[Federal Register Volume 60, Number 143 (Wednesday, July 26, 1995)]
[Notices]
[Pages 38378-38379]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-18320]
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NUCLEAR REGULATORY COMMISSION
Proposed Generic Communication Generic Letter 89-10, Supplement
7, Valve Mispositioning in Pressurized-Water Reactors
AGENCY: Nuclear Regulatory Commission.
ACTION: Notice of opportunity for public comment.
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SUMMARY: The Nuclear Regulatory Commission (NRC) is proposing to issue
Generic Letter 89-10, Supplement 7 to notify addressees that the NRC is
removing the recommendation that MOV mispositioning be considered by
pressurized-water reactor licensees in responding to GL 89-10, as was
done for boiling-water reactor licensees in Supplement 4. The NRC is
seeking comment from interested parties regarding both the technical
and regulatory aspects of the proposed generic letter supplement
presented under the Supplementary Information heading. This proposed
generic letter supplement and supporting documentation were discussed
in meeting number 276 of the Committee to Review Generic Requirements
(CRGR) on July 11, 1995. The relevant information that was sent to the
CRGR to support their review of the proposed generic letter is
available in the NRC Public Document Room under accession number
9507170370. The NRC will consider comments received from interested
parties in the final evaluation of the proposed generic letter
supplement. The NRC's final evaluation will include a review of the
technical position and, when appropriate, an analysis of the value/
impact on licensees. Should this generic letter supplement be issued by
the NRC, it will become available for public inspection in the NRC
Public Document Room.
DATES: Comment period expires August 25, 1995. Comments submitted after
this date will be considered if it is practical to do so, but assurance
of consideration cannot be given except for comments received on or
before this date.
ADDRESSES: Submit written comments to Chief, Rules Review and
Directives Branch, U.S. Nuclear Regulatory Commission, Washington, DC
20555. Written comments may also be delivered to 11545 Rockville Pike,
Rockville, Maryland, from 7:30 am to 4:15 pm, Federal workdays. Copies
of written comments received may be examined at the NRC Public Document
Room, 2120 L Street, NW. (Lower Level), Washington, DC.
FOR FURTHER INFORMATION CONTACT: David C. Fischer, (301) 415-2728.
SUPPLEMENTARY INFORMATION:
NRC Generic Letter 89-10, Supplement 7: Consideration of Valve
Mispositioning in Pressurized-Water Reactors
Addressees
All holders of operating licenses (except those licenses that have
been amended to a possession only status) or construction permits for
nuclear power reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this
generic letter to notify addressees about a revised NRC position
regarding consideration of valve mispositioning within the scope of
Generic Letter (GL) 89-10 for pressurized-water reactors (PWRs).
Although this generic letter forwards a new staff position, no specific
action or written response is required.
Background
In GL 89-10 (June 28, 1989), ``Safety-Related Motor-Operated Valve
Testing and Surveillance,'' the staff recommended, among other things,
that any motor-operated valve (MOV) in a safety-related system that is
not blocked
[[Page 38379]]
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 licensee MOV programs. When determining the maximum differential
pressure or flow for position-changeable MOVs, the licensees were asked
to 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 Reactor Owners Group (BWROG) submitted a backfit
appeal on the recommendations for position-changeable valves. The
staff, with the assistance of Brookhaven National Laboratory (BNL),
reviewed and evaluated the issues concerning the mispositioning of
valves from the control room and determined that the recommendations in
GL 89-10 should be changed for BWRs. The BNL study, which used
probabilistic risk assessment (PRA) techniques, and the NRC staff
evaluation and conclusions were transmitted in a letter from the NRC to
the BWROG dated February 12, 1992. The conclusions were communicated to
industry and the public at large via Supplement 4 to GL 89-10, also
dated February 12, 1992. Supplement 4 indicated that the NRC would
perform a similar review for PWRs and stated that GL 89-10 might be
revised, if warranted, to clarify the NRC position regarding
consideration of MOV mispositioning within the scope of GL 89-10 for
PWRs.
Description of Circumstances
By letter dated July 21, 1992, the Westinghouse Owners Group (WOG)
asked the NRC staff to notify PWR licensees that the provisions of GL
89-10 for valve mispositioning are not applicable to PWRs, based on
arguments similar to those made by the BWROG.
Discussion
Under contract to the NRC staff, BNL performed a study similar to
the one performed for BWRs of the safety significance of inadvertent
operation of MOVs in safety-related piping systems of three PWRs.
Consistent with Supplement 1 to GL 89-10, the scope of the study was
limited to MOVs in safety-related systems that could be mispositioned
from the control room. However, because the available PRA models do not
include active mispositioning of MOVs or the physical phenomena that
could inhibit repositioning, BNL's study of available plant models was
limited in its ability to address this issue. Given this limited scope,
BNL concluded that the risk insights from the mispositioning of
unlocked MOVs were similar for both PWRs and BWRs. Although PWRs tend
to have a higher core damage frequency (CDF) than BWRs, which would
suggest that the net increase in CDF from mispositioning of MOVs would
be higher for PWRs than for BWRs, PWRs typically have a lower
conditional containment failure probability, which would tend to
balance the overall risk to the public.
The NRC is removing the recommendation that MOV mispositioning be
considered by PWR licensees in responding to GL 89-10, as was done for
BWR licensees in Supplement 4, in light of the following:
Corrective actions have been taken by licensees subsequent
to the Davis-Besse event (i.e., detailed control room design reviews,
independent valve position verification programs, and operator training
improvements).
Corrective actions are being applied to many of the most
important valves under the other provisions of GL 89-10.
Other operational events are absent (other than Davis-
Besse) in which mispositioning MOVs from the control room actually set
up conditions that prevented repositioning.
The results of the BNL study for PWRs.
Implementation of this relaxation by licensees is voluntary.
Staff Position
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 PWRs. 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 recommendations 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 be called upon to function. This
position also does not supersede the NRC generic recommendations or
regulations on valve mispositioning that pertain to such other issues
as interfacing-systems loss-of-coolant accidents (ISLOCAs) or fire
protection (10 CFR Part 50, Appendix R).
\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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Backfit Discussion
This letter represents a relaxation of recommendations set forth in
GL 89-10 and prior supplements. Implementation of this relaxation is
voluntary and this generic letter supplement requests neither actions
nor information from licensees. Therefore, this generic letter
supplement is not considered a backfit and the staff has not performed
a backfit analysis.
Dated at Rockville, Maryland, this 19th day of July 1995.
For the Nuclear Regulatory Commission.
Brian K. Grimes,
Director, Division of Project Support, Office of Nuclear Reactor
Regulation.
[FR Doc. 95-18320 Filed 7-25-95; 8:45 am]
BILLING CODE 7590-01-P
