[Federal Register Volume 61, Number 34 (Tuesday, February 20, 1996)]
[Notices]
[Pages 6392-6397]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-3691]
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NUCLEAR REGULATORY COMMISSION
Proposed Generic Letter: Periodic Verification of Design-Basis
Capability of Safety-Related Motor-Operated Valves (M93706);
Opportunity for Public Comment
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
a generic letter to (1) more explicitly address the need for the
periodic verification of the capability of safety-related motor-
operated valves (MOVs) to perform their safety functions consistent
with the current licensing bases of nuclear power plants, (2) request
that each licensee establish a program, or ensure the effectiveness of
a current program, at each facility within its purview, to verify on a
periodic basis that safety-related MOVs continue to be capable of
performing their safety functions within the current licensing bases of
the facility, and (3) require that licensees provide written responses
to the generic letter relating to implementation of the requested
actions.
NRC regulations require that components important to the safe
operation of a nuclear power plant, including MOVs, be treated in a
manner that provides assurance of their performance. Appendix A,
``General Design Criteria for Nuclear Power Plants,'' and Appendix B,
``Quality Assurance Criteria for Nuclear Power Plants and Fuel
Reprocessing Plants,'' to Part 50 of Title 10 of the Code of Federal
Regulations (10 CFR Part 50) include broad-based requirements in this
regard. In 10 CFR 50.55a(f), the NRC requires licensees to comply with
Section XI of the American Society of Mechanical Engineers Boiler and
Pressure Vessel Code (ASME Code).
Nuclear power plant operating experience, valve performance
problems and MOV research have revealed that the focus of the ASME Code
on stroke time and leak-rate testing for MOVs was not sufficient in
light of the design of the valves and the conditions under which they
must function. For this reason, on June 28, 1989, the NRC staff issued
Generic Letter (GL) 89-10, ``Safety-Related Motor-Operated Valve
Testing and Surveillance.'' In GL 89-10, the staff requested that
licensees and permit holders ensure the capability of MOVs in safety-
related systems to perform their intended functions by reviewing MOV
design bases, verifying MOV switch settings initially and periodically,
testing MOVs under
[[Page 6393]]
design-basis conditions where practicable, improving evaluations of MOV
failures and necessary corrective action, and trending MOV problems.
The staff requested that licensees complete the GL 89-10 program within
approximately three refueling outages or 5 years from the issuance of
the generic letter. Permit holders were requested to complete the GL
89-10 program before plant startup or in accordance with the above
schedule, whichever was later.
Recommendation ``d'' of GL 89-10 requested that licensees and
permit holders prepare procedures to ensure that correct MOV switch
settings are maintained throughout the life of the plant. GL 89-10
stated that it may become necessary to adjust MOV switch settings
because of wear or aging and that additional measures beyond ASME Code
stroke-time testing should be taken to adequately verify that the
switch settings ensure MOV operability.
Recommendation ``j'' of GL 89-10 stated that licensees should
periodically verify MOV capability every 5 years or every 3 refueling
outages. Recommendation ``h'' of GL 89-10 requested that licensees
evaluate trends in MOV performance every 2 years or at each refueling
outage.
The staff has issued seven supplements to GL 89-10 that provided
additional guidance and information on GL 89-10 program scope, design-
basis reviews, switch settings, testing, periodic verification,
trending, and schedule extensions. Supplement 6 to GL 89-10 stated that
no licensee had adequately justified the use of static test data as the
sole basis for periodically ensuring MOV design-basis capability.
GL 89-10 and its supplements provide only limited guidance
regarding periodic verification and the measures appropriate to assure
preservation of design-basis capability. This generic letter provides
more complete guidance regarding periodic verification of safety-
related MOVs. Although this guidance could have been provided in a
supplement to GL 89-10, the staff considered preparation of this new
generic letter appropriate to allow closure of the staff review of GL
89-10 programs as promptly as possible.
The proposed generic letter was discussed in meeting number 280 of
the Committee to Review Generic Requirements (CRGR) on January 31,
1996. The relevant information that was sent to the CRGR will be placed
in the Public Document Room. The NRC will consider comments received
from interested parties in the final evaluation of the proposed generic
letter. The final evaluation by the NRC will include a review of the
technical position and, as appropriate, an analysis of the value/impact
on licensees. Should this generic letter be issued by the NRC, it will
become available for public inspection in the NRC Public Document Room.
DATES: Comment period expires April 22, 1996. Comments submitted after
this date will be considered if it is practical to do so; assurance of
consideration can only be given for those 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
20555-0001. 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: Thomas G. Scarbrough, (301) 415-2794,
e-mail: [email protected]
SUPPLEMENTARY INFORMATION:
NRC Generic Letter 96-XX: Periodic Verification of Design-Basis
Capability of Safety-Related Motor-Operated Valves (M93706)
Addressees
All holders of operating licenses (except those licenses that have
been amended to possession-only status) or construction permits for
nuclear power reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this
generic letter to (1) discuss the periodic verification of the
capability of safety-related motor-operated valves (MOVs) to perform
their safety functions consistent with the current licensing bases of
nuclear power plants, (2) request that addressees implement actions
described herein, and (3) require that addressees provide to the NRC a
written response to this generic letter relating to implementation of
the requested actions.
Background
NRC regulations require that components that are important to the
safe operation of a nuclear power plant, including MOVs, be treated in
a manner that provides assurance of their performance. Appendix A,
``General Design Criteria for Nuclear Power Plants,'' and Appendix B,
``Quality Assurance Criteria for Nuclear Power Plants and Fuel
Reprocessing Plants,'' to Part 50 of Title 10 of the Code of Federal
Regulations (10 CFR Part 50) include broad-based requirements in this
regard. In 10 CFR 50.55a(f), the NRC requires licensees to comply with
Section XI of the American Society of Mechanical Engineers Boiler and
Pressure Vessel Code (ASME Code).
Nuclear power plant operating experience, valve performance
problems and MOV research have revealed that the focus of the ASME Code
on stroke time and leak-rate testing for MOVs was not sufficient in
light of the design of the valves and the conditions under which they
must function. For this reason, on June 28, 1989, the NRC staff issued
Generic Letter (GL) 89-10, ``Safety-Related Motor-Operated Valve
Testing and Surveillance.'' In GL 89-10, the staff requested that
licensees and permit holders ensure the capability of MOVs in safety-
related systems to perform their intended functions by reviewing MOV
design bases, verifying MOV switch settings initially and periodically,
testing MOVs under design-basis conditions where practicable, improving
evaluations of MOV failures and necessary corrective action, and
trending MOV problems. The staff requested that licensees complete the
GL 89-10 program within approximately three refueling outages or 5
years from the issuance of the generic letter. Permit holders were
requested to complete the GL 89-10 program before plant startup or in
accordance with the above schedule, whichever was later.
Recommendation ``d'' of GL 89-10 requested that licensees and
permit holders prepare procedures to ensure that correct MOV switch
settings are maintained throughout the life of the plant. GL 89-10
stated that it may become necessary to adjust MOV switch settings
because of wear or aging and that additional measures beyond ASME Code
stroke-time testing should be taken to adequately verify that the
switch settings ensure MOV operability. Recommendation ``j'' of GL 89-
10 stated that licensees should periodically verify MOV capability
every 5 years or every 3 refueling outages. Recommendation ``h'' of GL
89-10 requested that licensees evaluate trends in MOV performance every
2 years or at each refueling outage.
The staff has issued seven supplements to GL 89-10 that provided
additional guidance and information on GL 89-10 program scope, design-
basis reviews, switch settings, testing, periodic verification,
trending, and schedule extensions. Supplement 6 to GL 89-10 stated that
no licensee had adequately justified the use of static test data as the
sole basis for periodically ensuring MOV design-basis capability.
[[Page 6394]]
GL 89-10 and its supplements provide only limited guidance
regarding periodic verification and the measures appropriate to assure
preservation of design-basis capability. This generic letter provides
more complete guidance regarding periodic verification of safety-
related MOVs. Although this guidance could have been provided in a
supplement to GL 89-10, the staff considered preparation of this new
generic letter appropriate to allow closure of the staff review of GL
89-10 programs as promptly as possible.
Discussion
Nuclear power plant utilities are nearing completion of the
verification of the design-basis capability of their GL 89-10 MOVs. The
NRC staff has been closing its review of individual GL 89-10 programs
on the basis of the completion of the design-basis verification of
safety-related MOVs at each nuclear power plant and the utility's
establishment of a program for periodic verification of MOV design-
basis capability and for the trending of MOV problems. The staff may
conduct a more complete review of licensee programs for MOV periodic
verification as part of the implementation of this generic letter.
The staff believes that various approaches can be taken by
licensees to establish a periodic verification program that provides
confidence in the long-term capability of MOVs to perform their design-
basis safety functions. With each approach, the licensee should address
potential degradation that can result in (1) the increase in thrust or
torque requirements to operate the valves and (2) the decrease in the
output capability of the motor actuator.
The staff has long recognized the limitations of using stroke-time
testing as a means of monitoring the operational readiness of MOVs (see
GL 89-04, Supplement 1, ``Guidance on Developing Acceptable Inservice
Testing Programs'') and has supported industry efforts to improve MOV
periodic monitoring under the inservice testing (IST) program and GL
89-10. As such, the staff would consider a periodic verification
program that provides an acceptable level of quality and safety as an
alternative to the current IST requirements for stroke-time testing and
could authorize such an alternative, upon application by a licensee,
pursuant to the provisions of 10 CFR 50.55a(a)(3)(i). Guidance in this
generic letter and GL 89-04 (Supplement 1) could be used by a licensee
in determining whether its periodic verification program provides an
acceptable level of quality and safety.
In Attachment 1 to this generic letter, the staff discusses
industry and regulatory activities and programs related to maintaining
long term capability of safety-related MOVs and provides the staff
position regarding American Society of Mechanical Engineers (ASME) Code
Case OMN-1. The staff also identifies attributes of periodic
verification programs that the staff considers to be effective and an
example approach in implementing those attributes. Additionally, as
discussed in Attachment 1, certain licensees developed MOV periodic
verification programs that the staff found acceptable during the
closure of its review of GL 89-10 programs.
Licensees may consolidate long-term MOV periodic verification and
trending activities as part of their programs to meet the Maintenance
Rule (10 CFR 50.65) and other applicable regulations.
Requested Actions
Each addressee of this generic letter is requested to establish a
program, or to ensure the effectiveness of its current program, to
verify on a periodic basis that safety-related MOVs continue to be
capable of performing their safety functions within the current
licensing bases of the facility. The program should ensure that changes
in performance requirements resulting from degradation (such as those
caused by age) can be properly identified and accounted for. Addressees
that have developed periodic verification programs in response to GL
89-10 should review those programs to determine whether any changes are
appropriate in light of the information in this generic letter.
Required Response
All addressees are required to submit the following written
responses to this generic letter:
1. Within 60 days from the date of this generic letter, a written
response indicating whether or not the addressee will implement the
action(s) requested herein. If the addressee intends to implement the
requested action(s), the addressee shall submit a schedule for
completing implementation. If an addressee chooses not to implement the
requested action(s), the addressee shall submit a description of any
proposed alternative course of action, the schedule for completing the
alternative course of action (if applicable), and the safety basis for
determining the acceptability of the planned alternative course of
action.
2. Within 180 days from the date of this generic letter, or upon
notification to NRC of completion of GL 89-10 (whichever is later), the
addressee shall submit a written summary description of its MOV
periodic verification program established in accordance with the
Requested Actions paragraph or the alternative course of action
established by the addressee in response to item 1 above.
All addressees shall submit the required written reports to the
U.S. Nuclear Regulatory Commission, Attn: Document Control Desk,
Washington, D.C. 20555-0001, under oath or affirmation under the
provisions of Section 182a, Atomic Energy Act of 1954, as amended, and
10 CFR 50.54(f). In addition, a copy of the report shall be submitted
to the appropriate Regional Administrator.
Backfit Discussion
10 CFR Part 50 (Appendix A, Criteria 1 and 4) and plant licensing
safety analyses require and/or commit that the addressees design and
test safety-related components and systems to provide adequate
assurance that those systems can perform their safety functions. Other
individual criteria in Appendix A to 10 CFR Part 50, or commitments
made by licensees in their Final Safety Analysis Reports, apply to
specific systems. In accordance with those regulations and licensing
commitments, and under the additional provisions of Criterion XVI of
Appendix B to 10 CFR Part 50, licensees are expected to take actions to
ensure that safety-related MOVs are capable of performing their
required safety functions.
Recommendation ``d'' of GL 89-10 requested that licensees and
permit holders prepare procedures to ensure that correct MOV switch
settings are maintained throughout the life of the plant. GL 89-10
stated that it may become necessary to adjust MOV switch settings
because of wear or aging and that additional measures beyond ASME Code
stroke-time testing should be taken to adequately verify that the
switch settings ensure MOV operability. The NRC staff issued GL 89-10
as a compliance backfit as defined in 10 CFR 50.109. The actions
requested in this generic letter are considered compliance backfits,
under the provisions of 10 CFR 50.109 and existing NRC procedures, to
ensure that safety-related MOVs are capable of performing their
intended safety functions. In accordance with the provisions of 10 CFR
50.109 regarding compliance backfits, a full backfit analysis was not
performed for this proposed action; but the staff performed a
documented evaluation, which stated the objectives of and reasons for
the requested actions and the basis for invoking the compliance
exception. A
[[Page 6395]]
copy of this evaluation will be made available in the NRC Public
Document Room.
Federal Register Notification
This generic letter is being issued for a 60-day public comment
period.
Paperwork Reduction Act Statement
The information collections contained in this request are covered
by the Office of Management and Budget clearance number 3150-0011,
which expires July 31, 1997. The public reporting burden for this
collection of information is estimated to average 75 hours per
response, including the time for reviewing instructions, searching
existing data sources, gathering and maintaining the data needed, and
completing and reviewing the collection of information. Send comments
regarding this burden estimate or any other aspect of this collection
of information, including suggestions for reducing this burden, to the
Information and Records Management Branch (T-6 F33), U.S. Nuclear
Regulatory Commission, Washington, D.C. 20555-0001, and to the Desk
Officer, Office of Information and Regulatory Affairs, NEOB-10202
(3150-0011), Office of Management and Budget, Washington, D.C. 20503.
Attachment 1--Activities and Programs Related to Maintaining Long-Term
Capability of Safety-Related Motor-Operated Valves
Over the last several years, licensees and permit holders have
conducted tests of a large number of MOVs under static and dynamic
conditions as part of the implementation of their GL 89-10 programs.
From these tests, licensees and permit holders have identified
significant weaknesses in the design and qualification of MOVs used in
nuclear power plants. These weaknesses caused many MOVs to fail to
operate properly during testing. Further, some MOVs operated adequately
under test conditions, but analyses of the test results subsequently
revealed that the MOVs might not have performed their safety functions
under design-basis conditions. Licensees and permit holders are
applying significant resources to ensure that, despite the potential
weaknesses in original design and qualification, MOVs are currently
capable of performing their safety functions under design-basis
conditions.
In completing their GL 89-10 programs, licensees and permit holders
may have based their confidence in the current design-basis capability
of some safety-related MOVs on the thrust/torque requirements obtained
directly from the dynamic testing without additional margin for age-
related degradation. For some valves, licensees may have employed other
methods (such as grouping) to establish design-basis capability. In
some cases, the thrust/torque requirements obtained from the dynamic
tests were significantly less than the thrust/torque required to
operate apparently identical MOVs. Below, the staff discusses a
research program conducted by the Electric Power Research Institute
(EPRI) that indicates the potential for the thrust/torque required to
operate a valve to increase with service. Aging can also decrease the
thrust/torque output of motor actuators. Therefore, an effective
program for periodic verification of MOV design capability will require
that licensees understand the performance of their safety-related MOVs
and the manner in which that performance can change with aging.
Static diagnostic tests provide information on the thrust/torque
output of the motor actuator and any changes to the motor-actuator
output as a result of aging effects. The thrust and torque required to
operate a valve are highly dependent on the differential pressure and
flow across the valve disk, which are not present during static
testing. Therefore, dynamic tests can provide information on the
thrust/torque requirements and any changes to those requirements as a
result of aging effects. Although not currently validated, efforts are
underway within the nuclear industry to develop methods to obtain
information from static tests that would allow prediction of valve
dynamic performance. As discussed below, EPRI has developed an
analytical methodology that, when combined with static test data,
provides bounding information on the thrust/torque requirements to
operate gate, globe and butterfly valves under dynamic conditions.
While there may be benefits to performing dynamic testing to
ascertain the thrust/torque requirements and changes to these
requirements as a result of aging, there are also potential detriments
to dynamic testing (e.g., blowdown testing by EPRI resulted in damage
to some valves). The staff has not concluded that dynamic testing is
the preferred method for periodic verification testing and believes
dynamic testing may not be appropriate for certain situations. The
proposed method for periodic verification testing and demonstration of
a particular valve's acceptability and ability to perform consistent
with its design basis are the responsibility of the licensee.
Electric Power Research Institute (EPRI)
A motor-operated valve (MOV) testing program conducted by EPRI has
provided significant information regarding the long-term design-basis
capability of safety-related MOVs. In addition to finding that the
thrust required to operate gate valves is typically greater than the
thrust originally predicted by valve vendors, the EPRI program found
that the thrust required to operate gate valves can increase with valve
strokes until a plateau is reached. Due to limited resources and their
view that only limited and acceptable globe and butterfly valve
degradation would occur with repetitive valve stroking, EPRI did not
perform similar preconditioning tests on the globe and butterfly valves
in its MOV program. Therefore, licensees will need to demonstrate that
the EPRI methodology predicts long-term bounding thrust/torque
requirements for globe and butterfly valves when applied as part of an
MOV periodic verification program. For example, information might be
evaluated from periodic dynamic verification testing of globe and
butterfly valves being planned by some licensees. EPRI also found that
certain valves could be damaged during high flow and blowdown
testing.\1\
\1\ In addition to information applicable to MOV periodic
verification, the EPRI program has revealed performance
characteristics of MOVs that might adversely affect a licensee's
determination of the current capability of certain MOVs. In
particular, EPRI found that a high percentage of gate valves were
damaged during hot water and steam blowdown testing with thrust
requirements unable to be predicted. For MOVs that might be damaged
under such conditions, EPRI established possible modifications to
valve internals for proper clearances and for rounding sharp edges.
With respect to globe valves, EPRI found that reliable prediction of
globe valve thrust requirements requires an appropriate seat or
guide area in thrust calculations. Although EPRI tested only one
globe valve under high temperature and blowdown conditions, the test
revealed significantly higher thrust requirements than predicted.
EPRI also found that load-sensitive behavior (or rate of loading)
can reduce actuator thrust output under dynamic conditions. EPRI has
furnished the results of their MOV tests to licensees through
industry meetings, and the NRC staff has disseminated the results of
the tests to licensees through information notices on the EPRI test
program and public meetings. Some licensees have already
incorporated this information into their MOV programs.)
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The Nuclear Energy Institute (NEI) submitted EPRI Topical Report
TR-103237, ``EPRI MOV Performance Prediction Program,'' describing the
methodology developed by EPRI to predict dynamic thrust and torque
requirements for gate, globe, and butterfly valves without dynamic
tests by licensees. The staff prepared a safety evaluation (SE) which
approves the topical report for use and reference. Hence, the staff
would find it acceptable
[[Page 6396]]
if a licensee applied the EPRI methodology (in accordance with this
generic letter and the conditions or limitations contained in the NRC
staff's SE) in establishing a program for periodic verification of MOV
design-basis capability.
Boiling Water Reactor (BWR) Owners' Group
The BWR Owners' Group submitted Topical Report NEDC 32264,
``Application of Probabilistic Safety Assessment to Generic Letter 89-
10 Implementation,'' which provides a methodology to rank the MOVs in
GL 89-10 programs with respect to their relative importance to core
damage frequency, including appropriate considerations regarding other
consequences to be added by an expert panel. The staff is issuing an SE
on the topical report. The staff considers the methodology acceptable
(in accordance with any conditions or limitations contained in the NRC
staff's SE) for ranking MOVs in BWRs because the plant-specific IPE-
based insights are supplemented by generic insights and expert review
involving additional considerations, such as external events and
shutdown issues. In addition, the use of the MOV rankings is in
combination with deterministic considerations that ensure a minimally
acceptable frequency of testing is established even for the least risk-
significant valves.
NRC Research Activities
In the 1980s, the NRC Office of Nuclear Regulatory Research (RES)
sponsored a test program by the Idaho National Engineering Laboratory
(INEL) to determine the thrust required to operate motor-operated gate
valves under dynamic flow conditions. The results of the EPRI valve
test program confirmed the findings of the NRC's smaller-scale test
program. More recently, preliminary results from the testing of valve
material samples sponsored by RES indicate that valve friction can
increase with aging.
With respect to MOV ranking, RES sponsored a study of appropriate
frequencies of periodic testing of MOVs based on their risk
significance. This work is summarized in an article titled ``Risk-Based
Approach for Prioritizing Motor-Operated Valves'' in NUREG/CP-0137,
``Proceedings of the Third NRC/ASME Symposium on Valve and Pump
Testing.''
American Society of Mechanical Engineers (ASME)
Licensees are currently bound by the requirements in their Code-of-
record regarding stroke-time inservice testing (IST), as supplemented
by the additional measures they establish to ensure that MOV design-
basis capability is maintained pursuant to their GL 89-10 commitments
or relief requests approved by the staff.
The ASME Operations and Maintenance Code Committee has developed a
method to verify MOV design-basis capability through periodic testing.
Through a non-mandatory code case (OMN-1, entitled: ``Alternative Rules
for Preservice and Inservice Testing of Certain Electric Motor Operated
Valve Assemblies in LWR Power Plants, OM Code 1995 Edition; Subsection
ISTC''), ASME is allowing the replacement of frequent stroke-time
testing with periodic exercising of all safety-related MOVs once per
cycle and diagnostic testing under static or dynamic conditions, as
appropriate.
With certain limitations, the staff considers the code case to meet
the intent of this generic letter:
(1) When implementing the code case, the staff notes as an
additional precaution that the benefits (such as identification of
decreased thrust output and increased thrust requirements) and
potential adverse effects (such as accelerated aging or valve damage)
need to be considered when determining appropriate testing for each
MOV.
(2) The code case states that the maximum inservice test frequency
shall not exceed 10 years. The staff agrees with this condition of a
maximum test interval of 10 years based on current knowledge and
experience. In addition to this maximum test interval, where a selected
test interval extends beyond five years, the licensee should evaluate
information obtained from valve testing conducted during the first
five-year time period to validate assumptions made in justifying the
longer test interval. Based on performance and test experience obtained
during the initial interval, a licensee may be able to justify
lengthened MOV periodic verification intervals.
(3) Some licensees are developing programs for risk-informed
inservice testing. As part of an industry pilot effort, two licensees
have submitted exemption requests to utilize a risk-informed approach
to determine inservice test frequencies for certain components, in lieu
of testing these components per the frequencies specified by the ASME
Code. Licensees involved in risk-informed IST programs that seek to
implement the ASME code case need to specifically address the
relationship of the code case to their pilot initiative.
Plant-Specific Programs
The staff has found effective programs for periodic verification of
safety-related MOV design-basis capability at nuclear power plants to
be characterized by several attributes, as follow:
A risk-informed approach may be used to prioritize valve
test activities, such as frequency of individual valve tests and
selection of valves to be tested.
The valve test program should provide adequate confidence
that safety-related MOVs will remain operable until the next scheduled
test.
The importance of the valve should be considered in
determining an appropriate mix of exercising and diagnostic testing. In
establishing the mix of testing, the licensee should consider the
benefits (such as identification of decreased thrust output and
increased thrust requirements) and potential adverse effects (such as
accelerated aging or valve damage) when determining the appropriate
type of periodic verification testing for each safety-related MOV.
All safety-related MOVs covered by the GL 89-10 program
should be considered in the development of the periodic verification
program. The program should include safety-related MOVs that are
assumed to be capable of returning to their safety position when placed
in a position that prevents their safety system (or train) from
performing its safety function; and the system (or train) is not
declared inoperable when the MOVs are in their nonsafety position.
Licensees should evaluate and monitor valve performance
and maintenance and periodically adjust the periodic verification
program, as appropriate.
Licensees of several facilities (for example, Callaway, Monticello,
and South Texas) had established MOV periodic verification programs
that the staff found acceptable during closure of its review of GL 89-
10 programs. One approach to MOV periodic verification that the staff
found acceptable is to diagnostically test each safety-related MOV
every 5 years (or every 3 refueling outages) to determine thrust and
torque motor-actuator output and any changes in the output. A specific
margin to account for potential degradation such as that caused by age
(in addition to margin for diagnostic error, equipment repeatability,
load-sensitive behavior, and lubricant degradation) is established
above the minimum thrust and torque requirements determined under the
GL 89-10 program. The selection of MOVs for testing and their test
conditions should take into account
[[Page 6397]]
safety significance, available margin, MOV environment, and the
benefits and potential adverse effects of static and dynamic periodic
verification testing on the selected MOV sample. Measures such as
grouping and sharing of valve performance between facilities are
appropriate to minimize the need to conduct more rigorous periodic
verification tests.
As discussed in this generic letter, the staff has long recognized
the limitations of using stroke-time testing as a means of monitoring
the operational readiness of MOVs (see GL 89-04) and has supported
industry efforts to improve MOV periodic monitoring under the IST
program and GL 89-10. As such, the staff would consider a periodic
verification program that provides an acceptable level of quality and
safety as an alternative to the current IST requirements for stroke-
time testing and could authorize such an alternative, upon application
by a licensee, pursuant to the provisions of 10 CFR 50.55a(a)(3)(i).
Dated at Rockville, Maryland, this 13th day of February, 1996.
For the Nuclear Regulatory Commission.
Theodore R. Quay,
Acting Director, Division of Reactor Program Management, Office of
Nuclear Reactor Regulation.
[FR Doc. 96-3691 Filed 2-16-96; 8:45 am]
BILLING CODE 7590-01-P