ML20137B689
| ML20137B689 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 03/17/1997 |
| From: | Sorensen J NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-96-05, GL-96-5, NUDOCS 9703240037 | |
| Download: ML20137B689 (5) | |
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Northern States Power Company Prairie Island Nuclear Generating Plant 1717 Wakonade Dr. East Welch, Minnesota $5089 March 17,1997 Generic Letter 96-05 U S Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Response to Generic Letter 96-05, Periodic Verification of Desian-Basis Capability of Safety-Related Motor-Operated Valves This letter is provided in response to Generic Letter 96-05, " Periodic Verification of Design-Basis Capability of Safety-Related Motor-Operated Valves." The Generic Letter requests a written summary of the motor-operated valve periodic verification program established in accordance with the Generic Letter requested actions, within 180 days of the date of the Generic Letter. The requested summary of the Prairie Island motor-operated valve periodic verification program is attached.
In the attachment to this letter we have made new Nuclear Regulatory Commission commitments, indicated as the statements in italics. Please contact Jack Leveille (612-388-1121) if you have any questions related to the Prairie Island response to Generic Letter 96-05.
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A Joel P Sorensen Plant Manager i
Prairie Island Nuclear Generating Plant
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< USNRC NORTHERN STATES POWER COMPANY March 17,1997 Page 2 c: Regional Administrator - Region Ill, NRC
- Senior Resident inspector, NRC NRR Project Manager, NRC
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Attachment:
Generic Letter 96-05180 Day Response i
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GL9605R2. DOC
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Attachment Generic Letter 96-05180 Day Response 4
4 NRC Generic Letter 96-05 requested addressees of the generic letter to establish a program, or to ensure the effectiveness of its current program, to verify on a periodic basis that safety-related motor-operated valves (MOVs) continue to be capable of performing their safety-s related functions within the current licensing basis of the facility. The program should ensure i
that changes in required performance resulting from degradation (such as those caused by 4
age) can be properly identified and accounted for, in addition, the generic letter requests that l
addressees that have developed periodic verification programs in response to GL 89-10 to review those programs to determine whether any changes are appropriate in light of the information in the generic letter.
3 As requested by Generic Letter 96-05, Prairie Island has evaluated its current MOV periodic j
verification program established in response to Generic Letter 89-10. Due to the availability of the recently established Joint Owners' Group (JOG) program, Prairie Island will modify its MOV i
periodic verification program to include participation in this large industry effort. Provided below is a summary of Prairie Island's 1) current MOV periodic verification program,2) modified MOV periodic verification program, and 3) schedule for transition to the modified program.
CURRENT MOV PERIODIC VERIFICATION PROGRAM i
The current program for periodic verification of the capability of safety-related MOVs to perform their safety functions consists of the following: 1) The performance of static q
testing on a three refueling cycle basis, including the performance of as found testing to programatically monitor and determine any actuator degradation and stem / stem nut lubrication degradation, and 2) Dynamic testing, when practicable and useful, to l
determine any valve aging phenomena and to monitor rate of loading. The intent of j
this testing is to verify that Prairie Island motor-operated valves will continue to operate l
when required, and to continuously evaluate the assumptions used to determine valves' settings.
d MODIFIED MOV PERIODIC VERIFICATION PROGRAM i
The current periodic verification program is to be modified as discussed below.
Implementath i of the Joint Owners' Group (JOG) Periodic Verification Proaram The JOG penodic verification program will be used for Prairie Island safety-related MOVs to provide periodic verification that the valves are capable of performing their safety functions.
The objectives of the JOG program are to 1) provide an approach for static testing of MOVs based on importance and margin,2) determine degradation related trends over a period of 4
i several years, and 3) use the acquired MOV degradation information to confirm, or if necessary to modify, the static MOV testing approach. The JOG periodic verification program is described in the report, " Joint BWR and Westinghouse Owners' Group Program on Motor-Operated Valves (MOVs) Periodic Verification," MPR-1807, Revision 0, February 1997.
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Attachmsnt March 17,1997 Page 2 In the modified MOV periodic verification program, static testing is to be performed as specified 1
by the JOG periodic verification program based on MOV risk prioritization and MOV j
performance margin. The current Prairie Island MOV periodic verification program does not i
use risk and margin to determine test frequency, it simply uses the 3 refueling cycle frequency that resulted from the Generic Letter 89-10 effort. Prairie Island willmodifyits pedodic verification program to include risk and margin criteria for testing. Consistent with the current MOV periodic verification program and the JOG periodic verification program, MOV margin is to include appropriate uncertainties and reflects margin above the included uncertainties. In i
other words, margin is not to be confused with uncertainties. The criteria for the frequency of static testing is presented in Table 1 below. This criteria includes both an increase in test frequency based upon risk and margin as well as a reduction in test frequency for lower risk, j
higher margin, valves.
Table 1 - Criteria for Static Test Frequency Risk / Margin Low Margin Medium Margin High Margin High Risk 1 Cycle 2 Cycles 3 Cycles Medium Risk 2 Cycles 4 Cycles 6 Cycles'
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Low Risk 3 Cycles 6 Cycles' 6 Cycles'
- Not to exceed 10 years.
Where:
Low Margin:
Margin < 5%
Medium Margin: 5% 5 Margin < 10%
High Margin:
10% 5 Margin This criteria for test frequency using risk and margin is discussed in greater detailin the above referenced Joint Owners' Group MPR-1807 document, and in Westinghouse Owners Group Engineering Report V-EC-1658. Rev. O, " Risk Ranking Approach for Motor-Operated Valves in Response to Generic Letter 96-05."
The above risk and margin criteria used as a basis for static test frequency are preliminary and are based on judgment and experience developed from the Generic Letter 89-10 programs.
The justification of the specific margin categories is to be confirmed in the JOG dynamic test program (and using additional dynamic testing planned by Prairie Island) The static test frequency recommendations of the JOG and, if necessary, the test results on which they are based, will be reviewed by Prairie Island and the modified Prairie Island MOV periodic verification program will be adjusted, as appropriate, based on the results of this review.
In the modified MOV periodic verification program, dynamic testing is to be performed as specified by the JOG periodic verification program. The JOG will select the valve candidates for dynamic testing based on the potential MOV degradation mechanisms and a valve mix that is representative of the different valves. The dynamic tests will be performed by utilities participating in the program with the test results provided to the JOG Steering Committee for review. The recommendations of the JOG related to dynamic testing and age related degradation and, if necessary, the test results on which they are based, will be reviewed by GL960SR2. DOC
Attachmtnt I
March 17,1997 Page 3 J
Prairie Island and the modified Prairie Island MOV periodic vedfication program will be adjusted, as appropriate, based on the results of this review.
Additional Elements of the Prairie Island MOV Periodic Verification Proaram As discussed above, dynamic testing of Prairie Island MOVs is to be performed as requested j
by the JOG, in addition to the JOG requested dynamic testing, Prairie Island will continue to perform dynamic testing, when practicable and necessary, as part of post maintenance testing activities. Dynamic testing will be performed following significant valve maintenance, such as, valve replacement or specific valve intemal work, including modifications, that could affect valve performance.
I Prairie Island may periodically perform dynamic testing of selected valves / valve types from
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which we desire to improve knowledge of their operation to better understand any aging phenomena and to better define their operating margin.
l Over the past five years Prairie Island has replaced thirty six (36) motor-operated valves within its Cooling Water System (Service Water) and one (1) in its Component Cooling System due to i
concems for aging / corrosion (over 20 % of its Generic Letter 89-10 population). Some of these valves will continue to be dynamically tested until we have assurance that the present settings continue to bound any increases in thrust requirements caused by the preconditioning effect discovered by the EPRI MOV Performance Prediction Program and to ensure that any additional aging of the valves is understood.
A comparison of Prairie Island static and dynamic testing results will continue to be used to evaluate rate of loading effects. These results will continue to be factored into the determination of the rate of loading uncertainty which is applied to those valves which can only 4
be statically tested.
I Use of as found static testing as a part of our periodic verification program to evaluate any actuator degradation and stem / stem nut lubrication degradation will continue.
SCHEDULE FOR IMPLEMENTATION OF MODIFIED PROGRAM Prairie Island will establish MOV risk and margin categorizations to support implementation of static testing at a frequency consistent with the JOG periodic verification program prior to the end of the Fall 1997 refueling outage of Unit 1. Prairie Island willperform dynamic MOV testing as requested by the JOG.
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GL960SR2. DOC l
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