ML18153B387
| ML18153B387 | |
| Person / Time | |
|---|---|
| Site: | Surry, North Anna  |
| Issue date: | 12/03/1993 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 93-664, GL-89-10, NUDOCS 9312130186 | |
| Download: ML18153B387 (4) | |
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VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 December 3, 1993 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 and 2 SURRY POWER STATION UNITS 1 AND 2 Serial No.
NL&P/MAE:
Docket Nos.93-664 R4 50-338 50-339 50-280 50-281 License Nos. NPF-4 NPF-7 DPR-32 DPR-37 GL 89-10 SAFETY-RELATED MOV GROUPING CRITERIA The Virginia Electric and Power Company (Virginia Power) Motor Operated Valve (MOV) Program was implemented to address the requirements of IEB 85-03, "Motor-Operated Valve Common Mode Failures During Plant Transients Due To Improper Switch Settings". The scope of affected systems was increased by Generic Letter 89-10, "Safety-Related Motor-Operated Valve Testing and Surveillance" and committed to by our letter dated December 26, 1989 (Serial No.89-530). Generic Letter 89-1 O requires the testing, inspection, and maintenance of safety-related MOVs as well as position-changeable MOVs. This program is to provide assurance that the valves will function when subjected to design-basis conditions during both normal operation and abnormal events.
BACKGROUND Based on good test results, improved MOV reliability, the impact of testing on plant outages, and the high cost of performing differential pressure testing, we have reconsidered our response to the recommendations provided in Generic Letter 89-1 O and the clarification provided in Supplement 1. The Generic Letter recognizes that it is not practicable to test all valves and Supplement 1 allows test results from one valve to be applied to a similar valve. Therefore, we intend to satisfy the intent of the Generic Letter with respect to differential pressure testing using the concept of grouping and plant specific test data. The NRC has recently provided inspectors direction for determining the sample size for differential pressure testing of similar MOVs in the NRC internal memorandum dated April 30, 1993, Guidance For Inspections Of Programs In Response To Generic Letter 89-10. The inspection guidance establishes the benchmark sample size for testing to be nominally 30% (no less than two MOVs) of the group.
090030 9312130186 931203 PDR ADOCK ** 05000280
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VIRGINIA POWER GROUPING CRITERIA Groups have been determined by selecting similar valves that are used in the same application. Valve similarity is defined by the valve manufacturer, type, model, size and manufacturers' drawing number. This division results in the smallest group size and ensures consistent valve design, material, manufacturing processes and tolerances. The application is defined by the system condition and configuration. In situations where a valve is used in both high and low differential pressure systems, using the test results from the valve in the high pressure system may bound the low pressure application. (Although there are similarities in groups between North Anna and Surry Power stations, no credit will be taken for test results between stations.)
The above criteria result in a very conservative selection of valves for each group. For North Anna Power Station, this approach divides the total number of safety related MOVs (249 valves) from 1 O manufacturers into 41 groups. For Surry Power Station, this approach divides the total number of safety related MOVs (190 valves) from 1 O manufacturers into 37 groups. Less restrictive criteria would result in fewer groups composed of more valves.
The number of valves in each group to be tested follows the NRC inspection guidance by testing a nominal 30% of the valves in a group and at least two valves in groups containing three or more valves. However, for groups containing only two valves, one valve will normally be tested. The test candidates within a group are chosen based on a prioritization scheme that considers testing availability, prior completed testing and safety significance of the MOV. The candidate selection process will result in the differential pressure testing of 52% of the testable valves in the program at North Anna and 58% of the testable valves in the program at Surry.
For gate and globe type valves, differential pressure testing will be performed using diagnostic equipment to the maximum extent possible to confirm the methodology used to determine the valves' thrust requirement is conservative and bounds expected operation.
Butterfly valves have inherent differences in valve characteristics, power transmission, and the actuator control scheme. Because of these differences, analytical confirmation of the torque requirements of butterfly valves should be sufficient. This position, though corroborated by the ongoing testing through EPRI, has not yet been accepted by the NRC. Consequently, uninstrumented differential pressure and flow testing will be performed on selected butterfly valves using the above grouping methodology.
Plug valves share many of the same characteristics as butterfly valves, the most significant being a primary torque controlled device.
As such, uninstrumented differential pressure testing will be performed where practicable on selected plug valves using the above grouping methodology.
CONCLUSION Dynamic testing in conjunction with 100% static testing will provide the confidence that the valves in the groups are not susceptible to a common mode failure due to a design deficiency in application or uncertainties in the industry sizing equations. Additionally, the dynamically tested valves will represent a significant percentage of valves and will conservatively envelope the spectrum of all valves with regard to age, wear, and refurbishment. This will provide the confidence that the MOVs are not experiencing systematic failures.
Currently implemented engineering, maintenance and testing programs at Virginia Power have resulted in an increase in the reliability of the MOVs at both North Anna and Surry Power Stations. Safety related MOV failures reported to the Nuclear Plant Reliability Data System (NPRDS) have decreased from 8% in 1989 to less than 1 % in 1992 at North Anna and have decreased from 10% to 2% at Surry in the same time frame. Testing utilizing the above grouping criteria provides additional assurance that the measures to verify and validate valve design basis information and reliability have yielded results commensurate with the intent of Generic Letter 89-10.
If you have any questions or require additional information, please contact us.
Very truly yours,
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W. L Stewart Senior Vice President - Nuclear cc:
U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, N.W.
Suite 2900 Atlanta, Georgia 30323 Mr. R. D. McWhorter NRC Resident Inspector North Anna Power Station Mr. M. W. Branch NRC Senior Resident Inspector Surry Power Station
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COUNTY OF HENRICO
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The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by W. L. Stewart who is Senior Vice President -
Nuclear, of Virginia Electric and Power Company. He is duly authorized to execute and file the foregoing document in behalf of that Company, and the statements in the document are true to the best of his knowledge and belief.
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,a Acknowledged before me this 3 ~ day of y c~ an li~v, 19 93.
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