ML20216C228
| ML20216C228 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 04/06/1998 |
| From: | Feigenbaum T NORTH ATLANTIC ENERGY SERVICE CORP. (NAESCO) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| AR#-98002647, GL-96-05, GL-96-5, NYN-98043, NUDOCS 9804140366 | |
| Download: ML20216C228 (7) | |
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a Nortli North Atlantic Energy Service Corporation P.O. Ilox 300 Atlaritic Seahroot,NiiO3874 0
(603) 474-9521 The Northeast Utilities System April 6,1998 Docket No. 50-443 NYN-98043 AR# 98002647 1
j United States Nuclear Regulatory Commission Attention: Document Control Desk Washington DC 20555-0001 Seabrook Station l
Response to NRC Safety Evaluation on Joint Owners' i
Groun - Program on Periodic Verification of Motor-Onerated Valves l
On October 30,1997, the Nuclear Regulatory Commission (NRC) issued a Safety Evaluation (SE), which within the conditions and limitations described in the SE, stated that the Staff l
considers the Joint Owners' Group (JOG) Program on MOV Periodic Verification an acceptable l
industry-wide response to Generic Letter (GL) 96-05. The NRC requested that the participating JOG utilities provide notification to the NRC of their plans to implement the JOG Program as i
described in Revision 2 of the Topical Report and to provide the NRC with justification for any deviations from the JOG Program.
This letter provides North Atlantic Energy Service Corporation's (North Atlantic) commitment i
to the JOG Program. North Atlantic plans to continue participating in the JOG MOV-Periodic Verification Program as a member of the Westinghouse Owners Group (WOG) and to implement the program elements described in Topical Report MPR-1807, Revision 2.
t in addition, the NRC requested that utilities update their commitment to the previous JOG 2
l Program identified in their response to Generic Letter 96-05. The update should include the following:
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Safety Evaluation on Joint Owner's Group Program on Periodic Verification of Motor-Operated Valves Described in Topical Report dated 10/30/97 (Topical Report MPR-1807, Revision 2).
2 Generic Letter 96-05," Periodic Verification of Design-Basis Capability of Safety Related Motor-Operated Valves", dated 9/18/96.
g 9804140366 980406 PDR ADOCK 05000443 P
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U.S. Nuclear Regulatory Commission NYN-98043/ Pag: 2 1
A.
A description of the MOV risk ranking methodology.
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A description of MOV periodic testing for valves not covered by the JOG program.
C.
A description of commitments made during the completion of the Generic Letter q
89-10 MOV Program.
The requested information is provided in the enclosure to this letter.
Should you have any questions regarding this letter, please contact Mr. Terry L. liarpster, Director of Licensing Services, at (603) 773-7765.
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Very truly yours, NORTli ATLANTIC ENERGY SERVICE CORP.
g M sg de L
Ted C. Feigenbaum '
Executive Vice President and Chief Nuclear Officer cc:
H. J. Miller, NRC Region I Administrator C. W. Smith, NRC Project Manager, Project Directorate 1-3 R. K. Lorson, NRC Senior Resident Inspector, Seabrook Station Thomas H. Essig U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Thomas G. Scarbrough U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 i
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ENCLOSURE TO NYN-98043 4
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1 A.
b'prth Atlantic Risk Ranking Methodology In support of periodic testing of MOVs, North Atlantic conducted an initial evaluation of the risk significance of each MOV.
This initial MOV risk ranking was developed based on a methodology that is similar to the BWR Owners Group MOV Risk Ranking Methodology; j
reference NEDC-32264-A," Application of Probabilistic Safety Assessment to Generic Letter 89-
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10 Implementation." The intent of the risk significance review we.s to support prioritization of Generic Letter 89-10 testing. This review focused upon two items relative to MOV performance in light of Generic Letter 89-10 concerns:
- 1. MOVs that are not required to be repositioned, and
- 2. MOVs that must actuate (open/close) to perform their safety function.
f With respect to the first item, a review was conducted of each MOV included in the Seabrook 89-10 program. Those MOVs which were included within the MOV program solely on the basis
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of the position changeable issue were determined to be of low risk significance. This is consistent with the work conducted by Brookhaven National Labs for the NRC in regard to PWRs.
With respect to the remaining scope of MOVs (i.e., item 2), a risk significance evaluation was conducted. This evaluation consisted of a review of each MOV, its relevant safety function (s) and those of the system (s) it supports. In addition, design and operating conditions were reviewed and those MOVs modeled in the Seabrook Station Probabilistic Safety Study (PRA) were identified.
For those MOVs not modeled in the PRA, an assessment was made as to the appropriateness of the MOV not being quantified within the PRA given the Generic Letter 89-10 concerns. These MOVs are categorized as low risk significance. It was determined, after this review, that changes to the PRA to incorporate additional MOVs were not necessary.
For those MOVs modeled in the PRA, an assessment was made as to the appropriateness of the existing modeling of these MOVs. Issues addressed by this review included:
potential failure modes versus the failure modes modeled in the PRA, failure rates given Generic Letter 89-10 concerns, e
valve design differential pressure, e
inter versus intrasystem common cause issues, j
e impacts on initiating event modeling, e
model completeness, e
4 cxternal events, and containment perfbrmance
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Based upon the above review, the PRA was requantified to obtain an MOV risk ranking. This
. quantitative risk ranking was subsequently adjusted to address additional issues, including shutdown risk (qualitative assessment using the Seabrook Shutdown PRA Model).
To support the Generic Letter 96-05 risk ranking, the initial risk ranking was revisited and a new risk based prioritization of MOVs was performed. The MOVs modeled in the Seabrook PRA were ranked using the Fussel-Vesely importance (FVI) measure. FVI is the fraction of the core damage frequency (CDF) sequences in which a given component " participates" (i.e., in which its failure is necessary for the sequence to go to MELT). Four categories are used, as follows:
lilGH FVi > 0.01
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MEDIUM FVi > 0.001 LOW FVI > 0.0001 j
NONE FV1 < 0.0001 h addition to FVI, the risk achievement worth (RAW) measure is used to modify the groupings.
RAW is the fractional increase in CDF given the component is out of service (or failed). For components with a RAW of greater than 10 (i.e., their failure would increase the CDF by a factor of 10), their Risk Rank is increased by one category (e.g., a component with a " LOW" FVI and a RAW >10 would be assigned a ranking " MEDIUM"). This use of RAW effectively accounts for uncertainty in the component reliability. The FVI ranking is based on nominal reliability; the RAW measure is based on the extreme low reliability, which is not realistic, but does address the upper bound failure rate case. Thus, the FV1 is used as the primary measure; RAW is the secondary measure.
The risk ranking scheme is conservative relative to the previous ranking because of the use of RAW. The MOVs have been ranked using the generic MOV demand failure rate (4.3E-03) for all MOVs.
Since all of the MOVs have been setup using Generic Letter 89-10 criteria, the generic demand failure rate is considered appropriate.
In some cases, the FVI measure may also include " transfer open/ closed during operation" failure mode in addition to " fail to open/close on demand". While the transfer failure mode is not applicable to the MOV program, it is included conservatively in the FVI results for convenience of calculation. In general, this conservatism is not important quantitatively.
As was the case in the previous evaluation, for MOVs not modeled in the PRA, an assessment was made as to the appropriateness of the MOV not being quantified given the Generic Letter 89-10 concerns. These MOVs are categorized as low risk significance. It was determined after this review, that changes to the PRA to incorporate additional MOVs into the PRA were not necessary.
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4 The risk ranking of GL 96-05 MOVs was assessed using the Expert Panel Concept that was initiatdd for the Maintenance Rule. The overall risk ranking for program MOVs was reviewed.
This review was part of the periodic assessment pursuant to Generic Letter 96-05, Periodic Verification of Design Capability of Safety Related Motor Operated Valves. The expert panel reviewed the risk based prioritization and factored in both maintenance and operational insights to establish a final risk based prioritization. The expert panel recommendations will be factored into determining the final MOV risk ranking.
H.
MOV Periodic Verification Outside the Scope of the JOG Proerm Safety-related motor-operated valve types not covered by the JOG MOV Periodic Verification Program will be tested consistent with Generic Letter 89-10 periodic verification requirements.
C.
Additional Generic Letter 89-10 Commitments North Atlantic committed to dynamically test an additional fifteen Generic Letter 89-10, rising stem, motor operated valves during refueling outages OR-05 and OR-06. The OR-05 dynamic test results and other historical dynamic test results will be used to substantiate the stem friction coefficient and rate ofloading factors used in Seabrook's MOV Program.
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The following table lists the additional fifteen MOVs that Seabrook committed to dynamically test in refueling outages OR-05 and OR-06 to validate a stem friction coefficient and rate of loading factions. The table lists the outage in which the valve was or will be tested.
MOV Stem Friction Coefficient Verification Program & Schedule Valve Stroke Direction Train Previous Scheduled Friction Testing Testing CS-V142 (1)
Close A
OR-05 Complete CS-V143 (1)
Close B
OR-05 Complete FW-V163 Open A
OR-05 Complete FW-V346 Open & Close A
OR-05 Complete Rll-FCV-611 Open & Close B
OR-06 Ril-V14 Close A
OR-05 Complete Ril-V21 Open B
OR-06 Ril-V22 Open A
OR-05 Complete Rii-V26 Open B
OR-06 Ril-V32 Open B
OR-06 RIl-V35 Open A
OR-05 Complete Ril-V36 Open B
OR-06 Ril-V70 Open A
OR-05 Complete SI-V112 Close A
OR-05 Complete l
SI-V139 Open B
OR-05 Complete Note 1: CS-V142 and CS-V143 are Seabrook's assigned valves for the JOG Periodic Verification Program and will be tested again in OR-06.
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