ML20003G676

Testimony on Behalf of Util on Doherty Contention 9 Re Containment Buckling.Prof Qualifications Encl

ML20003G676
Person / Time
Site:	Allens Creek File:Houston Lighting and Power Company icon.png
Issue date:	04/20/1981
From:	Mokhtarian K CBI SERVICES, INC. (FORMERLY CHICAGO BRIDGE & IRON
To:
Shared Package
ML20003G672	List: ML20003G671 ML20003G673 ML20003G674 ML20003G675 ML20003G676 ML20003G677 ML20003G678
References
NUDOCS 8104300481
Download: ML20003G676 (11)

Text

i 4-20-81 Q t L 191 psb M

1 UNITED STATES OF AMERICA 2

poC NUCLEAR REGULATORY COMMISSION

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2 ggF BEFORE THE ATOMIC SAFETY AND LICENSING BOARD t#s9*

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In the Matter of

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HOUSTON LIGHTING & POWER COMPANY)

Docket No. 50-466

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6 (Allens Creek Nuclear Generating)

Station, Unit No. 1)

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8 DIRECT TESTIMONY OF KAMRAN MOKHTARIAN ON BEHALF OF HOUSTON LIGHTING & POWER COMPANY 9

ON DOHERTY CONTENTION NO. 9-CONTAINMENT BUCKLING 10 0

Please state your name and place of employment.

11 A.

My name is Kamran Mokhtarian.

I am employed by Chicago 12 Bridge & Iron Company.

My business address is 800 Jorie 13 Boulevard, Oak Brook, Illinois.

14 0

Please describe your professional qualifications.

15 A.

A statement of my background and qualifications is, 16 attached as Exhibit KM-1.

17 0

WSy have you prepared this testimony?

18 A.

The purpose of this testimony is to address Doherty's 19 Contention No. 9 which alleges that the Applicant's steel 20 containment shell will not be strong enough to resist 21 buckling under the design loads.

Doherty's Contention No. 9 1

22 alleges:

23 That Intervenor's health and safety interests are inadequately protected because Applicant's steel 24 containment shell is not strong enough by design to resist dynamic and static loads which may 25 plausibly occur in the life of the atomic plant.

l l

26 The only specific basis stated in the contention for the 1

27 above allegations are four observations on containment 1

28 vessel bucking evaluation methods paraphrased from a l

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1 2 preliminary (Jan.1978) report of an NRC coasultant, namely:

3 (1)

Adequate experimental data for determining design 4

criteria did not exist.

5 (2)

Computer programs for determining building loads 6

do not predict experimental buckling results very well.

7 (3) That the ASME Section III Buckling Criteria 8'

Regulatory Guide 1.57 NE-3224 (sic) " permits designers 9

to select the method which yields a buckling stress 10 which is least conservative."

11 (4)

Until more test data is obtained to study the 12 effects of imperfections, asymmetric loading, load 13 interaction, dynamic and nonlinear effects, a con-14 servative factor of safety such as 3 should be used."

15 Q.

Will you describe how the containment for Allens Creek 16 is being designed?

17 A.

The steel containment vessel for ACNGS, as specified in 18 Subsection 3.8 of the PSAR, is being designed in accordance 19 with the requirements of the American Society of Mechanical 20 Engineers Boiler and Pressure Vessel Code (ASME Code) 21 Section III, Subsection NE.

Chicago Bridge & Iron Company 22 (CBI) is designing the steel containment vessel and its 23 appurtenances for the ACNGS.

The Applicant, through Ebasco, 24 has prepared the design specification required by Paragraph 25 NA-3250 of the ASME Code for use by CBI in their design of 26 the ACNGS steel containment vessel and its appurtenances.

27 This design specification establishes the minimum requirements 28 for the design of the vessel.

These requirements include l

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1 2 the identification of the load definitions and the establish-3 ment of appropriate load combinations and related acceptance 4

criteria to be employed in assessing structural stability 5

and buckling capacity.

6 CBI is performing the required analyses and design 7

activities to configure the steel containment vessel which 8

will comply with the Applicant's design specification.

CBI 9

upon completion of their ongoing design activities, will 10 prepare and submit to the Applicant a Certified Stress 11 Report in accordance with Article NA-3350 of the ASME Code.

12 0

How does this design 'rocess account for buckling?

13 A.

The PSAR Table 3.8-2 Atlines the buckling criteria in 14 use for ACNGS.

This criteria is based on the classical 15 linear theory with reductions applied to account for imper-16 fections in vessel geometry and other differences between 17 theoretical and actual load capacities.

18 Basically, the method used on ACNGS for the buckling 19 evaluation is the following:

20 1.

The containment vessel is mathematically modeled 21 using Kalnins' Shells of Revolution Program which has been 22 verified as producing results for axisymmetric shells 23 comparable to those of finite element programs recommended 24 in NUREG/CR-0793.

The Kalnins' Program is based on linear 25 theory.

The loads, as specified for ACNGS, are imposed on 26 this mathematical n.odel of the containment vessel in accord-l 27 ance with the specified loading combinations.

The program 28 has capabilities for axisymmetric and nonaxisymmetric stress l

1 1 2'

analyses of axisymmetric shell structures.

3 2.

For the buckling analysis, the maximum compressive 4

stresses at any azimuth are assumed to act uniformly all the 5

way around, resulting in a conservative analysis.

6 3.

The maximum stresses resulting from the sum of I

7 the static and dynamic loads will be compared to critical 8

buckling stresses using the specified stress interaction 9

equations which include the appropriate factors of safety.

10 This method of analysis accounts for the amplification 11 factors on stresses due to dynamic loadings.

These resulting 12 stresses, however, are treated as equivalent static stresses This is a 13 for comparison with critical buckling stresses.

14 conservative approach, since a structure can withstand 15 stresses due to dynamic loadings that are equal to or, in 16 many cases, greater than critical stresses from statically 17 applied loadings.

18 The buckling capacity of the shell is based on linear 19 bifurcation (classical) analyses reduced by capacity reduction 20 factors which account for the effects of imperfections and 21 nonlinearity in geometry and boundary conditions and by 22 plasticity reductica factors which account for nonlinea ity 23 in material properties.

factors of 24 In addition to the above reduction factors, safety are employed in the assessment of structural stability.

25 26 A factor of safety of 2.75 is applied wherever the critical The safety 27 buckling stresses are in the elastic range.

28 factor is linearly reduced from 2.75 to 2.0 between the l

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- +. - - - -

1 1 1 2'

proportional limit and the yield stress of the material.

3 Where the critical stresses approach the yield strength of 4

the material, material deformation becomes the controlling 5

factor rather than buckling.

6' In addition to meeting the requirements of PSAR Table 7

3.8-2, the design of ACNGS containment vessel will meet the 8:

requirements of ASME Code Case N-284, titled " Metal Con-9 tainment Shell Buckling Methods," issued August 25, 1980.

10 Q.

What do you understand to be the basis for Mr. Doherty's 11 contention?

12 A.

Mr. Doherty filed, as a basis for his contention on 13 containment buckling, his summary of a preliminary progress 14 report submitted to the NRC Staff in January, 1978, by 15 International Structural Engineers, Inc. (ISE).

ISE was 16 under a consulting contract with the NRC to study contain-17 ment buckling analysis.

The preliminary report included a 18 number of preliminary observations which we,re cited by 19 Mr. Doherty as criticisms of the present predictive methods 20 used for buckling evaluation of containment vessels.

ISE's 21 final report was published as NUREG/CR-0793, " Buckling 22 Criteria and Application of Criteria to Design of Steel 23 Containment Shell" (May, 197 9).

24 Q.

Would you discuss each of the observations made in the 25 consultant's preliminary report which Mr. Doherty cites?

26 A.

Those preliminary observations as paraphrased and cited 27 by Mr. Doherty in his contention are quoted and responded to 28 in the following four paragraphs:

1 2' 1.

" Adequate Experimental data for determining design 3l criteria did not exist."

4 over the past decade a systematic collection has been 5

made by cBI of several hundred technical papers known to contain experimental data on shell buckling.

These tests 6l.

7 include stiffened and unstiffened shells subjected to a 8

variety of loads or loading combinations.

Several of these 9

tests have been performed on models fabricated with procedures 10 representative of those used on containment vessels.

11 The final consultant's report recognized the fact that 12 adequate experimental data does exist for shells subjected 13 to axisymmetric static loadings.

The concern seemed to 14 remain that there may be a lack of data for shells subjected 15 to dynamic asymmetric loadings.

This concern will be conserva-16 tively accounted for in the methods employed in design and 17 analysis of ACNGS containment vessel.

The specified dynamic 18 loadings will be applied to a mathematical model of the 19 vessel.

A shells of revolution program having dynamic 20 analysis capabilities will be used.

The resulting stresses, 21 which include the effects of dynamic amplification factors, 22 will then be used as equivalent static stresses for buckling 23 evaluation of the vessel.

34 The asymmetric stress effects are also conservatively 25 treated by applying the maximum stress around the entire 26 azimuth as an axisymmetric (uniform) stress.

The final 27 consultants' report recommends this procedure as a con-28 servative approach.

1 2 2.

" Computer programs for determining buckling loads 3

do not predict experimental buckling results very well."

4 It is well recognized that the results of computer pro-5 grams based upon classical theory must be modified to predict 6

the buckling capacity of imperfect shells.

For the ACNGS 7

vessel, the classical buckling values are reduced by knockdown 8

and plasticity reduction factors, which conservatively 9-account for the difference between the theoretical elastic 10 buckling value for a perfect shell and the critical buckling 11 capacity of a fabricated shell.

12 Both the preliminary and the final consultants' reports 13 endorsed this approach as the preferred method of arriving 14 at the critical buckling loads.

15 3.

"That the ASME Section III Buckling Criteria 16 Regulatory Guide 1.57, NE-3224 (sic), permits designers to 17 select the method which yields a buckling stress which is 18 least conservative."

19 The classical linear buckling analysis with reductions 20 based on test results, which is the buckling evaluation 21 method used for ACNGS vessel, is the method preferred and 22 recommended by the consultants.

This approach, outlined in 23 previous paragraphs, is~.the most widely used approach for 24 shell buckling evaluation.

Applicant does not intend to 25 perform any buckling evaluation for the ACNGS vessel using 26 either of the other two methods permitted.

27 4.

"Until more test data is obtained to study the 28 effects of imperfections, asymmetric loading, load interaction,

1 2 dynamic and nonlinear effects, a conservative factor of 3

safety such as 3 should be used."

4 The final consultants' report recognized that imper-5 fections, asymmetric loadings, load interactions, dynamic 6

loadings, and nonlinear effects can all be treated in a 7

conservative manner, and that a safety factor of 2.0 will be 8

adequate.

As the final consultants' report states, "It is 9

felt that a safety factor of 2 is sufficient to achieve a 10 conservative design for all states of stress, if applied to 11 reduction factors obtained as the minimum of experimentally 12 obtained data."

This recommendation of the consultants' 13 Report is consistent with the buckling criteria of the ASME 14 Code Case N-284, the requirements of which will be met for 15 this vessel.

16 0

would you summarize your opinions concerning Mr.

17 Doherty's contention?

18 A.

The four (4) observations cited by Mr. Doherty's 19 contention have either been superceded in whole or in part 20 by their own authors in the final consultant's report to the 21 NRC (NUREG/CR-0793, May, 1979) or they are well accounted 22 for in the design of the ACNGS containment vessel.

The 23 method of analysis employed for the design of the ACNGS 34 containment vessel will result in a conservative prediction of 25 stresses and the buckling evaluation method employed will 26 produce a safe and conservative design.

27 28 i

I 1

Exhibit KM-1 2

EDUCATION AND PROFESSIONAL QUALIFICATIONS 3

KAMRAN MOKHTARIAN 4

RESIDENCE:

BUSINESS:

5 442 Claremont Court Chigago Bridge s Iron Co.

6 Downers Grove, Illinois 60516 800 Jorie Blvd.

7 Oak Brook, Illinois 60521 8

EDUCATION:

9 B.S. Degree in Civil Engineering, Cleveland State University 10 1963 11 M.S. Degree in Structural Mechanics, Northwestern 12 University, 1964 13 Graduate level courses at Illinois Institute of Technology 14 EXPERIENCE:

15 Employed by Chicago Bridge & Iron Co. from 1964 to present.

16 August 1964-August 1965 - Design Engineer: Working on design 17 of vacuum chambers and pressure 18 vessels.

19 August 1965-June 1966

- Field Engineer: Working on fab-20 rication and construction of tanks 21 and vessels in an oil refinery.

22 June 1966-August 1967

- Design Engineer: Working on design 23 and analysis of nuclear reactor 24 vessels.

25 August 1967-May 1972

- Group Leader: Having responsibility 26 for stress analysis of nuclear 27 reactor vessels and preparation 20 of ASME Code Stress Reports.

1 May 1972-Sept. 1975

- Supervisor of Stress Analysis:

2 Having responsibility for complete 3

design and analysis of nuclear 4

structures.

Supervising groups 5

of engineers performing heat 6

transfer analysis, fatigue and 7

fracture analysis, shell and 8

finite element analysis, and 9

buckling analysis.

Reviewing 10 and certifying complete code 11 design and stress reports.

12 Sept. 1975-July 1977

- Project Engineer: Having overall 13 engineering responsibility for 14 design and analysis of the 15 containment veaul for the Clinch 16 River Breeder Reactor Project.

17 Helped develop buckling criteria 18 to be used for the design of that 19 vessel.

20 July 1977-To Date

- Design Supervisor: Having respon-21 sibility for design of various 22 nuclear structures.

Supervising 23 groups of engineers working on M

design and analysis of various 25 containment vessels.

Helped with 26 developing buckling criteria to E

be used for design of Mark III 28 containment vessels.

Helped with

I the development of and authored 2

portions of the ASME Code Case I

N-284, titled " Metal Containment 4

Shell Buckling Design Methods".

5 PROFESSIONAL REGISTRATION:

6 Registered Professional Engineer in State of Ohio 7

HONOR SOCIETIES:

0 Tau Beta Pi 9

Pi Mu Epsilon 10 PUBLICATIONS:

11 "Hotspot Flexure of Plate on Circular Support",

I 12 Journal of the Engineering Mechanics Division of l

i 13 ASCE, June 1968 14 15 16 l

17 l

18 19 8

i 20 21 22 23 24 26 27 28 t