In the girder evaluations, beams J12-K12 and C11-C13 required the addition of cover plates. All eighteen column-girder moment connections were found to be adequate 8-5

with respect to the column flange stress, beam web shear stress and beam web crippling.

All bolted connections were also found adequate, having a safety factor from 1.00 to 1.92.

There are seventeen major columns and six smaller size eolumns.

All columns were found acceptable except the small column 013, which will be strengthened by adding a structural tee.

For column anchorages, the base plate anchor bolt assemblies at locations C-9, C-11 and C-13 have been modified by increasing the base plate area and providing additional anchor bolts. The new configuration has stresses within the elastic allowables.

All base plates were found adequate in bending.

Existing foundations in the west heater platform have been modified to resist the increased uplift loads due to DBE loading.

The modifications included increasing size of existing footings, providing grade beams between two existing footings, and constructing new independent foundations (outside of columns G13, H13 and L10).

The new foundations were found adequate with respect to soil bearing pressure and footing stresses.

(c)

East Heater Platform - the reevaluation was based on the addition of fifteen new braces.

The bracing members had a safety factor of from 1.32 to 2.60.

For the evalutation of girders and secondary beams, the two north-south girders, E1-F1 and G2-H2, required additional steel cover plates.

All sixteen column girder moment connections and bolted connections were found acceptable.

8-6

Evaluation of the sixteen major columns and four small columns identified that columns El and F2 are required to be strengthened by adding cover plates and structural tees. The column anchorages at El, E3, J2, Ktand L5 required modifications.

At E3, the column base anchorage will be modified by providing a knee-brace to the column and a new base plate and anchor bolt assembly.

For anchorages at columns El, J2, B1 and L5, modifications will also be provided.

In addition, base-plate modificatons will be implemented at. columns El, E3 and J2.

Existing foundations are to be modified to withstand the increased DBE uplift loads, this includes installing grade beams between columns El, Fl, KL and J2; increasing the size of footing at column E3; and adding an individual footing about 30' south of column L5.

(d)

South Extension - Eight new braces will be added.

All beams and girders were found acceptable.

The ten column-girder moment connections and bolted connections were evaluated, and found adequate.

All ten major columns met the reevaluation criteria. All column base anchorages were found acceptable except for columns M6, M8, P6, R6 and R8.

They will be strengthened by providing additional anchor bolts and increasing base plates areas.

For the foundations, new north-south grade beams will be constructed from columns M6 to N6 and M8 to N8 while a continuous grade beam will be added to connect columns P6, P7 and P8. In addition, one new spread footing will be constructed about 20' east of column P6.

8 -7

(e)

Heater Platforms and Extensions Deck - The post-tensioned decks were found adequate, meeting the seismic reevaluation criteria.

The-concrete deck slab has steel insert plates with embedded shear connections.- The steel insert plates were welded to the top of the deck steel framing girders.

For the west heater platform, the total resistance capacity of the connections was found to be greater than applied loads.

However, the-licensee planned to increase the weld size on the connections from 5/16" to 7/16" at some insert plates so as to achieve a minimum design margin of 1.1.

For the north extension, the connections can only resist 70% of the applied load in the north-south direction.

The licensee will increase the weld size and provide some additional shear connectors to the deck slab to establish the required design margin at 1.1 for the north-south direction capacity.

In the south extension, the total capacity of the connections in the east-west direction exceeded the total applied loads by a margin of 1.06.

The weld size on the connections in the east-west directions will be increased at some insert plates to achieve a 1.1 design margin. Finally, the connections in the east heater platform deck slab were required to be strengthened in both lateral directions, by increasing weld size and providing some additional shear connectors to the deck slab.

(f)

Deflection -

The time history analysis was used to calculate the maximum deflections associated with the four extensions and the pedestal.

It was found that the existing 1.5" gap is sufficient to accomodate the relative building-pedestal deflections.

(g)

Turbine-Generator Pedestal - ACI 318-77 code was the basis for the reevaluation, and the pedestal was found adequate.

If the concrete was assumed not to provide tension capacity per ACI 318-77, the horizontal reinforcements 'n the three walls were found to be overstressed by 2.9 to 4.5 times their allowable limit.

In accordance with 8 - 8

ACI 349-76, Appendix B4.3, however, the concrete would be capable of resisting tensile stresses on the order of 0.4f'c and hence the reinforcements would not be overstressed.

On this basis the three walls were concluded adequate by the licensee.

.8.4 Evaluation The seismic reevaluation of the turbine building complex including the ongoing and proposed modifications met the reevaluation criteria and hence appears sufficient.

The codes and standards that formed the basis of licensee's reevaluation are current day practices and hence are acceptable.

Our initial review identified several areas of concern.

They are the balance of plant structure general questions, 111 (1) to III (5),

and the specific questions, El to E4, as listed in Appendix A. As a result of the July, 1982 review meeting, Questions III (1),

II (2) and El still remained outstanding.

The remaining concern with Question El was the dynamic stability of the gantry crane against overturning and/or jumping off the track.

SCE's August 26, 1982 response satisfactorily resolved the concerns in Question El. Their September 15, 1982 response (Ref. 26) also resolved the concern in Question n1 (2), but not m (1).

The three remaining concerns with m (1),

as previously discussed in Section 7.4 for the control/administration building, also apply here to the turbine building.

8 -9

9.

FIELD ERECTED TANKS AND BURIED PIPING 9.1 Method and Criteria for Reevaluation of Field Erected Tanks There are two field erected tanks. at SONGS 1 site.

They are the refueling water storage tank and condensate storage tank.. They were designed in accordance with the methods set forth in Atomic Energy Commission's TID-7024.

The refueling water storage tank is a cylindrical welded steel tank with a domed top.

It has a mean diameter of 34' and a straight shell height of 3711".

The shell thickness varies between 0.25" to 0.329".

The foundation is a circular reinforced concrete slab, 35'6" in diametgr and 2'0" to 2'4-1" thick.

There are 32 anchor bolts, 1-5/8" in diameter and embedded 1'8" into the slab, to anchor the tank on its foundation.

The condensate storage tank is identical to the refueling water storage tank except the shell is uniformly 0.26" thick.

It rests on a 6" thick laver of rock which extends 2' beyond the tank's shell, and is surrounded by asphalt paving at its base.

Reevaluation of the two tanks is not yet completed, and Ref. 6 only briefly outlined some methodology and criteria.

The licensee indicated that the analysis will use the equivalent static analysis method, but did not specify whether soil-structure interaction will be considered.

The tank shell and anchorage will be evaluated against the AWWA Standard for Weld Steel Tanks for Water Storage, ANSI/AWWA D100-79, and the AISC Manual of Steel Construction, 8th Edition, respectively. The reevaluation for bearing pressure, sliding and overturning will be based on the criteria set forth in the balance of plant seismic reevaluation criteria (Ref. 10).

9-1

Our initial review of the above information regarding the methodology resulted in the Questions IV (1) to IV (3) in Appendix A. These questions concerned with the soil-structure interaction consideration, the -rigid tank assumption in computing hydrodynamic fluid pressures, and the evaluation of buckling-- potential. of tank shell near the base, respectively.

Except for the question on the rigid tank assumption, which became a closed item during the July, 1982 review meeting, the other two concerns will be addressed by the licensee as the reevaluation of the tanks proceeds.

Licensee's response to these two open items, when available, should be reviewed prior to full acceptance of the reevaluation methodology to be applied to the field erected tanks.

9.2 Method for Reevaluation of Buried Piping Reference 6 did not specify the methodology for the seismic reevaluation of buried piping (e.g. the salt water cooling pipe).

This became the Question IV (4) in Appendix A. During the July, 1982 review meeting, SCE responded that the method in the Bechtel Topical Report, BC-TOP-4A, Rev. 3, will be utilized for such reevaluation.

We concluded that this is an acceptable procedure, and the subject question was considered closed at the present time.

9-2

10.

GROUND MOTION TIME HISTORY AND IN-STRUCTURE RESPONSE SPECTRA 10.1.

Ground Motion Time History According to Ref. 9, a synthetic time history was generated to closely match the horizontal DBE design spectra at 2, 4, 7 and 10 percents of critical damping. The time history has a 20 second duration, digitized with 0.01 second intervals.

The vertical design time history was taken to be 2/3 of the horizontal time history.

Our review indicated that the development of the synthetic time history met the intent of the Standard Review Plan.

We conclude that the synthetic time history is sufficient with respect to its duration and spectral amplifications.

10.2 In-Structure Response Spectra For the purpose of generating in-structure response spectra, the licensee divided the structures into three groups.

They were the partially embedded structures, fully embedded structures, and non-structural slabs and equipment foundations at grade.

Note that the in-structure response spectra for the fuel storage building are not within the present scope of our review.

(a)

Partially Embedded Structures - This included the reactor building, administration and control building, ventilation equipment building, and turbine building.

The in structure response spectra were generated from time history analyses of the seismic analysis models of the buildings. To account for uncertainty in the material properties of the structure and soil, damping values, soil-structure interaction methods and structural modeling techniques, the computed spectra were smoothed and the peaks 10 -

1

associated with each of the structural frequencies were broadened by +15% in accordance with provisions of NRC Regulatory Guide 1.122.

(b)

Fully Embedded Structures -This included the fully -embedded shear walls in the reactor auxiliary building and circulating water system intake structure. The in-structure response spectra were taken as the ground design spectra.

The licensee stated that this was conservative by citing sufficient empirical data that usually indicated a reduction in ground motion with depth.

(c)

Non-Structural Slabs and Equipment Foundations at Grade - This included the administration-control building floor slab at EL+20', the ventilation equipment building floor slab at EL+19', the turbine building floor slabs at EL+14' and +20', and equipment foundations and other isolated slabs located at grade. Because these slabs and foundations are not integral with the superstructures, the in-structure response spectra were taken to be the ground design spectra.

During the July, 1982 review meeting, we questioned how the flexibility of floor slabs was accounted for in generating the vertical response spectra (see Additional Question No. 4 in Appendix B), and SCE's August 26, 1982 response satisfactorily addressed this question.

Therefore, we conclude that the generation of in-structure response spectra is sufficient.

For the partially embedded structures, however, the sufficiency of broadening the spectral peaks by +15% is contigent upon full acceptance of the licensee's response to Questions II (1) and III (1) on the effect of soil property variation.

10 - 2

11.

SIGNIFICANCE OF UP TO TEN PERCENT DBE SPECTRUM EXCEEDANCES As previously mentioned in Section 1, Introduction, NRC's September 16, 1982 letter to SCE (Ref. 23,) confirmed. their final position on the appropriateness of the 0.67g Housner spectra as the DBE input for the SONGS 1 seismic reevaluation.

SCE has recently assessed the significance of the up to 10% spectrum exceedance requirement with respect to the results of their previous seismic reevaluation of the structures and in-structure response spectra. Their August 16, 1982 letter to NRC (Ref. 24) presented the results and conclusions from their recent assessments, the highlights of which may be summarized in the following.

(a)

SCE stated that the increase in seismic loads and in-structure response spectrum would be minimal, being less than 10%, because of the following reasons:

o The structural damping values actually used in SCE's reevaluation analyses were usually lower than those allowed by NUREG/CR-0098, which was conservative.

In addition, the spectrum exceedance would be less than 10% for the higher damping values.

o Not all the structural frequencies were clustered within the frequency range where the 10% spectrum exceedances take place, and hence the increase seismic response would be less than 10%.

o Literatures cited by the licensee suggested that the 10% spectrum exceedance would not be uniform within the prescribed frequency range, but would rather assume a bell shape that maximizes around the 0.12 second period and tapers off toward the limits of the prescribed frequency range.

(b)

SCE reasoned that most allowable stresses imply a safety factor of 1 to 3 against failure and, therefore, in the few cases where the calculated stresses might approach

11. -

1

or exceed the allowable limits as a result of the spectrum exceedance, the likely result would be to decrease such implied safety factor by a small--amount.

(c)

In spite of all of the above reasonings, SCE assessed each individual structure by conservatively assuming that the 10% exceedance was effective regardless of the damping values and was uniform within the prescribed frequency range, that all structural modes of importance experienced a uniform 10% increase in modal response although some modes were actually outside the prescribed frequency range, and that all other normal operating loads also were increased by 10%.

On this conservative basis, SCE concluded that:

o The safety margins associated the ventilation equipment building, reactor auxiliary building, circulating water intake structure and seawall were not affected by the spectrum exceedance, in particular, because the last three structures were analyzed with the equivalent static analysis method that used only the peak ground acceleration as seismic input.

o For the turbine building and control/administration building, over 500 individual stress parameters were reveiwed.

Three items in the turbine building and eight items (including three masonry walls) in the control/administration building were identified as could be affected by the 10% spectrum increase.

Their reduced surplus margins were all between 0.90 and 1.0, except for the masonry wall WM-8 a that had a surplus margin of 0.87 in shear.

Due to the conservatism assumed in the assessment and the very small number of structural elements that could be affected by the spectrum exceedance, the decrease in the safety factors was

\\ not considered significant.

11 -

2

o The reactor building structures would not be affected because the frequencies of the fundamental modes were outside the prescribed frequency range of spectrum exceedance.

o The ground motion time histories used for the in-structure response spectrum generation have spectra that enveloped the Housner DBE spectra by an average margin of 7% to 15% depending on the damping values.

Therefore, the existing in-structure response spectra would be conservative enough to essentially offset the effect of the 10% spectrum exceedance except for the reactor auxiliary building, circulating water intake structure, non-structural slabs and equipment foundations at grade where the in-structure response spectra were taken to be identical to the DBE ground spectra and hence are subjected to the full 10%

spectrum exceedance requirement.

Based on licensee's above findings, we conclude that the 10% spectrum exceedance would not materially affect the existing results of the seismic reevaluation of the structures. Also, the existing in-structure response spectra would have sufficient margins except for those of the reactor auxiliary building, circulating water intake structure, non-structural slabs and equipment foundations at grade. At these locations, INEL/EG&G, the NRC consultant that is responsible for reviewing the seismic reevaluation of the piping and mechanical and electrical equipment, should evaluate the effect of the 10%

spectrum exceedance.

11 - 3

12.

SUMMARY

AND CONCLUSIONS We have reviewed the seismic reevaluation of the reactor 'building, the balance of plant structures (excluding the fuel storage building and other masonry walls), the methodology for reevaluation of field erected tanks and buried piping, the groung motion time history (excludingthe ground design spectra) and generation of in-structure response spectra.

The review was based on NUREG/CR-0098 (Ref. 10), SSRT guidelines for SEP soil-structure interaction review (Ref. 11), NRC Standard Review Plan, and other applicable NRC regulatory guides.

In general, we found that the seismic reevaluation was adequately performed.

Where required, the licensee proposed modifications to upgrade the deficient areas to possess a DBE seismic capability.

The July, 1982 review meeting resolved many of the concerns (Appendix A) we raised from our initial review.

Appendix B provides a summary of the resolutions to all the questions listed in Appendix A, and lists four additioonal questions raised during the said review meeting. Questions then remaining outstanding were later addressed by SCE's August 26 and September 15, 1982 letters to NRC (Refs. 21 and 26).

Items still remaining outstanding after reviewing these two responses are identified below:

I.

Open items on Seismic Reevaluation Program Plan:

Items 7 and 10.

Responses provided in Ref. 21 should be reviewed by the NRC consultant, INEL/EG&G.

II.

Reactor Building and Containment Sphere:

Questions 11 (1) -

We need clarification on whether strain dependent soil properties were considered in the one-dimensional response analysis of the site.

12 -

1

Question II (2) -

Licensee should provide quantitative assessment of the effect of the sphere enclosure building on the frequency shift of the spectral peaks on the in-structure response spectra.

IW.

Balance of Plant Structures:

Question 111 (1) -

The outstanding concern with Question II (1) also applies here.

In addition, we request the following information:

(a) The soil shear modulus that was used in the soil-structure interaction analysis of each BOP structure.

If G=4100 ksf was used, clarify why the probable difference in soil confining pressures between the B)P structures and the reactor building structures need not be accounted for in selecting G.

(b)

Quantitative assessment of the effect of the large reductions in the soil stiffness parameters due to the backfill conditions on the soil-structure interaction frequency variations.

(F)

Fuel storage building - not within our scope of review.

IV.

Field Erected Tanks and Buried Piping.

Questions IV (1) and IV (3).

Note that these questions only concern with the reevaluation methodology, and the reevaluation is yet to be completed.

V.

Additional Questions as Listed in Appendix B:

Ref. 21, Enclosure 4, resolved the concerns of all questions except Question No. 1. Ref. 21 indicated that the concrete expansion anchor bolts at the steel beam to masonry wall connections of the control/administration building have a maximum. safety factor against pullout failure of 1.82, which is substantially lower than that required by IE 79

02.

We request further justification on why conformance to the IE 79-02 requirement is not necessary.

12 - 2

In conclusion, the acceptibility of the sismic reevaluation of the SONGS 1 structures is contigent upon the following:

(a)

Satifactory responses from the licensee to resolve* the outstanding items identified above; (b)

NRC approval of the-seismic reevaluation of the fuel storage building and all masonry walls; and (c)

NRC approval of the seismic reevaluation of the field erected tanks and buried piping upon completion of the reevaluation by the licensee.

12 -

3

13.

REFERENCES

1.

"San Onofre Nuclear Generating Station Unit 1, NRC Docket 50-206-,

Seismic Reevaluation and Modification,"

Southern California Edison Company and San Diego Gas and Electric Company,- April 29, 1977.

2.

Memo from H. A. Levin to D. M. Crutchfeld, Systematic Evaluation program Branch, DOR, USNRC, January 3, 1980.

3.

Letter from K. P. Baskin of SCE to D. L. Ziemann, Op. Reactors Branch No.. 2, DOR,. USNRC, April 11, 1980.

4.

Letter from-K. P. Baskin of SCE to D. M. Crutchfield of NRC, December 8, 1981.

5. to Letter from R. W. Krieger of SCE to D. M. Crutchfield of NRC, February 9, 1982.

6.

SONGS 1 BOP Structures Seismic Reevaluation Program, Turbine Building and Turbine Generator Pedestal, Enclosure 1 to letter from K. P. Baskin of.SCE to D. M. Crutchfield of NRC. April 30, 1982.

7.

SONGS 1 Seismic Evaluation of Reinforced Concrete Masonry Walls, Vol.

1: Criteria; Vol. 2: Analysis Methodology; Vol. 3: Masonry Wall Evaluation; Computech Engineering Services, January, 1982.

8.

SONGS 1 Seismic Evaluation of Reinforced Concrete Masonry Walls, Vol.

4:

Fuel Storage Building, Computech Engineering Services, April, 1982.

9.

Letter from K. P. Baskin of SCE to D. M. Crutchfield of NRC, July 9, 1982.

10.

"Balance of Plant Structures Seismic Reevaluation Criteria", San Onofre Nuclear Generating Station Unit 1, February 17, 1981.

11.

N. M. Newmark and W. J. Hall, "Development of Criteria for Seismic Review of Selected Nuclear Power Plants,"

NUREG/CR-0098, N. M.

Newmark Consulting Engineering Services, Urbana, Illinois, September 30, 1977.

12.

"SSRT Guidelines for SEP Soil-Structure Interaction Review," prepared by Senior Seismic Review Team (SSRT) for USNRC, December, 1980.

13.

Letter from W. Paulson of NRC to R. Dietch of SCE, June 30, 1982.

14.

Letter from D. M. Crutchfield of NRC to R. Dietch of SCE, November 16, 1981.

15.

"Safety Evaluation by the Office of Nuclear Reactor Regulation Supporting Amendment No. 25 to Provisional Operating License No. DPR-13," SONGS 1, April 1, 1977.

16.

Balance of Plant (BOP)

SONGS Unit 1. "Soil-Strufture Interaction Methodology Report",

Revision 1, July 20,

1978, Woodward-Clyde Consultants, Orange, California.

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1

17.

Final Safety Analysis Report, San Onofre Nuclear Generating Station, Units 2 and 3.

18.

Balance of plant Mechanical Equipment and Piping Seismic Reevaluation Program, SONGS 1, April, 1982, attachment to letter from K. P. Baskin of SCE to D. M. Crutchfield of NRG, April 30, 1982.

19.

Letter from D. M. Crutchfield of NRC to K. P. Baskin of SCE, January 19, 1982.

20.

Letter from K. P. Baskin of SCE to D. M. Crutchfield of NRC, April 12, 1982.

21.

Enclosures 1 and 4 to letter from K. P. Baskin of SCE to D. M. Crutchfield of NRC, August 26, 1982.

22.

Letter from D. M. Crutchfield of NRC to R. Dietch of SCE, April 5, 1982.

23.

Letter from W. Paulson of NRC to R. Dietch of SCE, September 16, 1982.

24.

Letter from K. P. Baskin of SCE to D. M.-Crutchfield of NRC, August 16, 1982.

25.

Letter from K. P. Baskin of SCE to D. M. Crutchfield of NRC, July 9, 1982.

26.

Letter from K. P.

Baskin of SCE to D. M. Crutchfield of NRC, September 15, 1982.

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2

APPENDIX A QUESTIONNAIRE FOR THE JULY, 1982 SONGS 1 -REVIEW MEETING Listed herein is a reproduction of the questionnaire which was forwarded to the licensee via the letter from W. Paulson of NRC to R. Dietch of SCE, June 30, 1982 (Ref. 13).

The-references cited in the questionnaire are listed at the end of the questionnaire, and do not coincide with the reference list in Section 12 of the report.

A-1

0.

NCT 3650 MT DIABLO BLVD SUITE 190 ENGINEERING PO BOX1059 LAFAYETTE. CA 94549 INC.

1415) 283-0471 QUESTIONNAIRE ON SEISMIC REEVALUATION OF SONGS 1 STRUCTURES, FIELD ERECTED TANKS AND BURIED PIPING Open Items on Seismic Reevaluation Program Plan Your letter from K.. P. Baskin to D. M. Crutchfield of NRC, dated April 12, 1982, provided responses to the comments forwarded to you via ourJanuary 19, 1982 letter. Several items for the pro gram plan remain open, as delineated below. The item numbers are the same as those referred in our January 19, 1982 letter.

Item 1 "No explicit mention of the soil property variation range is made. The program for BOP structures refers to a Reference 3."

Your April 12,.1982 letter -indicated that you will respond by June 4, 1982.

Item 2 "The program lan for BOP structures refers to a Reference 8, Design Guide C-2.44. It appears to be a Bechtel inhouse docu ment which should be made available for review."

Your response is not detailed enough for us to complete our re view. We request a more detailed and precise comparison between C-2.44 and BC-TOP-4A for those sections actually referred to in your seismic reevaluation analyses of the structures.

Item 7 "At least one more time history analysis of the NSSS using a different set of time histories is required because nonlinear response of the system is very sensitive to characteristics of the input time histories while many of the comp.onents, according to the nonlinear analysis, have a safety margin of only 1.1."

For those components having a safety margin of 1.1, as shown in Table 3.9.1.5.2 of Ref. 1, their actual calculated safety margins were probably 1.10 or even less. Such small values of the safety margin may be Very sensitive to the nonlinear modelling, input motion characteristics, and analysis methodology. While we are still reviewing the verification document for the Westinghouse WECAN code, we believe at least one more time history analysis using a new set of time histories to be necessary. The infor mation provided in your April 11, 1981 letter from Baskin to Ziemann (Ref. 2) did not satisfactorily resolve the sensitivity concern mentioned above.

Item 10 "Verification of Westinghouse analysis codes was not provided."

WCAP-8281, "Verification of.the WECAN Computer Program Nonlinear A - 2

Questionnaire 0

Page2 Elastic Dynamic Analysis Capability," May, 1974 is still under review by the NRC staff and consultants.

We will discuss this subject further during the meeting.

II. Reactor Building and Containment Sphere Seismic reevaluation of-the reactor building, containment sphere and NSSS was reported in Ref.. 1. A set of open items was iden tified from a~previous review of Ref. 1 by the NRC staff and con sultants, which was forwarded to you during a November 14, 1979 meeting (Ref. 3)*.

Your response to these items was provided in Ref. 2.

A more recent review of Refs. 1, 2 and 3 by the NRC staff and consultants identified additional questions on Ref. 1 and the Ref. 3 open items that were not adequately resolved by your Ref. 2 responses. The comments are listed as follows.

(1) Soil property variability was not adequately accounted for because only one set of soil properties, corresponding to a shear modulus of 4100 ksf, was considered. The concern is primarily on the effect of soil property variation on the in-structure response spectra. For example, Ref. 1, showed that the soil rocking mode frequency varied from 3.7 to 5.0 Hz when the soil shear modulus was varied from 4100 to 8000 ksf. Such frequency uncertainty exceeded the +15o broadening of-the floor spectral peaks that was used in the reevaluation program. Provide your plan to account for the effect of the soil variability.

(2) Regarding the through-soil structure-to-structure interaction, Ref. 2 quantified the effect of the enclosure building on the reactor building while no information is available about such effect on the steel containment and in-structure response spectra. Provide this information so that we can complete our assessment of the reevaluation of the containment and its supported components and systems.

(3) Provide details on the trial and error method that was used in determining the soil springs in the reactor building model.

In addition, Ref. 2 did not satisfactorily address the Open Item No. 6 in Ref. 3 which questioned the two-order-magnitude difference between the horizontal and vertical soil springs of the reactor building model.

(4) The modal damping values of the reactor building model as shown in Table 3.7.2-3 of Ref. 1 differed from those presented in Ref. 3. Provide your reconciliation of this discrepancy.

(5) For the containment sphere finite element model, chere may not be enough number of elements of the steel shell in the sand filled cavity at the shell-base juncture to accurately predict A -3

Questionnaire the local bending stress distribution inthe shell. Provide your justification to circumvent this concern.

(6) The feedwater pipe load at the pipe penetration on the con tainment was included in the stress evaluation of the con tainment shell. Privide information Qn the magnitude of this pipe load and the method and source for its derivation.

(7) The axisymmetric finite element model for the containment shell does not account for the local stresses at and around the major penetrations. Provide clarification on how the containment local stresses at the penetrations were deter mined.

(8) Provide evaluation of the shell buckling potential near the shell-base juncture of the containment where high compressive stress in the hoop direction may develop due to thermal loads.

(9) Clarify the magnitue of the internal pressure that was used in computing the compressive membrane stresses shown in Table 3.8.2-4, Ref. 1, in the containment shell. The text in Ref.

1 appears to suggest that the 49.4 psig accident pressure was used throughout the shell stress computation, which would be unconservative as far as the compressive membrane stress eva luation is concerned.

III.

Balance-of-Plant Structures Comments on evaluation of the masonry walls are not included here, except where structure and masonry wall interaction occurs. The questions are divided into two categories, i.e., general and indi vidual structures. The general questions are those which apply to more than one of the Balance-of-Plant (BOP) structures.

General (Refs. 4,5,6,7,8,9,10)

(1) Where soil-structure interaction was included in the analysis, identify the soil properties that were used in determining the soil springs for each of such BOP structures. In addition, provide information on how the uncertainly in soil properties was accounted for, such as by considering a range of soil pro perty variation as recommended in the SSRT Guidelines for Soil Structure Interaction Review (Ref.

11).

(2) For the soil-structure interaction analysis of the control and administration building, turbine building and fuel storage building, how were the soil damping ratios computed where soil springs were used? Provide this information for each of these three buildings.

(3) Three dimensional structural models were used in the seismic reevaluation of the control and administration building, turbine building and fuel storage building. How were the connections A - 4

Questionnaire Page 4 between the elements representing the masonry walls and the elements representing the rest of the structure modelled?

(4) Variation of the modulus of elasticity, Em,.of the masonry walls with frequency was considered in the control and ad ministration building seismic model.

Was similar consideration given to the masonry walls represented in the ventilation building, turbine building and fuel storage building models?

(5) For out-of-plane nonlinear analyses of the individual masonry walls, such as for the turbine building, the effect of the building structure wastypically represented by an equivalent single-degree-of-freedom (SDOF) system. What is the criteria for determining the mass and spring stiffness of the SDOF system?

Individual Structures (A) Circulating Water System Intake Structure (Ref. 4)

Al. In the analysis of the exterior walls and base slabs, were their inertial loads accounted for in addition to the applicable earth pressure and hydrostatic and hydrodynamic pressures?

A2. The intake and discharge culverts below Elev. (-)7'9"" were analyzed as a box frame using the method of moment distribution.

(a) What and how were the dynamic earth pressures applied to the two side walls and the base slabs?

(b) Was culverts' inertial load included in the analysis?

(c)

Were shear loads and vertical seismic loads from the north and south Dumpwells included in the analysis, in addition to the application of concentrated moments that were equal to the allowable moments at the bases of these two walls?

A3. Partial restraints, where used, were specified at the beam ends or.plate edges representing walls or slabs, by applying allowable moments of the adjoining walls or slabs. This may not be conservative as far as the maximum positive moment is concerned because such allowable moments may exceed the nega tive moments that can possibly be developed due to the actual loads on the beam or plate under consideration.

A4. For the three pumpwell walls that exceeded the BOPSSR criteria, it was stated that failure of these walls would not occur under the DBE because of the "conservative assumptions" in computing the dynamic soil pressures. It is our understanding, however, that only 2/3 of the peak ground accelerations was used in the dynamic soil pressure calculations and that the effects of the three earthquake components were combined using the 1, 0.4, 0.4 rule, which is similar to the SRSS combination intended to recognize the unlikelihood of the simultaneous occurence of A -5

Questionnaire Page 5 the maximum effects from the three earthquake components.

Therefore, clarify the conservative assumptions cited in Ref. 4 that would preclude failure of the three walls under DBE until the walls are modified.

(B) Reactor Auxiliary Building (Ref. 4)

B1. How were the seismic loads (shear, moments, vertical inertial loads, etc.) from the above-grade portion of the building in cluded in the analysis of the embedded portion of the reinforced concrete structure?

B2. How was the inertial load of the metal deck roof diaphragm com puted? In addition to considering the masonry wall connection reaction forces, was the metal deck inertial load included in the evaluation of the metal decking?

(C) Ventilation Equipment Building (Ref. 4)

Cl. The worst condition soil bearing pressure occurred when the full effect of east-west seismic component was combined with 40%o of the effect of the north-south seismic component. It is our understanding, however, that a. north-south seismic analysis was not performed. Provide your clarification.

(D) Control and Administration Building (Ref. 5)

D1. What is the procedure for computing the cracked section moment of inertia, Icr, for the reinforced concrete walls and slabs that were represented by plate elements in the finite element model?

D2. A fixed base assumption was used in the analysis of the finite element model for static loads while a flexible base (soil structure interaction) was considered in the seismic analysis.

Provide your justification on this inconsistency.

(E) Turbine Building (Ref. 6)

El. How were the connections between the gantry crane legs and crane rails modelled in the three dimensional structura ana lysis model?

E2. How were the column.base connections modelled?

E3. Provide design details for the concrete slab to steel framing connections (steel inserts and shear connectors). Also, pro vide details on the shear connectors that are to be added where such modifications are necessary.

E4. The double-pin connections between the masonry wall tops and deck slabs are not intended to transfer in-plane shear loads from the masonry walls. Are they sufficient to accomodate the A - 6

Questionnaire Page.6 differential movement between the wall tops and deck slabs in the in-plane direction?

(F) Fuel Storage Building (Ref. 7)..

Fl. In considering soil-structure interaction,.-how were the soil springs and damping ratios distributed at the switehgear room wall footing?

F2. How was the foundation slab at Elev. 14'O" modelled in the three dimensional seismic analysis model?

F3. What is the definition of the "effective length" of wall in the derivation of the out-of-plane masonry wall properties?

F4. Horizontal and vertical analyses were separately performed, and the response time histories were then combined. Justify the validity of this approach because both analyses were non linear time history analyses.

P5. Was the linear, elastic.model developed for the frequency extraction only, and not for any response analysis?

F6. Your conclusions stated that "The 'as-built' structure was subjected to earthquake motions of the specified DBE level of 0.67g Housner for San Onofre Unit 1 and complied with the structural integrity acceptance criteria under this load."

It is our understanding that only the El Centro records were used in a structural integrity evaluation of the building while Fig. D.2 indicate that the El Centro records do not envelop the 0.67g Housner spectra. Provide your justification of the accuracy of aforementioned conclusion statement. Our particular concers are with the wall FB-7 and roof connections to walls FB-6 and FB-7.

F7. Provide information on the reevaluation of the foundation, which is not currently included in Ref. 7.

IV.

Field Erected Tanks and Buried Piping (Ref. 12)

(1) Justify the exclusion of soil-structure interaction consideration from the reevaluation of the field erected tanks.

(2) Justify the rigid tank assumption used in the reevaluation of the field erected tanks, such as in computing the hydrodynamic fluid pressures inside the tanks.

(3) Provide information on evaluating the buckling potential of the tank shell near the tank base.

(4) Provide the methodology for reevaluation of the buried piping.

A -7

Questionnaire Page 7 References

1.

"San Onofre Nuclear Generating Station Unit 1, NRC Docket 50 206, Seismic Reevaluation and Modification," Southern California Edison and San Diego Gas & Electrie Company, April 29, 1977.

2.

Letter from K. P. Baskin of SCE to D. L. Ziemann of-NRC, April 11, 1980.

3.

Memo from H. A. Levin to D. M. Crutchfield, Systematic Evaluation Program Branch, DOR, USNRC, January 3, 1980.

4.

Letter from K. P. Baskin of SCE to D. M. Crutchfield of NRC, De cember 8, 1981.

5. to Letter from R. W. Krieger of SCE to D. M. Crutch field of NRC, February 9, 1982.

6.

SONGS 1 BOP Structures Seismic Reevaluation Program, Turbine Building and Turbine Generator Pedestal, Enclosure 1 to letter from K. P. Baskin of SCE to D. M. Crutchfield of NRC, April 30, 1982.

7.

SONGS 1 Seismic Evaluation of Reinforced Concrete Masonry Walls, Vol. 4; Fuel Storage Building, prepared by Computech Engineering Services, April, 1982.

8.

SONGS 1 Seismic Evaluation of Reinforced Concrete Masonry Walls, Vol. 1: Criteria, Computech Engineering Services, January, 1982.

9.

SONGS 1 Seismic Evaluation of Reinforced Concrete Masonry Walls, Vol. 2: Analysis Methodology, Computech Engineering Services, January, 1982.

10.

SONGS 1 Seismic Evaluation of Reinforced Concrete Masonry Walls, Vol. 3: Masonry Wall Evaluation, Computech Engineering Services, January, 1982

11.

"SSRT Guidelines for SEP Soil-Structure Interaction Review," pre pared by Senior Seismic Review Team (SSRT) for NRC, December, 1980.

12.

San Onofre Nuclear Generating Station Unit 1,"Balance of Plant Mechanical Equipment and Piping Seismic Reevaluation Program" Southern California Edison, April, 1982 A - 8

APPENDIX B RESOLUTIONS TO THE APPENDIX A QUESTIONNAIRE This appendix summarizes the open/closed status, the need for licensee's written response and, where applicable, licensee's responses during the July, 1982 SONGS 1 SEP review meeting for the questions listed in Appendix A.

Four additional questions were raised during the July, 1982 review meeting which NRC also requested written responses from SCE.. They are:

(1)

Clarification of calculations for concrete expansion anchors in control administration building. SCE will provide a sketch of a typical anchor in concrete block walls (for connection to steel beam).

(2)

Calculation for ductility capacity of typical walls.

(3)

An estimate of the soil-structure interaction effect for a hypothetic fully embedded and an unembedded containment building.

(4)

Documentation accounting for vertical amplication of floor slabs when generating vertical in-structure response spectra.

B-i

0.

e.

Item Open/Closed Written No.

Status Response?

Remarks I-1 open yes See resolutions to Questions I (1) and 111(1).

1-2 closed no We foud that - BC-TOP-4A is the appropriate reference.

1-7 open yes I-10 open yes NRC is to complete the review.

II (1) open yes SCE will address the soil property variation and its effect on soil structure interaction.

II (2) open yes II (3) open yes SCE will provide detailed documen tation. SCE will also justify fixing the horizontal soil degree of freedom in the reduced reactor building model for NSSS analysis.

HI (4) closed no SCE provided clarification.

11 (5) closed yes SCE acknowledged that local bending stress could be underestimated by about 50%, and that increasing the computed stress by 50% would not present any concern.

II (6) open yes 11 (7) closed yes SCE used a detailed local model for stressed around penetrations.

II (8) closed no Thermal load is not an SEP seismic issue.

11 (9) closed yes 2 psi vacuum pressure was used.

SCE will clarify the 49.4 psi design pressure.

I (1) open yes SCE will address this concern for each applicable BOP structure.

III (2) open yes 111 (3) closed yes SCE described the design, and will provide a sketch.

III (4) closed no SCE's answer was "yes".

B-2

Item Open/Closed Written No.

Status Response?

Remarks 111 (5) closed no SCE provided a copy of letter from SCE to NRC, July 9, 1982 (Ref. 25).

The attgched information clarified the question.

Al closed no SCE answer was "yes".

A2 open yes SCE will provide dynamic earth pressure methodology for (a),

and documenation for (b) and (c) to address the effects of not including hydro dynamic loads and using improper base slab soil pressure distribution.

A3 open yes SCE will provide moments induced by normal operating loads on the culvert wall where negative moment greater than yield was discovered.

In walls containing water, SCE will also address the effect of potential leakage.

A4 closed no SCE will modify the three pumpwell walls.

B1 closed no SCE stated that loads were insignificant and were not included in analysis.

B2 closed no For first part of question, 1.5 times the peak spectral acceleration was used.

For second part of question, answer was "yes".

Cl closed yes SCE clarified the concern.

D1 closed no lor was used to ratio module of floor slabs to account for one way slab action.

D2 closed no A fixed base assumption would not significantly affect the stress results.

El open yes Connections were modeled as pinned joints.

SCE will provide detailed drawings and also evaluate the stability of gantry crane.

E2 closed yes Column bases were modeled as fixed ends. SCE will clarify how soil springs were applied to column bases.

B -3

S.

Item Open/Closed Written No.

Status Response?

Remarks E3 closed yes Details were shown.

E4 closed yes

-SCE indicated that sufficent rotation capacity-is available.

Will provide documentation.-

F1 to F7 open yes Questions were not discussed, and will be forwarded to NRC SEB.

IV (1) open yes Justification will be provided when modification design is complete.

IV (2) closed no Tanks will not be assumed rigid, and references were provided.

IV (3) open yes Buckling will be considered.

Future documentation will be provided.

IV (4) closed no BC-TOP-4A method will be used.

B-4

APPENDIX C REVIEW

SUMMARY

OF THE SEP SEISMIC. REEVALUATION PROGRAM PLAN Summarized here-are the conclusions from our initial revtew of licensee's SEP seismic reevaluation program, based on Refs. 1 and 10 for the reactor building structures and the BOP structures, respectively.

SCE's April 12, 1982 response (Ref. 20) resolved some of the concerns,, and the outstanding items became the Group I questions listed in Appendix A.

C-1

SAN ONOFRE UNIT 1 REVIEW

SUMMARY

OF THE SEISMIC REEVALUATION PROGRAM PLAN ITEM ADDRESSED?

ADEQUATE?

Soil and Foundation A.

Rock Site (Partly) no' B. Soil Site o

Foundation Input yes yes o

Generation of time history yes yes o

Modeling technique yes no (1,2,3) o Computer Codes (4)

C. Description of Foundation yes yes D. Free Field Input Spectrum yes yes Structural A. List and Description of Category I yes (5)

Structures or Structures Affecting Category I Systems or Components B. Modeling Techniques o

Damping yes yes o

Stiffness modeling yes no (2,3,6) o Mass Modeling yes no (2) o Consideration of 3-D effects yes yes C. Seismic Analysis Methods o

Response Spectrum, time history yes (7)(8) or equivalent static analysis o

Selection of significant modes yes yes o

Relative displacements yes yes o

Modal combinations yes yes o

Three component input yes yes o

Floor spectra generation yes yes o

Peak broadening yes yes o

Load combination yes yes C - 2

ITEM ADDRESSED?

ADEQUATE?

D. Analytical Criteria o

Codes and criteria, including yes yes AISC,ACI and NUREG/CR-0098 E. Computer Codes o

Description and verification yes no( 4 )(9)

Comments

1. No explicit mention of the soil property variation range is made to comply with SSRT SSI guidelines.

The program plan for BOP structures refers to a Reference 3.

2. The program plan for BOP structures refers to a Reference 8, Design Guide C-2.44.

It appears to be a Bechtel inhouse document which should be made available for review.

3. For the concrete enclosure building and containment sphere, it is not clear how soil-structure interaction is modeled. More information is needed to complete a review.

4. Computer codes applied to BOP structures are not described.

5. NRC staff will determine the completeness of the list.

6. For the Ventilation Equipment Building, the program assumes a rigid structure and neglects soil-structure interaction, in order to apply the static analysis method.

Justification is required.

7. Referring to Section 3.7.3.5. of program plan for BOP structures, clarification is needed on how multi-degree systems will be eval uated by static analysis method.

8. At least one more time history analysis of the NSSS using a dif ferent set of time histories is required because nonlinear response of the system is very sensitive to characteristics of the input time histories while many of the components, according to the nonlinear analysis, have a safety margin of only 1.1.

9. Verification of Westinghouse analysis code, WECAN, for NSSS analysis was not provided.

C -3 WILLIAM J.. HALL 3103 VALLEY BROOK DR.

CHAMPAIGN. ILLINOIS t82O 217 356.0663 September 27, 1982 Dr. Ting-Yu Lo L-90 Lawrence Livermore Laboratory P. 0. Box 808 Livermore, CA 94550 Re:

San Onofre Nuclear Generating Station - Unit 1 LLL Agreement 1523501

Dear Dr. Lo:

On September 6, 1982 I received four items on the noted project' for review and comment. These were sent to me by Dr. P-Y Chen, USNRC, and I note that a copy of the transmittal note was sent to you. My comments, based in part on review of previously submitted SONGS 1 material in my possession, follow.

The items received for review were as follows:

1.- rte r' dated 16 August.1982 (Baskin's office to Crutchfield) with attach ment titled "Seismic Safety Margins With Respect to the 84th Percentile Instrumental Spectrum" dated August 1982.

2. Letter dated 26 August 1982 (Baskin to Crutchfield) with enclosure titled "Enclosure 1 -- Responses to Open Items From The "Questionnaire on Seismfi Reevaluation of SONGS 1 Structures, Field Erected Tanks and Buried Piping' dated August 25, 1982.

3.

Letter dated 17 August 1982 (Baskin to Crutchfield) with enclosure en titled "Electrical Raceway Supports -- Seismic Reevaluation Criteria" dated August 13, 1982.

4.

Copies of 8 plans referenced in the foregoing submittals.

Item 1 --

"Seismic Safety Margins.

The first report appears to be directed toward ascertaining the significance of possible increases of up to 10.percent over the 0.67.g anchored Housner response spectrum, and specifically addresses four questions directed to SCE on April 5, 1982.

The introductory material in Section 2 (p. 2) refers to the effects of damping which are discussed as well in the Appendix to the submittal.

Many

.2 references are made to NUREG/CR-0098 (Newmark and Hall). For example on p. 5 of the Appendix it is noted, "It is believed.that the NUREG/CR-0098 damping values (Item 2,'Table 2) are conservative median values and that the one standard deviation values may more closely approximate a 'true' median".

Thereafter follows a tabulation of damping values significantly.higher than those given in NUREG/CR-0098.-

I should like to note that two sets of values were given in NUREG/CR-0098.

In the latter report Dr. Newmark and I stated on page 18, "The lower levels of the pair of values given for each item are considered to be nearly lower bounds, and are therefore highly conservative; the upper levels are consider ed to be average or slightly above average values, and probably are the values that should be used in design when moderately conservative estimates are made of the other parameters entering into the design criteria".

Careful study of the SONGS 1 attachment, Appendix Table 2, shows the upper.

(higher) values to be those tabulated, and I must assume the comment about one sigma.values noted above applies to values higher yet. The tabulated test data in Table 2 exceed in many cases the high values noted, in some cases show ranges of damping bracketing our suggested values, or in some cases values about the same as ours. The high values suggested by SCE may well be applicable under high levels of excitation, as might possibly be expected at the SONGS 1 site, although the rationale for.use of such values in analysis might'Be somewhat different than that given.

From a generic sense, one should note that velocity dependent damping is only an approximation to the actual damping mechanisms that are inherent in the system. Coulomb damping is employed primarily because it is easily handled analytically. Nonetheless it is a good approximation in many cases.

If carefully used it can be employed to represent effects from small levels of nonlinear behavior but in general is not a good approximation to hyster etic effects arising from cyclic nonlinear response (behavior). For example, if the piping is analyzed by the ASME Code, and high allowable stress limits are used, this approach in itself is intended to.approximate nonlinear be havior in some pseudo-manner.

Is it reasonable to employ high damping? To a degree, yes, since the system is highly stressed and strained, but more properly most likely because a great many elements of a complex system are coming into bearing, interacting, rubbing, etc. Unfortunately the various published test reports often do not describe the details of the entire system that is excited and that lead.to the damping values recommended.

I note in the answer to a question in Item 2 that the results of the analyses of mechanical equipment and piping will not. be available until 10/1/82 at the earliest. If the high damping values suggested by SCE are employed for such items and systems, it would seem to me the results of some variational type analyses should be given to show the sensitivity to such damping, and this in turn needs to be evaluated carefully in the light of the margins that are

0'..

.3.

demonstrated to exist. Also there should be-sufficient documentation for the equipment system to give reasonable assurance that the.assumed damping values can be.-attained.

Throughout the answers to questions there are also many references -tolhaving analysis spectra (corresponding to specific time histories one assumes) that exceed the Housner spectra. Obviously exceedance sugglests conservatism and is in keeping with the current state-of-the-art.

However-, for nonlinear' systems research is beginning to show-even more clearly that merely meeting a spectrum bound is not entirely sufficient. for defining nonlinear response.

The response, including time history of response, is highly dependent on the nature of the input, and this is the reason past recommendations have empha sized the importance of using five or so time history inputs.

The principal purpose of the extensive preceding discussfon is to point out that the sensitivity of the noted parameters needs to be assessed in evalu ating the margins of safety. In many cases, fortunately, the seismic effect is only a fraction of the total response effect for an element or system.

One perceives from response 1 of the Conclusions (Section 4.0) of Item 1 that the foregoing may well be the case generally for SONGS 1. Some further discussion of this.point with SCE might be desirable especially for systems falling within the pressure coolant boundary.

Comments-on some other specific points in Item lfollow. Some of the margin statemehts are difficult to assess. For example at the top of page 6 in the answePM' Question 1 a factor of 1.13 is cited.

Similarly, values less than one are noted in Table 1 (p. 9) and Table 2 (p. 10). However, one suspects that most of these items may well be of a type that can be characterized as local distress; i.e., overstressing (assuming that is the basis for the safety factor assessment) of one element may have little or no effect on the structural system performance as a whole. This point needs to be checked out more fully and documented. I spent considerable time going through docu ments in my possession to try to identify exactly where Column B6, Beam BC-13, Connection TS, etc. might be located but could not specifically identify the locations and their relationship to the remainder 'of the system. In other words I could not confirm with certainty that the elements would be local interacting elements whose overstress would lead to no effects of consequence.

In the answer to Question 3 the low ratio of vertical to horizontal acceler ation was noticeable, but the demonstration that the vertical response ex ceeded the criteria generally was convincing.

Item 2 "Responses to Open Items.

and Item 4_-- plans Under Item 1 some earlier comment has been made about one part of Item 2.

The only other comment I have pertains to the discussion of ductility capa city that is given in a four-page answer near the end of the submittal and

the 27 Page Appendix A. Since I do not know the background for the question I trust the appropriate USNRC group will review the answer-carefully. I was:

encouraged to note the low ductilities given in Table 1, and these appear generally reasonable to me.

The large calculated ductilitF limitscan be achieved of course onlyif the wall and its reinforcement are constructed with quality materials in atcare ful fashion. Small discontinuities in the reinforcement may (and often do) degrade the strain capacity below the 80 value given at the bottom of the second page of the response. One-question comes to my mind about this topic and that concerns the salt water-environment of SONGS 1'.

Have inspection or tests been made to demonstrate that over the years degradation of properties has not occurred?

Undoubtedly this point has been addressed in previous questioning.

Item 3 "Electrical Raceway Supports.....

This response appears reasonable in principle.

The key to meeting the de sired margins of strength rests in attention to details of manufacture and construction practice, particularly as it pertains to connections.

A copy of the foregoing comments is being transmitted directly to Mr. W. T.

Russ el I JJS.NRC.

Sincerely yours, W. J. Hall WJH:efh cc:

Mr. W. T. Russell. USNRC