IR 05000498/1993006
| ML20046A144 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 07/15/1993 |
| From: | Westerman T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | |
| Shared Package | |
| ML20046A141 | List: |
| References | |
| 50-498-93-06, 50-498-93-6, 50-499-93-06, 50-499-93-6, GL-89-10, NUDOCS 9307270017 | |
| Download: ML20046A144 (17) | |
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APPENDIX U.S. NUCLEAR REGULATORY COMMISSION
REGION IV
Inspection Report:
50-498/93-06; 50-499/93-06 Operating Licenses: HPF-76; NPF-80 Licensee: Houston Lighting & Power Company P.O. Box 1700 Houston, Texas 7725I Facility Name: South Texas Project Electric Generating Station (STP), Units 1 and 2 Inspection At: STP, Bay City, Texas Inspection Conducted: June 7-11, 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:
A. Trusty, Consultant, EG&G Idaho-INEL
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T. niesterman, Chief, Engineering Section Date Division of Reactor Safety, Region IV Inspection Sumary Areas Insoected:
Special, announced inspection of the implementation of the licensee's program to meet commitments to Generic letter 89-10 " Safety-Related Motor-0perated Valve Testing and Surveillance," and followup.
Results:
The licensee's motor-operated valve program was capable of
satisfactorily demonstrating the operability of motor-operated valves subject to Generic Letter 89-10 and generally fulfilled the licensee's commitments in this area (Section 1).
The licensee had not established a margin to account for stem
lubrication degradation (Section 1.2).
Stem factors were calculated at control switch trip rather than the
points of flow cutoff or seat contact (Section 1.2).
9307270017 930720 DR ADOCK 0500
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-2-The licensee's response to the Limitorque 10 CFR Part 21 report on ac
motor degradation in a harsh environment was comprehensive and very prompt (Section 1.2).
The licensee's diagnostic testing capabilities were advanced and
included the use of stem-mounted thrust and torque strain gages (Section 1.3).
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For the motor-operated valves reviewed during this inspection, valve
factors were in the range of 0.23 to 0.30 in the opening direction and 0.46 to 0.64 in the closing direction. Observed stem friction coefficients were between 0.074 and 0.190 (Section 1.3).
Based on preliminary test results, the licensee's design basis
assumptions for valve factor and stem friction coefficient were potentially nonconservative for some motor-operated valves (Section 1.3).
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The licensee was not calculating valve factors for tests conducted at
less than 80 percent of the maximum expected differential pressure (Section 1.3).
Acceptance criteria were found to be insufficient for the evaluation of
torque measured during dynamic diagnostic tests (Section 1.3).
A nonconservative error was identified in one of the licensee's
evaluations of stem factor, but the valve in question had sufficient margin to account for the corrected evaluation (Section 1.3).
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Thrust measurements were being extrapolated by a linear method that had
not been validated by analytic means (Section 1.3).
The linear extrapolation of torque measurements had not been validated
and was dependent on a potentially nonconservative assumption (Section 1.3).
For tests conducted at below 80 percent of the maximum expected
differential pressure, thrust and torque measurements had not been extrapolated, raising the possibility that certain motor-operated valves with demonstrably marginal capability had not been identified (Section 1.3).
t A significant error was identified in the licensee's analysis of the
opening differential pressure trace of Motor-0perated Valve AISIMOV0008A (Section 1.3).
Motor-0perated Valve B2RCMOV0001B (power-operated relief valve-block
valve) was underthrusted at control switch trip and overthrusted at-total thrust.
It had also been assigned a potentially nonconservative
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valve factor in the design basis calculations. The licensee was requested to provide status on the disposition of this motor-operated
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valve prior to Unit 2 startup. The concern related to the valve factor assumed in the design basis calculations also needs to be dispositioned prior to Unit I startup (Section 1.3).
Motor-Operated Valve CICVMOV8348, a 2-inch globe valve, exhibited an
unusually high rate-of-loading effect and an unexpected, very small differential pressure effect (Section 1.3).
Two dynamic tests were identified that showed the characteristics of
static tests, apparently due to a failure to attain an appreciable
percentage of the design-basis flow rate during the test (Section 1.3).
The methodology used to zero diagnostic differential pressure traces was
inconsistent and not well proceduralized (Section 1.3).
The recent failure of an SB-1 actuator worm shaft clutch was attributed
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to an improper heat treatment and may have generic implications (Scction 1.3).
The depth of the licensee's analysis of pressure locking and thermal
binding was not clear. This area will require additional evaluation by the licensee (Section 1.4).
The licensee intended to utilize both dynamic and static testing for the
purpose of periodically verifying motor-operated valve capability (Section 1.5).
A revised motor-operated valve trending program was scheduled for full
implementation by September 1993 (Section 1.6).
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Summary of Insoection Findinos:
Inspection Followup Item 498/9306-01; 499/9306-01 was opened
(Section 1.2).
Inspection Followup Item 498/9306-02; 499/9306-02 was opened
(Section 1.3).
Inspection Followup Item 498/9306-03; 499/9306-03 was opened
(Section 1.3).
Inspection Followup Item 498/9306-04; 499/9306-04 was opened
(Section 1.3).
Inspection Followup Item 498/9306-05; 499/9306-05 was opened
(Section 1.3).
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t Inspection Followup Item 498/9306-06; 499/9306-06 was opened
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(Section 1.3).
t Inspection Followup Item 498/9306-07; 499/9306-07 was opened
(Section 1.3).
Inspection Followup Item 498/9306-08; 499/9306-08 was opened
(Section 1.3).
Inspection Followup Item 498/9306-09; 499/9306-09 was opened
(Section 1.3).
Inspection followup Item 498/9306-10; 499/9306-10 was opened
(Section 1.3).
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i Inspection Followup Item 498/9306-11; 499/9306-11 was opened'
(Section 1.3).
Inspection Followup Item 498/9306-12; 499/9306-12 was opened
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(Section 1.4).
Inspection Followup Item 498/9230-02; 499/9230-02 was closed
(Section 2).
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Attachments
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Attachment 1 - Persons Contacted and Exit Meeting Attachment 2 - South Texas Project Gate Valve Data f
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-5-DETAILS 1 GENERIC LETTER (GL) 89-10 ' SAFETY-RELATED MOTOR-OPERATED VALVE [MOV)
TESTING AND SURVEILLANCE" (2515/109)
On June 28, 1989, the NRC issued GL 89-10, which requested licensees and construction permit holders to establish a program to ensure that switch settings for safety-related MOVs were selected, set, and maintained properly.
Subsequently, five supplements to the GL have been issued. NRC inspections of licensee actions implementing commitments 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-Operated 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 I program review at South Texas Project'
is documented in NRC Inspection Report 50-498/92-06; 50-499/92-06. A followup
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inspection was documented in NRC Inspection Report 50-498/92-30; 50-499/92-30.
The inspection documented by this report was the initial inspection of the MOV program implemented for testing at South Texas Project under Part 2 of TI
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2515/109, and was focused on the verification of program implementation.
Nevertheless, programmatic issues were addressed during this inspection in response to followup of findings in the Part 1 inspection and in the context of issues that developed during the course of the inspection.
As an overall assessment, the inspectors concluded that the licensee's MOV program was capable of successfully demonstrating the operability of MOVs subject to GL 89-10.
For the most part, the program appeared to implement the licensee's commitments to the GL.
The principal focus of the inspection was to select and review in depth several M0Vs from the GL 89-10 program.
The selection was based on an
information matrix provided by the licensee as requested by the inspectors.
The selection was biased toward MOVs that appeared to have less than average 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 inspectors reviewed the design basis calculation of design flow, temperature, and the maximum expected differential pressure (MEDP), the sizing and switch setting calculation, the diagnostic i
test data package, and the diagnostic traces using M0 VATS 3500 software. The i
following MOVs were selected for review:
AICVM0V0025 Charging to Regenerative Heat Exchanger Control Valve BIRHMOY0066B Residual Heat Removal (RHR) Pump B to Chemical and Volume Control (CVCS) Letdown i
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A151H0V0008A HHSI Pump to RCS Hot Leg AISIMOV0019A Low Head Safety Injection (LHSI) to RCS Hot Leg 1 CICVMOV0ll2C Centrifugal Charging Pump Suction from Reactor Water Storage Tank (RWST)
B2RCMOV0001B Pressurizer Block Valve The selected MOVs were gate valves and were configured as shown below:
Actuator Closure Control Valve Size (inches)
AICYMOV0025 SB-0 LIMIT
BIRHM0V0066B SB-00 LIMIT
CISIMOV0004C SB-1 LIMIT
AISIM0V000BA SB-1 LIMIT
AISIM0V00019A SB-1 LIMIT
CICYMOV0ll2C 58-00 LIMIT
B2RCMOV0001B SB-00 LIMIT
1.1 Desion-Basis Reviews The inspectors reviewed the calculations determining the MEDP (alternately referred to as the design-basis differential pressure), design flow conditions, design temperature, and other design parameters for each of the
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MOVs selected for review. These calculations had been prepared for the licensee by the valve supplier, Westinghouse. The calculations appear 2d to acceptably address the design basis considerations of the selected MOVs.
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1.2 MOV Sizino and Switch Settino The licensee utilized the standard Limitorque equation to determine the minimum thrust requirements for their MOVs. For most valves, a valve factor of 0.48 and 0.55 was assumed in the open snd closing direction. The licensee
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assumed a stem friction coefficient of 0.20 for non-Westinghouse valves and a
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stem friction coefficient of 0.15 for Westinghouse MOVs.
The inspectors observed that the MOV program included margin to account for load-sensitive behavior (also known as " rate-of-loading") for those MOVs that were torque switch controlled, but did not include margin for load-sensitive behavior for limit-controlled valves. The deletion of. load-sensitive behavior margin in turns of thrust delivered at torque switch trip under static verses dynamic condition is generally considered appropriate for a limit-controlled M0V, because the operation of the MOV relies on motor capability to drive the
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valve to a preset position without the torque switch being included in the-
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control circuit. However, this assumption is valid only as long as the
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_7 licensee validates that assumed stem friction coefficient used to determine actuator thrust capability is conservative enough to bound all operating conditions.
The inspectors noted that the licensee had not established a margin to account for stem lubrication degradation. Over a typical 18-month operating cycle, the grease applied to the valve stem may tend to harden or become impregnated with dust or other debris. The overall effect is to increase the stem factor (and stem friction coefficient) resulting in less thrust delivered to the stem for any given amount of applied torque. At this time, there is very little test data in the industry to quantify the effects of stem lubrication degradation. Some licensees have made interim assumptions in the range of 5 to 10 percent to account for this phenomenon, though it is possible that for certain configurations and lubricants, the degradation may be negligible. The licensee stated that the trend analysis program now u place will evaluate for the effects of stem lubrication degradation and that :spropriate margins will be established if they are shown to be necessary. The establishment of margin, as appropriate, for the effects of stem lubricant degradation, will be generically inspected at each site during the closeout of GL 89-10, Phase 2.
The inspectors noted that the licensee was calculating the stem factor (torque divided by thrust) and stem friction coefficient for each diagnostic test at
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the point of control switch trip. Since the stem factor is used to calculate the amount of thrust that the motor and actuator can deliver to the valve stem in an effort to close or open the valve against design flow conditions, the more appropriate point to evaluate stem factor is the point of flow cutoff or at seat contact. Optimally, the point between flow cutoff and seat contact that gives the highest ratio of torque to thrust should be considered as a conservative torque to thrust conversion efficiency, i.e., least efficient conversion of torque thrust. The inspectors evaluated three HOVs in this manner and in each case found that the licensee's stem facter calculation was slightly higher (more conservative) than the stem factor calculated by the inspectors. This, however, may not always be the case. The licensee acknowledged the inspectors' concern and stated that it would reevaluate its-methodology for calculating stem factors. 'This issue was identified as an inspection followup item (498/9306-01; 499/9306-01).
The inspectors reviewed the licensee's response to the Limitorque 10 CFR Part 21 letter dated May 13, 1993, concerning the effect of ambient temperatirre on the starting torque of ac motors. The licensee had evaluated the impact of the Part 21 report on all GL 89-10 MOVs and had identified 10 MOVs in Unit I and 8 H0Vs in Unit 2 that needed to be modified due to an unacceptable decrease in the previously calculated motor capability margin.
The 10 Unit i valves had been modified by increasing the overall gear ratio to compensate for the decrease in starting torque. Modifications to the affected Unit 2 valves were pending at the time of the inspection. The inspectors-reviewed the calculation of reduced starting torque for MOV CISIMOV0004C and verified that the methodology was consistent with the guidance provided in the
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Part 21 letter. The inspectors considered the licensee's response to the
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-8-Limitorque Part 21 letter to be very prompt and comprehensive and to represent a strength in the MOV program.
1.3 Desian-Basis Caoability The licensee's MOV testing program was delineated in Procedure OPMP05-ZE-309,
"MOV Diagnostic Testing Procedure," Revision 7, dated February 28, 1993. The inspectors reviewed portions of this procedure along with the static and dynamic diagnostic test data packages and the M0 VATS 3500 diagnostic traces for each of the seven MOVs selected for review. On the basis of this review, the inspectors concluded that the licensee had satisfactorily demonstrated the immediate operability of these MOVs. The licensee will need to perform additional evaluation on some of the MOVs to consider them fully addressed under the "two-stage approach" discussed in the GL.
The dynamic tests reviewed by the inspectors were performed under the following conditions:
AICVM0V0025 92.6% of closing design-basis differential pressure BIRHMOV00668 49.1% of closing design-basis differential pressure CISIMOV0004C 124.0% of closing design-basis differential pressure AISIM0V0008A 92.2% of closing design-basis differential pressure A1SIMOV00019A 89.7% of closing design-basis differential pressure CICVMOV0ll2C 18.3% of closing design-basis differential pressure MOV B2RCH0V0001B was tested under static conditions only.
The licensee utilized the M0 VATS 3500 diagnostic evaluation system in combination with Teledyne stem-mounted torque and thrust strain gages.
For thrust measurements on some MOVs, the licensee utilized stem load sensors, stem strain rings, and stem strain transducers. However, the licensee preferentially used the stem-mounted strain gages and indicated that the use of these devices would be increased in the future. During most tests, the licensee provided instrumentation to detect springpack deflection,
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compensator spring deflection, valve position, switch actuations, motor current, and other parameters. The inspectors considered the diversity of instrumentation and the use of the advanced software to represent a strength in the licensee's program.
Test data for the selected M0Vs revealed valve factors in the range of 0.23 to 0.30 in the opening direction and 0.46 to 0.64 in the closing direction.
Observed stem friction coefficients were between 0.074 and 0.190. A summary of the MOVs reviewed by inspectors is shown in Attachment 2.
Based on the preliminary results, the licensee's assumptions of a stem friction coefficient of 0.15 and a valve factor of 0.45 and 0.55 are potentially nonconservative.
The licensee will need to revise some of their design-basis calculations to
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reflect valve-specific dynamic test results. Also, the licensee will need to evaluate their data to determine appropriate valve factors and stem friction coefficients to use for those MOVs that cannot be tested under dynamic conditions. The licensee indicated that their test data will be reviewed and
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-9-the best available data will be applied as part of the evaluation process.
The reduction of test data for review of design basis calculations and for the evaluations of valves that cannot be dynamically tested will be generically inspected at each site during the closeout inspection of GL 89-10.
While reviewing the dynamic test packages, the inspectors noted that apparent
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valve factors had not been calculated from test data and compared to the assumed valve factors for MOVs that were tested at less than 80 percent of the design-basis differential pressure. The inspectors indicated that all tests of safety related MOVs need to be evaluated to assure operability problems do not exist even where tests are conducted at less than'80 percent of design-basis conditions. Based on test results from other utilities, the inspectors indicated that meaningful data may be obtained from tests conducted at less than 80 percent of design-basis conditions, and that this data may be useful for those MOVs that are not practicable to test under dynamic conditions. The licensee had revised the requirements in Procedure OPMP05-ZE-309 to include this feature, but had not implemented the new requirements. The licensee indicated that they would reevaluate those valves tested below 80 percent of design basis conditions to meet the requirements of their new diagnostic test procedure. This issue was identified as an inspection followup item (498/9306-02; 499/9306-02).
The inspectors identified a deficiency in the acceptance criteria used to evaluate the torque levels measured during differential pressure tests.
Procedure Engineering Instruction (EI) 4.05-05, " Review of Differential Pressure Test Data Rising Stem Valves," Revision 3, stipulated that the calculated degraded voltage torque for limit-closed valves should be greater than the measured torque at seat contact (differential pressure effect torque)
extrapolated to the design-basis differential pressure.
In addition to the design-basis thrust requirement, the measured torque at control switch trip, which is of concern with regard to the degraded voltage capability of the motor / actuator, but this consideration was not included in this acceptance evaluation.
Similarly, the extrapolated differential pressure effect torque (in lieu of the measured total torque) was compared to the actuator rated torque as the structural acceptance criterion. The inspectors were concerned that these comparisons could potentially result in failure to identify an
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overtorque or degraded voltage problem.
Procedure El 4.05 had recently been revised and identified as Addendum 44 to Procedure OPMP05-ZE-0309. The revised acceptanca criteria contained the correct torque comparisons.
However, the licensee had not used the revised procedure for any differential pressure tests at the time of this inspection. The licensee agreed to review
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the existing diagnostic differential pressure test data for limit-closed M0Vs to determine whether any torque-related problems were missed by the use of the nonconservative acceptance criteria. This issue was identified as an j
inspection followup item (498/9306-03; 499/9306-03).
The licensee calculated the actual stem factor based on the measured values of i
torque and thrust and compared this to the assumed stem factor, which is typically based on a stem friction coefficient of 0.15. During the review of
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MOV AICVM0V0025, the inspectors identified that the licensee had used the j
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wrong stem factor for the assumed stem friction coefficient. When the actual and the assumed stem factors were compared, the actual stem factor was lower than the assumed value. However, if the comparison had been made with the correct assumed stem factor, then the actual stem factor would have been higher.
Because of this error, licensee personnel did not perform an additional evaluation to determine whether the increase in stem friction coefficient would affect MOV operability. However, based on review of the test data, the inspectors did not identify an operability concern with this valve.
Where testing was conducted at 80 percent or greater of the design-basis differential pressure., the licensee utilized a straight-line extrapolation of the thrust to overcome differential pressure using the ratio of design-basis differential pressure to the test differential pressure. However, the licensee had not performed multi-point testing or developed other methods to justify the long-term acceptability of its extrapolation method. Therefore, the inspectors considered the licensee's extrapolations to design-basis conditions to be the first stage of a two-stage approach where the valves have been setup using the best available data, as discussed in GL 89-10. The justification of extrapolation will be generically inspected at each site during the Phase 2 closeout inspections of GL 89-10.
The licensee used a linear extrapolation method to estimate the amount of torcue necessary to overcome differential pressure effects at design-basis conditions for those tests that are performed at less than the MEDP. Two assumptions are implied by the use of a linear method to extrapolate torque.
First, for torque to be a linear function of the differential pressure, thrust must also be a linear function.
Second, and of more potential concern, for torque to be a linear function of differential pressure the stem factor (and stem friction coefficient) must be constant over the range from the test differential pressure to the MEOP. Depending on the M0V in question, the stem
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factor may increase somewhat over this range, which would result in the torque being nonlinear with respect to differential pressure. The two implied assumptions raise ouestions with regard to the licensee's torque extrapolation method. This issue was identified as an inspection followup item (498/9306-04; 499/9306-04).
The licensee's diagnostic test analysis process did not include an extrapolation of measured thrust or torque when differential pressure tests were conducted at less than 80 percent of the MEDP. The inspectors were concerned that this exclusion could result in the failure to best identify an operability problems on the tested M0V. 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 c.learly unacceptable and yet might still pass the licensee's acceptance criterie.
The licensee stated that the policy for determining when an extrapolation should be performed would be reevaluated. Section 5.0 of Procedure OPHP05-ZE-0309 indicated that extrapolations would be conducted for tests conducted below 80 percent of the MEOP, but this new procedure had not yet been used for a
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-11-i dynamic test. Also, the procedure was not clear on how extrapolations of test results below 80 percent would be handled with respect to test acceptance.
The licensee stated that all existing differential pressure tests that were conducted at less than 80 percent of the MEDP would be reviewed to identify any obvious HOV capability problems. This issue was identified as an inspection followup item (498/9306-05; 499/9306-05).
The inspectors identified an error in the etaluation of the opening differential pressure trace of MOV AISIMOV0008A. The licensee had determined that the highest thrust in the opening direction (in this case the pullout thrust) was 13,857 pounds-force (1bf). Based on review of the diagnostic trace, the inspectors determined that the measured pullout force was approximately 18,400 lbf. The licensee agreed that an error had been made in the analysis of this trace and that a reevaluation would be performed. The inspectors noted that the MOV had sufficient margin to account for the increased thrust requirement in the open direction. The licensee stated that a station problem report would be initiated to determine the cause of the error and the need for any generic corrective actions. This issue was identified as an inspection followup item (498/9306-06; 499/9306-06).
During review of the static diagnostic trace of MOV B2RCMOV0001B (power-operated reactor valve block valve), the inspectors noted that the licensee had identified two deficiencies associated with the thrust acceptance criteria. The thrust measured at limit switch trip in the closing direction was slightly less than the calculated thrust required to close the valve under the design-basis condition. Because of the limit-closed feature of this valve and the fact that the available thrust at degraded voltago was much ersater than the calculated required thrust, the inspectors agreed with the licensee that this was not a true operability concern. Nevertheless, the licensee stated that it intended to reset the limit switch of this MOV to achieve the required thrust at limit switch trip. Another concern was the fact that the total thrust corrected for errors (16,362 lbf) exceeded the actuator rated thrust (16,000 lbf). The licensee stated that they were in possession of preliminary test results of SB-00 actuators (performed by KALSI) and had received concurrence from KALSI that the actuator ratings could be increased to at least approximately 18,900 lbf. This would permit the licensee to increase the limit switch setting on this MOV to resolve the underthrust proolem, while not exceeding the revised interim thrust rating. However, the inspectors identified an additional concern regarding the valve factor that had been assumed in the design-basis calculation. The valve factor assumption for this valve is very important since it cannot be tested under dynamic conditions. Based on its testing program, Westinghouse (the nuclear steam system supplier for this plant) had assigned a valve factor of 0.45 for this valve. An identical valve tested under full blowdown conditions at another nuclear plant had shown an apparent valve factor of approximately 0.6.
The licensee stated that this information, together with other data, would be assessed to determine the valve factor that best predicts the behavior of j
MOV B2RCMOV00018. A higher valve factor would necessitate a higher limit
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switch setting. The issues discussed above were identified as an inspection followup item (498/9306-07; 499/9306-07).
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-12-The inspectors reviewed the test package and diagnostic traces for MOV CICVMOV8348, a 2-inch globe valve (centrifical charging pump seal water injection flow control bypass) that has torque closure control. This MOV exhibited a 38 percent rate-of-loading (load-sensitive behavior) effect despite the fact that the differential pressure trace showed that there was only a very minimal dynamic effect on the valve during the closing stroke.
The small dynamic effect was a surprising result considering that the test was conducted at 2840 pounds per square inch differential (psid). The inspectors noted that despite the high differential pressure, the flow rate established during the test was only 64 gallons per minute (gpa) compared to a design-basis flow rate of 164 gps. The licensee agreed to review the test results for this valve to determine the validity of the differential pressure test and to determine the cause of the unusual rate-of-loading condition.
The licensee stated that the same valve in Unit 2 was scheduled to be tested and that this test could provide additional information regarding the causes of the behavior of the Unit I valve. This issue was identified as an inspection followup item (498/9306-08; 499/9306-08).
During the review of the dynamic test traces for MOVs BIRHMOV00668 and CICVMOV8348, the inspectors observed that the dynamic traces were similar to the static traces, in that there was little or no apparent increase in force caused by dynamic effects prior to hard seat contact. For both valves, the percentage of design-basis flow achieved during the test was much less than the observed percentage of the design basis differential pressure. This brings into question the validity of a design-basis test when flow conditions are significantly below the design flow rate.
In the case of MOV BIRHMOV0066B, an additional concern was identified regarding the validity of the measured differential pressure, in that there may have been a large pressure drop caused by a heat exchanger located upstream of the valve, which was within the boundary of the pressure drop being measured by the system pressure instruments. The licensee intended to apply the two-stage approach for these MOVs and will reevaluate the dynamic tests to determine if the current evaluation is valid. Further, the licensee planned to review the system test lineup to determine if they can better achieve design-basis conditions. Based on this review, the licensee may decide to retest these MOVs. This issue was identified as an inspection followup item (498/9306-09; 499/9306-09).
i During review of diagnostic traces using the MOVATS 3500 software, the I
inspectors observed that the licensee's method for zeroing thrust and torque traces was not consistent. This was especially evident for differential pressure traces, which rarely exhibited the classic " plateau" areas, indicating the transition region between tension and compression. Mistakes in j
the zeroing process can introduce errors in the measured parameters that are
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not accounted for by the standard margin analysis. The guidance for zeroing
traces was provided in Procedure OPMP05-ZE-0309, Addendum 24. The guidance provided in this procedure was not sufficient to handle the special difficulties encountered in zeroing differential pressure tracos. The licensee agreed that Addendum 24 was deficient and stated that it would be reviewed and most likely revised to ensure that a consistent and correct
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-13-methodology would be used to zero diagnostic traces. This issue was identified as an inspection followup item (498/9306-10; 499/9306-10).
During an internal inspection of MOV B2SIMOV00318 (SI-31B) on April 29, 1993, the licensee discovered a broken piece of the worm shaft clutch in the actuator. Station Problem Report 931506 was initiated to resolve the deficiency. The worm shaft clutch is a critical component and its failure could prevent motorized operation of the MCV. Limitorque stated that this was the first reported instance by a nuclear utility of a failure of a worm shaft clutch under normal operation. The licensee sent the broken clutch to Limitorque for evaluation. Limitorque determined that the high carbon Type 4140 material used in the clutch had been subjected to an improper material hardening process. The hardening process involves the annealing time and temperature and the quenching method used to achieve the desired material properties. As a result of the improper material hardening process, the subject clutch had an increased surface hardness and an increase in brittleness, which increased the probability of the observed failure. The licensee was in the process of replacing worm shaft clutches on actuators that had been purchased under the same shop order as the actuator for MOV SI-318 and sending the old clutches to Limitorque for analysis.
It is the inspector's understanding that Limitorque presently has this issue under evaluation as a potential 10 CFR 21 notification. This issue has potential generic implications and will be tracked as an inspection followup item (498/9306-11; 499/9306-11).
1.4 pressure Lockino and Thermal Bindino The Office for Analysis and Evaluation of Operational Data completed a study of pressure locking and thermal binding of gate valves. The Office for Analysis and Evaluation of Operational Data concluded in its report that licensees have not taken sufficient action to provide assurance that pressure locking or 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.
The inspectors reviewed the licensee's evaluations of the potential for pressure locking and thermal binding of gate valves. The inspectors also reviewed the licensee's actions taken to prevent pressure locking and thermal binding.
In 1988, the licensee developed a pressure lock / thermal binding evaluation matrix for 218 safety-related gate valves. The matrix consisted of 50 locked-open valves, 31 locked-closed valves, 84 normally-open valves, and 53 normally-closed valves. The locked-open and locked-closd valves were considered acceptable since they would not be used during normal operation.
The matrix also identified 33 of the normally-open valves and 10 of the normally-closed vc'ves as remaining Opened or closed during normal operation and would, therefore, not be required for emergency conditions or conditions pertinent to causing pressure locking or thermal binding. Some valves were considered acceptable because no problems were noted when the valves were
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-14-cycled during the nors:a1 hot functional testing. During hot functional testing, Unit 1 MOV XCV0006 bound and was subsequently modified. However, the Unit 2 companion valve did not bind during testing and, therefore, was not modified. The inspectors were unable to obtain a clear understanding of whether the licensee's previous methodology of evaluation had taken into account a sufficiently broad scope. The licensee agreed with the inspectors that the depth of the evaluations was not clear and that further evaluations would be necessary in this area. The licensee was unable to provide documentation that normally open valves had been sufficiently evaluated in the event of maintenance, surveillance, or testing activities which might preclude the reopening of these valves for a long period of time. The licensee's clarification of the methodology used for evaluation of pressure locking and thermal binding and the evaluation of normally open valves will be reviewed during a future inspection. This issue was identified as inspection followup item (498/9306-12; 499/9306-12).
1.5 periodic Verification of MOV Canability During the GL 89-10 Part 1 inspection, the licensee stated that periodic
verification of MOV capability had been scheduled on a 5-year interval or every third refueling outage, whichever is longer, as recommended by GL 89-10.
The licensee was intending to perform dynamic as well as static testing for this verification. During this inspection, the licensee stated that their position on periodic verification had not changed. The NRC will review the licensee's actions with regard to this issue during future inspections.
1.6 MOV Failures. Corrective Actions. and Trendin.g 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 revise their existing procedure definir<g the MOV tracking and trending program. The licensee projected that a data base would be started in August 1993 and new specifications for the MOV tracking and trending program would be developed by Septer.iber 1993, after which the program would be subsequently implemented. The full implementation of this trending program will be reviewed during a future inspection.
2 FOLLOWUP (92701)
2.1 (Closed) -nsoection Followuo Item 498:499/9230-02: SB-00 Actuator Overthrust This item involved three MOVs with SB-00 actuators in Unit 1, which were subject to thrust loads in excess of the 16,000 lbf limit, with the overthrust ranging from 3 to 5 percent. The licensee had committed to document a justification for the overthrust condition of these three MOV '
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-15-The inspectors reviewed the licensee's documented review of Westinghouse test data concerning the three valves that were left in an overthrust condition.
Westinghouse Report V-EC-1345 "Qualificrtion Test Report For Limitorque SS-0 And 58-00 Valve Actuators For Increased Thrust Rating South Texas Units 1 & 2 (Houston Light & Power Co.)," Y-EC-1345, Revision 0, provided justification that the three valves that were left in the overthrust condition were acceptable. The report stated that the 58-00 actuators are qualified for 1875 cycles of operation at a maximum valve seating thrust of 135 percent of the original rating or 18900 lbf. The inspectors concluded that the licensee had acceptably addressed the issues related to this inspection followup item.
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ATTACHMENT 1 1 PERSONS CONTACTED 1.1 Licensee Personnel
- H. Pate, Senior Nuclear Licensing Engineering Specialist
- T. Jordan, General Manager, Nuclear Engineering
- G. Parkey, Plant Managec
- S. Head, Deputy Licensing Manager
- M. Pacy, Manager, Design Engineering
- S. Rosen, Vice President, Nuclear Engineering
- J. Groth, Vice President, Nuclear Generation
- A. Harrison, Supervising Engineer, Nuclear Licensing
- H. Ludwig, Manager, Nuclear Training
- S. Phillips, Licensing Engineer i
- C. Rowland, Mechanical Supervisor, Motor-0peracor Valve
- F. Cox, Field Testing Supervisor, Motor-0perator Valve
- C. Ayala, Supervising Engineer, Licensing
- C. Walker, Manager, Public Information
- F. Hallen, Manager, Planning and Assessment
- J. Wittman, Supervisor, Electrical Planning, Maintenance
- M. Montrith, Supervisor, Quality Assurance Surveillance
- H. Chakravorty, Director, Nuclear Safety Review Board 1.2 NRC Personnel
- J. Tapia, 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 conducted on June 11, 1993. During this meeting, the inspectors reviewed the scope and findings of the report. The licensee did not identify as proprietary any information provided to or reviewed by the inspector.
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ATTACHMENT 2 SOUTH TEXAS PROJECT GATE VALVE DATA VALVE VALVE SIZE TEST DYNAneC Ft1M ID Alf*
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NLMBER
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CONDr!10NS VALVE PRIC110N MMSE11VE MANUFACTURER FAC10E COEFFICIENT REBAVIOR AICVOV0025 4*
2870 psW (Open)
0.30 (Opca)
0.158 (Static)
10.6 %
WESTINGilOUSB 2870 psW (Chee)
0.64 (Chee)
0.190 (Dynamic)
0.108 (Static)
-1.7 %
BIRHMOV00668 4*
275 psW (Open)
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WESTINGIIOUSB 275 psM (Cbac)
0,060 (Dynamic)
CISIMOV0004C 6*
1606 p W (Open)
074 (Opca)
0.150 (Statie)
6.2 %
i WESTINGl{OUSE 1612 psW (Cloac)
0.51 (Cbec)
0.190 (Dynamic)
A1SIMOV000&A 6*
1575 psM (Opce)
0.23 (Open)
0.094 (Static)
-3.0 %
i WESENGilOUSE 1575 psW (Cbec)
0.62 (Cbec)
0.081 (Dymmic)
AISIMOV0019A B*
314 paid (Open)
0.23 (Open)
0.088 (Static)
10.4 %
WESTINGIIOUSB 295 psM (Chae)
0.46 (Chae)
0.074 (Dynamic)
CICVMOV0112C 6*
22 psM (Open)
0.128 (Static)
8.8 %
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0.121 (Dynamic)
WESTING 110USE 32 psM (Cbse)
'Buically a static trace showing no dyname effects.
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