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Information Notice No. 83-82: Failure of Safety/Relief Valves to Open at BWR - Final Report
SSINS No.: 6835 IN 83-82 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 December 20, 1983 Information Notice No. 83-82: FAILURE OF SAFETY/RELIEF VALVES TO OPEN AT BWR - FINAL REPORT Addressees: All nuclear power reactor facilities holding an operating license (OL) or construction permit (CP). Purpose: This information is being provided as a final supplement and update to Information Notices 82-41 and 83-39. An update is provided on meetings, testing results, conclusions, and courses for future action involving the Target Rock two-stage safety/relief valves (SRVs). No specific action or response is required. Description of Circumstance: Synopsis of Triggering Event: On July 3, 1982, Georgia Power Company's Plant Hatch was operating at 100% power when a spurious high-pressure signal caused a reactor scram. A Group 1 isolation occurred, high pressure coolant injection (HPCI) and reactor core isolation cooling (RCIC) turbines auto-started and injected, and the recirculation pumps tripped. HPCI, RCIC, and the feedwater pump turbines tripped at the high water level setpoint. Repressurization continued beyond the high-pressure scram setpoint without relief valve actuation until the system pressure reached 1180 psig, at which point three of the eleven SRVs actuated, rapidly relieving pressure. Setpoints for the eleven SRVs were 1080, 1090, and 1100 psig. Synopsis of Industry Response to the Event: Georgia Power and a number of other utilities using the two-stage Target Rock SRVs formed an owners' group and, together with General Electric and the Target Rock Company, began a testing program designed to learn the cause of the Hatch event and the cause for the apparent setpoint drift upward in bench testing of SRVs from other plants. Test parameters and initial results are given in Information Notices 82-41 and 83-39. Recent Additional Information: A total of 34 valves were subjected to screening tests, establishing a data base from which it was concluded that labyrinth seal friction and disc-to-seat sticking were the causes for the setpoint drift phenomenon. A characteristic pop "signature" was plotted for each event. The labyrinth seal problem was found to have been caused by lower than design tolerance clearances. This may have been an "as-built" condition or the result of 8311010035 . IN 83-82 December 20, 1983 Page 2 of 2 creep during operation. The disc-to-seat sticking problem resulted from corrosion of the stellite material. The magnitude of the Hatch problem was likely to have been related to an earlier event in which there was an intrusion into the primary system of a nonionic chlorinated hydrocarbon which decomposed under reactor conditions and caused a conductivity of 21 micromhos per centimeter and a pH of 4.6. The stellite material is susceptible to this type of corrosion. Based on discussions with General Electric Company representatives we understand that a program of revised maintenance procedures intended to minimize upward setpoint drift are in preparation for potential issuance as a Service Information Letter. If you have any question regarding this matter, please contact the Regional Administrator of the appropriate NRC Regional Office, or this office. Edward L. Jordan Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Technical Contact: Mary S. Wegner, IE (301) 492-4511 Attachment: List of Recently Issued IE Information Notices .
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