ML18114A529
| ML18114A529 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 05/02/1979 |
| From: | Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 308, NUDOCS 7905070637 | |
| Download: ML18114A529 (2) | |
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VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIBGIN IA 23261 Mr. Harold*R. Denton, Director Office of Nuclear Reactor Regulation U. s. Nuclear Regulatory Co.mmission Washington, DC 20555
Dear Mr. Denton:
- SHOW:CAUSE:ORDER May 2, 1979 Seri a 1 No. 3 08 LQA/EAB:pwc Docket Nos. 50-280 50-281 SURRY* POWER. STAT I OWUN I TS 1 --AND* 2
VIRGINIA ELECTRIC ANo:powrn*coMPANY,'
On March 13, 1979 the Commission issued the Show Cause Order for Surry Power Station Units 1 and 2 requiring Vepco to reanalyze the facility's piping systems for seismic loads using an* appropriate piping code and to show caus*e why we should not make any necessary modifications fol lowing this reanaly-sis. This action was made effective immediately by the NRC and required shut-down within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />.
This order was issued without Virginia Electric and Power Company being given the opportunity to discuss the specific details of the Surry pipe stress analysis and the inherent co~servatfsm in the design which w~ feel justified con-tinued operation.
We nevertheless fully complied with the Order and promptly initated the reanalysis work which is continuing and we have not as yet identified that a s_lgnlficant safety problem exists.
The pipe stress and pipe support reanalyses for Surry l to date, using soil-structure interaction results, have not shown any systems or supports that require design modification because of earthquake loading.
We were aware this was a distfoct possibility at the time of the Show Cause Order; however, we have only recently been able to demonstrate this on the basis of reanalysis.
The original basis for earthquake design of piping systems was conserva-tive in comparis~n with current regulatory req~irements.
The use of soil-structure interact ion CSSI )_ analysis techniques upon which the engineering profession may satisfactorily rely have been reported in NUREG/CR-069*3 and agreed to in principal by the NRC Staff. The techniques are being applied to the s*urry plant in order to better evaluate the conservatisms in earthquake design of the piping systems.
Using SSl analysis, amplified response spectra hav~ been developed at various
- levels in the plant structures. These spectra indicate the original Surry design bas is to have been very conservative.
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VIRGINIA ELECTRIC AND POWER COMPANY TO Mr. Harold R. Denton 2
These spectra have been applied to sample pipe stres.s analysis problems, the details of which are being furnished today in an actompanying letter (Vepco serial no. 260/41379), addressed to Mr. Victor Stello in respon~e to his April 13 letter. A comparison has been made of original earthquake stress values compared to (1) stress levels using SSI results under Regulatory Guides 1.60 and 1.61 data, and (2)stress levels using SSlresults under Surry FSAR data.
Several conclusions are evident. A comparison of Regulatory Guide 1.60 and 1.,61 criteria against the FSAR criteria using SSI indicates the earthquake stress levels are in reasonable agreement.
It cin also be substantiated that inertial stresses calculated in
~ccordance with the FSAR or Regulatory Guide 1.60 and l.61 are substantially less than those resulting from the original design criteria. These results also demon-strate that stress~s due to ineitial effects may be small compared with the total design stresses.
We believe this kind of comparison, although done on a 1 imited basis, is indicative of the total pipe stress analysis effort.
We did not expect to find pipe overstress problems under earthquake loading at the time of the Order to Show Cause.
The analysis effort so far has demonstrated this.
We be 1 i eve this trend will be evident as pipe support evaluation continues.
- The likelihood of extens1ve field modifications for either piping or supports is considered to be remote.
If design modifications are required, we would notify you immediately and seek your input and review, as your continued involvement is essential to this project.
You are aware of the economic impact of outages on Surry 1, the increased use of oil to replace the nuclear energy and the reli~bility of service to Vepco 1s customers as it has been a subject of congressional hearings.
We firmly believe Surry l can be returned to service while the reanalysis is underway and still not jeopardize the health and safety of the public.
This information should be sufficient for you to recommend to the Commissioners that Surry l be returned to service immediately.,
We therefore urge you to schedule a meeting as soon as possible to make this recommendatione We stand ready to assist with any supportive technical presentations you deem necessarye Very truly yours, C. M. Stallings Vice President-Power Supply and Production Operations