ML14138A105

Forwards Summary of Resolution for Items Discussed at 821110 Meeting Re SEP Topic III-6, Seismic Design Considerations. Evaluations Supporting NRC Review Also Encl

ML14138A105
Person / Time
Site:	San Onofre
Issue date:	11/26/1982
From:	Paulson W Office of Nuclear Reactor Regulation
To:	Dietch R SOUTHERN CALIFORNIA EDISON CO.
Shared Package
ML13308A812	List: ML13308A811 ML14138A105
References
TASK-03-06, TASK-3-6, TASK-RR LSO5-82-11-084, LSO5-82-11-84, NUDOCS 8212010023
Download: ML14138A105 (12)

Text

NOY2 1982 Docket No..50-206 LS05-82-11-084 Mr. R. Dietch, Vice President Nuclear Engineering and Operations Southern California Edison Company 2244 Walnut Grove Avenue Post Office Box 800 Rosemead, California 91770

SUBJECT:

SEP TOPIC 111-6, SEISMIC DESIGN CONSIDERATIONS SAN ONOFRE NUCLEAR GENERATING STATION, UNIT 1 Based upon the information presented in our meeting of November 10, 1982, the staff has reached preliminary conclusions regarding the following issues:

1. Adequacy of the Reactor Coolant Loop Analysis

2. Position Regarding the Vent Stack

3. Seismic Design Adequacy of Electrical Equipment and Instruments (Structural Integrity)

4.

Inclusion of Seismic Anchor Movements in the Evaluation of Piping a

and Their Supports

5. Mechanical Equipment Structural Integrity

6. Effects of Ground Motion Amplitude on Seismic Response

7. Uncertainty in Soil Structure Interaction Our evaluation of these issues from the information you presented is contained in Enclosure 1. It is our understanding that your analyses for Balance of Plant Mechanical Equipment and Piping (BOPMEP) conform to the criteria we provided in our September 20, 1982 letter except in the areas you identified. It is requested that you confirm this understanding by updating your Seismic Reevaluation Criteria which was submitted as to your October 8, 1981 letter.

The staff will issue a draft Safety Evaluation Report (SER) in December 1982.

This draft SER will be based upon the information received to date, will identify areas of continuing review and information needed to complete the review, and will identify those aspects of the reevaluation program which havo been found 4cceptable.

-8212010023 821126 sI PDR ADOCK 05000206 p.

PDR NRC FORM 318 (10-80) NRCM 0240 OFF ICIAL RECORD COPY USGPO: 1981-335-960

Mr. R. Dietch

-2 Enclosures 2 through 5 are reports received from consultants supporting the staff's review.

Our review of these reports is not yet complete.

The staff would like to discuss these reports with you during the week of November 29, 1982, to ensure a common understanding of the questions iden tified in these reports. In addition, please have available for review the piping analyses for the following stress problems:

MS-363 FW-04 SI-51 MS-01 From the piping stress problems, also provide the analyses for the six most highly stressed supports for these systems.

Sincerely, Walter Paulson, Project Manager Operating Reactors Branch No. 5 Division of Licensing

Enclosures:

As stated cc w/enclosures:

See next page

• See previous concurrence SEPB

• SEPB*

SEPB*

SEPB*

OR ORB SURNAME 11/22/82 11/22/82 11/22/82 11/22/82 11/

82 11 DATEN FOR 318 (1..8..

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NRC FORM 318 (10-80) NRCM 0240 OFFICIAL R EC ORD CO PY USGPO: 1981-335-960

Mr. R. Dietch

-2 Enclosures 2 through 5 are reports recieved from consultants supporting the staff's review. Our review of these reports is not yet complete. The staff would like to discuss these reports with you during the week of November 29, 1982, to issue insure a common understanding of the questions identified in these reports. In addition, please have available for review the piping analyses for the following stress problems:

MS-363 FW-04 SI-51 MS-01 From the piping stress problems, also provide the analyses for the six most highly stressed supports for these systems.

Sincerely, Walter Paulson, Project Manager Operating Reactors Branch No. 5 Division of Licensing

Enclosures:

As stated cc w/enclosures:

See next page OFFICE

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URNAME YChen:bl EMcKenna RHermann WRussel WPaulson DC*rutchfield S R A E k.....................

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uNc FORM 318 (10-80) NRCM 024o OFFICIAL RE CO RD COPY USGPO: 1981-335-960

Mr. R. Dietch San Onofre Unit 1 Docket No. 50-206 cc Charles R. Kocher, Assistant General Counsel James Beoletto, Esquire Southern California Edison Company Post Office Box 800 Rosemead, California 91770 David.R. Pigott Orrick, Herrington & Sutcliffe 600 Montgomery Street San Francisco, California 94111 Harry B. Stoehr San Diego Gas & Electric Company P. 0. Box 1831 San Diego, California 92112 Resident Inspector/San Onofre NPS c/o U. S. NRC P. 0. Box 4329 San Clemente, California 92672 Mayor City of gan Clemente San Clemente, California 92672 Chairman Board of Supervisors County of San Diego San Diego, California 92101 California Department of Health ATTN:

Chief, Environmental Radiation Control Unit Radiological Health Section 714 P Street, Room 498 Sacramento, California 95814 U. S. Environmental Protection Agency Region IX Office ATTN:

Regional Radiation Representative 215 Freemont Street San Francisco, California 94111 Robert H. Engelken, Regional Administrator Nuclear Regulatory Commission, Region V 1450 Maria Lane Walnut Creek, California 94596

LIST OF ENCLOSURES AND ATTACHMENTS :

Summary of Resolution for Items-Discussed at the November 10, 1982 Meeting. :

Structural Review of SONGS-1 Seismic Reevaluation by Lawrence Livermore National Laboratory. :

Partial Review Comments of SONGS-1 Piping Systems and Equipments by Idaho National Engineering Laboratory (EG&G). :

Review of Seismic Reevaluation of Reactor Building and Balance of Plant Structures of the SONGS Unit 1 by NCT Engineering, dated September 1982. :

Review comments from Professor W. J. Hall.

• closure 1

SUMMARY

OF RESOLUTION FOR ITEMS DISCUSSED AT THE NOVEMBER 10, 1982 MEETING 1.. Adequacy of Reactor Coolant Analysis The use of only one time history for the analysis of the NSSS nonlinear systems is questionable because nonlinear response of the system is very sensitive to the characteristics of the input time histories.. Also,.

uncertainties exist between the model frequencies of structures, piping and components that can change results and which have not been considered.

Many of the components, according to the nonlinear analysis, have a safety margin of only 1.1.

In addition, the staff's position on the appropriate ness of the 0.67g Housner spectra is that the licensee should demonstrate adequate safety margin to accommodate up to 10% exceedance in ground spectra.

Your response to this latter issue did not specifically consider nonlinear nature of the system behavior.

The uncertainty in soil-structure interaction study also adds to the complication of this issue.

Therefore, it is the staff's position that the licensee should perform three more

,time history analyses of the NSSS system using the three real earthquake time histories used for the Fuel Storage Building analyses.

Furthermore, in order to account for the uncertainty in soil-structure interaction, each time history analysis should consider the following range of soil stiffness:

Best Estimate soil stiffness (KBE),

0. 7KBE and 1. 3 KBE The analyses should be performed in such a manner that the characteristic of each time history combined with one of the three soil stiffnesses will produce the most conservative responses.

-2

2.

Vent Stack The licensee should perform an analysis to-ensure the structural-integrity of the stack under combined dead load and seismic loads,-or demonstrate that the consequences of failure of the stack will not damage the safety related structures, piping and/or equipment.

3. Seismic Design Adequacy of Electrical Equipment and Instruments (Structural Integrity)

In an earlier conference call with the licensee the staff agreed that the licensee does not need to address the instrument supports and load path for the restart of the plant. This is contingent upon verification that the completed anchorages have been analyzed and evaluated including the assurance of both anchorage and cabinet attachment adequacy. However, the subject issue should be included in the scope of SEP Topic 111-6, "Seismic Design Considerations."

4. Inclusion of Seismic Anchor Movements (SAMs) in the Evaluation of Piping and their Supports.

(i) Piping Stresses due to Seismic Anchor Movements The staff position is that seismic anchor movements on piping should be evaluated in either Equations (9) or (10) of the ASME Code,Section III, in the seismic reevaluation program.

Besides being evaluated for fatigue considerations, the ASME Code requires that the primary and secondary stresses must be combined and evaluated to prevent plastic instability. Thus the stresses due to SAMs must be evalua ted by Equation (9) or Equation (10) of the ASME Section III Code.

-3 In addition, the licensee's use of Code Case N-318 for increasing the allowable stress, Sa, is inappropriate. The Code Case applies only for localized stress for rectangular attachments to a straight pipe while the effect of SAMs on piping is likely to be most significant at the elbows.

(ii)

Pipe Support Seismic Loads The licensee presented some information concerning the use of SRSS method in combining the seismic inertia and seismic anchor movement loads for the pipe support seismic loads.

The staff feels that the information provided does not justify the use of SRSS method for the combination of loads due to piping inertia and the SAMs. The basis provided for the validity of the SRSS combination of SAM and inertial loads is not appropriate.

As indicated in Reference 1, SRSS is a statistically valid estimate of the most probable com bination if:

1) the quantities being combined are independent; and 2) the quantities are symmetrical in regard to positive and negative values.

Since it is the support motion inducing both the SAM and inertial responses, condi tion 1 is not satisfied. It is not necessary that the quantities be rapidly varying in time and of short duration. Also, as indicated in Reference 2, if response frequencies are sufficiently far apart, peak combination will tend to be an absolute summation of responses. Therefore, it is the staff's position that the licensee should have used the absolute sum method for all cases.

The previous cases where such a procedure has been accepted by the NRC relied upon the overall seismic conservatisms in the application of the current licensing criteria for seismic design (i.e., SRP methods) to compensate for at most a 30% to 40% increase in support loading.

Since

-4 these overall criteria are not being applied in the Systematic Evaluation Program, combination of SAM and inertial leads for pipe supports is not deemed appropriate.

5. Mechanical Equipment Structural Integrity The licensee's criteria for active mechanical components are that stresses will be maintained within yield, per footnote d, page 10 of NRC Guidelines.

Therefore, it is acceptable. However, concerning the stresses in the valve body, the licensee should either:

1) Demonstrate that the valve body deformations and strength are acceptable under applied loads consistent with the maximum strength of the attached piping, or

2) Demonstrate'that the existing valve body configuration for active valves is equivalent to that of current ASME Code requirements as a part of the resolution of SEP Topic III-1, "Classification of Structures, Systems and Components."

6. Effects of Ground Motion Amplitude on Seismic Response The staff expressed concern that the occurrence of a smaller earthquake than the SSE may result in higher seismic response of the plant facility in some frequency ranges due to decreases in damping and increase in soil stiffness.

For the Ventilation, Fuel and Control/Administration Buildings the licensee presented the results of studies considering the following two soil stiff ness parameters:

Case 1:

Backfill native or 95 percent compacted San Mateo sand.

Case 2:

Backfill as characterized in August 12, 1982 Report.

-5 The licensee-indicated that the envelope of the instructure response spectra due to Cases 1 and 2 is used for tite reevaluation and it envelopes the. instructure resonse spectra due to'smaller earthquakis entirely. In addition, for the Fuel Storage Building, the licensee has indicated that sufficient margin in the time. history used for analysis exists to cover the effects of smaller earthquakes on the seismic response of the building.

For the Containment Sphere/Reactor Building, the licensee used the NRC Seismic Safety Margin Research Program (SSMRP, Auxiliary Feedwater System Projects) results to indicate that SCECo/Bechtel results provide sufficient margin to cover the~effects of the difference in seismic response for Cases 1 and 2, and therefore, the effects of smaller earthquakes on the seismic response of the building would not exceed that due to the SSE.

Although SSMRP studies are based on state-of-the-art methodologies using a probabl istic approach and cannot be fully relied upon to serve as a licensing basis for the facility, it is the staff's judgement that the seismic response due to a smaller earthquake than the SSE will not produce higher response than that of SSE.

In view of the above discussions, the staff concludes that if the newer time histories (as described by SCE at the November 10, 1982 meeting) are not used in analysis, the licensee's analyses provide reasonable assurance that the responses from earthquakes smaller than the SSE would not result in detrimental responses.

-6

7. Uncertainty in Soil-Structure Interaction (SSI)

In response to the NRC staff's question on'the issue of vlariation in soil properties to account for uncertainties in the computation and application of soil-structure interaction parameters, the licensee has provided infor mation in a letter dated September 15, 1982.

From the staff's review of the licensee's information, the licensee's estimates of the variation in both soil shear modulus and overall soil-structure interaction frequency appear to be reasonable. Due to the fact that the soil condition at SONGS 1 site are very uniform and have been extensively tested and studied, the licensee's procedure in the broadening of in-structure response spectra by

+ 15% would be sufficient to cover the frequency shift resulting from the variation in soil properties (soil strain, soil shear modulus, and the backfill conditions), the variation in structural mass distribution, struc tural stiffness and the SSI methodolgy. Therefore, the staff concludes that the licensee's response is acceptable contingent upon the following:

1.

Adequate response on soil property and backfill conditions at the site under SEP Topic II-4.F, "Settlement of Foundations and Buried Equipment,"

reviewed by the Hydrologic and Geotechnical Engineering Branch.

2. Issues discussed in the contractor reports.

-7

REFERENCES:

1. E. Rabinowicz, "An Introduction to Experimentation," Addison - Wesley Publishing Company, 1970.

2. "Probability Evaluation for Dynamic Response Combinations," Nuclear Services Corporation, July 2, 1976.