ML13310B661
| ML13310B661 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 08/30/1984 |
| From: | Baskin K Southern California Edison Co |
| To: | Eisenhut D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML13310B665 | List: |
| References | |
| NUDOCS 8409040155 | |
| Download: ML13310B661 (5) | |
Text
Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE KENNETH P. BASKIN ROSEMEAD, CALIFORNIA 91770 TELEPHONE VICE PRESIDENT 818-572-1401 August 30, 1984 Director, Office of Nuclear Reactor Regulation Attention:
Mr. Darrell G. Eisenhut, Director Division of Licensing U. S. Nuclear Regulatory Commission Washington, D.C.
20555 Gentlemen:
Subject:
Docket No. 50-206 Approval for Plant Restart San Onofre Nuclear Generating Station Unit 1 San Onofre Unit 1 has been shut down since February 27, 1982.
That outage was originally scheduled for fourteen weeks in order to inspect steam generators and to implement seismic modifications to the north and west turbine decks as approved in an NRC SER on the seismic reevaluation program.
As the outage progressed, additional upgrades were identified and further commitments for upgrades were made by letters dated June 15, 1982 and June 24, 1982. Those commitments were intended to accelerate completion of the remaining seismic upgrades such that at the end of the outage the seismic reevaluation program would be complete and the plant would be designed to withstand a 0.67g Housner seismic event. The NRC agreed with the commitments of SCE's letters and pursuant to the Commission's regulations in 10 CFR Parts 2 and 50, issued an "Order Confirming Licensee Commitments on Seismic Upgrading" dated August 11, 1982. That order requires the unit to remain in a shutdown condition until the modifications to which SCE committed are complete, and NRC approval for restart is obtained. The purpose of this letter is to provide an overview of the seismic upgrades that will be completed by the end of the current outage and to request NRC approval for restart.
The seismic upgrade program at San Onofre Unit 1 was initiated in the 1970's as a phased program aimed at giving priority first to those systems required to maintain reactor coolant system integrity, then to plant structures, and finally to supporting systems and components.
As indicated in Table 2-1 of our December 23, 1983 letter (attached for reference), several modifications, additions and analyses were completed prior to 1982 that provided a substantial increase in the seismic withstand capability. Table
.9 2-2 of that submittal listed analyses and modifications which have been or will be completed during the current outage. It should be noted from the list, that during the current outage the modifications to all safety related structures will be completed, masonry walls representative of those at Unit 1 have been tested and shown to have a seismic withstand capability of 0.67g, a new auxiliary feedwater tank has been constructed, approximately 80% of the electrical raceway supports identified in the seismic reevaluation program have been installed and all pipe supports reaured to achieve asafe shutdown condition will be installed.
8409040155 840830 PDR ADOCK 05000206 P D R
Mr. D.
August 30, 1984 As SCE began implementing the modifications to meet the commitments specified in the June 1982 letters, it became apparent that continuing the upgrades using the criteria and assumptions specified in those letters could affect the economic viability of the unit.
As a result, SCE initiated discussions with the NRC staff to develop alternate methods and criteria for ensuring the seismic withstand capability of the plant. The result was SCE's proposed Return to Service Plan submitted on December 23, 1983. The basic premise of this plan is that all San Onofre Unit 1 structures and systems whose failure could cause an accident and/or whose function is required to achieve and to maintain a safe hot shutdown will be available following a 0.67g earthquake. This plan was approved by the NRC in their letter dated February 8, 1984. A copy of the NRC's letter is attached for reference.
Upon return to service in the fourth quarter of this year, San Onofre Unit 1 will be a significantly different plant than that licensed for operation in 1967 and-significantly different even than at the beginning of the current outage. The plant will, with completion of the current upgrades, be capable of safely shutting down even considering the occurrence of a 0.67g Housner earthquake. This seismic event represents a return period of between 10-6 and 10-7 per year. In view of this, it is concluded that the seismic hazard is no longer a significant concern for San Onofre Unit 1.
Earthquake experience has shown that structures and systems generally have seismic capability well beyond that to which they were originally designed. As described in our December 23, 1984 submittal, industrial plants have significant inherent capability to resist large seismic events.
For example, the El Centro Steam Plant in the Imperial Valley of Southern California experienced an earthquake in 1979 estimated to have caused ground acceleration of approximately 0.5g. There was no damage to high-pressure or high-temperature piping at the plant. A report prepared by the NRC staff, "Equipment Response at the El Centro Steam Plant during the October 15, 1979 Imperial Valley Earthquake," NUREG/CR-1665, noted that "the piping systems are hung in a more flexible manner than would be required by current NRC criteria" and that "in most cases, the piping is supported in a similar manner to older operating nuclear plants." This experience demonstrates that a conventional plant, probably designed for ground acceleration of O.lg or 0.2g, can withstand a much greater ground acceleration, probably on the order of 0.5g.
In order to more fully characterize the seismic risk at San Onofre Unit 1, probabilistic risk assessments done at other nuclear plants have been evaluated.
The results indicate that the seismic risk at San Onofre Unit 1 when it returns to service at the end of this year will be roughly equivalent to that at nuclear power plants in other parts of the country. It is estimated that the core damage frequency due to seismic risk is on the order of 2 x 10-5 per year and represents a level almost an order of magnitude less than the core damage frequency safety goal of 1 x 10- 4/year. In addition, recognizing the uncertainty associated with any calculation of seismic risk, a further evaluation of the risk associated with the seismic
Mr. D.
August 30, 1984 hazard was provided in our July 30, 1984 submittal. In that submittal the relative improvement in plant safety which has been obtained during the current outage was evaluated. The conclusion was that the seismic risk associated with the plant is a factor of 35 to 125 lower than prior to the current modifications. Finally, our December 23, 1984 submittal provided a review of risk studies done at other nuclear plants to identify the dominant contributors to seismic core melt frequency based on these studies. These items were then compared to the status of the current plant. Based on this evaluation, it was determined that virtually every dominant contributor category has been eliminated by work already completed.
The above considerations indicate that San Onofre Unit 1 has substantial protection from a large seismic event and that the risk from the plant for this initiating event is comparable to that at other sites in the country. With completion of the modifications in the fourth quarter of this year, the plant will represent a roughly two order of magnitude improvement in earthquake safety.
Due to the conservative assumptions used in determining the seismic hazard and the inherent capability of industrial structures such as San Onofre, it is concluded that there is a very high assurance that the operation of the unit does not pose an undue risk to the health and safety of the public. It is our intent to return the unit to reliable commercial operation upon completion of the current modifications in the fourth quarter of this year. Therefore, we request NRC approval for restart of San Onofre Unit 1.
If you require additional information, please let me know.
Very truly yours, Enclosures
- 1. Letter, M. 0. Medford, SCE, to D. M. Crutchfield, NRC, dated December 23, 1983
- 2. Letter, Harold R. Denton, NRC, to K. P. Baskin, SCE, dated February 8, 1984
AD12 S~l NRC-SEP December 23, 1983 Director, Office of Nuclear Reactor Regulation Attention: D. M. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Return to Service Plan Seismic Reevaluation Program San Onofre Nuclear Generating Station Unit 1 Over the last several months, we have met with NRC management and NRC staff personnel to discuss a return to service plan for the seismic reevaluation program. As discussed in these meetings, the basic premise of this plan is that all San Onofre Unit 1 structures and systems whose failure could cause an accident and/or whose function is required to get to and maintain a safe shutdown (hot standby, Mode 3) will be available following a 0.67g earthquake.
The details of the return to service plan are provided in the enclosed report. Based on the implementation of this plan, San Onofre Unit 1 can return to power without undue risk to the health and safety of the public even considering the possibility of a major earthquake at the plant site.
As discussed in our previous meetings, it is necessary that SCE obtain agreement with the NRC staff on the criteria to be applied to the seismic reevaluation program for return to service by mid-January 1984. As such, it is imperative that any questions you may have regarding our intentions in the enclosed plan be resolved as soon as possible. If there is anything that we can do to facilitate the NRC staff review, we will be pleased to provide additional information and/or meet with you as appropriate.
If you have any questions or comments on the enclosed plan, please contact me as soon as possible.
Very truly yours, M. 0. Medford Manager, Nuclear Licensing JLR:0541F bcc: (See attached sheet)
~r2~Z7J~4V
REGULATORYW ORMATION DISTRIbUTION SY EM (RIDS)
ACCESSION NOR:8409040155, DGC.DATE4:84/08/30 NOTARIZE s NO DOCKET #
FACIL:50-206 San Onofre:Nuclear Station, Unit 1, Southern Californ 05000206 AUTHNAME AUTHOR AFFII4ATION BASKINK,Pq Southern California Edison Co.
RECIPNAME RECIPIENT AFFILIATION EISENHUTD.G, Division of Licensing
SUBJECT:
Requests approval for restartbased on 14stedcosideretions indicating that unit has substantial protection from large seismic event & risk for initiating event comparable to other sites, P DISTRIBUTION CODE: IE OP IVED:LTR ENCL '
SZEt.
TITLE: StartwUp Repor/ Refueling Report (50 Dkt)
NQTES:J Hanchett icy POR Documents. NRR/DL/SEP Icy.
.05000206 0L:03/27/67 RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAMEi LTTR ENCL ID CODE/NAME LTTR ENCL NRR ORBS BC 04 3
3 INTERNAL: IE FILE; 01 1
1 NRR/DHFS DEPY07 1
1 NRR/DHFS DIR 08, 1
1 NRR/DHFS/PSR81I 1
1 NRR/DSI/CPB 1Z 1
1 RGN2/DRSS/EPRPB 1
RM/DDAMI/MIB 09c 1
EXTERNAL:
ACRS 13 5:
i5 LPOR 03 1
1 NRC PDR 02 1
1 NSIC 05 1
1 NTIS 1
1 NOTES:
2 2
TOTAL NUMBER OF COPIES REQUIRED:
UTTR 21 ENCL 21