ML20057G131
| ML20057G131 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 10/08/1993 |
| From: | Runyan M, Vickery R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | |
| Shared Package | |
| ML20057G127 | List: |
| References | |
| 50-298-93-08, 50-298-93-8, GL-89-10, NUDOCS 9310200223 | |
| Download: ML20057G131 (1) | |
See also: IR 05000298/1993008
Text
APPENDIX B
U.S. NUCLEAR REGULATORY COMMISSION
REGION IV
Inspection Report:
50-298/93-08
Operating License:
Licensee: Nebraska Public Power District
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P.O. Box 98
Brownville, Nebraska 68321
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Facility Name: Cooper Nuclear Station (CNS)
Inspection At: CNS, Brownville, Nebraska
Inspection Conducted:
September 13-17, 1993
Inspectors:
M. Runyan, Reactor Inspector, Engineering Section
Division of Reactor Safety
R. Vickrey, Reactor Inspector, Engineering Section,
Division of Reactor Safety, Region IV
Accompanying Personnel:
M. Holbrook, Consultant, EG&G Idaho-INEL
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[8- >J- Ti3
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Approved:
T. WestermNn, Chief, Engineering Section
Date
Division of Reactor Safety, Region IV
Inspection Summary
Areas Inspected:
Special, announced inspection of the implementation of the
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licensee's program to meet commitments to Generic Letter (GL) 89-10, " Safety-
Related Motor-Operated Valve Testing and Surveillance," and followup.
Results:
The licensee's motor-operated valve (MOV) program was marginally capable
of successfully darionstrating the capability of MOVs subject to Generic Letter 89-10 and generally fulfilled the licensee's commitments in this
area (Section 1).
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The execution of the MOV program lacked attention to detail and appeared
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to suffer from insufficient quality oversight (Sections 1 and 1.8).
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Changes made to the scope of the GL 89-10 program since the last MOV
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inspection appeared acceptable (Section 1.1).
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9310200223 931008
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ADOCK 05000298
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The clarity, comprehensiveness, and precision of the design basis
reviews were considered a strength in the program (Section 1.2).
The use of conservative assumptions for valve factor and stem friction
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coefficient was considered a strength in the program (Section 1.3).
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The licensee's method of evaluating the capability of direct
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current (DC) motors did not account for uncertainties associated with
use of generic DC motor curves (Section 1.3).
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The program did not specify an allowance for stem lubrication
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degradation (Section 1.3).
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The licensee's effort to test motor-operated valves at maximum
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achievable differential pressure and flow was considered a strength in
the program (Section 1.4).
The licensee had not justified the use of linear extrapolation of
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measured thrust values (Section 1.4).
The program did not provide a procedure for the performance of thrust
extrapolations (Section 1.4).
A violation was identified for the licensee's failure to provide changes
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to diagnostic uncertainties when data is outside the calibration range
and for failure to incorporate extrapolated opening thrust data in the
acceptance criteria (Section 1.4).
A 't .
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'n was identified for failure to provide a formal, documented
de.,ig:. ce, < ication of several safety significant activities related to
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the testing sl evaluation of motor-operated valves (Section 1.4).
A violation was identified for failure to properly document the
necessary acceptance criteria of 29 motor-operated valve differential
pressure tests prior to returning the valves to service (Section 1.4).
A violation was identified for failure to perform adequate corrective
actions in response to identification of a potentially malfunctioning
motor-operated valve (Section 1.4).
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An unresolved item was identified for a potential operability problem
with valve CS-MOV-MO5A (Section 1.4).
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The licensee's proposed statistical method to be used in the evaluation
of a group of similar valves was potentially nonconservative
(Section 1.4).
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The licensee did not extrapolate motor-operated valve data when tests
were conducted at less than 75 percent of the design basis differential
pressure (Section 1.4).
Several errors were identified in the placement of software marks on
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diagnostic system traces, though none of the errors affected the
operability assessments of the valves reviewed in the inspection
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(Section 1.4).
The dynamic diagnostic trace for valve RHR-MOV-M039A did not show
evidence of hard seat contact, though other information showed that seat
contact was probably attained (Section 1.4).
Uncertainties in the measurement of line pressures during dynamic
diagnostic testing were not included in the evaluation of acceptance
criteria (Section 1.4).
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The torque measurement provided in the diagnostic testing program was
considered a strength (Section 1.4).
During the inspection, a motor-operated valve failed to open because of
a malfunctioning limit switch.
Potential generic concerns were under
review (Section 1.4).
Thrust information for valve RHR-M0V-920MV was lost because of a sensor
failure. The licensee had not decided on a disposition (Section 1.4).
Four of the seven motor-operated valves selected for review showed
little or no differential pressure effects on their dynamic diagnostic
traces (Section 1.4).
The licensee was unable to provide sufficient justification that the
methodology used to disposition valves potentially susceptible to
pressure locking and thermal binding was adequate (Section 1.5).
The licensee had not developed justification for the intended use of
static tests for periodic verification of motor-operated valve
capability (Section 1.6).
The licensee intended to implement a motor-operated valve tracking and
trending program by the end of 1993 (Section 1.7).
The inspection results indicated an underutilization of quality-related
measures to provide an independent oversight of the motor-operated valve
program (Section 1.8).
A change in the refueling outage schedule may result in the licensee
requesting an additional extension to complete the GL 89-10 program
(Section 1.9).
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Summary of Inspection Findings:
Inspection Followup Item 298/9308-01 was opened (Section 1.3).
Inspection Followup Item 298/9308-02 was opened (Section 1.4).
Inspection Followup Item 298/9308-03 was opened (Section 1.4).
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Violation 298/9308-04 was opened (Section 1.4).
Violation 298/9308-05 was opened (Section 1.4).
Violation 298/9308-06 was opened (Section 1.4).
Violation 298/9308-07 was opened (Section 1.4).
Unresolved itts 298/9308-08 was opened (Section 1.4).
Inspection Followup Item 298/9308-09 was opened (Section 1.4).
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Inspection Followup Item 298/9308-10 was opened (Section 1.4).
Inspection followup Item 298/9308-11 was opened (Section 1.4).
Inspection Followup Item 298/9308-12 was opened (Section 1.4).
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Inspection Followup Item 298/9308-13 was opened (Section 1.4).
Inspection Followup Item 298/9308-14 was opened (Section 1.4).
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Inspection Followup Item 298/9308-15 was opened (Section 1.4).
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Inspection Followup Item 298/9308-16 was opened (Section 1.5).
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Attachments
1
Attachment 1 - Persons Contacted and Exit Meeting
Attachment 2 - CNS Gate Valve Data
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DETAILS
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GENERIC LETTER (GL) 89-10 " SAFETY-RELATED MOTOR-0PERATED VALVE TESTING AND
SURVEILLANCE"
(2515/109)
On June 28, 1989, the NRC issued Generic Letter (GL) 89-10, which requested
licensees and construction permit holders to establish a program to ensure
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that switch settings for safety-related motor-operated valves (MOVs) were
selected, set, and maintained properly.
Subsequently, five supplements to the
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generic letter have been issued and one issued for coment. NRC inspections
of licensee actions implementing comitments to GL 89-10 and its supplements
have been conducted based on guidance provided in Temporary Instruction
(TI) 2515/109, " Inspection Requirements for Generic Letter 89-10, Safety-
Related Motor-0perated Valve Testing and Surveillance."
Instruction TI
2515/109 is divided into Part 1, " Program Review," and Part 2, " Verification
of Program Implementation." The TI 2515/109, Part 1 program review at CNS is
documented in NRC Inspection Report 50-298/92-02.
The inspection documented
by this report was the initial inspection at CNS under Part 2 of TI 2515/109,
and, thus, was focused on verification of program implementation.
Nevertheless, programatic issues were addressed during this inspection in
response to followup of findings in the Part 1 inspection and in the context
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of issues that deve'.oped in the course of the inspection.
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As an overall assusment, the inspectors concluded that the licensee's M0V
program was marginally capable of demonstrating the capability of MOVs subject
to GL 89-10.
The program generally implemented the licensee'- comitments to
the generic letter. However, the execution of the program iaued attention to
detail and appeared to suffer from insufficient quality oversight.
The principle focus of the inspection was to select and review in depth
several MOVs from the GL 89-10 program.
The selection was based on an
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information matrix provided by the licensee as requested by the inspectors.
The selection was biased toward MOVs that appeared to have less than average
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margin; otherwise an attempt was made to select various valve and actuator
sizes and tests conducted under various differential pressure conditions.
For each MOV selected, the inspr.ctors reviewed the design basis calculation of
design flow, temperature, and '.he maximum expected differential pressure
(MEDP), the sizing and switch setting calculation, the diagnostic test data
package, and the diagnostic traces using V0TES 2.31 software.
The following
MOVs were selected for review:
CS-MOV-MO5A
Core Spray Pump "A" Miniflow Recirculation Valve
HPCI-M0V-M014
Steam Supply to HPCI Turbine
MS-M0V-M077
Main Steam Line Drain Outboard Isolation
RHR-MOV-M016B
Residual Heat Removal Pumps "B"
and "D" Miniflow Bypass
RHR-M0V-M039A
Suppression Pool / Spray Loop "A" Isolation
RHR-MOV-920MV
Augmented Offgas Steam Supply Upstream Shutoff
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SW-MOV-M089A
Residual Heat Removal Heat Exchanger "A" Service Water
sutlet
Each of the selected MOVs was torque closed and configured as shown below:
Actuator
Valve Type
Valve Size (inches) and Vendor
CS-MOV-M05A
SMB-00
Gate
3"
Anchor / Darling
HPCI-M0V-M014
SB-1
Gate
10" Anchor / Darling
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MS-MOV-M077
SMB-000
Gate
3"
Anchor / Darling
RHR-M0V-M016B
SMB-4
Gate
4"
Anchor / Darling
RHR-MOV-M039A
SMB-1
Gate
18" Anchor / Darling
RHR-MOV-920MV
SMB-00
Gate
3"
Anchor / Darling
SW-MOV-M089A
SMB-3
Globe
18" Anchor / Darling
1.1 Scope of the GL Program
The inspectors reviewed changes made to the scope of the licensee's GL 89-10
Program since the last MOV inspection.
The total number of M0Vs in the
program had changed from 93 at the time of the last inspection to 86. At the
time of the last inspection, several of the system level design basis review
calculations were not complete.
In order to ensure that MOVs in essential
systems were appropriately considered, all of the M0Vs in these systems were
preliminarily determined to be within the scope of the program until the
system level design basis review was completed.
Six of the valves excluded
were normally closed valves in series with another valve, neither of which had
an active design basis safety-related function.
The inspectors did not
identify any concerns related to the licensee's M0V program scope.
1.2 Desian-Basis Reviews
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The inspectors reviewed the calculations determining the design-basis
differential pressure, design flow conditions, design temperature, and other
design parameters for each of the MOVs selected for review.
These
calculations had been prepared for the licensee by a contractor, ERIN, Inc.
The calculations appeared to acceptably address the design basis
considerations of the selected MOVs. The clarity, comprehensiveness, and
precision of the design basis reviews were considered a strength in the
program.
1.3 MOV Sizing and Switch Settinq
The inspectors reviewed the Nebraska Public Power District (NPPD) program
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description, "CNS M0V Program Plan," Revision 6, dated January 29, 1993,
project instruction 122-89-10.08, " Component level Design Review," Revision 1,
dated December 16, 1992, and the licensee's calculction packages developed for
determination of thrust and torque requirements for the selected valves.
The licensee's gate valve thrust equation typically incorporated a valve
factor of 0.50 for wedge gate valves and 1.10 for globe valves.
For
determination of actuator output thrust capability, the licensee assumed a
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stem friction coefficient of 0.20.
A margin of 10 percent was set aside to
address MOV load sensitive behavior (also known as " rate of loading") for
Limitorque SMB operators and 5 percent was assigned for SB operators. Minimum
thrust requirements were adjusted to account for diagnostic equipment
inaccuracy and torque switch repeatability.
Thrust requirements were revised
to reflect the results of extrapolation to design-basis conditions (where
required). The licensee's assumptions for valve factors and stem friction
coefficients, which were conservative and universally applied, were considered'
a strength in the program.
For determination of maximum actuator output torque at reduced voltage
conditions for direct current (DC) motors, the licensee deviated from
Limitorque's standard method, in that the DC motor's rated starting torque was
not used in combination with a voltage factor to account for the worst-case
degraded voltage available at the motor terminals.
Instead, the licensee
determined the maximum in-rush current that would be present under degraded
voltage conditions, and used this value to obtain the output torque from the
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DC motor performance curves. This result was then combined with the product
of the unit ratio, actuator efficiency, and application factor to obtain the
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worst-case actuator output.
The inspectors were concerned that the licensee's
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method did not account for the uncertainties associated with use of generic DC
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motor performance curves.
Licer.see personnel stated that their use of
application factors of less than 1.0 for all cases would account for these
uncertainties. However, the licensee did not have documentation to support
this position. This issue was identified as an inspection followup item
(298/9308-01).
Licensee personnel stated that they are currently in the process of revising
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MOV thrust calculations to account for tha new torque switch repeatability
margins contained in Limitorque's Maintenance Update 92-2.
The licensee had
not identified any potential operability concerns based on an initial
screening. The licensee indicated that their program documentation will be
revised to include the new torque switch repeatability values.
The inspectors noted that an allowance was not made to account for potential
degradation of the stem lubricant. Based on an 18-month stem lubrication
frequency and choice of lubricant, the licensee indicated that lubricant
degradation should not be a problem at Cooper. The licensee was developing a
plan to conduct as-found testing dJring the next refueling outage to support
this position.
1.4 Design-Basis Capability
The inspectors reviewed Nuclear Projects and Construction Department
Procedure 60-10, " Differential Pressure Test Data Analysis and Evaluation,"
Revision 0, dated March 9, 1993; Project Instruction 122-89-10.09, "MOV
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Performance Evaluation," Revision 0, dated February 18, 1993; static test
results, and dynamic test packages for the selected valves.
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The dynamic tests reviewed by the inspectors were performed under the
following conditions
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Percent of Opening Design
Percent of Closing Design
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Basis Differential Pressure
Basis Differential Pressure
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CS-M0V-M05A
88.2
89.6
HPCI-M0V-M014
84.8
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MS-MOV-M077
84.8
84.9
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RHR-MOV-M016B
98.8
104.3
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RHR-MOV-M039A
106.2
106.2
RHR-MOV-920MV
59.8
59.8
SW-MOV-M089A
102.3
102.3
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The inspectors reviewed the selected dynamic test data using the industry
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standard equation, the valves' mean seat diameters, and the dynamic test
conditions. This review indicated gate valve factors up to 0.48 (see
Attachment 2). Observed load sensitive behavior was approximately -5 percent,
meaning that the thrust at torque switch trip averaged slightly higher under
dynamic than under static conditions.
This was an abnormal load sensitive
behavior condition, but not statistically significant since it did not exceed
the magnitude of the measurement uncertainties.
Based on this small sample,
it appeared that the licensee's valve factor assumption for gate valves was
conservative.
The inspectors' review of the MOV matrix and discussions with the licensee
revealed that the licensee had made an aggressive effort to test MOVs at the
maximum achievable differential pressure and flow conditions.
This was
considered a strength in the program.
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To determine the capability of an M0V tested at less than design basis
differential pressure, the licensee linearly extrapolated the thrust necessary
to overcome differential pressure at the tested conditions to design basis
end nions. However, the licensee had not demonstrated that this method of
extrapolation is conservative under design basis conditions. The licensee
expressed an intention to use test data from the Electric Power Research
Institute (EPRI) Performance Prediction Program, or from other utility multi-
point dynamic tests in an effort to develop a justification for their
extrapolation method.
Until the licensee develops a justification, the
inspectors considered the licensee's extrapolation to be the first stage of a
two stage approach, where the valves are set up using the best available data,
as discussed in GL 89-10. This issue was identified as an inspection followup
item (298/9308-02).
For testing conducted at less than design basis conditions, the licensee's
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procedures did not specify a methodology to extrapolate the forces observed
during dynamic testing to those that would be required under design basis
conditions.
lhis extrapolation, which forms an important part of the
confirmation of MOV operability after a dynamic test is performed, was being
accomplished without procedural guidance based on the expertise of the
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analyst. The licensee stated that a procedure would be generated to cover
this activity.
Subsequent to the exit meeting, this issue was identified as
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an inspection followup item (298/9308-03).
The inspectors noted that the licensee's diagnostic procedures did not provide
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a method for identifying and adjusting diagnostic equipment uncertainties when
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observed force measurements fell outside the diagnostic equipment's
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calibration range.
This method is necessary to ensure that the uncertainties
associated with measured thrust values are correctly accounted for prior to
comparison with MOV thrust limits.
The inspectors identified that the total
thrust measured during the dynamic test of RHR-MOV-39A was outside of the
calibration range and that no correction was made to the error applied to the
measured value.
Sufficient margin was available to accommodate the corrected
error range. Additionally, the inspectors noted that acceptance criteria did
not exist for extrapolation of the forces required to overcome differential
pressure when the opening stroke is conducted at less than design basis
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conditions. The extrapolated opening force was not compared to the valve and
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actuator structural limits and/or actuator output capability (at degraded
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voltage conditions) to ensure that limits were not exceeded during a design
basis accident. These conditions were considered contrary to 10 CFR 50,
Appendix B, Criterion V, " Procedures," which states, in part, that " activities
affecting quality shall be prescribed by documented procedures of a type
appropriate to the circumstances." The two examples described above each
represent a critical safety significant activity that was not prescribed by an
appropriate documented procedure. These activities were not performed as a
result of the failure to provide an appropriate procedure. A review of the
selected test results indicated that no actual limits were exceeded.
This
issue was identified as a violation (298/9308-04).
During review of the documentation associated with the MOVs selected for
review, the inspectors noted that with the exception of design basis reviews
(contracted to ERIN, Inc.) there was no indication that program documents had
received a formal design verification review.
Some of the safety-related
activities that appeared to be lacking a design verification were calculations
detailing MOV diagnostic test target windows (thrust limits associated with
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test acceptance), open and close stroke evaluations (comparisons between
target and measured values), acceptance criteria checklists (qualitative and
quantitative acceptance points), and the direct evaluation of the diagnostic
traces themselves (including placement of software marks and extraction of
quantitative data from the traces). Based on discussions with the licensee,
it was apparent that some of these activities were informally reviewed but
that these efforts lacked consistent documentation.
Some of the signatures
and dates in the paperwork were typed rather than signed and several examples
were found where specified signatures were missing.
The inspectors concluded
that this aspect of the licensee's MOV program was contrary to the
requirements of 10 CFR 50, Appendix B, Criterion 3, " Design Control," which
states, in part, that " design control measures shall provide for verifying or
checking the adequacy of design," and that " design control measures shall be
applied to items such as the ... delineation of acceptance criteria for
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inspections and tests." This issue was identified as a violation
(298/9308-05).
During review of the licensee's MOV test procedures, the inspectors identified
that a significant procedural error had been made concerning acceptance
criteria checklists. The checklist corresponding to the review of static
diagnostic test information for acceptance had been inadvertently placed in
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the dynamic diagnostic test procedure, Maintenance Test Procedure 7.3.35.6,
"DP Testing of Motor Operated Valves Using V0TES," Revision 0.
Likewise, the
dynamic test checklist had been placed in the static test procedure,
Maintenance Test Procedure 7.a.35.5, " Testing of Motor Operated Valves Using
VOTES," Revision 0.
As a result of this error, 29 MOVs tested under dynamic
conditions during refueling outage 15 (RE15) were returned to service without
an acceptable evaluation of the diagnostic test data.
Documented evaluations
of the following acceptance criteria were missing from the dynamic test
packages (taken from the misplaced dynamic test checklist):
" Valve fully opened and closed;
Measured running load is not greater than packing friction load
used in the component level calculations;
If MOV was flow tested under less than MEDP, conditions and
extrapolated data were used during evaluation, proper review had
been performed and documented under Test Supervisor's summary
section of this Attachment, in order to ensure that MOV would meet
design parameters under MEDP conditions;
If springpack displacement was measured, design parameters as
specified per Table 2, Attachment 3, have not been exceeded."
The licensee stated that some of these criteria were considered at the time of
package closeout, including an extrapolation of differential pressure data,
but that this effort was not documented and no signature or initial block was
provided to identify the analyst who performed these evaluations.
After the MOVs were returned to service, but within no specified time frame,
the licensee completed an "MOV Data Analysis Report" which did provide a
documented extrapolation of differential pressure data and other evaluations
relevant to the determination of an M0V's capability to perform its safety
function.
Because of this evaluation, the inspectors did not have reason to
conclude that any MOVs in service at the time of the inspection had not been
eventually checked for operability.
However, at the time the valves were
returned to service, the operability status was not properly documented. This
deficiency was considered to be contrary to 10 CFR 50, Appendix B,
Criterion XI, " Test Control," which states, in part, that " test results shall
be documented and evaluated to assure that test requirements have been
satisfied." This issue was identified as a violation (298/9308-06).
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During review of the dynamic force traces for Core Spray Pump "A" Minimum Flow
Valve CS-M0V-M05A, the inspectors noted a significant loading peak that
occurred approximately one second prior to achieving hard seat contact.
CS-MOV-MO5A is a 3-inch Anchor Darling solid-wedge gate valve with the disc
orientated horizontally in a vertical run of piping. The valve has a safety
function in the open and closed direction. The valve was tested at
approximately 89 percent of its design basis differential pressure.
The MOV
Data Analysis Report for CS-MOV-MOSA contained references to the loading
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condition and attributed the condition to flow and differential pressure
causing the disc to ride on the upper side of the valve guidas, but no actions
were taken to further investigate or correct the problem. The inspectors were
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concerned because there is no known method to reliably extrapolate force
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requirements when nonpredictable behavior is present. Evaluation of valve
operability in light of the anomaly was not conducted. This inaction was
considered contrary to 10 CFR 50, Appendix B, Criterion XVI, " Corrective
Action," which states, in part, that " measures shall be taken to assure that
conditions adverse to quality, such as... deficiencies, [and] deviations...
adverse to quality are promptly identified and corrected." This issue was
identified as a violation (298/9308-07).
After questioning from the inspectors, the licensee initiated a deficiency
report and an operability determination to document their course of action for
CS-MOV-M05A.
The licensee stated an intention to initiate an engineering work
request to identify methods for improving valve performance.
In parallel with
these efforts, the licensee extrapolated the maximum force measured in the
anomalous portion of the valve stroke in an effort to show that the torque
switch would not open prematurely. However, this linear extrapolation
resulted in only a 3.94 percent margin, which is not large enough to account
for torque switch repeatability. The staff has a low confidence in linear
extrapolation of nonpredictable behavior. However, the licensee determined
that the core spray system would be able to deliver the required flow to ine
reactor vessel based on testing conducted by General Electric in 1974 where
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the core spray pumps were run with their minimum flow valves full open and
rated flow was still maintained. The licensee expressed confidence that
conservatisms in the design basis calculations could also be utilized to
demonstrate operability.
The inspectors considered the licensee's initial
response to be sufficient to justify an interim operable status, but that
completion of the evaluations in the licensee's corrective action plan would
be necessary to establish long-term confidence that the valve is capable of
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performing its safety function. The inspectors identified this issue as an
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unresolved item (298/9308-08).
During review of Section 3.4 of Project Instruction 122-89-10.09, "MOV
Performance Validation," the inspectors noted that the licensee intends to
evaluate dynamic test data by calculating the mean of test parameters, after
adjusting for the maximum uncertainties associated with the parameters.
The
bounding parameter would then be based on this mean, plus one standard
deviation of the mean value, which would bound approximately 84 percent of the
data.
The licensee justified the application of one standard deviation to the
mean based on the test results being adjusted for maximum uncertainties.
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However, the inspectors were concerned that the addition of one standard
deviation would not provide adequate confidence that the resultant bounding
parameter would be adequate for setup of valves that cannot be dynamically
tested. Subsequent to the exit meeting, this issue was identified as an
inspection followup item (298/9308-09).
The licensee's diagnostic test analysis process did not include sn
extrapolation of measured thrust or torque when differential pressure tests
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were conducted at less than 75 percent of the MEDP. The inspectors were
concerned that this exclusion could result in the failure to use the best
available information to evaluate the capability of the MOV in question.
For
example, a test conducted at 75 percent of the MEDP may indicate a closing
thrust only marginally less than the calculated thrust capability at degraded
voltage or the thrust available at torque switch trip.
In this case, the
valve would be clearly unacceptable, yet might still pass the licensee's
acceptance criteria. The licensee stated that these considerations were taken
into account primarily by application of engineering judgement, but it was not
clear how consistently this process was applied.
Subsequent to the exit
meeting, this issue was identified as an inspection followup item
(298/9308-10).
During review of the diagnostic traces associated with the seven MOVs selected
for review, the inspectors noted that several VOTES 2.31 software marks were
placed incorrectly. On RHR-MOV-M039A, the software mark for point C5 (running
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load near the end of the stroke) was placed in an area where differential
pressure effects were clearly evident.
Since the thrust at C5 is subtracted
from the thrust at point C10 (flow cutoff) to determine the differential
pressure effect that is then extrapolated to design basis conditions (for
tests conducted at differential pressures less than the MEDP), the placer nt
of C5 in the dynamic portion of the trace is nonconservative and could result
in underestimation of the thrust required to overcome design basis conditions.
This did not create a problem for RHR-MOV-M039A, since the test was conducted
at a differential pressure in excess of the MEDP. Also noted on the dynamic
trace of RHR-MOV-M039A, the software mark for point C11 (hard seat contact)
was placed in the very early portion of the differential pressure effect
region.
In fact, the mark for point C11 was placed 12 seconds earlier in the
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valve stroke than the mark for point C10. This would indicate that hard seat
contact occurred 12 seconds prior to flow cutoff, which is not possible. The
licensee concurred that point C11 was mismarked in this case, but maintained
(justifiably) that this error had no effect on the evaluation of this M0V. On
the opening dynamic diagnostic trace of HPCI-MOV-M014, the inspectors noted
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that the placement of point 010 (force after seat pullout) was
nonconservative. The analyst who placed this mark apparently missed the
presence of an additional thrust peak beyond the pullout peak. The thrust at
the incorrectly marked position of 010 was 11,780 pounds-force (lbf). The
thrust at the position where 010 should have been marked was approximately
12,500 lbf. This error did not affect the operability evaluation of this M0V,
since the extrapolated thrust to overcome differential pressure based on
12,500 lbf at 010 was still less than the pullout force indicated at point 09
(disc pullout).
(However, as discussed earlier in this report, the licensee's
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program was not configured to determine those cases where an extrapolated 010
was greater than 09). Given the number of diagnostic t* races reviewed during
this inspection, the number of errors discovered was not excessive.
Nevertheless, a good verification process should have detected these problems.
The licensee indicated that its commitment to initiate a third party review of
M0V program activities will include review of diagnostic traces. This should
result in more precise utilization of the V0TES software. This issue was
,
identified as an inspection followup item (298/9308-11).
The inspectors noted that the closing dynamic diagnostic trace for
RHR-MOV-M039A did not show positive indication of hard seat contact. The
typical inflection in the slope of the thrust trace was not present and the
final thrust load rate was observed to be approximately eight times less than
the corresponding load rate on the static trace. The licensee contacted
Liberty Technology, Inc. (Liberty, supplier of the VOTES diagnostic system) to
provide technical assistance in evaluating the inspectors' concern with this
,
M0V. The licensee stated that Liberty believed that the valve had fully
closed during the dynamic test because the subsequent opening stroke indicated
a pullout force that was in excess of the pullout force corresponding to the
previous static diagnostic test. Liberty concluded that the high pullout
force indicated that the valve disc had wedged into the closed seat. The
,
inspectors accepted the opinion expressed by Liberty as being credible but
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still considered the anomalous thrust trace indication to be potentially
'
inconsistent with this position. The licensee intended to reevaluate the test
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results. Subsequent to the exit meeting, this issue was, identified as an
inspection followup item (298/9308-12).
The inspectors noted that uncertainties associated with the measurement of
line pressure had not been considered in the evaluation of test results for
initial acceptance of M0V dynamic diagnostic tests. Differential pressure was
computed as the difference between the uncorrected values measured at an
upstream and a downstream pressure sensor. The licensee provided an error
analysis of various pressure instruments that are utilized for MOV testing.
This analysis listed estimated pressure measurement errors ranging from
approximately 1 to 3 percent. Using the highest error of 3 percent and
applying a square root sum of the squares (SRSS) computation, the anticipated
error for two pressure instruments being used to measure the differential
pressure across an MOV would be approximately 4 percent. For marginal MOVs
tested at less than design basis differential pressure conditions, this
magnitude of uncertainty could be significant. The licensee indicated an
intent to include pressure measurement uncertainty in the evaluation of
dynamic MOV tests.
The licensee's diagnostic system included measurements taken with the V0TES
force sensor and the displacement measuring transducer (DMT), which measures
springpack displacement. The displacement of the calibrated springpack is
then used to determine output torque. The inspectors emphasized the
importance of measuring torque for the purposes of observing valve / actuator
torque limits, determination of stem friction coefficients, and for improving
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overall diagnostic capability. The inspectors considered this area of the
licensee's program to be a strength.
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On September 15, 1993 during this inspection, MOV CS-M0V-M07B failed to open
)
during the performance of Technical Specification surveillance procedure
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6.3.4.2.
The MOV motor did not energize, indicating a problem in the starting
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circuit. The inspectors were concerned with this event because this MOV had
been fully closed out under GL 89-10. The licensee examined the limit switch '
finger assembly and discovered that the inside contact on LS-4 was not making.
This problem was repaired, and the valve was successfully stroked. As a
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followup to any generic issues that may result, this issue was identified as
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an inspection followup item (298/9308-13).
During testing of RHR-MOV-920MV, a VOTES sensor failure occurred, resulting in
the loss of all thrust information from the test. The test was performed at
approximately 60 percent of the MEDP. Torque information was available and
did not indicate any operability problems with the M0V. However, the lack of
thrust information prevented a complete assessment of the operability of this
!
MOV to perform its safety function. At the time of this inspection, the
licensee had not decided what actions would be taken to complete this HOV
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under GL 89-10. This issue was identified as an inspection followup item
(298/9308-14).
The inspectors noted that the dynamic diagnostic traces associated with four
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of the seven MOVs selected for review exhibited no or very limited
differential pressure effects. The M0Vs that showed this phenomenon were
MS-MOV-M077, RHR-MOV-M016B, RHR-MOV-920MV, and CS-MOV-MO5A.
For
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RHR-MOV-920MV, this effect was limited to the springpack deflection trace as
no thrust trace was available. The licensee described to the inspectors the
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test lineups used in each of these tests, but no particular aspect of the
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testing process appeared to definitively explain the apparent lack of flow
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effects. The licensee indicated an intent to review the results of these and
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other similar tests to determine the validity and applicability of the test
1
issue was identified as an inspection followup item
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l.5 Pressure lockina and Thermal Bindina
The NRC Office for Analysis and Evaluation of Operational Data (AE00) recently
completed a study of pressure locking and thermal binding of gate valves.
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AE00 concluded that licensees have not taken sufficient action to provide
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assurance that pressure locking or thermal binding will not prevent a gate
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valve from performing its safety function.
NRC regulations require that
!
licensees design safety-related systems to provide assuance that those
systems can perform their safety functions.
In Generic Letter 89-10, the
staff requested licensees to review the design bases of their safety-related
MOVs.
The inspectors reviewed the licensee's evaluations of the potential for
pressure locking and thermal binding of gate valves. The licensee hired an
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independent engineering group to conduct an M0V pressure locking and thermal
binding susceptibility evaluation.
The evaluation report, R122-89-10.07,
" Pressure Locking and Thermal Minding Susceptibility Evaluation," was
completed in May 1993. The evaluation addressed all MOVs contained in the CNS
GL 89-10 program. The results of the evaluation indicated that eleven valves
were potentially susceptible to pressure locking and two were potentially
susceptible to thermal binding. The licensee reviewed these valves and
provided dispositions.
Four valves were considered to be not susceptible
-
after further evaluation, two valves were scheduled for nodification during
the 1994 outage, six valves were dispositioned through plant procedure
char.ges, and one valve was dispositioned on the basis that valve signatures
did not reveal any pressure locking concerns. The inspectors were not
convinced that the results of a valve signature test was a conclusive
methodology in determining that the valve was not susceptible to pressure
locking.
Furthermore, the evaluation report results stated that "A valve may
be initially described as potentially susceptible, but if the M0V is stroked
during normal plant / system operation or during surveillance testing and a
maintenance history review revealed no repeated failures potentially
attributable to PL/TB, the ultimate classification depicted under the
conclusion will be 'not susceptible'." The inspectors review of the
evaluation results revealed that 18 valves had been dispositioned as "not
susceptible" using this approach.
The inspectors were unable to obtain a
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clear understanding of whether the licensee's methodology of evaluation had
incorporated a sufficiently broad scope of information.
The licensee was unable to provide sufficient justification that the
methodology used to disposition potentially susceptible valves was adequate.
The licensee will need to provide this justification at a later date. This
issue was identified as an inspection followup item ('298/9308-16).
1.6 ffJriodic Verification of M0V Caoability
During the GL 89-10 Part 1 inspection, a concern was identified regarding the
use of static testing for periodic verification of M0V capability. During
this inspection, the licensee restated their intention to use static testing
for periodic verification. The licensee had not developed justification to
show that static tests could confirm design basis capability, which is
necessary because as yet there is no conitrmed correlation between static and
dynamic test results.
The NRC will review the licensee's actions with regard
to this issue during future inspections.
1.7 M0V Failures. Corrective Actions. and Trendina
During the GL 89-10 Part 1 inspection, the licensee had procedures in place
that, if followed, would result in a trending program meeting the
recommendations of the GL.
Since the licensee had not fully implemented its
GL 89-10 MOV program, the implementation of the tracking and trending program
was not complete at that time. During this inspection the licensee stated
that they planned to implement their tracking and trending procedures by the
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end of 1993.
The full implementation of this trending program will be
reviewed during a future inspection.
1.8 Quality Assurance /0uality Control
The CNS MOV Program Plan designates program responsibilities. Among those
responsibilities are that the Quality Assurance Division is responsible for
,
ensuring that necessary resources are allocated to meet all the quality
assurance requirements established for the MOV program.
The inspectors noted
that the involvement of quality assurance, quality control, and self
assessn.ent was minimal in the area of MOV testing. lio quality assurance
audits had been performed in this area.
Documentation of a single quality
control surveillance was provided to the inspectors, but this effort appeared
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to be mostly administrative in content.
Involvement of quality control
inspectors in the MOV program appeared to be limited to the control of lifted
leads and jumpers. The licensee had not performed or contracted any self
assessments of the MOV program. Collectively, these facts indicated an under-
utilization of quality-related measures to provide an independent oversight of
the program. The inspectors concluded that this deficiency contributed to the
)
negative findings of this inspection.
1.9 Schedule
The licensee has received an approved extension for completion of the GL 89-10
program.
This approval extended the completion date from June 28, 1994, to
January 1,1995. Because of an extended outage over the summer of 1993, tne
licensee will potentially move the next refueling outage to approximately
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February 1995, during which the remaining MOV tests are planned.
If this were
to occur, the licensee would need to request an additional extension to
complete the program.
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ATTACHMENT 1
1 PERSONS CONTACTED
1.1
Licensee Personnel
- M. Dean, Nuclear Licensing and Safety Supervisor
- J. Meacham, Site Manager
- E. Mace, Senior Manager, Site Support
- R. Gardner, Plant Manager
- M. Young, Maintenance Supervisor
,
- J. Flaherty, Engineering Manager
- M. Bennett, Nuclear Licensing Engineer
- S. Harsh, Engineering Technician
- B. Kochanowicz, Mechanical Engineer
- N. Dingman, MOV Program Supervisor
- M. Estes, Senior Manager Operations
- L. Bray, Regulatory Compliance Specialist
- M. Tumicki, MOV Project Engineer
- K. Almquist, Project Manager
- M. Fletcher, Quality Assurance Engineer
- S. Bray, Quality Assurance Operations Supervisor
- R. Wilber, Division Manager, Nuclear Engineering and Construction
1.2 Other Personnel
- E. Simbles, Erin Engineering
- S. Resch, Omaha Public Power District
- R. Sanchez, Stone and Webster
- L.
Briley, Volt Technical Services
1.3 NRC Personnel
- R. Kopriva, Senior Resident Inspector
In addition to the personnel listed above, the inspectors contacted other
,
personnel during the inspection.
- Denotes personnel that attended the exit meeting.
2 EXIT MEETING
An exit meeting was cor
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on September 17, 1993.
During this meeting, the
inspectors reviewed t~
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and findings of the report.
The inspectors
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informed the licensee
,at reoprietary information reviewed during the
inspection would not
d',ulged in the inspection report.
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ATTACHMENT 2
COOPER GATE VALVE DATA
Diagnostics: VOTES System with DMT for Torque Measurements
VALVE
VALVE SrLE
TEST
DYNAlWC
SIM
MAD"
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NUMBER
&
CONDrI10NS
VALVE
FUt3C110N
SINE 11VE
,
MANUFACTURER
FAL M *
COEFFICHINT
BU3tAVIOR
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CS-M O-
3"
340 psid (close)
Not
0.06 (Dynamic)
-0.4 %
M05A
340 psid (Open)
Determined
0.06 (Static)
Solid-Wedge Gate
RH R-MO-
4'
316 psid (Close)
Not
Not
Not
M016B
316 psid (Open)
Determined
Determined
Determined
Solid-Wedge Gate
RH R-MO-
18"
322 psid (Close)
0.48 (Close)
0.10 (Dynamic)
-5.0 %
M039A
322 psid (Open)
0.32 (Open)
0.11 (Static)
Solid-Wedge Gate
'Ihe dynamic valve factors listed were calculated by the licensee using a mean seat diameter.
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A negative number indicates that the thrust observed at CST during the dynamic test was greater than the thrust observed
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at CST during the static test.
E VALVE DATA
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