ML13333A678
| ML13333A678 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 02/12/1988 |
| From: | Medford M Southern California Edison Co |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| GL-87-12, NUDOCS 8802170014 | |
| Download: ML13333A678 (2) | |
Text
Southem California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD, CALIFORNIA 91770 M.O.MEDFORD TELEPHONE MANAGER OF NUCLEAR ENGINEERING (818) 302-1749 AND LICENSING February 12, 1988 U. S. Nuclear Regulatory Commission Attention:
Document Control Desk Hashington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Generic Letter 87-12 San Onofre Nuclear Generating Station Unit 1 By letter dated September 24, 1987, Southern California Edison provided a response to Generic Letter 87-12, applicable to Unit 1 of the San Onofre Nuclear Generating Station, regarding the loss of residual heat removal while the reactor coolant system is partially filled.
In response to Question 1 of the Generic Letter, it was stated that as a prerequisite to initiating reactor coolant system (RCS) draindown, plant procedures require that the RCS be at less than 140OF temperature and typically at least 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> must have elapsed since reactor shutdown. It was also stated that in the case of exceptions to the 120 hour0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> requirement, specific written authorization by the plant superintendent is required.
This letter is to advise the NRC of the basis under which the plant superintendent will authorize, in writing, RCS draindown in less than 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br />.
The calculations cited in response to Question 5 of the Generic Letter had indicated that upon loss of residual heat removal capability with RCS in mid-loop (partially filled), 15-44 minutes are available before bulk boiling would occur. These calculations were bounded by decay heat rates existing at 5 days (120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br />) and 50 days after reactor shutdown and also assumed a fuel burnup history consisting of three consecutive 18 month full power cycles separated by refueling intervals of two months duration. Since the actual time available before start of bulk boiling is dependent on variables such as the actual fuel burnup history and other plant conditions applicable to a 8802170014 880212 PDR ADOCK 05000206 P
Document Control-Desk February 12, 1988 particular situation, the 120 hour0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> requirement may, in certain situations, present an undue restriction. It is, therefore, reasonable to permit RCS draindown to mid-loop when the following two conditions can be satisfied:
a)
RCS temperature is maintained less than 140*F b) calculated decay heat load is sufficiently low that in the event of RHR loss at any point of the draindown process, at least 15 minutes are available before bulk boiling would start and alternate core cooling methods would become necessary.
If you have any questions, please let me know.
Very truly yours, cc: 3. B. Martin, Regional Administrator, NRC Region V F. R. Huey, NRC Senior Resident Inspector, San Onofre Units 1, 2 and 3