ML20128A730

Safety Evaluation Accepting Licensee 920921 120-day Response to Suppl 1 to GL 87-02 Re in-structure Response Spectra

ML20128A730
Person / Time
Site:	Prairie Island
Issue date:	11/30/1992
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20128A652	List: ML20128A650 ML20128A717 ML20128A730
References
GL-87-02, GL-87-2, NUDOCS 9212030436
Download: ML20128A730 (2)

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. ENCLOSURE 2 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR-REACTOR REGUL61LQN-EVALUATION OF THE NORTHERN STATES POWER COMPANY'S i

PRAIRIE ISLAND NUCLEAR GENERAlfNG PLANT, UNITS'l'AND 2-I 120-DAY RESPONSE TO SUPPLEMENT NO 1 IQ_AfNERIC LETTER 87-02 ,

DOCKET NOS. 50-282 AND 50-306. a BACKGROUND By its letter of September 21', 1992 to NRC, the licensee, Northern States ,

Fower (NSP), has committed to use the Seismic Qualification Utility Group-(SQUG) methodology as documented in Generic Implementation Procedure, Revision 2 ' GIP-2) to resolve the A-46 issue at Prairie Island Nuclear Generating Plant-(PINGP) Units 1 & 2. _-

t EVALUATION For the USl A-46 issue resolution of PINGP, NSP has provided the procedures- l and criteria-used-to generate.in-structure response spectra (IRS). The staff reviewed the submittal, and found the following-information:

1. The licensing basis ground motica at PINGP-is'specified in terms of Housner spectra on ' soil site tied to a peak ground acceleration (PGA) of 0.129 for the SSE and. 0.069 for the 08E. NSP used the time history. method using"a

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ground acceleration time history motion 1 developed from the ground response spectra-(GRS) for-development of.the design basis' IRS.

2. A lumped mass stick model with; springs to account for interaction with~the soil was used in generating _the. IRS. The three-dimensional mathematical model was subjected to the ground acceleration time history, n 1 the response time history of- the: horizontal acceleration at.each t .ss point of the mathematical model was generated. _ The totalcresponse was determined by computing the square root of the-sum of squares of the maximum response of '

each mode. Using this response acceleration time history att selected mass ~

points, the IRS for the-desired damping values were calculated.

3. NSP states that the model was analyzed for earthquake motion-in both- _

2-horizontal directions acting non-concurrently. However, the submittal did not show how the analysis took into account the effects ~ of-two horizontal components as' well as the vertical component off the earthquake motion.-- ,

4. In order tofdetermine the total ~ spectral acceleration at the point of- ..'

-support of the' equipment or piping in the three-dimensional = dynamic.

-analysis, a torsional acceleration was considered by multiplying the

- translational ' acceleration by the factor shown -in the submittal .

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2 Additional live load (snow load) cf 50 psf on the roof of each structure was also considered in the dynamic analysis.

6. The IRS provided in the submittal for the reactor building, the turbine building, and the auxiliary building are for the OBE (0.069) only. -NSP states that the IRS for the SSE (0.129) will be obtained by multiplying the OBL IRS by a factor of 2.0, which is the ratio of the SSE (0.129) to OBE (0.06g) maximum ground acceleration. It also states that a similar procedure has been taken to generate the IRS for the screen house.

6. There is no indication in the submittal about consideration of variation of the foundation medium properties in the dynamic analysis.

7. Although no mention is made of any peak broadening of the IRS, the spectra curves provided by NSP show some minimal amount of peak broadening to produce the design IRS.

Based on our review of the licensee response and the staff positions delineated in the SSER No. 2, we conclude that the procedure used to generate the IRS is adequate, and the IRS presented in the submittal are accepted as

" conservative, design" IRS according to the pertinent definition in SSER 2.

Furthermore, NSP states in the submittal that the-licensee may generate and use realistic, median-centered IRS as an additional option per the provision of the GIP-2 for resolution of USI A-46 issue. NSP is requested to provide all information related to the " realistic, median-centered". IRS generation for NRC review before implementation, should such an option be taken for resolution of the USl A-46 issue.

l The staff's evaluation is based on an assumptior snat the statements made in

the submittal, including the procedures used in generation of the floor response spectra, correctly reflect the FSAR and other licensing basis. The staff may audit the process by which the IRS were generated.

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Based on our review of the licensee response and the staff positions delineated in the SSER No. 2, we conclude that the procedure used to generate

< the IRS is adequate, and the IRS presented in the submittal are accepted as l " conservative, design" IRS according to the pertinant definition in SSER 2.

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QCT 0 2 R Mr. Neil Smith, Chairman Seismic Qualification Utility Group c/o EPRI 1019 19th Street, N.W.

Washington, DC 20036

SUBJECT:

NRC RESPONSE TO SEISMIC QUALIFICATION UTILITY GROUP (SQUG)

Re: Letter, 8. Smith, EPRI, To J. Partlow, NRR, dated August 21, 1992, concerning USI A-46 Issues.

Dear Mr. Smith:

This is to acknowledge the receipt of the SQUG response to Supplement No. 1-to Generic Letter (GL) 87-02, and Supplemental Safety Evaluation (SSER) No. 2 on o the SQUG Generic Implementation Procedure-fcr Geismic Verification of Nuclear Plant Equipment, Revision 2, as corrected February 14, 1992 (GIP-2). -The NRC staff believes that successful implementation of the entire GIP-2, supple -

mented by the staff's SSER No. 2, by each SQUG licensee will result in cost-effective plant safety' enhancement for their USI A-46-plants.

The staff also believes that the positions delineated in Supplement No.n1 to GL 87-02 and SSER No. 2 are clear and correct, and should not be misinterpret-ed. The staff's comments on SQUG's August 21, 1992, letter and attachment are provided in the enclosure to this letter. If you need further clarification concerning our response, please contact Mr. James Norberg at'SO4-3288.

Sincerely, r

0 James G. Partlow

. Associate Director for Projects Office of Nuclear Reactor Regulation

Enclosure:

As stated 3M 3 ' f . N

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ENCLO$URE I. NRC's Comments on the SOUG Letter of Auaust 21. 1992:

1. In regard to the hsue of seismic qualification, the staff reiterates the position stated in the SSER No. 2, in that the GIP-2 methodology is not considered to be a seismic qualification method, rather, it is an acceptable evaluation method, for USl A-46 plants only, to verify the seismic adequacy of the safe-shutdown equipment and to ensure that the pertinent equipment seismic requirements of General Design Crit 3rion 2 and the purpose of the NRC regulctions relevant to equipment seismic adequacy including 10 CFR Part 100 are satisfied.

2. The second paragraph on page-2 of your letter addressed the issue of timing of staff response to additional information requested from a licensee. Although you are correct in your statement regarding the sixty-day period for response to initial submittal of in-structure response spectra (ISRS) Information, we do not agree that the same concept applies to a licensee's submittal of additional information received following a rejection or a question from the staff. To elimirate any potential misunder-standing in this regard, the staff has determined that it will respond to any submittal of additional information received from a licensee within 60 days. However, in this response, the staff will either state its approval (or rejection) of the information provided, or indicate the time duration needed for the review of such information, prior to transmitting a follow-up response of acceptance (or rejection) to the licensee. This time duration will vary depending on the complexity of the submittal.

3. Regarding the EBAC and ANCHOR computer. codes, the staff's evaluations and concerns stated in the SSER No. 2 are correct and valid. The ANCHOR code does not consider the effects of base plate flexibility on the anchorage capacity.

4. With respect to transfer of knowledge regarding major problems identified, and lessons learned, in the USI A-46 plant walkdowns and third-party reviews, we request that you include the NRC in the distribution of written comunications to all member utilities in this regard, and inform the NRC staff of any planned workshops on A-46 implementation for possible staff participation.

II. RC's Comgatj on th' e Procedure for Reviewino the GIP

1. The staff supports SQUG's establishment of a Peer Review Panel composed of seismic experts since it should serve to enhance the review process of substantive changes to the technical requirements in the GIP, prior to its submittal to NRC for approval. However, since the NRC no longer intends to help finance a Peer Review Panel, the staff does not believe it

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2-is appropriate to-participate in the selection of the Peer Review '

members, who will be financed by SQUG/EPRI. We would like to emphasize that staff's review of a p.oposed GIP change will receive thorough independent NRC evaluation and will be assessed on its merits.

2. With respect to the NRC review and approval of the changes to-the GIP (Item 5, page 3 of the procedure), the staff's position on the issue of its response timing is identical to that delineated in the response to a licensee submittal of additional information (refer to item P. of NRC's Coreents on the SQUG 1etter in this enclosure). This comment also applies to the section " LICENSING CONSIDERATIONS" on page 5 of the Attachment to the SQUG letter.

3. With respect to item 4, " Additional Restrictions," the text should be expanded to reflect that new information which indicates that existing GIP criteria and guidelines may be unconservative should be evaluated for potential 10 CFR Part 21 implications.

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