ML16288A283

Proposed Resolution of Generic Issue 128, Electrical Power Reliability

ML16288A283
Person / Time
Issue date:	06/14/1989
From:	Remick F Advisory Committee on Reactor Safeguards
To:	Zech L NRC/Chairman
References
Download: ML16288A283 (2)

Text

D890614 The Honorable Lando W. Zech, Jr.

Chairman U.S. Nuclear Regulatory Commission Washington, D.C. 20555

SUBJECT:

PROPOSED RESOLUTION OF GENERIC ISSUE 128, "ELECTRICAL POWER RELIABILITY" During the 350th meeting of the Advisory Committee on Reactor Safeguards, June 8-10, 1989, we discussed the NRC staff's proposed resolution of the subject generic issue. Our Subcommittee on AC/DC Power Systems Reliability also met with members of the staff and its contractor on June 7, 1989 to review this matter. We also had the benefit of the documents referenced.

The staff's proposal is still another example of piecemeal resolution of isolated issues, a practice we have criticized in numerous reports. It is an example also of the continuing inability or unwillingness of the staff to develop resolutions based on reliability rather than sometimes arbitrary or prescriptive criteria. We continue to believe that issues such as these should be addressed and implemented through the Individual Plant Examination (IPE) program along with assessments of the associated risk reductions.

These points are elaborated below.

Generic Issue 128 (GI-128) was identified in NUREG-0933, "A Prioritization of Safety Issues," Revision 5, March 1987, as the integration of three separate safety issues, namely:

o Generic Issue 48 (GI-48), Limiting Conditions for Operations (LCOs) for Class 1E Vital Instrument Buses, which deals with a safety concern that some operating nuclear power plants do not have administrative controls or technical specifications governing operational restrictions for their Class 1E 120 v ac vital instrument buses and associated inverters that may result in the failure of the plants' safety systems to perform their safety functions when required.

o Generic Issue 49 (GI-49), Interlocks and LCOs for Class 1E Tie

Breakers, which deals with a safety concern that independent, redundant Class 1E ac or dc buses can be interconnected via tie breakers which may be left closed by mistake. When left closed, the tie breakers can compromise the independence of the redundant safety-related buses and, in some cases, may prevent the emergency diesel generators from supplying emergency power when needed.

o Generic Issue A-30 (GI A-30), Adequacy of Safety-Related DC Power Supplies, which deals with a safety concern that some plants may not have adequate provisions (e.g., monitoring, maintaining, and tests) for assuring that the dc power supplies are available and capable of per-

forming their safety functions when needed.

The staff's proposed resolution of GI-128 is to issue two separate generic letters with related information requests pursuant to 10 CFR 50.54(f),

"Conditions of Licenses," to inform the licensees of related concerns and to obtain information for the staff to assess whether necessary actions have been taken to resolve these concerns. One generic letter would address GI-48 and GI-49, and the other would address GI A-30.

The proposed resolutions for the GIs considered will probably improve the reliability of electrical systems if properly interpreted for the plants for which changes are required. However, as pointed out by the staff, there are interrelationships among these GIs and several related GIs and USIs that will affect how these changes influence plant performance. This argues for an integrated approach to the identification of needed changes in plant hardware and procedures, such as that proposed for the IPE program. This will result in a more efficient use of resources and improved results compared to the piecemeal approach characteristic of the current issue resolution process.

Further, the inability of the staff to develop and apply reliability theory (instead of obsolescent criteria such as the single-failure criterion) to important plant systems leads to proposed solutions the effects of which cannot be evaluated in terms of increased reliability or decreased risk.

Rather, what one achieves is compliance with regulations without a quantita-tive measure of what improvement has been achieved. An example of this is the proposed resolution of GI-48 associated with plant inverters. Here the emphasis is on establishing LCOs to be incorporated into the plant technical specifications rather than on specifying a reliability goal. The LCO ap-proach gives no assurance that the power supply will be reliable; rather it requires that there be a limitation on plant operation if the power supply is unavailable. This provides little or no increase in the likelihood that the inverter, a key component and one that has been found unreliable in many plants, will be available when needed.

In summary, we recommend that the resolution of GI-128 be implemented through the IPE program along with assessments of the associated risk reductions.

Sincerely, Forrest J. Remick Chairman

References:

1. Idaho National Engineering Laboratory, EG&G Idaho, Inc., EGG-NTA-7727, Revision 3, "Technical Findings for Proposed Integrated Resolution of Generic Issues 128 (Issue 48 and Issue 49)," Prepared for the U.S.

Nuclear Regulatory Commission, FIN No. D6025, March 1989

2. Idaho National Engineering Laboratory, EG&G Idaho, Inc., EGG-NTA-8197, Revision 1, "Technical Findings, Generic Issue 128 (Issue A-30), Ade-quacy of Safety Related DC Power Supplies," Prepared for the U.S.

Nuclear Regulatory Commission, FIN No. D6025, March 1989