ML20205L724
| ML20205L724 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 03/27/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20205L671 | List: |
| References | |
| NUDOCS 8704020180 | |
| Download: ML20205L724 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO USE OF ASME CODE CASE N-411 LIMERICK GENERATING STATION, UNIT 2 PHILADELPHIA ELECTRIC COMPANY DOCKET N0.: 50-353
1.0 INTRODUCTION
By letter from J. S. Kemper to W. R. Butler dated March 27, 1986 (Reference 1), the Philadelphia Electric Company (PECo) requested author-ization to use the damping values of ASME Code Case N-411, " Alternative Damping Values for Seismic Analysis of Classes 1, 2 and 3 Piping Sections,Section III, Division 1," in lieu of the damping values currently identified in the Limerick Unit 2 FSAR. The staff responded to that request by letter dated May 30, 1986 (Reference 2). That letter provided details of the staff's position on the applicability and conditions for acceptable use of ASME Code Case N-411. One of the conditions identified was that damping values from Code Case N-411 may be used only in piping analyses for which enveloped response spectra are used. After reviewing the staff's position described in Reference 2, the applicant informed the staff that Code Case N-411 damping values had been used for piping systems analyzed using the independent support motion (ISM) response spectrum method.
Subsequent to the identification of the analysis inconsistency, four meetings between PECo and the staff were held in Bethesda, Maryland on October 8, November 7, and December 3,1986, and January 15, 1987.
In those meetings, the applicant presented its various analytical approaches including the results of reanalyses to justify the use of the ISM method with N-411 damping (ISM /N-411) for Limerick Unit 2 piping. Details of the reanalyses were subsequently submitted to the staff by letters dated December 24, 1986, and January 13 and 26, 1987 (References 3, 4 and 5).
2.0 EVALUATIO,N_
References 3, 4 and 5 provided details relative to various approaches to justify the use of the ISM /N-411 method for Limerick Unit 2 piping systems. During the October 8, 1986 meeting, the applicant indicated that there are thirty-one piping systems (six within the General Electric scope of supply and twenty-five within the Bechtel scope of supply) analyzed using the ISM /N-411 method.
For the six NSSS piping systems, two-time history analyses usino FSAR damping were performed (recirculation loop A andmainsteamlineD). A comparison of the results of those two-time history analyses with the results of the ISM (SRSS)/N-411 method showed j
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o that both methods gave similar predictions of piping stresses and restraint loads at similar locations and that adequate margins with respect to piping allowable stresses and support design loads remained.
In Reference 3, the applicant further demonstrated similarities of main steam lines A, B and C with main steam line D as well as similarities of recirculation loop B with recirculation loop A.
The similarities con-sidered included piping layout, support locations, natural frequencies of the piping, response spectra groupings, governing load combinations, piping stress and restraint loads. Based on the demonstrated simi-larities, the applicant concluded that the designs of the four NSSS piping systems, which have not been specifically reanalyzed by the time history methodology, are acceptable.
From the information presented by the applicant, the staff agrees with the applicant's conclusion.
With respect to the twenty-five B0P piping systems using the ISM (absolute sum)/N-411 method, three piping systems (feedwater line A RHR return line A and main steam line D SRV discharge lines) were reanalyzed by the time history methodology (and were shown to be acceptable by a comparison of the results of the ISM absolute sum)/N-411 method with the results of the time history analyses. The applicant then further extended those three-time history evaluations to the acceptability of feedwater line B, RHR return line B and all other MSRV discharge lines on the basis of their respective similarities.
In Reference 4 the applicant also indicated that there are three piping systems for which the ISM /N-411 method were utilized only for the annulus pressurization (AP) evaluation.
For those piping systems, the majority of modes are excited at frequencies greater than 20 Hz where N-411 damping has no effect because R. G. 1.61 damping is greater than or equal to N-411 damping above 20 Hz. Nevertheless, the effects of AP loading for frequencies below 20 Hz were assessed and were detennined to be acceptable because adequate margins relative to design allowable remained. For the remaining 80P piping systems using the ISM /N-411 method, a study calculation approach was used. Study calculations were performed using either ISM (absolute sum) with R. G.1.61 damping or enveloped response spectra with N-411 damping.
In Reference 5 the applicant stated that all study calculations have been completed and the results were determined to be satisfactory because pipe stresses were below code allowables and no restraint modifications were required. The applicant further stated that it has reviewed four study calculations that had the most significant increases in maximum pipe stresses between the study calculation and the existing record calculation for impact on nozzle loads and valve accelerations and has determined that they were not adversely impacted by the use of ISM (absolute sum)/N-411. Based on the results of its assessment as described above, the applicant concluded that it has adequately demonstrated the acceptability of those twenty-five BOP piping systems.
From the information provided by the applicant, the staff 4
agrees with the applicant's conclusion.
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3.0 CONCLUSION
Based on its review of the applicant's evaluation as described above, the staff concludes that the applicant has provided an adequate just-ification for the acceptability of those thirty-one piping systems using the ISM /N-411 method. The analyses performed using the ISM /N-411 rethod may remain the calculations of record.
It should be noted that use of the ISM /N-411 technique will be limited to those cases only since they were shown to be acceptable by studies that compared results with results of analyses performed using currently acceptable methods. Any future piping design, or analyses / reanalyses of piping systems other than those identified above, or reanalyses of those thirty-cne piping systems because of a significant change in the routing of the pipe and/or pipe support modification should be performed using one of the following analytical methods approved by the staff:
Time history analysis with FSAR damping.
Enveloped response spectra analysis with ASME Code Case N-411 damping.
ISM (absolutesum)responsespectraanalysiswithR.G.I.61
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References:
1.
Letter from J. S. Kemper to W. R. Butler, " Limerick Generating Statier Unit 2. Use of Alternate Damping and Spectral Shi# ting Criteria," dated March 27, 1986.
2.
Letter from W. R. Butler to E. G. Bauer dated May 30, 1986 - Same Subject.
3.
Letter from S. J. Kowalski to W. R. Butler, "Use of ASME Code Case N all for Limerick Unit 2," dated December 24, 1986.
4.
Letter from S. J. Kowalski to W. R. Butler dated January 13, 1987 - Same j
Subject.
5.
Letter from S. J. Kowalski to W. R. Butler dated January 26, 1987 - Same Subject.
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