ML18031B291
| ML18031B291 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 04/08/1987 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-79-02, IEB-79-2, TAC-R00015, TAC-R00016, TAC-R00017, TAC-R00019, TAC-R00020, TAC-R00021, TAC-R00022, TAC-R00023, TAC-R00024, TAC-R15, TAC-R16, TAC-R17, TAC-R19, TAC-R20, TAC-R21, TAC-R22, TAC-R23, TAC-R24, NUDOCS 8704160224 | |
| Download: ML18031B291 (42) | |
Text
ACCESSION NBR:
FAC IL: 50-259 50-2wo 50-296 AUTH. NAllE QRIDLEY> R.
RECIP. MANE REGULATORY
.GRADATION DISTRI HUT ION SY il (R IDS) 8704160224 DOC. DATE: 87/04/08 NOTARIZED:
NO Browns Ferry Nuclear Pouer Station>
Unit 1>
Tennessee Browns Ferry Nuclear Power S+ation>
Unit 2>
Tennessee Bl owns Ferry Nuclear Power Station>
Unit 3>
Tennessee AUTHOR AFFILIATION Tennessee Valley Authority RECIPIENT AFFILIATION Document Control Branch (Document Control Des! )
DOCKET 05000259 05000260 0 50002'96 SUBJECT; Forwards response to request d'or addi info re" seismic design issues involving cable trays> electrical conduits> HVAC> CRD>
hydraulic sos piping 8c IER 79-02 5 79-14 programs.
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OR Submittal:
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TENNESSEE VALLEYAUTHORITY 5N 157B Lookout Place APR 08 1987 U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Mashington, D.C.
20555 Gentlemen:
In the Matter of Tennessee Valley Authority Docket Nos. 50-259 50-260 50-296 BROWNS FERRY NUCLEAR PLANT (BFN) SEISMIC DESIGN ISSUES
RESPONSE
TO REQUEST FOR ADDITIONAL INFORMATION Enclosed are TVA's responses to the request for additional information items contained in enclosure 2 of the letter from R. J. Clark to S. A. Mhite dated July 31, 1986, concerning the seismic design issues involving cable trays; electrical conduit; the heating, ventilating, and air-conditioning system (HVAC); the control rod drive (CRD) hydraulic system piping; and the Inspection and Enforcement Bulletins (IEB) 79-02 and 79-14 programs.
In
- addition, a discussion of the TVA program to evaluate seismic adequacy of small bore piping is provi.ded as requested in the September 11, 1986 telephone conversation between TVA and NRC/NRR personnel.
The following enclosures contain the discussions of the subject issues.
Enclosure 1:
Enclosure 2:
Enclosure 3: : :
Enclosure 6:
Cable Trays Conduit Qualification Program (with attachment)
HVAC Concerns CRD Return Lines (with attachment)
IEB 79-14 and 79-02 Small Bore Piping The discussion of each seismic design issue in the enclosures is divided into three sections.
Part I
Background
Part II Corrective Acti.on Program Part III Conclusion/Request for Review For those issues where TVA has determined NRC review and approval of certain programs or criteria are necessary, the request for review and approval is made in Part III of the associ.ated enclosure.
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U.S. Nuclear Regulatory Commission APR 08 1987 In order to provide more information on certain programs discussed in enclosures 1 through 6, the following are being submitted as additional enclosures to this letter.
DNE Program Document, "Inspection and Seismic Qualification of Existing Electrical Conduit and Conduit Supports",
issued October 16, 1986 Project Instruction BFEP-PI 85-02, Revision 3, "Seismic Qualification of Existing Electrical Conduit and Conduit Supports,"
issued October 15, 1986 Design Criteria BFN-50-723, "Seismically Qualifying Conduit Supports,"
issued March 28, 1986, as modified by Exception No. EX-BFN-50-723-1, dated May 29, 1986 TVA test report WR28-4-900-176, "An Experimental Xnvestigation of Vibration Damping in Aluminum Electrical Conduit," dated March 1986 TVA test report WR28-4-900-140, "A Preliminary Study of Vibration Damping in Electrical Conduit," revised March 1986 Wyle Laboratories Seismic Qualification Test Report No. 17743-1, "Test Report on Seismic Qualification/Verification of Various Aluminum Electrical Conduit Configurations," dated May 9, 1986 Project Instruction BFEP-PI 86-05, Revision 0, "NRC-OXE Bulletin 79-02/79-14 Program Document for Browns Ferry Nuclear Plant,"
Project Instruction BFEP-PI 85-01, Revision 1, "Implementation of NRC-OIE Bulletins 79-02/79-14 for Browns Ferry Nuclear Plant" TVA BFN Standard Practice/Xnstruction, SMMI-5.1-A, "Verifying Correct Installation of Concrete Expansion Anchors" TVA BFN Mechanical Maintenance Instruction, BF MMI-99, "Instructions for the Implementation of NRC XE Bulletin 79-14, Units 1, 2, and 3" TVA Quality Xnformation Release No. QIRCEB86016, "Control Rod Drive Hydraulic (CRDH) System Analysis Guidelines," dated August. 13, 1986
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U.S. Nuclear Regulatory Commission APR 0S
>Sr'lease refer questions regarding this submittal to Raymond Lewis, BFN Site Licensing, (205) 729-3585.
Very truly yours, TENNESSEE VALLEY AUTHORITY R. Gridley Director Nuclear Safety and Licensing Enclosures cc (Enclosures):
Mr. G.
G. Zech, Assistant Director Regional Inspections Division of TVA Projects Office of Special Projects U.S. Nuclear Regulatory Commission Region II 101 Marietta St.,
NM, Suite 2900 Atlanta, Georgia 30323 Browns Ferry Resident Inspector Browns Ferry Nuclear Plant P.O.
Box 311
- Athens, Alabama 35611
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VI
SEXSMXC DESIGN ISSUES
RESPONSE
TO REQUEST FOR ADDITIONAL INFORMATION ENCLOSURE 1
SEISMIC DESXGN XSSUES CABLE TRAYS
Seismic Desi n Issues Cable Tra s The following is provided in response to the July 31, 1986 letter from R. J. Clark to S.
A. Mhite and Request for Additional Information Item No.
1 of enclosure 2 to that letter:
1.
Cable Trays please provide background information, the TVA long-tenn corrective actions and the implementation schedule regarding the seismic design of the cable trays.
Part I Background On February 18,
- 1981, a Corrective Action Report (CAR No.81-035) was initiated which identified the adverse condition of overfilled cable.trays and cable penetrations in the cable spreading, rooms.
The root cause analysis stated the condition existed as a result of "the immense modification program over the past years and the application of Flamemas tie-28 Several corrective actions were initiated in the period of March 1981 to June 1985.
These actions were concerned with prevention of overfilling additional cable trays and did not address the problem of existing overfilled cable trays or the effects of the additional weight on the cable tray supports.
In June
- 1985, an in-depth study of all three units by Browns Ferry Engineering Project concluded that cable trays and supports were originally designed for deadweight loads only.
Although TVA, beginning in 1970, had added lateral supports and bracing to improve the seismic capability, the study indicated that the cable tray system was not seismically qualified.
Part II Corrective Action Program'n order to resolve the cable tray seismic qualification issue, TVA has instituted a two-part program consisting of (1) an interim qualification program to justify operations before final resolution of the issue, and (2) a long-term qualification program to meet and ensure continued compliance with NRC guidelines.
To establish the interim qualification program, TVA, in July 1985, contracted with United Engineers and Constructors (UE&C) to define interim acceptance criteria which provide a "reasonable level of assurance that the cable tray/supports will maintain structural integrity and that the cable will maintain functionality during a Design Basis Earthquake (DBE)."
After defining the interim criteria, UE&C performed field walkdowns and calculations to evaluate the BFN unit 2 cable tray based on the criteria.
In February 1986, a five-volume seismic report, "Interim Evaluation of Cable Tray/Supports for Browns Ferry Nuclear'Plant Unit No. 2," was issued with the recommendations for interim seismic qualification.
The UE&C report was sent to NRC for review in May 1986.
Fourteen problem areas were identified in the report along with the proposed modifications to correct them.
The majority of these proposed modifications has been installed by TVA. All modifications will be completed by restart.
For long-term qualification, TVA is planning to use the methodology of NUREG-1030 which was developed to resolve Unre'solved Safety Issue (USI)
A-46, Seismic Qualification of Equipment in Operating, Nuclear Power Plants.
TVA contracted with EQE, Inc., to evaluate the "cable tray system using the results of their damage surveys conducted in power plants and industrial facilities having experienced actual earthquake ground motions.
The results of this survey are to be incorporated into a report expected to be completed in early 1987.
NRC's resolution of USI A-46 and the completion of the EQE evaluation is expected to enable TYA to seismically qualify the cable tray system for long-term operability.
Part III Conclusion The modifications which arose from the interim qualification program.are discussed in Part II. It is not anticipated that the long-term qualification program will require extensive modifications.
No design basis changes are now required or anticipated in regard to the long-term seismic qualification of cable trays.
In regard to interim requirements, conditional NRC approval of the interim qualification program for unit 2 restart was granted in the NRC/NRR Safety Evaluation on this subject dated February 5, 1987.
Approval is contingent on TVA providing:
1.
Confirmation of the completion of the 14 modifications on tray/supports discussed in the VEDIC report, and 2.
Verification that the interim acceptance criteria have been met after the modifications.
The requested confirmation and verification will be provided in a subsequent submittal.
1-2
SEISMIC DESIGN ISSUES
RESPONSE
TO REQUEST FOR ADDITIONAL INFORMATION ENCL'OSURE 2
SEISMIC DESIGN ISSUES CONDUIT QUALIFICATION PROGRAM
Seismic Desi n Issues Conduit uglification Pro ram The following is provided in response to the July 31, 1986 letter from R. J. Clark to S.
A. White and Request for Additional Information Item No.
2 of enclosure 2 to that letter:
2.
Conduit Qualification Program please provide information similar to Item 1 above (background information, long-term corrective actions, and implementation schedule) for the conduit qualification program.
Part I Background Historical background on the issue of seismic design of conduits is provided in Section I.C, "Executive Summary and Historical Background," of the DNE Program Document, "Inspection and Seismic Qualification of Existing Electrical Conduit and Conduit Supports,"
which is provided as an additional enclosure to this submittal.
Part II Corrective Action Program The following documents, provided as additional enclosures to this
'submittal, present the details of the BFN conduit seismic qualification program:
DNE Program Document, "Inspection and Seismic Qualification of Existing Electrical Conduit and Conduit Supports," issued October 16, 1986 Program overview.
Project Instruction BFEP-PI 85-02, Revision 3, "Seismic Qualification of Existing Electrical Conduit and Conduit Supports,"
issued October 15, 1986 Details DNE's methods for inspection and seismic qualification of existing electrical conduits and conduit supports in Class I structures at BFN.
The following documents, provided as additional enclosures to this submittal, present additional supporting information for the conduit qualification program:
Design Criteria BFN-S0-723, "Seismically Qualifying Conduit Supports,"
issued March 28,
- 1986, as modified by Exception Number EX-BFN-50-723-1, dated May 29, 1986 Gives seismic qualification requirements.
TVA test report WR28-4-900-176, "An Experimental Investigation of Vibration Damping in Aluminum Electrical Conduit," dated March 1986 Describes TVA tests used in determining natural frequencies and damping values for aluminum electrical conduit.
2-1
TVA test report WR28-4-900-140, "A Preliminary Study of Vibration Damping in Electrical Conduit," revised March 1986 Describes tests used to determine damping values for steel electrical conduit.
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Wyle Laboratories Seismic Qualification Test Report No. 17743-1, "Test Report on Seismic Qualification/Verification of Various Aluminum Electrical Conduit Configurations," dated May 9, 1986 Demonstrated "that the specimens tested possessed sufficient structural integrity to withstand the prescribed qualification level seismic environment."
The majority of the design and modification work associated with the conduit qualification program has been completed.
Remaining inspection and qualification activities are expected to lead to requirements for additional modifications.
Modifications required for unit 2 interim-qualification are scheduled for completion by restart.
Part III Conclusion and Request for Review Certain aspects of the conduit qualification program involve establishing a new BFN design basis for interim and final seismic qualification of conduit.
In this regard, NRC is requested to take the following actions:
a.
Review and approve for interim qualification, applicable to unit 2 restart until completion of cycle 6 refueling outage, the allowable stresses given in Exception No. EX-BFN-50-723-1 to design criteria BFN-50-723.
b.
Review and approve for interim qualification, applicable to unit 2 restart until completion of cycle 6 refueling outage, utilization of the seismic experience data base as presented as Part IV of the DNE Program Document "Inspection and Seismic Qualification of Existing Electrical Conduit and Conduit Supports."
c.
Review and approve the long-term use of the damping values shown in Section 3.0, "Analytical Basis," of Design Criteria BFN-50-723 and justified in "Basis for Critical Damping for Conduit," provided as an attachment to this enclosure.
2-2
BA" S FOR CFI'ICAL DC!~ ING FOR CONDUIT TVA conducted vibration tests on electrical conduit at the Norris Testing Laboratory to determine the damping inherent in conduit, systems.
The first series of tests were conducted on 1.5 and 3 inch steel
- conduit, under a variety of conditions including cable loading amplitude of excitation, and the presence or absence of a fire barrier mat.
As can be seen in Figures 1 and 2. It was observed that damping increased more for steel conduit wrapped with two fire barrier mats.
Based on the results of these
- tests, TVA selected to conservatively use a
5 percent damping value for steel conduit.
The second series of tests were conducted on 0.75, 1.0, 1.5, 3.0, and 5.0 inch aluminum conduit under a variety of conditions including cable loading, amplitude of excitation and excitation method.
As can be seen in Figure 3, it was observed that damping increased with increased initial displacements for the 0.75, 1.0, 1.5, and 3.0 inch aluminum conduit.
Damping ratios for the 5 inch aluminum were relatively constant as a function of initial displacement.
Based on the results of these tests, TVA conserve ively selected the following damping values for aluminum conduit.
CONDUIT SIZE (inches)
PERCENT (Critical Dam in
)
0.5 - 1.5 2.0 - 3.0 4.0 - 5.0 15 10 7
El ec Cr i ca 1
Condu i t Damp ing Tests Hax imum Hires (1. Il Ibm~ft):
Hi th mat No mat 25 fU 28 C
15 E
18 I
2 5
6 7
~
0 9
Number oF Cyc1es Figure 1:
Damping Results for 1.J" Conduit
Electrical Conduit Damping Tests Tost Conditions:
3.27 1bmift, with mat
- 3. 27 1bm<ft, no mat l
~
2 3
5 6
7 9
9 Number of Cycles F i gur e 2:
Damp ing Resu 1 ts for 3"
Condu i t
Electr i ca 1
Condui t Damp ing Tests 45 48
~ 75n
.75n I
L-5'.5c 1.5c
~ 750 1.5c.75n
. 75 "
and
- 1. 5 ".
( 1-bo 1 t )
1.5c 38 25 O)
C 28 Q
E 15 C3 1,5
~ 5c I ~ 750
.75c
~
6
~
C 3C 3c lf 75n
~ 75
~ 75n I. sl I ~ 5c
.75n 1.5c I 11%
1.5" (2-bolt)
I ~ Sd 3l 3c 3&
3&
3&
3~:HG"'
"n 9 flh~g~
8 58 3&
158 3&
5" 3"
(no wiring) 258 ln I t I a 1
Di sp 1 acement (Hi 1 s)
Figure 3: Summary of Aluminum Conduit Results
SEISMIC DESIGN ISSUES
RESPONSE
TO REQUEST FOR ADDITIONAL INFORMATION ENCLOSURE 3
SEISMIC DESIGN ISSUES HVAC CONCERNS
Seismic Desi n Issues Heatin Ventilatin And Air-Conditionin HVAC Concerns The following is provided in response to the July 31, 1986 letter from R. J. Clark to S.
A. White and Request for Additional Information Item No.
3 of enclosure 2 to that letter:
3.
HVAC Concerns please provide the program to identify discrepancies between the installed system and the backfit design for staEE review and approval.
Part I Background Initially, HVAC ducts and duct supports at BFN were fabricated to industry standards without consideration of seismic loads.
In 1970, the need for HVAC ducts to be designed Eor earthquake loads was identified.
As a result, modification of existing HVAC ducts and supports was initiated.
An HVAC seismic design criteria was issued in July 1970 and transmitted to the BFN Project Manager for implementation.,
The duct construction was based on the Sheet Metal and Air-Conditioning National Association (SMACNA) standards, with both the pocket-lock and companion-flange types being used.
Several field evaluations (at least one per unit) were made by design engineers to review the as-built installations against the design criteria.
Recommendations were made as a result of the field evaluations and changes were made accordingly.
In January
- 1986, a significant condition report was written against the design criteria (BFN-50-721) used for installation and qualification of supports for the HVAC system.
That report questioned whether the design criteria was adequate to ensure the necessary seismic qualification of the HVAC system.
In addition, field investigations of the HVAC system led to concerns that significant discrepancies might exist between the as-built system and the provisions of the design criteria.
Part II Corrective Action Program The Eollowing summarizes the preliminary program of inspections and engineering evaluation which was instituted in order to address the HVAC seismic qualification concerns and the plans for a further program to provide final resolution of those concerns.
In 1986, a team consisting of individuals experienced in HVAC system design and construction, performed a field walkdown of selected safety-related HVAC systems.
The inspection was to determine:
a.
If an eEfective effort had been made to follow the requirements of the issued design criteria.
Comparison of the actual versus required span length was used in the inspection to quantify this observation.
3-1
b.
To what extent the duct systems had been modified since installation.
Modifications could have originated Erom one or both of the following sources:
- i. Changes in duct requirements, such as addition of personnel intrusion barriers or other HVAC equipment.
ii. Attaching of other systems to the HVAC ducts, stiffeners, or supports.
The results of this and additional preliminary field walkdowns and evaluations indicate that further inspections and engineering analysis are needed-in order to fully address seismic qualification oE HVAC systems.
TVA is currently in contact with an architect/engineering firm concerning the development and implementation of a seismic qualification program Eor the system.
It is expected that the program will include:
a.
Performing further Eield walkdowns to establish the exact, nature and extent of the deficiencies in the as-built system, b.
Defining new seismic qualification criteria, c.
Evaluating the as-built system versus the criteria, and d.
Designing and installing those modifications required to achieve qualiEication.
Part IIX Conclusion As discussed in Part II, the complete details oE the HVAC seismic qualification program have not been established at this time (March 1987).
The program may involve establishment of a design basis Eor HVAC seismic qualifications which would require NRC approval.
The possibility exists that an interim qualification program will need to be established Eor unit 2 restart.
However, the HVAC seismic qualification program is not sufficiently developed at this time to make those determinations.
3-2
SEISMXC DESIGN XSSUES
RESPONSE
TO REQUEST FOR ADDITIONAL INFORHATXON ENCLOSURE 4
SEISMIC DESIGN XSSUES CRD RETURN LINES
Seismic Desi n Issues Control Rod Drive CRD Return Lines The following is provided in response to the July 31, 1986 letter from R. J. Clark to S.
A. White and Request for Additional Information Item No.
4 of enclosure 2 to that letter:
4.
Control Rod Drive (CRD) Return Lines please provide the basis for the
- 51. damping factor used in the seismic re-analysis of the CRD
- piping, a summary oE the results of the analysis, a list of intended modifications and a schedule Eor completion of the modifications.
Part I Background In 1973, TVA recognized that the BFN CRDH system designer, Reactor Controls, Inc., had performed no explicit seismic analysis of the insert and withdrawal lines.
This design deficiency was reported to the AEC-DRO Region II in March of that year, in compliance with paragraph 50.55(e) of 10 CFR 50.
As corrective action, TVA modiEied some of the insert and withdrawal line supports with the intention of complying with a design criteria for seismically supporting field-routed piping, two inches and smaller.
(That criteria later became BFN-50-712.)
BFN was licensed for operation on that basis.
In September
- 1985, TVA's engineering staff questioned the seismic adequacy of existing CRDH insert and withdrawal piping supports while designing a
modification for one of the supports.
A field investigation revealed that the typical structural frame supports for the CRDH piping bundles were flexible in the horizontal direction perpendicular to the pipe axes, making their ability to resist seismic loads without overstress or excessive deElection questionable.
Adequate seismic design documentation could not be located.
Consequently, TVA contracted with Impell Corporation to address the concerns by performing an as-built analysis of the BFN unit 2 insert and withdrawal piping and supports.
Part II Corrective Action Program In order to resolve the concerns over seismic qualification of the CRDH return lines, a program of analysis of the as-built piping and supports has been conducted in conjunction with a program to develop and implement new analysis guidelines for support modifications.
Impell began field inspections in October 1985 to obtain as-built data on the CRDH system piping and supports.
During, November
- 1985, TVA evaluated the need for special guidelines Eor this problem which involves supports for 185 one-inch diameter insert pipes; and 185 3/4-inch diameter withdrawal pipes.
(A single frame supports up to 100 pipes and the piping extends from the hydraulic control units outside the drywell to the CRD mechanisms on the reactor vessel.)
Preliminary analysis guidelines were provided to.Impell in December
- 1985, and preliminary analyses were begun at that time.
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By the end of February 1986, Impell had obtained preliminary analysis results.
After review of these analyses by TVA, Impell, and General Electric, the following significant adjustments were made to the preliminary analysis guidelines:
1.
The loading conditions for analysis, particularly the thermal conditions for reactor scram under normal and abnormal circumstances, were refined; 2.
Excess conservatism was reduced in the seismic response calculations by using five-percent damped floor response spectra; 3.
Realistic support deflection limits under seismic loading were established; and 4.
Provisions were made for an augmented Class 2 fatigue evaluation.
The adjusted guidelines were finalized in April 1986 and formally issued in August 1986 (Reference 1).
A more detailed discussion of the analysis guidelines is given in the attachment to this enclosure.
As of November 1986, Impell and TVA.had completed the analysis of the unit 2 CRDH system in accordance with the analysis guidelines.
Extensive support modifications have been designed and installation is underway.
Modifications on the unit 2 CRDH system will be completed before restart.
E Part III Conclusion and Request for Review The program for resolution of concerns over the CRDH system seismic qualification includes an increase from 0.5-percent (OBE) and one-percent (DBE) to five-percent (DBE) in the level of damping assigned to the CRDH piping in the seismic analysis.
This constitutes a change to the original BFN design basis for the CRDH system.
The discussion provided in the attachment to this enclosure justifies the use of the'ive-percent damping coefficient on an integrated basis, which includes an assessment of the overall (coupled) behavior of the piping, bolted clamps, and structural support components.
In regard to this matter, NRC is requested to take the following action:
Review the attached justification and safety evaluation and approve, as a new BFN design basis, the use of a five-percent damping coefficient for analysis of the BFN CRDH system piping and supports.
Subsequent to NRC staff approval and completion of the unit 2 modification activity, the BFN FSAR will be amended to reflect the use of a five-percent damping coefficient for CRDH system piping.
4-2
ENCLOSURE 4 ATTACHMENT JUSTIFICATION FOR THE USE OF FIVE-PERCENT DAMPED FLOOR RESPONSE SPECTRA IN THE ANALYSIS OF CRDH SYSTEM PIPING AND SUPPORTS Anal sis Overview The guidelines for CRDH piping and support analyses have been developed to ensure that the originally intended safety margins are provided for all loading conditions, while excess conservatism is avoided.
In order to avoid problems with thermal expansion and fatigue, care had to be taken to preserve sufficient pipe flexibilityto allow the thermal movements while ensuring acceptable pipe stresses and support loads for combined thermal and seismic activity.
The design basis floor response spectra used for typical piping,
- analysis, based on 0.5 and one-percent damping (for OBE and
- DBE, respectively), is too conservative to achieve a proper balance between thermal and seismic inertial stress for the CRDH system piping, and supports.
(The same general observation has been made recently by other organizations in the nuclear industry, including NRC in NUREG-1061, Volume 2.)
In this particular
- case, use of excessively conservative seismic response spectra would have resulted in a less reliable and less safe CRDH system design due to over-restraint of the piping by rigid supports.
TVA recognized the need to define more realistic seismic response spectra for CRDH piping analysis in March 1986.
At that time, TVA also recognized that some potential unconservatisms in the original BFN analysis methodology needed to be eliminated for the analysis of the CRDH piping.
The following details the major differences from the typical piping analysis methodology which have been incorporated by the CRDH analysis guidelines:
l.
Use of the five-percent damped response spectra.
(The typical approach uses 0.5-percent damped spectra for OBE and one-percent damped spectra for DBE.)
2.
Use of vertical response spectra equal to two-thirds of the horizontal ground spectra.
(The typical approach uses a flat vertical response spectra equal to 0.067 g for OBE and 0.13 g for DBE.)
3.
Use of 10-percent peak broadening for response spectra.
(Peak broadening, is not used in the typical approach.)
4.
Calculation of DBE seismic response spectra and setting OBE response spectra equal to two-thirds of DBE response.
(The typical approach uses 0.5-percent damped spectra for OBE and one-percent damped spectra for DBE.)
5.
Explicit support displacement limit of one-eighth inch for DBE loads.
(Support displacement limits are not explicitly defined by the typical approach.)
6.
Application of 20-percent uncertainty factor for deadweight loads on.
supports.
(No deadweight uncertainty factor is applied under the typical approach.)
~
-3 7.
Specific load combination techniques which produce a reasonably, but not excessively, conservative consideration of multipipe seismic loads on the frame supports.
(No explicit requirements for multipipe seismic load combinations were defined in the original analysis of the CRDH system.)
In addition, an augmented Class 2 fatigue evaluation was performed which demonstrates the low fatigue usage factors for the CRDH piping system as modified.
The highest calculated usage factor for CRDH piping outside the drywell was 0.06 and 0.01 inside the drywell.
This data provides assurance that the design is safe for both seismic and thermal expansion conditions.
In conclusion, the analysis guidelines provide for a more appropriate and precise analysis of the CRDH piping and supports than the typical piping, analysis methodology would allow.
After completion of all modifications,. the CRDH system piping and supports will meet or exceed all safety margins intended by the original BFN design basis.
Safet Evaluation The following information is provided as technical justification for the use of five-percent damped floor response spectra in the analysis of the CRDH system piping and supports, and as documentation of TVA's conclusion that use of five-percent damping for analysis of this system forms a conservative basis for the design of the system.
There are three main elements to the evaluation.
1.
Test data on conduit supported similarly to the CRDH piping; 2.
Actual physical arrangement and calculated stress results; and 3.
Recent studies on pipe damping at high strain levels.
Conduit Test Data As part of the seismic qualification program for electrical conduit, TVA conducted a series of damping tests on aluminum and steel conduits (References 2, 3, and 4).
These tests indicate damping values in excess of five-percent, even for relatively low stress levels.
The support arrangements for the tested conduit and the CRDH piping are very similar in that both
,support arrangements utilize similar clamp/guides for supports.
This similarity in support configuration provides the basis for the judgment that the conduit test data indicating damping values greater than five-percent is applicable as well to the CRDH piping.
Physical Arrangement and Stress Calculations Evidence of the adequacy of the five-percent damped spectra for application to the CRDH system is oEfered by consideration of the physical arrangement of the CRDH piping system and the calculated stress results.
The piping is supported by rigid guides which have gaps between the inside surface of the guide and the outside surface of the pipe.
This supporting arrangement increases effective damping and reduces the tendency for reasonant
- response, particularly in-phase resonant response with other pipes on the same support frame.
The piping is schedule 80 stainless steel one-inch and 3/4-inch nominal diameter.
There are Eew in-line valves (none in the drywell) and those valves are small rugged units without extended structures of significance.
All calculated pipe stresses and component accelerations and nozzle loads are well within acceptable limits.
Pipe clamp and guide loads are also well within rated limits which are based on conservative safety factors.
Finally, the combination of seismic loads and scram thermal loads produces calculated total pipe stresses around yield so that high structural damping is expected for the seismic plus scram load cases which control the support Erame designs.
Recent Pipe Damping Studies The expectation of high structural damping has been substantiated by recent NRC-sponsored studies for pipe damping at high strain levels (Reference 5).
Those studies predict seismic inertial load safety factors greater than three for piping designs of this type which are based on Eive-percent damped response spectra and ASHE piping code allowable stresses.
Effective damping is shown to reach 30 to 50 percent of critical as plastic hinges are Eormed in the piping before its structural integrity or functionality is significantly impaired by seismic inertial loads.
Conclusion Given the evidence cited above, TVA has determined that a five-percent damping factor represents a reasonable, conservative basis for the design oE the BFN CRDH system piping and upports.
References 1.
TVA Quality Information Release No.
QIRCEB86016 entitled, "Control Rod Drive Hydraulic (CRDH) System Analysis Guidelines, August 1986" 2.
TVA Report No. MR28-4-900-140 entitled, "A Preliminary Study of Vibration Damping in Electrical Conduit, March 1986 Revision" 3.
TVA Report No. WR28-4-900-176 entitled, "An Experimental Investigation of Vibration Damping in Steel Electrical Conduit (Interim Report),
March 1986" 4.
TVA Report No. VJR28-4-900-179 entitled, "An Experimental Investigation oF Vibration Damping in Steel Electrical Conduit (Interim Report),
March 1986" 5.
EG6G Idaho, Incorporated, Report EGG-EA-7380 (Draft) entitled, "An Evaluation of Damping in Piping Systems at High Strain Levels," Published September
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V
SEISMIC DESIGN ISSUES
RESPONSE
TO REQUEST FOR ADDITIONAL INFORMATION ENCLOSURE 5 SEISMIC DESIGN ISSUES IEB 79-14 AND 79-02
Seismic Desi n Issues Ins ection 6 Fnforcement IE Bulletins 79-14 and 79-02 The following is provided in response to the July 31, 1986 letter from R. J. Clark to S.
A. White and Request for Additional Information Item No.
5 of enclosure 2 to that letter:
5.
IE Bulletins 79-14 and 79-02 please provide a concise description of the reevaluation criteria Eox the piping system with identification of changes from the
- FSAR, a statement confirming that all operability evaluations are complete, and a schedule for completion of Phases I, II, and III of the pxogram.
Part I Background Programs were initiated in 1979 to comply with IEB 79-02 and 79-14 regarding the adequacy of piping system anchor bolts and supports.
A 1983 NRC inspection oE the ongoing 79-02 and 79-14 programs at BFN resulted in a favorable report with no open items identiEied.
In 1985, after a major portion of the 79-14 program was complete, questions suxfaced regarding the adequacy of the pxevious inspections.
Later in 1985, it was determined that some repairs made under the 79-02 program were out of specified design tolerances.
Further, it was determined that certain piping systems and their supports, previously excluded from the initial scopes of the 79-02 and 79-14 programs, requixed inspection and evaluation under these bulletins.
In 1986 and early 1987, the 79-02 and 79-14 programs were revised to address previous concerns.
The program details are presented in Part II.
Part II Corrective Action Program The following is a description of each of the three phases of the IEB 79-02 and 79-14 program.
Phase I The initial evaluation of the inspection data for potential safety problems will be performed, completed, and documented almost concurrently with the inspection.
As individual inspection deviations are discovered, they will be sent to engineering Eor evaluation.
At any time, if the deviation is determined to be a potential safety
- problem, a seismic analyst's discrepancy resolution input sheet (BFEP-PI 85-01,.1) will be initiated and action will be taken in accordance with facility technical specifications within the appropriate limiting condition Eor operation.
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Phase IX The second phase of evaluation shall be to evaluate each system for code compliance.
Following the receipt of the Phase I inspection data package (i.e.,
one system in one unit) and any verification walkdown information, engineering shall evaluate all data with respect to existing analysis and code requirements.
Phase III Modifications resulting from reanalysis and/or support design is the next step to ensure compliance.
The following documents, provided as additional enclosures to this submittal, present the details of the BFN IEB 79-02 and 79-14 programs.
Project Instruction BFEP-PI 86-05, Revision 0, "NRC-OIE Bulletin 79-02/79-14 Program Document for Browns Ferry Nuclear Plant" Project Instruction BFEP-PI 85-01, Revision 1, "Implementation of NRC-OXE Bulletins 79-02/79-14 for Browns Ferry Nuclear Plant" The following documents, provided as additional enclosures to this submittal, present additional supporting information for the BFN IEB 79-02 and 79-14 programs:
TVA BFN Standard Practice/Instruction, SMMI-5.1-A, "Verifying Correct Installation of Self-Drilling Anchor Bolts" TVA BFN Mechanical Maintenance Instruction, BF MMI-99, "Xnstructions for the Implementation of NRC IE Bulletin 79-14, Units 1, 2, and 3" Part IIX Conclusion and Request for Review The implementation of the IEB 79-02 and 79-14 programs will proceed accor.ding to the following schedule.
Unit 2 and Common Areas:
Phase I completed before restart; Phases XI and XXX completed before the end of next unit 2 refueling outage (cycle 6 refueling outage)
Units 1 and 3:
Phases I, II, and III completed before restart.
In regard to the IEB 79-02 and 79-14 programs and implementation schedule, the NRC staff is requested to take the following actions.
a, Review the programs as presented in BFFP-PI 86-05 and BFEP-PI 85-01, and approve their use in resolution of IEB 79-02 and 79-14 for BFN;
b.
Approve the following schedule for completion of the three phases oE the IEB 79-02 and 79-14 program for un'it 2 only.
Phase I:
Completion beEore the end of cycle 5 refueling outage Phase II:
Completion before the end of cycle 6 refueling
- outage, but after the end of cycle 5 refueling outage Phase III: Completion before the end of cycle 6 refueling
- outage, but after the end of cycle 5 refueling outage.
In regard to changes to the BFN FSAR, it is planned that the IEB 79-02 and 79-14 program will utilize an artificial time history for analysis of the piping systems involved, in place of the El Centro earthquake record originally utilized for piping design analysis.
Justification Eor the use of the artificial time history in analysis will be provided for NRC staEE review in a separate submittal.
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SEISMIC DESIGN ISSUES
RESPONSE
TO REQUEST FOR ADDITIONAL INFORMATION ENCLOSURE 6
SEISMIC DESIGN ISSUES SMALL BORE PIPING
Seismic Desi n Issues Small Bore Pi in The following is provided in response to a telephone request on September 11,
- 1986, by NRC/NRR to provide background and program information on the seismic qualification of Class I small bore piping.
Part 'I Background The majority of the Class I small bore (one-half to two-inch diameter) piping at BFN was field routed and field supported, with installation in accordance with American National Standards Institute standards.
The first design criteria recorded for the small bore piping supports was "Design Criteria for Supporting Process Instrument Piping and Instrument Air l.ines," dated Hay 3, 1971.
An additional design criteria, "Criteria for Seismically Qualifying Field Run Piping Sizes 1/2 through 2 Inches,"
was issued on November 29, 1972.
The two criteria were re-issued as controlled document BFN 50-712 in 1972.
In 1984, a nonconformance report (NCR BFNMEB 8406) was written due to the application of BFN 50-712 to the installation of schedule 160 pipe.
Use oE schedule 160 pipe was not addressed in the design criteria.
During the review of BFN 50-712 for addition of, schedule 160 pipe, it was determined that the qualification of some baseplates in the typical support details of the criteria could not be verified and that no weld details were specified.
In regard to the use oE schedule 160 pipe, it was determined that some support members Eor field routed schedule 160 piping could be underdesigned since their selection was based on the tables in the design criteria for schedule 40 and 80 piping.
A signiEicant condition report (SCR BFNCEB 8520) was written addressing those conditions and BFN 50-712 was revised to place the support details on hold until resolution of the SCR.
Part II Corrective Action Program In order to address the concerns surrounding the seismic qualification of Class I small bore piping, a preliminary evaluation was done of the as-built systems.
The preliminary field walkdowns and evaluations indicate that further inspections and engineering analysis are needed in order to fully address seismic qualification of small bore piping systems.
TVA is currently in contact with an architect/engineering, firm concerning, the development and implementation of a seismic qualification program for the system.
It is expected that the program will include:
a.
Performing further field walkdowns to establish the exact nature and extent of the deficiencies in the as-built system, b.
Defining an acceptance criteria for the existing installation, c.
Evaluating the as-built system using the acceptance
- criteria, and'-1
ar
d.
Designing and installing any modifications required to achieve qualification of the Class I small bore piping.
Part III Conclusion As discussed in Part II, the complete details of the Class I small bore piping seismic qualification program have not been established at this time (March 1987).
The possibility exists that an interim qualification program will need to be established for unit 2 restart.
Mowever, the program is not sufficiently developed at this time to make that determination.
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