ML16281A453
| ML16281A453 | |
| Person / Time | |
|---|---|
| Issue date: | 04/11/1989 |
| From: | Remick F Advisory Committee on Reactor Safeguards |
| To: | Stello V NRC/EDO |
| References | |
| D890411 | |
| Download: ML16281A453 (2) | |
Text
D890411 Mr. Victor Stello, Jr.
Executive Director for Operations U.S. Nuclear Regulatory Commission Washington, D.C. 20555
Dear Mr. Stello:
SUBJECT:
PROPOSED RESOLUTION OF GENERIC ISSUE 101, "BWR WATER LEVEL REDUNDANCY" During the 348th meeting of the Advisory Committee on Reactor Safe-guards, April 6-8, 1989, we reviewed the NRC staff's proposed resolution of Generic Issue 101, "BWR Water Level Redundancy." Our Subcommittee on Instrumentation and Control Systems met with the NRC staff on March 29, 1989, to discuss this matter. We also had the benefit of the document referenced.
We concur in the staff's proposed resolution. We reached this con-clusion primarily because we believe that the emergency procedures used by BWR licensees make it highly likely that operators will recognize the erroneous indications that would result from breaks in the sensing lines used for water level indication and will be able to take appropriate compensatory action. We believe also that these breaks are not very likely to occur, and because, given a sensing line break, there are backup systems that would produce reactor scram and there is a variety of ways in which removal of decay heat can be accomplished.
We found the technical analysis in NUREG/CR-5112, "Evaluation of Boiling Water Reactor Water-Level Sensing Line Break and Single Failure,"
somewhat opaque. Even after discussion with the staff, we found it not very useful in reaching a decision on the appropriateness of the pro-posed resolution. We were especially puzzled by the decision made by the analysts to ignore common mode failures in their risk calculations.
It is the experience of most analysts in today's PRAs that common mode failures make a significant contribution to system unavailability. When we questioned the analysts about ignoring it, we received no technical justification other than a statement that including it would have significantly increased the cost of the analysis. We suggest that future reliability analyses either include a consideration of common mode failures or provide appropriate justification for neglecting them.
Sincerely, Forrest J. Remick Chairman Reference
U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Re-search, NUREG/CR-5112, EGG-2536: "Evaluation of Boiling Water Reactor Water-Level Sensing Line Break and Single Failure," March 1989 cc: S. J. Chilk, SECY J. L. Blaha, EDO E. S. Beckjord, RES W. Minners, RES R. L. Baer, RES A. J. Szukiewicz, RES C. B. Bartlett, RES D. Persinko, NRR