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"Consideration of Valve Mispoitioning in Boiling Water Reactors" (Generic Letter 89-10, Supplement 4)
February 12, 1992 TO: ALL LICENSEES OF OPERATING NUCLEAR POWER PLANTS AND HOLDERS OF CONSTRUCTION PERMITS FOR NUCLEAR POWER PLANTS SUBJECT: GENERIC LETTER 89-10, SUPPLEMENT 4, "CONSIDERATION OF VALVE MISPOSITIONING IN BOILING WATER REACTORS" In Generic Letter (GL) 89-10, "Safety-Related Motor-Operated Valve (MOV) Testing and Surveillance," the staff recommended, among other things, that any MOV in a safety-related system that is not blocked from inadvertent operation from either the control room, the motor control center, or the valve itself be considered capable of being mispositioned (referred to as position-changeable MOVs) and be included in licensees' MOV programs. When determining the maximum differential pressure or flow for position- changeable MOVs, the licensee should consider the fact that the MOV must be able to recover from mispositioning. Supplement 1 to GL 89-10 limited the prevention of inadvertent MOV operation within the context of the generic letter to the potential for MOV mispositioning from the control room. The Boiling Water Reactors Owners' Group (BWROG) submitted a backfit appeal on the recommendations for position-changeable valves. The staff, with the assistance of Brookhaven National Laboratory (BNL), has reviewed and evaluated the issues concerning mispositioning of valves from the control room and has determined that the recommendations in GL 89-10 should be changed for boiling water reactors (BWRs). The BNL study, which used probabilistic risk assessment techniques, and the staff's evaluation were included in a letter from NRC to the BWROG dated this same date. The staff no longer considers the recommendations for inadvertent operation of MOVs from the control room to be within the scope of GL 89-10 for BWRs. However, the staff believes that consideration of valve mispositioning benefits safety. Modifying the provisions in GL 89-10 for valve mispositioning does not affect the GL 89-10 provisions for licensees to review safety analyses, emergency procedures, and other plant documentation to 9202070037 . -2- determine the design basis(1) fluid conditions under which all MOVs in safety-related piping systems may intentionally be called upon to function. This position also does not supersede the NRC's generic recommendations or regulations on valve mispositioning that pertain to other issues such as intersystem loss-of-coolant accidents (ISLOCA) or fire protection (10 CFR 50, Appendix R). This modification to the recommendations addresses only BWR plants. The NRC will perform a similar review for pressurized water reactors (PWR). The NRC staff will review results of the PWR study and may revise GL 89-10, if warranted, appropriately to clarify the NRC's position regarding consideration of valve mispositioning within the scope of GL 89-10 for PWRs. The BWROG may complete the design basis reviews consistent with the position herein. This generic letter contains no information collection requirements and therefore is not subject to the requirements of the Paperwork Reduction Act of 1980 (44 U.S.C. 3501 et seq.). James G. Partlow Associate Director for Projects Office of Nuclear Reactor Regulation 1 Design basis conditions are those conditions during both normal operation and abnormal events that are within the design basis of the plant.
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