ML20028A393
| ML20028A393 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 11/12/1982 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20028A392 | List: |
| References | |
| NUDOCS 8211190369 | |
| Download: ML20028A393 (2) | |
Text
ENCLOSURE e
SAFETY EVALUATION REPORT RANCHO SECO SEISMIC QUALIFICATION OF THE AUXILIARY FEEDWATER SYSTEM In troduction Since the accident at Three Mile Island attention has been focused on the ability of pressurized water reactors to provide reliable decay heat removal.
While it is recognized that alterna~te methods may be available to remove decay heat following transients or accidents, heat removal via the steam generators is the first choice for accomplishing a safe shutdown of the plant.
Therefore, there should be reasonable assurance that the auxiliary feedwater system (AFW) can withstand the postulated Safe Shutdown Earthquake (SSE), consistent with other safety-related systems in the plant.
.To address this concern, the NRC developed and initiated Mfitiplant Action C-14, " Seismic Qualification of Auxiliary Feedwater Systems."
The objective of this plan is to increase, to the extent practicable, the capability of those plants without seismically qualified AFW to. withstand earthquakes up to the SSE level.
This program was implemented with the issuance of NRC Generic Letter 81-14, dated February 10, 1981.
Our review of the licensee's responses to this letter is the subject of this evaluation.
Evaluation The enclosed report was prepared for us by our consultant, Lawrence Livermore National Laboratory, as part of our technical assistance contract program.
.The report provides their technical evaluation of the licensee's conformance to the requirements of Generic Letter 81-14. We have reviewed the consultant's report and concur with its conclusions.
Subsequent to the consultant's review, we gave additional consideration to the potential failure of the air-operated flow control valves (FCV's).
In the event the FCV's should fail to the closed position, the seismically-qualified motor-operated valves which bypass these FCV's provide assurance that auxiliary feedwater can be supplied to the steam generators.
If, however, the FCV's should fail to the open position (which does occur on loss of control air).,
a concern arises regarding potential overfill of the steam generators.
The licensee's submittal of January 8,1981 depicts an upgraded AFW which includes new fully-seismically qualified flow control valves.
In the interim, plant procedures cover loss of AFW control and delineate three alternate manual control schemes that could be used to prevent overfill.
These schemes involve: manually closing the FCV's locally with the handwheels, starting / stopping the AFW pumps, and/or throttling flow with other manual values in the system.
We have determined that, prior to the installation of the upgraded system, the manual control schemes are adequate to prevent steam generator overfill.
8211190369 821112 PDR ADOCK 05000312 P
PDR Additionally, we have reviewed those branch connections to/from the AFW that do not have a second isolation valve.
In each case, the boundary is protected by a manual valve that is locked closed and under administrative controls. In that no single active failure will cause loss of safety function, we find this boundary condition to be acceptable.
Conclusion Based upon our review of the consultant's technical evaluation report, we conclude that there is reasonable assurance that the auxiliary feedwater system has sufficient capability to withstand a safe shutdown earthquake and accomplish its safety function.
Accordingly, we are'not contemplating requiring any seismic upgrading of this system under the NRC Multiplant Action C-14 program.
We consider the consultant's technical report to be final, in that no further technical effort is required.
This safety evaluation was prepared by Mr. J. T. Beard, Operating Reactors Assessment Branch.
e e
.