Information Notice No. 97-07: Problems Identified During Generic Letter 89-10 Closeout Inspections
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
March 6, 1997
NRC INFORMATION NOTICE 97-07: PROBLEMS IDENTIFIED DURING GENERIC LETTER 89-10
CLOSEOUT INSPECTIONS
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to the general conclusions derived from NRC
inspections of programs developed at nuclear power plants in response to
Generic Letter (GL) 89-10, "Safety-Related Motor-Operated Valve Testing and
Surveillance." It is expected that recipients will review the information for
applicability to their facilities and consider actions, as appropriate, to
avoid similar problems. However, suggestions contained in this information
notice are not NRC requirements; therefore, no specific action or written
response is required.
Background
In response to operating events, research results, and the findings in NRC
Bulletin 85-03, "Motor-Operated Valve Common Mode Failures During Plant
Transients due to Improper Switch Settings," the NRC staff requested in
GL 89-10 that holders of nuclear power plant operating licenses and
construction permits ensure the design-basis capability of their safety-
related motor-operated valves (MOVs) by periodically reviewing MOV design
bases, verifying MOV switch settings, testing MOVs under design-basis
conditions where practicable, improving evaluations and corrective actions
associated with MOV failures, and determining trends of MOV problems. The NRC
staff issued seven supplements to GL 89-10 to provide further guidance to the
industry on implementation of the generic letter.
On September 18, 1996, the NRC staff issued GL 96-05, "Periodic Verification
of Design-Basis Capability of Safety-Related Motor-Operated Valves." GL 96-05
contains detailed guidance on the development of long-term programs to ensure
the design-basis capability of safety-related MOVs. It also includes updated
information on long-term MOV performance. In the area of MOV periodic
verification, the recommendations of GL 96-05 supersede those of GL 89-10.
Over a number of years, industry and NRC activities associated with GL 89-10
have increased, reflecting both the evolution of technological development and
experience gained over time and the rising expectations of both the industry
and the NRC staff. Activities have included generic communications,
workshops, MOV Users' Group meetings, symposia on
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pumps and valves, and a massive MOV testing and analysis effort by the
Electric Power Research Institute (EPRI). As a result, information on MOV
performance has been widely disseminated over the past few years.
Description of Circumstances
Most nuclear power plant licensees have notified the NRC that they consider
their programs to verify the design-basis capability of safety-related MOVs in
response to GL 89-10 to be complete. The NRC staff has been conducting
inspections of the development, implementation, and completion of these
programs. In performing the inspections, the NRC staff has followed Temporary
Instruction (TI) 2515/109, "Inspection Requirements for Generic Letter 89-10,
Safety-Related Motor-Operated Valve Testing and Surveillance." The NRC staff
recently updated this TI to provide guidance on GL 89-10 closeout inspections
and on the scope of GL 89-10 programs. The NRC staff plans to complete its
review of the GL 89-10 programs at most nuclear plants in 1997.
Through MOV testing, analyses, and operational events over the past few years,
the nuclear industry and the NRC staff have identified weaknesses in the
original design, manufacture, maintenance, and testing of safety-related MOVs.
During inspections to review completion of GL 89-10 programs, the NRC staff
has found that some licensees have not fully verified the design-basis
capability of their safety-related MOVs. For example, the NRC staff has found
that little testing bases existed in support of original assumptions by some
licensees (and actuator and valve manufacturers) for friction coefficients and
efficiencies affecting thrust and torque requirements and actuator output when
sizing and setting MOVs. As a result, licensees have had unexpected
difficulty in demonstrating to the staff that they have adequately completed
their GL 89-10 programs.
When reviewing the development and implementation phases of the GL 89-10
programs, the NRC inspectors identified specific items and concerns that
needed attention before completion of the programs. These items and concerns
are discussed in the inspection reports prepared by the NRC staff. During
inspections to evaluate completion of the GL 89-10 programs, the NRC staff
found that some licensees had not resolved the items and concerns identified
in the previous inspection reports. In addition, some licensees had not
recognized that the MOV program has to be kept up to date on the basis of new
information on MOV performance.
In GL 89-10, the NRC staff recommended that MOVs within the scope of the
generic letter be tested under design-basis conditions where practicable. In
Supplement 6 to GL 89-10, the NRC staff provided guidance for licensees on
grouping MOVs that were not practicable to test dynamically. Some licensees
have also chosen to group MOVs to minimize the amount of dynamic testing under
their GL 89-10 programs. The MOV grouping guidelines recommend that dynamic
test data be obtained on a reasonable sample of MOVs and that the resulting
information be applied to the remaining MOVs in the group.
During GL 89-10 closeout inspections, the NRC staff found that some licensees
provided weak justification for the design-basis capability of MOVs that have
not been dynamically .
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tested. As stated in Supplement 6 to GL 89-10, the NRC staff considers plant-
specific test data to be the best source of information when attempting to
justify the design-basis capability of MOVs. The plant-specific test data
would be obtained from the specific MOV being evaluated or, if testing was not
practicable, from other similar MOVs under similar fluid conditions at the
plant.
In developing the justification for the design-basis capability of MOVs that
are not dynamically tested, it is important to consider the extent and
reliability of the information being applied to the MOV under evaluation. For
example, MOVs of similar manufacture and fluid conditions have been found to
have a range of performance characteristics. Therefore, reliance on data from
a few MOVs tested under industry programs or at other plants might be
insufficient to justify the design-basis capability of similar MOVs at a
specific plant. Plant-specific testing needs to be repeatable or at least
validated through the performance of statistically valid testing.
If MOV-specific data and plant-specific data for similar MOVs are not
available, other sources of information appropriate for the plant's MOVs must
be found. In the search for this information, the range of performance under
similar fluid conditions needs to be considered. For example, EPRI made
significant efforts to predict bounding thrust requirements through its
program of separate effects tests, flow loop testing, and analytical
methodology. In a safety evaluation (SE) dated March 15, 1996 (Accession
number 9608070280), the NRC staff approved the EPRI MOV Performance Prediction
Methodology (PPM) when used in accordance with certain conditions and
limitations. Selective application of the EPRI test data or methodology might
not be reliable without full consideration of the NRC staff SE on the EPRI
PPM. Further, the NRC staff has determined that it is difficult to select the
specific point of flow isolation of tested valves and to apply flow isolation
data from one valve to another.
Key parameters to be addressed in verifying the design-basis capability of
MOVs are valve friction coefficients (i.e., valve factor), stem friction
coefficients, and load sensitive behavior (i.e., rate-of-loading effects).
During GL 89-10 closeout inspections, the NRC staff found that some licensees
were using qualitative arguments to justify assumptions for these quantitative
parameters. As discussed previously, MOVs that have not been dynamically
tested need to have adequate justification for their design-basis capability.
The most reliable source of information on valve friction coefficients, stem
friction coefficients, and load sensitive behavior is the specific licensee's
plant. Licensees can best demonstrate the validity of their assumptions for
these parameters by ensuring that sufficient test data are available for their
specific plants and by analyzing the data for the plant- and valve-specific
parameters.
Pressure locking and thermal binding of gate valves were particular MOV
performance problems identified in GL 89-10. To some extent, the NRC staff
has addressed licensee responses to this issue in GL 89-10 inspections. The
NRC staff issued GL 95-07, "Pressure Locking and Thermal Binding of Safety-
Related Power-Operated Gate Valves," to provide specific recommendations to
licensees and to request their responses in regard to pressure locking and
thermal binding of gate valves. GL 95-07 also requested that licensees submit.
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their responses to this issue separate from their submittals on their GL 89-10
programs. Nevertheless, the NRC staff may request information from licensees
during GL 89-10 inspections regarding the operability of specific MOVs found
to be susceptible to pressure locking or thermal binding.
On February 28, 1992, the NRC staff issued NRC Information Notice (IN) 92-18,
"Potential for Loss of Remote Shutdown Capability During a Control Room Fire."
In that IN, the NRC staff alerted licensees to conditions (sometimes referred
to as "hot shorts") found at several plants that could result in the loss of
capability to maintain the reactor in a safe shutdown condition in the
unlikely event that a control room fire forced reactor operators to evacuate
the control room. During NRC inspections of MOV programs and other licensee
activities, the NRC staff has identified weaknesses in the responses of some
licensees to potential short-circuiting of MOV control circuitry in the event
of a plant fire.
Attachment 1 to this information notice contains examples of licensee problems
in supporting specific aspects of their bases for stating GL 89-10 actions
have been completed. Attachment 2 contains a list of recently issued NRC
information notices.
Related Generic Communications
BL 85-03 "Motor-Operated Valve Common Mode Failures During Plant Transients
Due to Improper Switch Settings," dated November 15, 1985
GL 89-10 "Safety-Related Motor-Operated Valve Testing and Surveillance,"
dated June 28, 1989
GL 89-10 "Safety-Related Motor-Operated Valve Testing and Surveillance,"
Sup. 1 dated June 13, 1990
GL 89-10 "Safety-Related Motor-Operated Valve Testing and Surveillance,"
Sup. 2 dated August 3, 1990
GL 89-10 "Safety-Related Motor-Operated Valve Testing and Surveillance,"
Sup. 3 dated October 25, 1990
GL 89-10 "Safety-Related Motor-Operated Valve Testing and Surveillance,"
Sup. 4 dated February 12, 1992
GL 89-10 "Safety-Related Motor-Operated Valve Testing and Surveillance,"
Sup. 5 dated June 28, 1993
GL 89-10 "Safety-Related Motor-Operated Valve Testing and Surveillance,"
Sup. 6 dated March 8, 1994
GL 89-10 "Safety-Related Motor-Operated Valve Testing and Surveillance,"
Sup. 7 dated January 24, 1996
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GL 95-07 "Pressure Locking and Thermal Binding of Safety-Related Power-
Operated Gate Valves," dated August 17, 1995
GL 96-05 "Periodic Verification of Design-Basis Capability of Safety-
Related Motor-Operated Valves," dated September 18, 1996
IN 92-17 "NRC Inspections of Programs Being Developed at Nuclear Power
Plants in Response to Generic Letter 89-10," dated February 26,
1992
IN 92-18 "Potential for Loss of Remote Shutdown Capability during a Control
Room Fire," dated February 28, 1992
IN 96-48 "Motor-Operated Valve Performance Issues," dated August 21, 1996
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
signed by
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: Thomas Scarbrough, NRR
(301) 415-2794
E-mail: tgs@nrc.gov
William Burton, NRR
(301) 415-2853
E-mail: wfb@nrc.gov
Attachments:
1. Examples of Problems Identified During GL 89-10
Closeout Inspections
. Attachment 1
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EXAMPLES OF PROBLEMS IDENTIFIED DURING GL 89-10 CLOSEOUT INSPECTIONS
Thrust and Torque Requirements for Non-Dynamically Tested Motor-Operated
Valves (MOVs)
Some licensees had made general assumptions regarding the reduction in valve
factor that were based on increasing valve size, differential pressure, or
fluid temperature without sufficient test data to justify these assumptions
quantitatively. In addition, some licensees have had difficulty in justifying
the capability of certain MOVs that have been sized and set on the basis of
unsupported assumptions for thrust or torque requirements. Licensees
typically predict the thrust required to operate gate and globe valves from
the sum of (1) the product of a valve factor, differential pressure across the
valve, and the area of the valve disk; (2) the product of the system pressure
and the stem cross-sectional area; and (3) the drag of the valve packing
material on the valve stem. Some licensees assumed a generic valve factor of
0.5 (or less) in predicting the thrust required to operate non-dynamically
tested gate valves on the basis of their assumption that the selected valve
factor was conservative. However, industry and plant-specific gate valve
testing has revealed thrust requirements can exceed that predicted by a 0.5
valve factor. Similarly, industry and plant-specific globe valve testing has
revealed that a valve factor of 1.1 to predict the thrust requirements might
not be adequate for all globe valves. With respect to butterfly valves,
industry and plant-specific testing has revealed that vendor calculations
might not adequately predict the torque required to operate some butterfly
valves. On the basis of industry testing and analyses, the Electric Power
Research Institute (EPRI) is revising its application guide for predicting MOV
thrust and torque requirements.
Use of Industry Valve Information
Some licensees have found that testing of certain MOVs under dynamic
conditions is impracticable and that sufficient test information on similar
MOVs at their plants is not available. Consequently, these licensees have
obtained MOV performance information from other licensee or industry test
programs and the MOV Performance Prediction Methodology (PPM) developed by
EPRI. In comparing test data from other sources, it is important to
understand the similarity of the valves; test conditions of differential
pressure, temperature, and flow; diagnostic equipment and uncertainty;
evaluation of the data and any anomalies (such as high static seating loads);
and calculation of valve factor (including flow area assumptions). In
addition, sufficient data need to be obtained to account for the variability
in thrust requirements for similar valves under applicable conditions. EPRI
tested a sample of valves of varying manufacture, type and size to validate a
bounding methodology for predicting thrust requirements for a wide variety of
valves. The NRC staff identified concerns regarding certain specific MOV
tests by EPRI during its review of the methodology. These concerns were
resolved with respect to the bounding nature of the EPRI methodology in
developing the NRC staff safety evaluation.
Some licensees were not addressing the results of the EPRI methodology that
predicted potential valve damage and unpredictable thrust requirements for
specific valves, and some . Attachment 1
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licensees did not address the limitations on the applicability of the EPRI
methodology (such as limitations due to the specific valve manufacturer).
Justification for Stem Friction Coefficient and Load Sensitive Behavior
Assumptions
The efficiency of the conversion of actuator output torque to stem thrust is a
function of the stem friction coefficient and the dimensions of the valve stem
and its thread. Load sensitive behavior relates to the change in this
efficiency when different thrust levels are exerted through the stem.
Typically, as the thrust level increases, the stem friction coefficient
increases and the thrust delivered at the torque switch trip decreases
(referred to as a "rate-of-loading" effect). Some licensees initially assumed
a stem friction coefficient of 0.15 (or less) or rate-of-loading effect of 15
percent (or less) and planned to justify these assumptions as part of their
dynamic testing under GL 89-10. However, in some cases, insufficient data or
higher-than-expected values obtained during the MOV testing caused the staff
to question the licensee's initial assumptions when the data were evaluated in
a statistically valid manner. For example, one licensee may have to revise
the initial assumption for rate-of-loading effects up to 25 percent. Stem
friction coefficient and rate-of-loading effects may vary between MOVs because
of factors such as stem lubricant, lubrication frequency, environmental
conditions, and manufacturing tolerances of the stem and stem nut. Therefore,
it is difficult to apply information on stem friction coefficient and rate-of-
loading effects from sources other than the licensee's testing program. EPRI
developed bounding values for load sensitive behavior associated with gate
valves as part of its MOV PPM. The NRC staff discusses conditions and
limitations of the EPRI methodology in a safety evaluation dated March 15,
1996. Also, some licensees have improperly considered load sensitive behavior
(or rate-of-loading effects) to be a random uncertainty, rather than a bias
error or a bias/random combination error.
Grouping of MOVs
In GL 89-10, the NRC staff recommended that licensees test their safety-
related MOVs under design-basis conditions where practicable. In Supplement 6
to GL 89-10, the NRC staff reiterated that recommendation but provided
information on grouping MOVs in situations where a licensee either is not able
to test some MOVs under design-basis conditions or chooses not to dynamically
test some MOVs. For example, the NRC staff considered it important to (1)
assess, when grouping MOVs, such similarities as valve manufacturer, model and
size, valve flow, temperature, pressure, installation configuration, valve
materials and condition, seat/guide stresses, and performance during testing;
(2) test a representative sample of MOVs in each group (nominally 30 percent
and no less than 2 MOVs); (3) test each MOV in a group with diagnostics under
static conditions; and (4) evaluate any adverse information from individual
MOV testing and determine its applicability to the entire group. Some
licensees have used approaches for grouping and testing MOVs other than those
described in Supplement 6 to GL 89-10. The NRC staff has found that some
licensees have not adequately justified testing only one MOV in a group, or a
very small sample of MOVs in the group. Also, some licensees have selected a
valve factor based on a sample of tests that does not accommodate reasonable
variation in the valve factor for other MOVs in the .
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group (for example, the bounds on the valve factor for a group of valves was
not always appropriate for the scatter observed in the data). Although some
licensees have grouped MOVs in ways that could not be justified, some other
licensees have established such a large number of groups (as many as 50) that
it is difficult to have sufficient test data for each group. Some licensees
have adequately justified including MOVs with small variations in size into
the same group in order to minimize the number of groups and allow sufficient
data to be obtained for each group.
Degraded Voltage Calculations
The NRC staff discussed in Supplements 1 and 6 to GL 89-10 determination of
the voltage assumed at MOVs for design-basis conditions. Various methods are
used by licensees to determine the reduction in voltage from the grid to the
MOV being evaluated. During GL 89-10 closeout inspections, the NRC staff
found that some licensees had not fully justified their assumptions for the
grid voltage assumed in their MOV calculations. For example, some licensees
assumed full grid voltage as the starting point for calculations, rather than
the degraded grid relay setpoint.
Justification for Weak Link Analyses
In Information Notice 96-48, "Motor-Operated Valve Performance Issues," the
NRC staff discussed recent failures of MOV keys. Some licensees have also
identified cracks in motor shafts for some MOVs. Further, missing bolts or
incorrect bolting material has been found in some MOVs. These problems could
be related to inadequate justification of the weak link components in MOV
analyses. For example, replacement of a motor pinion key with a key of
stronger material could cause the weak link to shift to another internal part,
such as the motor shaft.
Analytical Evaluation of Potential Pressure Locking of Gate Valves
In Supplement 6 to GL 89-10, the NRC staff provided one acceptable approach
for addressing potential pressure locking and thermal binding of MOVs. In GL
95-07, "Pressure Locking and Thermal Binding of Safety-Related Power-Operated
Gate Valves," the NRC staff gave more detailed information and recommendations
to address potential pressure locking and thermal binding of gate valves.
During recent GL 89-10 inspections, the NRC staff identified weaknesses in
some approaches used by licensees to evaluate the effects of pressure locking
of MOVs. Some licensees are relying on analytical approaches (without test-
based justification) to provide confidence that the motor actuator can
overcome the thrust resulting from pressure locking of its valve. The NRC
staff found that some licensees assumed overly optimistic actuator
efficiencies in predicting the thrust delivered by the motor actuator under
pressure locking conditions. In addition, the staff found that some licensees
have insufficient justification for assumptions of significant leakage from
the valve bonnet over a short period, and of a very low increase in bonnet
pressure with rising temperature.
. Attachment 1
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Evaluation of Test Data
Some licensees have not thoroughly evaluated test data to ensure that the
results are reliable. For example, an abnormally low thrust requirement or a
back-calculated valve factor might indicate that the design-basis differential
pressure and flow were not achieved during the test. Further, anomalies in
the data traces could reveal valve or actuator damage. Some licensees have
not justified extrapolation of test data based on percentage of design-basis
differential pressure and absolute value of differential pressure as discussed
in the EPRI MOV program.
Tracking and Trending of MOV Problems
Tracking and trending are important aspects of a licensee's periodic
verification program. The NRC staff provided comments on MOV tracking and
trending methods in initial reports of GL 89-10 inspections. It also
identified weaknesses in the development of MOV tracking and trending methods
at some nuclear plants. During GL 89-10 closeout inspections, the NRC staff
found that some licensees have not fulfilled their plans to develop MOV
tracking and trending methods and that some licensees have highly informal
methods without specific guidelines or schedules.
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