ML20034F623
| ML20034F623 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 02/24/1993 |
| From: | Hebert J Maine Yankee |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| JRH-93-37, MN-93-20, NUDOCS 9303040060 | |
| Download: ML20034F623 (3) | |
Text
MaineYankee AEUABLE ELECTRICITY FOR MAINE SINCE 1972 EDISON DRtVE. AUGUSTA, MAINE 04330. (207) 622-4868 t
February 24, 1993 MN-93-20 JRH-93-37 UNITED STATES NUCLEAR REGULATORY COMMISSION Attention: Document Control Desk Washington, DC 20555
References:
(a)
License No. DPR-36 (Docket No. 50-309) l (b) USNRC Letter to MYAPCo dated January 26, 1993 - Resident Inspection Report 50-309/92-21 l
Subject:
Inspection Report 92-21: Response to Notice of Violation Associated with the Verification of an Engineering Design Review Gentlemen:
The attachment to this letter responds to the Notice of Violation contained in Reference (b).
In this attachment, we have restated the violation, provided our response, and have addressed our actions taken and planned to prevent recurrence.
Please contact us should you have any questions regarding this matter.
Very truly yours,
'O U
James R. Hebert, Manager Licensing & Engineering Support Department JVW/ jag Attachment c:
Mr. Thomas T. Martin Mr. Charles S. Marschall Mr. E. H. Trottier i
Mr. Patrick J. Dostie I
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- g if 030081 9303040060 930224 MSMW PDR ADOCK 05000309 t
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Notice of Violdion:
Diiring an inspection from November 20 through December 31, 1992, a violation of NRC
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requirements was identified. In accordance with the " General Statement of Policy and Procedure for NRC Enforcement Actions," 10CFR Part 2, Appendix C (1992), the i
violation is listed below:
A.
10CFR Part 50, Appendix B, Criterion III, states, in part, that licensees shall establish design control measures for verifying the adequacy of design reviews.
Contrary to the above, in December 1989, Maine Yankee failed to properly verify l
the adequacy of a design review of the Primary and Secondary Component Cooling Systems.
As a result, Maine Yankee failed to ensure that the plant operated with adequate loss of coolant accident heat removal capacity between December i
1989 and December 1993.
Maine Yankee Response:
Stone and Webster Engineering Corporation (SWEC) design basis flow calculations for the component cooling water systems that were performed in 1989 assumed that l
Secondary Component Cooling (SCC) flow through valve SCC-T-227 would be negligible when the valve closed in response to a Containment Spray Actuation Signal (CSAS).
I When SWEC assembled the calculation inputs during 1989, a Maine Yankee engineer reviewed the post loss of Cooling Accident (LOCA) SCC system lineup and verified that SCC-T-227 would be closed. However, the engineer overlooked the assumption that SCC-i T-227 was leak tight.
When recent maintenance activities discovered flow through SCC-T-227 in the closed position, plant startup was delayed while the SWEC SCC flow calculation was revised to include this flow. Maine Yankee calculations determined that for flows through SCC-T-227 up to about 150 gpm, flows to the Residual Heat Removal (RHR) heat exchanger would still be adequate to provide post-LOCA heat removal capacity. Since design flow through SCC-T-227 in the closed position is 65 gpm, no change to the maximum allowable service water inlet temperature was required to incorporate the actual design leak rate for the valve. Therefore, the operating limits for maximum allowable service water temperatures were adequate to ensure SCC heat removal capacity from December 1989 to December 1992 because the design leak rate for SCC-T-227 is bounded by the allowable leak rate.
However, the maintenance activities referenced above also determined that leakage l
through SCC-I-227 was initially measured at about 400 gpm and could only be improved to about 225 gpm by making external adjustments. Therefore, a bounding calculation was performed which evaluated current system conditions and, as a result, Maine Yankee conservatively reduced maximum allowable service water inlet temperatures by 20af as an interim measure to allow plant startup to proceed while formal t
calculations to change to the SWEC thermal analysis were performed.
The formal
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calculations to change the SWEC thermal analysis are complete and the results require a 4' reduction in maximum allowable service water inlet temperature based on a total leakage flow of 400 gpm to nonsafeguards components.
Operating procedure restrictions are being revised accordingly.
i Substantial margin exists between actual service water inlet temperatures and maximum allowable service water temperatures.
Maine Yankee has reviewed service water temperature history for December 1989 through December 1992 and determined that the revised allowable temperatures based on a 400 gpm leak have not been exceeded.
Therefore, we conclude that the plant has operated with sufficient SCC system heat s
removal capacity from 1989 to the present time as indicated in Section 4.2 of the inspection report, Reference (b), which is attached to the NRC Notice of Violation.
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Immediate Corrective Action and Results Achieved:
i T'he SCC-T-227 leakage was discovered on December 13, 1992, while the plant was preparing to start up.
Plant start up was delayed until engineering verified that
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SCC system capability was adequate at current service water temperatures, which' was completed on December 14, 1992, i
Corrective Action Taken to Avoid Further Violations:
The root cause of this violation was a failure to perform an adequate review of an j
assumption in an engineering analysis.
Maine Yankee is revising Procedure 17-21-5, ENGINEERING CALCULATIONS / ANALYSES to i
include additional guidance to prevent recurrence. This procedure revision should i
be completed by March 31, 1993.
In addition, the procedure revisions will be discussed at future Engineering Department meetings to assure full awareness of this issue.
i The procedure revision will include specific requirements for an engineer reviewing i
engineering calculations to ensure that key assumptions and their bases are identified and to ensure that the assumptions are reasonable.
i Full Compliance Date:
Full compliance for the measured flows through SCC-T-227 was ensured on December 14, l
1992, when engineering completed a preliminary calculation showing that SCC System capability would meet design basis requirements. The formal calculation which added 400 gpm leakage to the SWEC calculations was completed 01/08/93 and resulted in a 4*F reduction of maximum allowable service water inlet tentperature for SCC system operability.
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