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Information Notice No. 88-30, Supplement 1: Target Rock Two-Stage SRV Setpoint Drift Update
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 February 2, 1990 Information Notice No. 88-30, SUPPLEMENT 1: TARGET ROCK TWO-STAGE SRV SETPOINT DRIFT UPDATE Addressees: All holders of operating licenses or construction permits for nuclear power reactors. Purpose: This information notice supplement is intended to alert addressees to continuing problems associated with setpoint drift occurring in Target Rock two-stage safety/relief valves (SRVs) originally described in Information Notices (INs) 82-41, 83-39, 83-82, 86-12, and 88-30 (References 1 - 5). It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice do not constitute NRC requirements; therefore, no specific action or written response is required. Background: On July 2, 1982, at Hatch Unit 1, all 11 Target Rock two-stage SRVs failed to open at their setpoints of 1080 psig, 1090 psig, and 1100 psig. Pressure in the reactor coolant system (RCS) rose to 1180 psig before three SRVs on one steamline opened and relieved RCS pressure rapidly. This incident focused concern on a problem that was beginning to be seen in those SRVs called "setpoint drift." The Georgia Power Company, the General Electric Company (GE), and the Target Rock Company initiated a study of the cause of the event at Hatch Unit 1. Other utilities that had installed two-stage Target Rock SRVs joined Georgia Power in an owners' group to look at the nature of the problem and its solutions. Similar problems had been observed throughout the industry, and reports of these problems indicated that the number of valves affected and the extent of the observed setpoint drift had been increasing. The problem was ultimately identified as one or both of two situations: (1) binding in the labyrinth seal area caused by tolerance buildup during manufacturing, or (2) disc-to-seat bonding caused by oxides of the disc and seat material forming a continuous film and inhibiting disc movement. 9001290102 . IN 88-30, Supplement 1 February 2, 1990 Page 2 of 3 To address these problems, additional maintenance was performed to refurbish valves and to replace parts found to be out of tolerance in the labyrinth seal area. This repair proved to be effective in some cases; however, problems caused by disc-to-seat bonding continued. A material, PH13-8 Mo, whose oxide would not form a continuous film with the oxide of the seat material, was chosen for new discs. Trial tests of valve performance, after installing the new discs on about 50 percent of the valves at a plant, has been conducted. Test Results: Initial results in 1987 and 1988, at Hatch 1, Brunswick 2, and Hatch 2 showed that the performance of PH13-8 Mo had a marked improvement over the performance of Stellite discs. However, in 1988, Fermi 2 results were less optimistic. Plant Year Disc Material Deviation Range Hatch 1 1987 Stellite -2.50 - +6.11% PH13-8 Mo -1.65 - +1.94% Brunswick 2 1988 Stellite -1.40 - +9.30% PH13-8 Mo -0.10 - +4.00% Hatch 2 1988 Stellite +0.20 - +4.10% PH13-8 Mo -1.10 - +2.90% Fermi 2 1988 PH13-8 Mo -0.20 - +4.28% Subsequently, the NRC was informed (in Licensee Event Report 50/366-89/007) that valves from Hatch 2 were tested, with the following results: Valve Disc Setpoint As-found Deviation No Material (psig) SP (psig) (percent) F013A PH13-8 Mo 1100 1077 - 2.09 F013B Stellite 1090 1199 +10.00 F013C PH13-8 Mo 1090 1129 + 3.58 F013D Stellite 1100 1115 + 1.36 F013E Stellite 1110 1135 + 2.25 FO13F Stellite 1090 1103 + 1.19 F013G Stellite 1090 1150 + 5.50 F013H PH13-8 Mo 1110 1227 +10.54 F013K PH13-8 Mo 1100 1201 + 9.18 F013L PH13-8 Mo 1110 1137 + 2.43 F013M Stellite 1100 1118 + 1.64 The range for new discs is -2.09 percent to +10.54 percent. Of particular interest are valves H and K. This range of deviation reflects a magnitude of bonding that had not been reported in valves with new discs before. On November 1, 1989, the licensee for the Brunswick 2 plant reported by the Emergency Notification System that valve number F013L lifted 10.4 percent high at 1242 psig during testing. The new disc had been installed on this valve. . IN 88-30, Supplement 1 February 2, 1990 Page 3 of 3 The owners' group, GE, and Target Rock are evaluating this information and developing plans about future actions to resolve the disc-to-seat bonding. The NRC continues to monitor the issue. This information notice requires no specific action or written response. If you have any questions about this matter, please contact the technical contact listed below or the appropriate NRR project manager. Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical Contact: Mary S. Wegner, AEOD (301) 492-7818 References 1. Information Notice No. 82-41, "Failure of Safety/Relief Valves to Open at a BWR" 2. Information Notice No. 83-39, "Failure of Safety/Relief Valves to Open at a BWR - Interim Report" 3. Information Notice No. 83-82, "Failure of Safety/Relief Valves to Open at a BWR - Final Report" 4. Information Notice No. 86-12, "Target Rock Two-Stage SRV Setpoint Drift" 5. Information Notice No. 88-30, "Target Rock Two-Stage SRV Setpoint Drift Update" Attachment: List of Recently Issued NRC Information Notices .
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