RIS 2000-12, Resolution of Generic Safety Issue B-55, Improved Reliability of Target Rock Safety Relief Valves
| ML003726865 | |
| Person / Time | |
|---|---|
| Issue date: | 08/07/2000 |
| From: | Matthews D Division of Regulatory Improvement Programs |
| To: | |
| Hammer C, NRR/DE, 415-2791 | |
| References | |
| TAC MA8606 RIS-00-012 | |
| Download: ML003726865 (4) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001 August 7, 2000
NRC REGULATORY ISSUE SUMMARY 2000-12 RESOLUTION OF GENERIC SAFETY ISSUE B-55, IMPROVED
RELIABILITY OF TARGET ROCK SAFETY RELIEF VALVES
ADDRESSEES
All holders of operating licenses for nuclear power reactors, except those licensees who have permanently ceased operations and have certified that fuel has been permanently removed from the reactor vessel.
INTENT
The U.S. Nuclear Regulatory Commission (NRC) is issuing this regulatory issue summary (RIS)
to notify addressees about the staffs resolution of Generic Safety Issue (GSI) B-55, Improved Reliability of Target Rock Safety Relief Valves." This RIS does not transmit any new requirements or staff positions. No specific action or written response is required.
BACKGROUND INFORMATION
Target Rock safety relief valves (SRVs) are currently installed in the main steam systems of
22 boiling-water reactors (BWRs). There have been several occurrences of improper operation of these SRVs both in spuriously opening and blowing down the reactor coolant and in opening at pressures significantly above technical specification requirements. There are two different designs of Target Rock SRVs. The earlier design is the three-stage SRV, which has had a history of spuriously opening and failing to reseat. This behavior was exhibited during several events which mostly occurred in the 1970s. The later design is the two-stage SRV,
which is a modification of the three-stage SRV and was designed to eliminate the spurious opening and blowing down problem. Currently, there are 11 BWRs that use three-stage SRVs, and 11 BWRs that use two-stage SRVs.
GSI B-55 was prioritized by the NRC staff as a "medium" priority issue on the basis of concerns about the three-stage SRVs. Beginning in 1978, two-stage SRVs were installed in several BWRs and during operation and surveillance testing, these two-stage SRVs had problems with opening at pressures exceeding the technical specification limits. As a result, the staff also included this upward setpoint drift problem in GSI B-55 for resolution.
SUMMARY OF ISSUE
The BWR Owners Group (BWROG), General Electric Company (GE), and the individual licensees undertook several actions to improve the performance of three-stage and two-stage SRVs. For the three-stage SRVs, licensees began implementing GE Service Information Letter (SIL) 196, Supplement 3, which recommended increasing the SRV setpoints to raise the simmer margin between the normal reactor pressure and the SRV setpoints. Licensees also began implementing more frequent maintenance and testing of the three-stage valves. These activities were aimed at reducing the three-stage pilot valve seat leakage and have been shown to be effective through successful operating experience over many years. For the two-stage SRVs, the primary cause of the upward setpoint drift problem was determined to be corrosion bonding of the pilot valve disk to its seat. To reduce or counteract the corrosion bonding, several design improvements were developed and implemented, and three different modifications were ultimately found to significantly improve performance. These three modifications are (1) the installation of ion beam implanted platinum pilot valve disks, (2) the installation of Stellite 21 pilot valve disks, and (3) the installation of additional pressure actuation switches. The ion beam implanted platinum and Stellite 21 pilot valve disks have improved the performance of the two-stage SRVs by reducing the corrosion bonding of the pilot valve disks to their seats. Additional pressure actuation switches counteract the effects of corrosion bonding by actuating the SRVs at the proper setpoints with external air power.
As a result of the actions that have been taken by BWROG and the individual BWR licensees to improve the performance of Target Rock SRVs, the staff has closed GSI B-55. The issue closeout is documented in a memorandum from S.J. Collins, Director, NRC Office of Nuclear Reactor Regulation to W.D. Travers, NRC Executive Director for Operations, dated December 17, 1999, which may be found in the NRC Agencywide Documents Access and Management System (ADAMS) under Accession Number ML993620214. In summary, the staff determined that the BWROG and the licensees have significantly improved the performance of the three-stage and two-stage Target Rock SRVs and that they are continuing to evaluate and improve the performance of the SRVs, as necessary, with sufficient resources. Therefore, the staff found that no new requirements were necessary as a result of this generic issue. If, in the future, the staff finds that actions need to be taken to improve the performance of these SRVs, the existing quality assurance, maintenance rule, and codes and standards regulations (i.e.,
10 CFR Part 50, Appendix B; 10 CFR 50.65; and 10 CFR 50.55a) provide the staff with regulatory mechanisms for pursuing additional improvements, if needed, on a plant-specific basis.
Backfit Discussion
This RIS requests no action or written response. Consequently, the staff did not perform a backfit analysis.
Federal Register Notification
A notice of opportunity for public comment was not published in the Federal Register because this RIS is informational, and the public was afforded numerous opportunities to comment in meetings with the BWR Owners Group as the matter was being studied, and at the NRC staffs presentation to the Advisory Committee on Reactor Safeguards on October 1, 1999, on the proposed resolution of GSI B-55. If there are any questions about this matter, please contact the person listed below or the appropriate Office of Nuclear Reactor Regulation project manager for a specific nuclear power plant.
/RA/Charles E. Ader FOR
David B. Matthews, Director Division of Regulatory Improvement Programs Office of Nuclear Reactor Regulation Attachment: List of Recently Issued NRC Regulatory Issue Summaries Technical contact: Gary Hammer, NRR
301-415-2791 E-mail: cgh@nrc.gov If there are any questions about this matter, please contact the person listed below or the appropriate Office of Nuclear Reactor Regulation project manager for a specific nuclear power plant.
/RA/Charles E. Ader FOR
David B. Matthews, Director Division of Regulatory Improvement Programs Office of Nuclear Reactor Regulation Attachment: List of Recently Issued NRC Regulatory Issue Summaries Technical contact: Gary Hammer, NRR
301-415-2791 E-mail: cgh@nrc.gov Distribution: EMEB RF JShapaker FCherny HVandermolen PUBLIC REXB r/f DOCUMENT NAME: C:\Accession No. ML003726865.wpd
- See previous concurrence INDICATE IN BOX: C=COPY W/O ATTACHMENT/ENCLOSURE, E=COPY W/ATT/ENCL, N=NO COPY
OFFICE EMEB:DE C TECH:ED N EMEB:DE C EMEB:DE C RES:DSARE DD:DE D:DE
NAME GHammer * BCalure * DTerao * EImbro * FEltawila* RWessman* JStrosnider*
DATE 5 / 25 /00 5 / 18 /00 5 / 26 /00 6 / 9 /00 6/14/00 6/20/00 6/21/00
OFFICE ADPT OGC REXB:DRIP D:DRIP
NAME BSheron* BPoole* LMarsh* DMatthews DATE 6/22/00 8/1/00 8/2 /00 8/ 7 /00
OFFICIAL RECORD COPY
Attachment LIST OF RECENTLY ISSUED
NRC REGULATORY ISSUE SUMMARIES
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Regulatory Issue Date of Summary No. Subject Issuance Issued to
_____________________________________________________________________________________
2000-11 NRC Emergency 6/30/2000 All holders of operating licenses Telecommunications System for nuclear power reactors
2000-10 Technical Information of Facilitate 6/30/2000 All NRC licensees Public Access to the U.S. NRC
Agencywide Documents Access and Management System (ADAMS)
2000-09 Standard Review Plan for 06/26/2000 All material licensees regulated in Licensee Requests to Extend the accordance with 10 CFR Parts 30,
Time Periods Established for 40, and 70
Initiation of Decommissioning Activities
2000-08 Voluntary Submission of 03/29/2000 All holders of OLs for nuclear Performance Indicator Data reactors, except for those licensees who have permanently ceased operations and have certified that fuel has been permanently removed from the reactor vessel
2000-07 Use of Risk-Informed 03/28/2000 All holders of OLs for nuclear Decisionmaking in License reactors, except for those Amendment Reviews licensees who have permanently ceased operations and have certified that fuel has been permanently removed from the reactor vessel
2000-06 Consolidated Line Item 03/20/2000 All holders of OLs for nuclear Improvement Process for Adopting reactors, except for those Standard Technical Specifications licensees who have permanently Changes for Power Reactors ceased operations and have certified that fuel has been permanently removed from the reactor vessel
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OL = Operating License CP = Construction Permit