"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
SUBJECT: GENERIC LETTER 89-10, SUPPLEMENT 4,
"CONSIDERATION OF VALVE MISPOSITIONING IN BOILING
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
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
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
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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