"Information on Schedule and Grouping, and Staff Responses to Additional Public Questions" (Generic Letter 89-10, Supplement 6)
March 8, 1994
TO: ALL LICENSEES OF OPERATING NUCLEAR POWER PLANTS AND HOLDERS OF
CONSTRUCTION PERMITS FOR NUCLEAR POWER PLANTS
SUBJECT: GENERIC LETTER 89-10, SUPPLEMENT 6, "INFORMATION ON SCHEDULE AND
GROUPING, AND STAFF RESPONSES TO ADDITIONAL PUBLIC QUESTIONS"
BACKGROUND
In Generic Letter (GL) 89-10 (June 28, 1989), "Safety-Related Motor-Operated
Valve Testing and Surveillance," the U.S. Nuclear Regulatory Commission (NRC)
staff requested holders of operating licenses and construction permits to
provide additional assurance of the capability of safety-related
motor-operated valves (MOVs) and certain other MOVs in safety-related systems
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. Supplement 1 to GL 89-10 (June 13, 1990) provided the
results of public workshops held to discuss the GL. In Supplement 2 to
GL 89-10 (August 3, 1990), the NRC staff stated that inspections of program
descriptions would not commence until January 1, 1991; thus, the program
descriptions did not need to be available on site until that date. Based on
the results of NRC-sponsored MOV tests, Supplement 3 to GL 89-10 (October 25,
1990) requested licensees of boiling-water reactor (BWR) nuclear plants to
take action in advance of the GL 89-10 schedule to resolve concerns about the
capability of MOVs used for containment isolation in the steam supply line of
the high pressure coolant injection and reactor core isolation cooling systems
and in the supply line of the reactor water cleanup system, as well as other
systems directly connected to the reactor vessel. Supplement 4 to GL 89-10
(February 12, 1992) allowed BWR licensees to not address inadvertent MOV
operation as part of their GL 89-10 program because a staff study indicated no
significant increase in core melt probability resulting from inadvertent MOV
operation in BWR plants. Supplement 5 to GL 89-10 (June 28, 1993) requested
licensees to provide information on their actions to address increased MOV
diagnostic equipment inaccuracy.
DISCUSSION
On February 25, 1993, the NRC staff held a public workshop to discuss GL 89-10
and to answer questions from the public on the inspections of licensee
programs developed in response to the GL. In this supplement to the GL, the
staff further clarifies the positions on the schedule for completing the MOV
testing to verify design-basis capability recommended in GL 89-10 and grouping
of MOVs to establish valve setup conditions. The staff responses to other
general public questions and a list of recently issued NRC GLs are also
provided in the enclosures to this supplement.
9402280155
.Generic Letter 89-10, Supp. 6 - 2 - March 8, 1994
GL 89-10 Schedule
In GL 89-10, the NRC staff requested nuclear power plant licensees to develop
a program to verify the capability of safety-related MOVs to perform their
safety function by June 28, 1994, or three refueling outages after
December 28, 1989 (whichever is later). Some licensees justified longer
schedules. From its inspections of GL 89-10 programs, the NRC staff found
some licensees to have made insufficient progress toward completing their
GL 89-10 programs in a timely manner. In GL 89-10, the staff stated that
nuclear power plant licensees must notify the staff of any changes to their
schedule commitments to GL 89-10 but that licensees should retain the
justification on site for NRC staff review.
Licensees are responsible for taking actions to correctly set up MOVs with
known inadequacies. GL 89-10 requested licensees to develop and implement a
program to verify the capability of their MOVs to operate under design-basis
conditions. As a minimum, the staff expects all licensees to have their
valves set up with the best available industry data by the original completion
date accepted by the staff, whether or not all testing has been completed.
The staff will consider whether subsequent MOV failures represent inadequate
corrective action for known MOV inadequacies contrary to the requirements of
Criterion XVI, Corrective Action, of Appendix B, "Quality Assurance Criteria
for Nuclear Power Plants and Fuel Reprocessing Plants," of Part 50 to Title 10
of the Code of Federal Regulations (10 CFR).
If a licensee does not believe that it can meet its current schedular
commitment for verifying the capability of MOVs within the scope of GL 89-10,
the following information will be needed to evaluate the licensee's
justification for extending the GL 89-10 test program for capability
verification and to establish appropriate audit/inspection plans and
schedules:
(1) the completion status of the licensee's GL 89-10 program as of the
current commitment date;
(2) for those MOVs whose capability will not be verified by dynamic testing
by the current commitment date:
(a) for each valve: the valve type, size, safety function, design-
basis differential pressure and flow, and the available valve
factor (or similar capability measure), and a discussion of the
relative risk significance of the valves involved;
(b) confirmation that the functionality of these MOVs has been
established using the best available information; and
(c) the schedule for completing both the MOV testing and any needed
corrective actions.
.Generic Letter 89-10, Supp. 6 - 3 - March 8, 1994
In addition to reviewing the above information, the staff will consider the
following factors (as available in inspection reports) in assessing the
licensee's justification for schedule extensions:
(1) the extent of completed MOV testing under dynamic conditions where
practicable and meaningful;
(2) the extent that plant and industry data have been used to establish the
sizing and setting methodology;
(3) the maintenance and modification activities to improve the performance
of the MOVs and to provide assurance that marginal and deficient MOVs
have been addressed; and
(4) the justifications for any grouping methods including design-basis test
data and comparison with industry data.
MOV Grouping
In GL 89-10 and its supplements, the NRC staff requests that licensees test
each MOV under design-basis differential pressure and flow conditions where
practicable. However, the staff recognizes that it is not practicable to test
each MOV within the scope of GL 89-10 in situ under dynamic conditions.
Therefore, if a licensee does not perform prototype testing at a test facility
for each MOV that is not practicable to test in situ, the licensee will have
to group MOVs that are not practicable to test in a manner that provides
adequate confidence that the MOVs are capable of performing their design-basis
function. As indicated in NRC Information Notice (IN) 92-17 (February 26,
1992), "NRC Inspections of Programs Being Developed at Nuclear Power Plants in
Response to Generic Letter 89-10," some licensees are attempting to group
MOVs, which could be dynamically tested in situ, to reduce the number of MOVs
to be dynamically tested under their GL 89-10 programs.
The staff continues to recommend testing MOVs under design-basis conditions
where practicable. Paragraph l of GL 89-10 allows licensees to propose
alternatives to the recommendations of the generic letter where justification
is provided. Grouping data from design-basis differential pressure testing of
similar MOVs at or near design-basis test conditions may be an acceptable
option to establish design-basis valve setup conditions.
If a licensee chooses to group MOVs, the staff believes the following
considerations are particularly important:
(1) verification of design adequacy of the grouped MOVs through a review and
analysis of both industry and plant-specific data;
(2) use of benchmarked data from a representative sample of the MOVs
(nominally 30 percent and no less than two MOVs) in the group tested at
or near plant-specific design-basis conditions;
.Generic Letter 89-10, Supp. 6 - 4 - March 8, 1994
(3) diagnostic testing of each MOV in the group under at least static
conditions;
(4) to the extent practicable, selection of valves for dynamic testing in
the group based on a prioritization scheme that considers greatest
safety-significance and least performance margin;
(5) validation of design-basis assumptions for all MOVs in the group based
on benchmarked data;
(6) in assessing group feasibility, consideration and documentation of such
similarities as: valve manufacturer, model and size; valve flow,
temperature, pressure, hydraulics, and installation configuration; valve
materials and condition; seat/guide stresses; and performance during
static and dynamic testing (as applicable) as evidenced by full-stroke
diagnostic traces; and
(7) if an MOV in a group fails or reveals adverse performance during testing
or operations, evaluation of the applicability of that information to
each MOV in the group.
In describing these considerations, the staff is not requiring any specific
grouping methodology.
In response to Question 24 in Supplement 1 to GL 89-10, the staff stated that
it expects licensees to ensure that data intended for use in demonstrating the
operability of an MOV have been obtained under the provisions of a quality
assurance program in accordance with Appendix B of 10 CFR Part 50. As further
information, licensees using data from tests performed under an approved
program (for example, other licensee data) developed in accordance with
Appendix B of 10 CFR Part 50 need not verify or audit the tests covered by
other licensee Appendix B procedures or processes.
Additional Public Questions
In an enclosure to this GL supplement, the staff responds to the additional
questions raised during the February 25 public workshop, including questions
involving the scope of GL 89-10 programs and the prioritization of MOVs based
on probabilistic risk assessments. The staff has paraphrased these additional
questions and grouped them by subject. The staff addressed many of the
questions previously either in general or in detail. The staff references
other documents where particular questions have been addressed. In the
enclosure, the staff provides examples of methods to address certain aspects
of GL 89-10 (such as test acceptance criteria) found acceptable during staff
review of GL 89-10 programs. Licensees may develop different, but equally
acceptable, methods to address those aspects of GL 89-10. Licensees may
contact their NRC project manager for discussion of plant-specific questions.
.Letter 89-10, Supp. 6 - 5 - March 8, 1994
BACKFIT DISCUSSION
On the basis of operating experience and research results, the NRC staff
determined several years ago that MOV tests beyond those previously accepted
under the inservice testing program are necessary to satisfy the NRC
regulations. As that determination constituted a backfit, and as discussed in
GL 89-10, Supplement 1 (June 13, 1990), the staff prepared GL 89-10 in
accordance with NRC procedures for the issuance of staff guidance containing
backfit provisions. This GL supplement and its enclosure (1) restate staff
positions contained in the GL and its earlier supplements, (2) provide
additional guidance for meeting the staff positions contained in the generic
letter and its earlier supplements, (3) relax the staff position on the need
for in situ testing of each MOV, and (4) require the submittal of specific
information if a licensee intends to extend its GL 89-10 schedule.
Backfit analyses for the restated and relaxed staff positions are not
required. A backfit analysis was not prepared for the additional guidance in
this GL 89-10 supplement because the compliance backfit analysis associated
with the original GL and its earlier supplements is applicable. This guidance
does not increase the recommendations associated with the staff positions
contained in the GL or its earlier supplements. Rather, the guidance provides
detailed methods of implementation of the basic GL 89-10 program which the
staff has found to be acceptable based on the individual inspections and
reviews of licensee programs which the staff has conducted to date. The use
of this guidance is voluntary and the staff will review alternate methods on a
case by case basis.
The staff prepared this GL supplement in response to questions and comments
received during a public workshop on February 25, 1993. Some licensees have
indicated their intention to extend their schedule commitment for completing
MOV testing under the GL 89-10 programs. The staff has evaluated the
justifications prepared by those licensees on a case-by-case basis. In this
GL supplement, the staff describes the information that the staff needs to
evaluate the licensee justifications for schedule extensions. In their
original response to GL 89-10, certain licensees did not commit to the
recommendation in GL 89-10 to test each safety-related MOV where practicable,
but rather, indicated plans to group MOVs to limit the amount of dynamic
testing. In this GL supplement, the staff describes important considerations
in grouping MOVs that the staff has been discussing with those licensees. If
a licensee intends to extend its MOV dynamic testing schedule, the staff will
expect the licensee to provide assurance that all MOVs are set up adequately
by the original completion date accepted by the staff. If a licensee intends
to group MOVs, the staff will expect the licensee to justify valve grouping
including the applicability of the dynamic test data of MOVs in the group and
to take action for all MOVs in the group in response to any adverse
performance of the dynamically-tested MOVs. Therefore, if a licensee modifies
its commitments regarding schedule or grouping of MOVs in accordance with the
provisions of this GL supplement, the staff has determined that the intent of
GL 89-10 would be appropriately met.
.Letter 89-10, Supp. 6 - 6 - March 8, 1994
The NRC published this GL supplement for public comment in the Federal
Register on July 22, 1993. The staff reviewed the public comments and revised
the GL supplement as appropriate. The staff placed the public comments and
staff responses in the NRC Public Document Room.
REPORTING REQUIREMENTS
Pursuant to section 182a of the Atomic Energy Act of 1954, as amended, and
10 CFR 50.54(f), each addressee that intends to modify its current commitment
to GL 89-10 and extend its schedule for responding to the generic letter is
required to submit the information described below. The submittal shall be
addressed to the U.S. Nuclear Regulatory Commission, ATTN: Document Control
Desk, Washington, D.C. 20555, under oath or affirmation. A copy shall also be
submitted to the appropriate Regional Administrator.
If a licensee intends to extend its current schedular commitment for verifying
the capability of MOVs within the scope of GL 89-10, the following information
shall be submitted at least 60 days prior to the current commitment date to
assist the staff in evaluating the licensee's justification for extending the
GL 89-10 test program for capability verification and establishing appropriate
audit/inspection plans and schedules:
(1) the completion status of the licensee's GL 89-10 program as of the
current commitment date;
(2) for those MOVs whose capability will not be verified by dynamic testing
by the current commitment date:
(a) for each valve: the valve type, size, safety function, design-
basis differential pressure and flow, and the available valve
factor (or similar capability measure), and a discussion of the
relative risk significance of the valves involved;
(b) confirmation that the functionality of these MOVs has been
established using the best available information; and
(c) the schedule for completing both the MOV testing and any needed
corrective actions.
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
June 30, 1994. The public reporting burden for this collection of information
is estimated to average 50 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 (MNBB-7714), U.S.
Letter 89-10, Supp. 6 - 7 - March 8, 1994
Nuclear Regulatory Commission, Washington, D.C. 20555, and the Desk Officer,
Office of Information and Regulatory Affairs, NEOB-3019, (3150-0011), Office
of Management and Budget, Washington, D.C. 20503.
Compliance with the following request for information is purely voluntary.
The information would assist NRC in evaluating the cost of complying with this
generic letter:
(1) the licensee staff time and costs to perform requested inspections,
corrective actions, and associated testing;
(2) the licensee staff time and costs to prepare requested reports and
documentation;
(3) the additional short-term costs incurred as a result of the inspection
findings such as the costs of the corrective actions or the costs of
down time; and
(4) an estimate of the additional long-term costs which will be incurred in
the future as a result of implementing commitments such as the estimated
costs of conducting future inspections or increased maintenance.
If you have any questions about this matter, please contact the technical
contact or lead project manager listed below, or the appropriate Office of
Nuclear Reactor Regulation project manager.
Sincerely,
/s/'d by Luis A. Reyes
Luis A. Reyes
Acting Associate Director for Projects
Office of Nuclear Reactor Regulation
Enclosures:
1. Public Questions during the February 1993 Workshop on GL 89-10
2. List of Recently Issued NRC Generic Letters
Technical contact: Thomas G. Scarbrough
(301) 504-2794
Lead Project Manager: Allen G. Hansen
(301) 504-1390
Generic Letter 89-10, Supp. 6
Enclosure 1
PUBLIC QUESTIONS DURING THE FEBRUARY 1993 WORKSHOP ON GENERIC LETTER 89-10
General
The NRC staff received general questions regarding the need for a single
approach to resolving the motor-operated valve (MOV) issue throughout the
industry, the need to continue licensee efforts to improve MOV performance,
the parallel efforts of the NRC staff and industry in such areas as
probabilistic risk assessment (PRA) studies, and the sharing of technical
information among the NRC staff and licensees.
NRC Response
As discussed under BACKGROUND in Generic Letter (GL) 89-10, the NRC staff
issued GL 89-10 to request that nuclear power plant licensees develop programs
to verify the capability of safety-related MOVs to perform their design-basis
functions as a result of NRC Bulletin 85-03, NRC-sponsored MOV research, and
operating experience at nuclear power plants. GL 89-10 and its supplements
provided one recommended approach to the resolution of the concerns regarding
the performance of MOVs in nuclear power plants. The NRC staff required
licensees to respond to the recommendations of the GL, but did not require
licensees to follow its specific recommendations if a licensee could justify a
different approach. For example, some licensees provided a response that
indicated their intent to develop a justifiable grouping methodology to
minimize the number of MOVs to be tested under dynamic conditions. The staff
indicated in its replies to those licensee submittals, and during inspections,
that licensees will be expected to justify that their particular approach will
resolve the concern for the performance of safety-related MOVs at their
plants.
During the implementation of GL 89-10, licensees have discovered more MOV
problems than envisioned by the staff when the generic letter was issued in
1989. Although the staff believes that licensees have made progress toward
resolving the concerns regarding the performance of MOVs in nuclear power
plants, the staff does not consider that sufficient progress has been made at
all plants to generically reduce the scope of the program or lengthen its
completion schedule. The staff will discuss proposals on specific MOV
programs with licensees as requested. Information on individual schedule
extensions is provided in the body of Supplement 6 to GL 89-10.
The staff performs independent regulatory oversight of activities on MOV
issues performed by licensees, the Electric Power Research Institute (EPRI),
and the Nuclear Management and Resources Council (NUMARC). The staff will
continue to meet with the industry to discuss MOV issues.
The staff periodically informs licensees of generic information on MOV issues.
For example, the staff issues information notices and participates in meetings
.Generic Letter 89-10, Supp. 6 - 2 - Enclosure 1
of the MOV Users Group. The staff believes that licensees would benefit from
increased cooperative efforts to resolve concerns regarding the performance of
MOVs.
Scope and the Use of PRA Studies in Prioritizing MOVs
The NRC staff received questions on the scope of GL 89-10 involving such areas
as the status of the staff's study of valve mispositioning in pressurized-
water reactor (PWR) nuclear plants, the use of PRA studies within the GL 89-10
program, the removal of certain valves under various flow conditions from the
GL 89-10 program, and the consideration of MOVs identified in emergency
operating procedures.
NRC Staff Response
The staff discussed the scope of GL 89-10 in response to Questions 3 to 13 and
25 in Supplement 1 and in Supplement 4 to the generic letter. The staff has
not changed the scope of GL 89-10 from the discussions in Supplements 1 and 4.
Except where valve mispositioning is applicable, a licensee may eliminate MOVs
from its GL 89-10 program where the licensee can clearly demonstrate that
operation of that valve does not represent a safety function and that its
operation is not necessary to permit the operation of its safety-related
equipment.
In response to Question 25 in Supplement 1 to GL 89-10, the staff stated that
a licensee might justify that sufficient margin exists for the extrapolation
of test results to demonstrate that a specific MOV would operate under design-
basis conditions. In its response to Question 25 in Supplement 1, the staff
provided examples of a significantly oversized MOV and an MOV where static
loads dominate the loads during design-basis conditions. For example, a
licensee might determine that the scope of MOVs to be dynamically tested may
be reduced by eliminating MOVs in hard-piping ventilation systems with low
design-basis differential pressure in which static loads are significant
compared to dynamic loads. Licensees may determine that certain MOVs are not
practicable to test or that the test would not provide useful results in
justifying design-basis capability. However, the licensee should continue to
include those MOVs within the other aspects of the GL 89-10 program.
As discussed in Supplement 4 to GL 89-10 and NRC Information Notice (IN) 92-17
(February 26, 1992), "NRC Inspections of Programs Being Developed at Nuclear
Power Plants in Response to Generic Letter 89-10," the NRC staff has
contracted a national laboratory to perform a core melt frequency study of the
effect of valve mispositioning in PWR plants. This study is complete and the
staff is considering the findings to make a determination on the issue.
In response to Question 12 in Supplement 1 to GL 89-10, the staff stated that
a licensee may choose to give priority to MOVs that it considers to be most
important to safe and reliable operations. In Supplement 3 to GL 89-10, the
staff requested BWR licensees to give high priority to MOVs used for
containment isolation in certain high pressure systems connected directly to
the reactor vessel. In discussing possible extensions of the schedule for
.Generic Letter 89-10, Supp. 6 - 3 - Enclosure 1
completing MOV testing under GL 89-10, the staff has requested individual
licensees to prioritize their MOVs to ensure that testing for the most safety
significant MOVs is completed in a timely manner. For example, the staff will
consider whether the licensee assigned a higher priority to testing of MOVs
that must operate to perform an active safety function than to testing of MOVs
that only receive a confirmatory signal to operate. Also, the licensee could
assign a lower priority to MOVs with significant design margin.
The staff considers the use of PRA studies to be appropriate as an input for
prioritizing the schedule for testing MOVs in response to GL 89-10. However,
the staff does not consider PRA studies to be sufficiently reliable to allow
their use as the sole basis for eliminating safety-related MOVs from the
GL 89-10 program. Further, PRA studies alone are not well-suited for common-
mode problems such as the weakness in the original design and qualification of
MOVs. The staff is performing an independent assessment of the use of PRA
studies for prioritizing MOVs within the GL 89-10 program. Upon request, the
staff will meet with industry representatives to discuss this issue.
As discussed in response to Question 3 in Supplement 1 to GL 89-10, the GL
scope includes gate, butterfly, and globe valves. Although licensees have
found gate valves to be susceptible to the largest number of performance
problems, they also have discovered performance problems with butterfly valves
at several plants. In response to a specific comment, the staff does not
believe that GL 89-10 should be limited to gate valves.
The staff discussed the removal of MOVs from the scope of GL 89-10 programs in
response to Questions 3 and 6 in Supplement 1 to GL 89-10. For example, the
staff eliminated MOVs in sheet-metal ducting systems because static running
loads would likely be significant compared to dynamic loads. In light of
Supplement 4 to GL 89-10 on mispositioning, a BWR licensee may delete an MOV
from its GL 89-10 program if the licensee can demonstrate that the MOV does
not have to change position to perform a safety function. In response to a
specific question, if an MOV is pulled closed by flow (such as a globe valve
with flow over the seat), the licensee could justify that the MOV does not
need to be included in the GL 89-10 test program for the closing direction.
As indicated by the discussion of scope in Supplement 1 to GL 89-10, except
where valve mispositioning is applicable, licensees do not need to consider
MOVs identified in emergency operating procedures as within the scope of
GL 89-10 if they are not within the design basis of the plant.
Additional information on grouping of MOVs is provided in the body of
Supplement 6 to GL 89-10.
MOV Sizing and Switch Settings
The NRC staff received questions regarding the responsibility of licensees to
validate assumptions used in their calculations (including parameters provided
by valve vendors), to consider various uncertainties within the MOV
calculations, to ensure the structural capability of safety-related MOVs in
.Generic Letter 89-10, Supp. 6 - 4 - Enclosure 1
performing their design-basis functions, and to justify the use of a
contractor study on the overthrust capability of certain valve actuators.
NRC Staff Response
As discussed in response to Questions 19 and 20 in Supplement 1 to GL 89-10,
MOV tests and problems have revealed that valve vendors underestimated the
thrust and torque required to operate many valves under dynamic conditions.
As indicated in IN 92-17, the staff has found during inspections of GL 89-10
programs that some licensees had not justified their assumptions used in
validating the size and settings of the MOVs within the scope of GL 89-10.
The staff expects licensees to validate their assumptions for thrust and
torque requirements to open and close their valves based on the best available
MOV test data.
As further information, the staff considers the best available MOV test data
(in order of reliability) to be valve-specific data, plant-specific data, EPRI
test data, and industry test data. Where it is not practicable to test an MOV
under sufficient dynamic conditions to demonstrate design-basis capability,
licensees may use engineering or statistical methods to determine appropriate
assumptions for such parameters as valve and stem friction, and load sensitive
behavior from other MOVs, where justified.
As required by Appendix B, "Quality Assurance Criteria for Nuclear Power
Plants and Fuel Reprocessing Plants," of Part 50 to Title 10 of the Code of
Federal Regulations (10 CFR), the staff expects licensees to include
appropriate margin to account for uncertainties in their design assumptions.
As discussed in IN 92-17, staff inspections found that some licensees had not
addressed uncertainties such as actuator repeatability and diagnostic
equipment inaccuracy. The staff also expects licensees to include sufficient
margin to provide assurance that the MOV will remain capable of performing its
design-basis function until the next test.
Under BACKGROUND in GL 89-10, the staff stated that licensees should be aware
that increasing MOV thrust by increasing torque switch settings may subject
the valve components to increased forces. In IN 92-83 (December 17, 1992),
"Thrust Limits for Limitorque Actuators and Potential Overstressing of Motor-
Operated Valves," the staff alerted licensees to possible overstressing of
MOVs during operation and testing. As further explanation, the staff expects
licensees to provide adequate justification to ensure that the structural or
operating capability of the MOVs within the scope of GL 89-10 is not exceeded
when performing their design-basis functions. The staff will review this
justification during GL 89-10 inspections.
Several licensees contracted Kalsi Engineering to evaluate the structural
thrust capability of Limitorque actuators. Limitorque has endorsed the Kalsi
study to justify specific thrust limits above the published structural ratings
of the actuators but, at this time, has not increased the structural ratings
of its actuators. In IN 92-83, the staff alerted licensees to the review by
the NRC staff of the Kalsi study. As is the staff's longstanding practice,
.Generic Letter 89-10, Supp. 6 - 5 - Enclosure 1
licensees that rely on contractor studies are responsible for justifying their
use. For example, licensees using the Kalsi overthrust report will be
expected to implement the provisions of that report and to periodically
inspect the actuators to identify any adverse effects from the increased
thrust above the structural ratings. Licensees that rely on contractor
studies are responsible for evaluating any subsequent MOV problems that might
be attributable to the contractor study and taking corrective action to
address the problem for all MOVs whose setup is based on the contractor study.
The staff will consider whether any such failure indicates that the licensee
may not have met the NRC regulations for design control.
MOV Testing
The NRC staff received questions in such areas as the testing of MOVs where
practicable, the testing of MOVs under all design-basis conditions (including
degraded voltage), the collection of test data during MOV testing, the
measurement of thrust and torque during MOV testing, the acceptance criteria
for evaluating MOV tests, the extrapolation of test data, the discovery of new
information that might reveal problems with design-basis capability of MOVs,
the need to verify design-basis capability for those valve types for which
reliable diagnostic equipment might not be available, the determination of
minimum voltage at the motor terminals, the application of prototype test data
for MOVs installed in nuclear plants, the use of the results of the EPRI MOV
Performance Prediction Program, and quality assurance controls for the
proposed industry MOV test data base.
NRC Staff Response
GL 89-10 and its supplements recommend that licensees test MOVs within the
scope of the generic letter under design-basis differential pressure and flow
conditions where practicable. For MOVs that cannot be tested under these
conditions, Supplement 1 to GL 89-10 recommended that the MOVs be tested under
maximum achievable conditions to provide the best available MOV test data.
Since then, licensee results from testing similar MOVs have shown that
specific valve testing provides the best available data. However, a licensee
might justify an alternative approach, such as grouping, where the licensee
has sufficient information to demonstrate the validity of its approach. For
example, some licensee test results have indicated that grouping globe valves
may be justifiable. Nevertheless, recent testing by Commonwealth Edison
Company and EPRI revealed high thrust requirements for certain globe valves
tested. Information on grouping is provided in the body of Supplement 6 to
GL 89-10. As discussed under Scope, licensees may justify instances where
dynamic testing (although practicable) is not necessary on a case-by-case
basis.
In response to Question 22 in Supplement 1 to GL 89-10, the staff stated that
licensees should consider the safety implications of performing design-basis
testing of MOVs in situ. As further explanation, the staff does not expect
licensees to test MOVs under all design-basis conditions (such as degraded
voltage). Such testing might damage the MOV or jeopardize the safety of the
plant and is impractical to perform. The staff expects licensees to
.Generic Letter 89-10, Supp. 6 - 6 - Enclosure 1
demonstrate the degraded voltage capability of MOVs by a justifiable
analytical method.
In response to Question 30 in Supplement 1 to GL 89-10, the staff stated that
measured parameters from MOV tests should be capable of providing information
to assist the licensee in demonstrating that the MOV will operate under
design-basis conditions. As further explanation, licensees need only collect
information that is required to evaluate the test data. If the collection of
that information can be performed with sufficient accuracy without
installation of additional test equipment, the staff does not expect licensees
to modify plant systems to obtain test data.
In response to Question 31 in Supplement 1 to GL 89-10, the staff stated that
the actuator must be able to deliver the required amount of torque or thrust.
In response to Question 30 in Supplement 1 to GL 89-10, the staff stated that
if only one parameter (such as thrust) was measured rather than two or more
parameters (such as torque and thrust), the licensee may need to ensure that
additional margin is available in the demonstration that the MOV will operate
under design-basis conditions. As further explanation, if a licensee measures
only thrust and assumes a stem friction coefficient to estimate the torque
required to operate the valve, the staff expects the licensee to validate its
assumption for stem friction coefficient. Licensee testing has indicated that
stem friction coefficients are valve specific and may range from less than 0.1
to greater than 0.2. Although laboratory testing might show a low stem
friction coefficient, licensees have not demonstrated that a specific
assumption for stem friction coefficient can be made at a nuclear plant based
on laboratory test results.
NRC regulations in Appendix B to 10 CFR Part 50 require that tests of
safety-related MOVs be evaluated. In IN 92-17, the staff reported that
weaknesses had been found during GL 89-10 inspections in acceptance criteria
at some plants for MOV testing before returning the MOV to service. Several
licensees (for example, Comanche Peak) have developed detailed acceptance
criteria that the staff considers acceptable. Further, the BWR Owners' Group
is developing acceptance criteria that may be adequate when completed. Below,
the staff summarizes criteria for the evaluation of test data that have been
found acceptable. Other criteria may also be acceptable.
1. Static Test Acceptance:
. Available thrust and torque is within the window defined by the licensee
design-basis calculations and margins.
. Diagnostic traces do not indicate significant abnormalities or anomalies
that might affect operability.
. Valve stroke times conform with requirements of Section XI of the
American Society of Mechanical Engineers (ASME) Code and the applicable
technical specifications.
.Generic Letter 89-10, Supp. 6 - 7 - Enclosure 1
2. Differential Pressure Test Acceptance:
. The valve fully opens with appropriate open torque switch bypass
indication and fully closes with diagnostic indication of hard seat
contact and control room indication.
. The control switch settings provide adequate thrust margin to overcome
design-basis requirements, including consideration of diagnostic
equipment inaccuracy, control switch repeatability, load sensitive
behavior, and margin for degradation until the next test.
. The motor output capability at degraded voltage is in excess of the
control switch setting including consideration of diagnostic equipment
inaccuracy, control switch repeatability, load sensitive behavior, and
margin for degradation until the next test.
. The maximum thrust and torque achieved by the MOV including diagnostic
equipment inaccuracy and control switch repeatability do not exceed the
allowable structural capability limits for the individual parts of the
MOV.
. The diagnostic traces do not indicate any significant abnormalities or
anomalies that might affect MOV operability.
After returning the MOV to service, the licensee performs a more detailed
followup evaluation of test data for such items as the following:
. In the event of greater-than-predicted thrust or torque requirements,
evaluate other applicable MOVs (such as parallel train valves) before
plant startup. If plant is operating, evaluate promptly in accordance
with GL 91-18 (November 7, 1991), "Information to Licensees Regarding
Two NRC Inspection Manual Sections on Resolution of Degraded and
Nonconforming Conditions and on Operability."
. Perform a detailed evaluation of the diagnostic trace for such items as
bent stem, spring pack gap, and stem/stem nut interface problems. For
example, compare in-rush motor current to running current for magnesium
rotor degradation.
. Incorporate valve factors and stem friction coefficients into MOV sizing
and switch setting methodology to ensure thrust windows are correct.
In response to Question 25 in Supplement 1 to GL 89-10, the staff stated that
licensees may extrapolate the results of MOV tests to design-basis conditions
where justified. As further explanation, the staff does not have a specific
percentage of design-basis differential pressure where the test results can be
reliably extrapolated to design-basis conditions. Licensees may justify their
own method of extrapolation and the extent of that extrapolation. The staff
describes one extrapolation method developed by the Idaho National Engineering
Laboratory (INEL) in NUREG/CR-5720 (June 1992), "Motor-Operated Valve Research
Update." Licensees may use that method if justified for their MOVs. The
.Generic Letter 89-10, Supp. 6 - 8 - Enclosure 1
staff does not have any current plans to mandate the use of the extrapolation
method outlined in NUREG/CR-5720.
At the February 25 workshop, a participant asked a question on whether
unwedging forces need to be extrapolated. The staff believes that only thrust
and torque required to overcome dynamic fluid forces need to be extrapolated
from test conditions to design-basis conditions. A licensee might justify
that unwedging forces do not need to be extrapolated from test conditions to
design-basis conditions.
As required through Criterion XVI, Corrective Action, of Appendix B to 10 CFR
Part 50, it is the responsibility of licensees to ensure that adverse
information from MOV testing does not reveal a problem with other MOVs in the
plant. In IN 92-17, the staff reported that GL 89-10 inspections had found
that some licensees did not appear to be aware of their obligations in this
area. Although test information might not be sufficient to justify the
capability of a similar MOV, adverse test information can reveal a potential
operability problem with other MOVs that a licensee must address. The
requirements in Criterion XVI of Appendix B also apply to new information that
might reveal a problem with the design-basis capability of MOVs, such as
increased MOV diagnostic equipment inaccuracy.
In response to Question 30 in Supplement 1 to GL 89-10, the staff stated that
it did not plan to insist that licensees use diagnostic equipment in
implementing GL 89-10, but believed that such equipment would be almost
essential for adequate implementation of the generic letter. As further
explanation, licensees are responsible for demonstrating the design-basis
capability of MOVs even where uncertainties exist in available diagnostic
equipment. However, the staff will consider this factor in reviewing
justifications for schedule extensions for completing testing under GL 89-10.
In response to Question 36 in Supplement 1 to GL 89-10, the staff briefly
described its position on the consideration of degraded voltage in evaluating
MOV capability under GL 89-10. In IN 92-17, the staff reported that many
licensees are updating their degraded voltage studies. Below, the staff
provides a more detailed explanation of an acceptable approach to considering
degraded voltage with respect to MOV capability.
For 480-Vac motors, the licensee determines minimum voltage at the motor
terminals considering cable size and length, temperature, and thermal
overload resistance. The licensee considers the worst-case postulated
motor control center (MCC) voltage based either on the lower of the
voltage supplied from the diesel generator or the offsite supply. Where
the offsite supply is the limiting case, as is typical, the licensee
uses the degraded grid relay setpoint as the starting point for
determining the minimum voltage at the motor terminals for ac motors.
The appropriate setpoint to be used is for the degraded grid relay which
provides for separation from the offsite supply, and connection to the
emergency diesel generator with or without a specific time delay or
concurrent accident signal.
.Generic Letter 89-10, Supp. 6 - 9 - Enclosure 1
In addition to the degraded grid voltage relays, some plants use an
additional alarm relay (set higher than the degraded grid voltage
relays) to alert the operator to a sustained degraded grid condition.
The licensee would not use the alarm relay setting to calculate the
voltage required at the MOVs. Likewise, the staff does not consider
taking credit for administrative procedures and operator response (to
separate from the offsite supply) to be acceptable unless these actions
have been evaluated and accepted by the staff.
For dc motors, the licensee uses the worst-case battery voltage profile
(including aging and temperature factors). The licensee properly
accounts for voltage drops from the battery to the MCC. After
determining the minimum voltage at the motor, the degraded voltage
factor is calculated. The degraded voltage factor is then multiplied by
the rated motor output torque and compared to the torque required.
In Technical Update 92-02, Limitorque states that, between 90 and 99 percent
of rated voltage, the degraded voltage factor is equal to one and that the
application factor makes allowances for motor torque loss up to 90 percent
voltage. In Technical Update 92-02, Limitorque also states that the degraded
voltage factor is applied if motor terminal input voltage is less than
90 percent of the motor rated voltage at any time during the valve stroke.
For ac-powered MOVs, the degraded voltage factor is equal to the square of the
ratio of the minimum motor terminal voltage to the motor rated voltage. For
dc-powered MOVs, the degraded voltage factor is equal to the minimum motor
terminal voltage divided by the motor rated voltage. However, Limitorque has
only approved this approximation for motor voltages over 70 percent.
The following is a summation of two acceptable methods for calculating the
expected ac-motor terminal voltage at degraded bus voltage conditions:
Method One: A motor circuit one-line diagram is constructed consisting
of the known cable and overload heater impedances. The motor impedance
is calculated by the following formula:
Z(m) = V(r)
SQRT(3) x I(lr)
where Z(m) = motor impedance
V(r) = motor nominal voltage
I(lr) = rated locked rotor current
The motor resistance and reactance are calculated from the above
impedance using the locked-rotor power factor. Then, a voltage divider
calculation is performed with the result being the calculated motor
terminal voltage under worst-case bus voltage conditions.
Method Two: A motor current value, representative of worst-case
conditions, is assumed. Some licensees assume nominal locked rotor
current, which should be the most conservative. Other licensees are
assuming alternate values such as current at torque switch trip, which
.Generic Letter 89-10, Supp. 6 - 10 - Enclosure 1
may not be conservative because the current at torque switch trip may
depend on the applied voltage and consequently may be higher under
degraded voltage conditions. Additionally, current at torque switch
trip is not always the worst case because unseating current could be
higher in some cases. Also, if the current was derived from a test at
less than full differential pressure, the current at torque switch trip
also might be underestimated as a result of differences in inertial
forces. Therefore, the licensee justifies the use of any current value
less than that of nominal locked-rotor current. Motor terminal voltage
is then calculated by multiplying the assumed motor current times the
cable and overload impedances and subtracting this value from the
worst-case bus voltage. The licensee uses the power factor provided by
Limitorque for locked-rotor conditions.
For dc motors, an acceptable approach to determine the worst-case motor
voltage is more straightforward. The locked-rotor resistance of the motor is
calculated from actual locked-rotor current test data. Then, appropriate
values are assumed for cable, overload heater, and starting resistor
resistances.
In response to Question 26 in Supplement 1 to GL 89-10, the staff describes
the demonstration of the applicability of prototype test data to MOVs
installed in nuclear plants. As indicated in Supplement 1, the staff believes
that the most justifiable method of demonstrating applicability is to use
performance-based criteria where the MOV in question is tested under partial
dynamic conditions and its performance is related to the performance of the
prototype MOV under similar conditions. However, each licensee may develop
its own method of justifying the applicability of prototype test data.
Since the staff issued Supplement 1 to GL 89-10, EPRI has established an MOV
Performance Prediction Program that might provide important information to
assist licensees in demonstrating the design-basis capability of MOVs that
cannot practicably be tested under dynamic conditions. The staff expects
licensees to proceed with their GL 89-10 programs and not to wait for the
completion of the EPRI program. Where the EPRI program does not provide
sufficient information regarding an MOV, the staff expects each licensee to
provide justification for the design-basis capability of the MOV.
In response to Question 28 in Supplement 1 to GL 89-10, the staff stated that
the capability of an MOV under design-basis conditions might be demonstrated
by means of a data base of test results if properly justified. The staff also
indicated that the MOV Users Group might be able to provide assistance in
developing such a data base. Recently, the MOV Users Group indicated that it
is planning to develop a data base of tests conducted by licensees. The staff
expects the industry MOV test data base to be established and maintained with
appropriate quality assurance controls.
.Generic Letter 89-10, Supp. 6 - 11 - Enclosure 1
Periodic Verification and Post-Maintenance Testing
The NRC staff received questions on the use of static tests to satisfy the
recommendation in GL 89-10 to periodically verify the design-basis capability
of MOVs, the frequency of periodic verification of design-basis capability,
and the use of motor current following valve packing adjustments or
replacement.
NRC Staff Response
Recommendation d of GL 89-10 requests licensees to periodically verify that
MOVs within the scope of GL 89-10 are capable of performing their design-basis
functions. In response to Question 33 in Supplement 1 to GL 89-10, the staff
stated that the licensee should develop a method to ensure that, following the
initial demonstration that the MOV would operate under design-basis
conditions, the MOV switches remain set adequately. As indicated in IN 92-17,
many licensees have stated their intent to rely on static test data to address
the GL 89-10 recommendation on periodic verification. In recommendation d of
GL 89-10 and in response to Question 35 in Supplement 1 to GL 89-10, the staff
stated that the ASME Code Section XI stroke-time testing required by 10 CFR
Part 50 would not satisfy this provision of GL 89-10. The staff discussed the
relationship between ASME Section XI and GL 89-10 in response to Question 49
in Supplement 1 to GL 89-10.
The staff is not prohibiting licensees from attempting to justify static
testing as a method of verifying periodically the design-basis capability of
MOVs. However, based on the results of GL 89-10 inspections to date, no
licensee has as yet justified the use of static test data for periodically
demonstrating the design-basis capability of MOVs. The staff will review the
justification provided by licensees during inspections when licensees begin
implementing their method for periodically verifying the design-basis
capability of MOVs.
In GL 89-10, the staff recommended that the design-basis capability of MOVs be
verified approximately every five years but noted that an alternative schedule
might be justified. As further information, a licensee may evaluate the
safety significance of an MOV in determining an appropriate frequency for
periodically verifying design-basis capability.
In response to Question 38 in Supplement 1 to GL 89-10, the staff stated that
the licensee should justify that the MOV switch settings remain correct, or
have been adjusted adequately, upon completion of any activity involving the
MOV that might affect its ability to operate under design-basis conditions.
Since then, the industry has found the use of motor current to not always
reliably predict changes in thrust delivered in operating a valve. However,
Commonwealth Edison Company has developed a method of using motor current when
sufficient margin is available following valve packing adjustments.
.Generic Letter 89-10, Supp. 6 - 12 - Enclosure 1
Trending
The NRC staff received a question on the staff's expectations regarding
tracking and trending of MOV problems in response to GL 89-10.
NRC Staff Response
In response to Question 39 in Supplement 1 to GL 89-10, the staff referred
licensees to Attachment A to GL 89-10 for MOV problems that could be trended.
The staff has documented in its GL 89-10 inspection reports instances in which
licensees have developed thorough trending programs.
Schedule
The NRC staff received questions on the need to complete the GL 89-10 program
within the schedule recommended in the generic letter and the justification
necessary to extend the schedule commitment date.
NRC Staff Response
Information on schedule is provided in the body of Supplement 6 to GL 89-10.
In addition to testing under recommendation c of GL 89-10, the staff discusses
the long-term aspects of the MOV program in recommendations d, f, h and j of
the generic letter.
Pressure Locking and Thermal Binding of Gate Valves
The NRC staff received questions on the need to consider pressure locking and
thermal binding of gate valves as part of a licensee's response to GL 89-10,
the drilling of a hole in the valve disk to prevent pressure locking, the
schedule for evaluating pressure locking and thermal binding, and the need for
detailed measurements of external heat loads in evaluating the potential for
pressure locking and thermal binding.
NRC Staff Response
The NRC Office for Analysis and Evaluation of Operational Data (AEOD) has
completed AEOD Special Study AEOD/S92-07 (December 1992), "Pressure Locking
and Thermal Binding of Gate Valves." The staff issued the AEOD report in
NUREG-1275, Volume 9 (March 1993), "Operating Experience Feedback Report -
Pressure Locking and Thermal Binding of Gate Valves." In its report, AEOD
concludes that licensees have not taken sufficient action to provide assurance
that pressure locking and thermal binding will not prevent a gate valve from
performing its safety function.
The NRC regulations require that licensees design safety-related systems to
provide assurance that those systems can perform their safety functions. In
GL 89-10, the staff requested licensees to review the design bases of their
safety-related MOVs. In complying with the NRC regulations, licensees are
expected to have evaluated the potential for pressure locking and thermal
.Generic Letter 89-10, Supp. 6 - 13 - Enclosure 1
binding of gate valves and taken action to ensure that these phenomena do not
affect the capability of MOVs to perform their safety-related functions. If a
licensee identifies a potential for pressure locking and thermal binding of
gate valves, the NRC regulations require that the licensee take action to
resolve that problem.
Based on information from staff inspections and discussions, the staff
considers the following to be an acceptable approach to addressing pressure
locking and thermal binding of gate valves within the scope of GL 89-10:
1. Document an evaluation of the gate valves within the scope of GL 89-10
as having operational configurations with a potential for pressure
locking or thermal binding, including the basis for determining whether
the valves (a) are susceptible to pressure locking or thermal binding or
(b) can be removed from further consideration. For example, solid wedge
disk gate valves might not be susceptible to pressure locking. Double
disk gate valves are not likely to be susceptible to thermal binding.
The evaluation would include consideration of the potential for an MOV
to undergo pressure locking or thermal binding during surveillance
testing. For example, the inboard containment isolation MOV in the
reactor core isolation cooling (RCIC) system steam line at a plant
recently failed in the closed position following closure for routine
surveillance testing. The cause was believed to be pressure locking.
The evaluation also would include review of generic studies for site-
specific applicability, such as in the areas of thermal effects and
design-basis depressurization.
Examples of unacceptable reasons for eliminating valves from
consideration of pressure locking or thermal binding are (1) leakage
rate, (2) engineering judgment without justification, and (3) lack of
event occurrence at the specific plant.
The AEOD study indicated that safety-related gate valves involved in
pressure locking events were
. low pressure coolant injection (LPCI) and low pressure core spray
(LPCS) system injection valves
. core spray (CS) valves
. residual heat removal (RHR) shutdown cooling (SDC) isolation
valves
. RHR hot leg crossover isolation valves
. RHR containment sump and suppression pool suction valves
. high pressure coolant injection (HPCI) steam admission valves
.Generic Letter 89-10, Supp. 6 - 14 - Enclosure 1
. RHR heat exchanger outlet valves
. emergency feedwater isolation valves
The AEOD study indicated that safety-related gate valves involved in
thermal binding events were
. reactor depressurization system isolation valves
. RHR inboard suction isolation valves
. HPCI steam admission valves
. power-operated relief valve (PORV) block valves
. reactor coolant system letdown isolation valves
. RHR suppression pool suction valves
. containment isolation valves (sample line, letdown heat exchanger
inlet header)
. condensate discharge valves
. reactor feedwater pump discharge valves
A recent event at a plant involving possible pressure locking of a RCIC
valve indicates that MOVs in steam lines also are susceptible to
pressure locking.
2. Document an analysis of the safety-related gate valves (identified in
1 above) with the potential for either pressure locking or thermal
binding to ensure all such valves can be opened to perform their safety
function under all modes of plant operation. Credit for bonnet pressure
decay within the valve response time might not be acceptable unless
operation of the actuator motor at locked-rotor conditions would not
degrade motor torque capability.
Specific acceptable modifications and actions to prevent pressure
locking or thermal binding are listed on page 7 of NUREG/CR-1275.
The NRC regulations require an analysis under 10 CFR 50.59 for any valve
modifications and the establishment of adequate post-modification and
inservice testing of any valves installed as part of the modification.
For example, the licensee would evaluate the effects of drilling the
hole in the disk if used to resolve a pressure locking concern. One
consideration in this evaluation is the fact that the MOV will be
leaktight in only one direction.
As required through Appendix B to 10 CFR Part 50, the licensee would
establish training for plant personnel to perform any necessary actions
.Generic Letter 89-10, Supp. 6 - 15 - Enclosure 1
and incorporate specific procedural precautions/revisions into the
existing plant operating procedures. For example, plant personnel might
periodically stroke certain valves to reduce the potential for thermal
binding.
If an MOV is found to be susceptible to pressure locking or thermal binding
and the licensee relies on the capability of the MOV to overcome pressure
locking or thermal binding, the staff will review the licensee justification
during inspections in consideration of the uncertainties surrounding the
prediction of the required thrust to overcome these phenomena. If the staff
finds that a licensee has not adequately addressed the potential for pressure
locking and thermal binding of gate valves, enforcement actions and schedules
for response will depend on the safety significance of the issue at the plant.
With respect to a particular question on the consideration of external heat
loads, licensees may evaluate the effects of these loads in a bounding manner
to minimize the need for detailed measurements and analyses in the plant.
From the evaluation of licensee activities during GL 89-10 inspections, the
staff will determine whether regulatory action is necessary with respect to
other types of power-operated valves (such as air-operated valves) in regard
to the potential for pressure locking and thermal binding.
Miscellaneous
The NRC staff received miscellaneous new questions on plans for a generic
letter on air-operated valves (AOVs), the need for on-line continuous
monitoring of MOVs, the plans for a proposed NRC staff meeting with MOV
experts from other countries, the role of vendors in resolving the MOV issue,
and the status of NRC staff comments on the EPRI MOV Performance Prediction
Program.
NRC Staff Response
The staff has been considering the issue of performance of AOVs and currently
does not believe that a generic letter is necessary.
Use of on-line continuous monitoring would be a licensee decision.
The staff has requested the International Atomic Energy Agency (IAEA) to set
up a meeting under the aging program to discuss problems with the performance
of MOVs in other countries and the resolution of those problems.
The staff encourages licensees to work closely with the vendors to resolve MOV
performance concerns.
The staff sent a letter in December 1992 to EPRI discussing issues regarding
the EPRI MOV program.
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021