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Information Notice No. 83-26: Failure of Safety/Relief Valve Discharge Line Vacuum Breakers
SSINS No.: 6835 IN 83-26 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 May 3, 1983 Information Notice No. 83-26: FAILURE OF SAFETY/RELIEF VALVE DISCHARGE LINE VACUUM BREAKERS Addressees: All nuclear power reactor facilities holding an operating license (OL) or construction permit (CP). Purpose: This information notice is provided as an early notification of a potentially significant problem pertaining to recently installed vacuum breakers on safety/ relief discharge lines on boiling water reactors. It is expected that the recipients will review the information for applicability to their facilities. No specific action or response is required at this time. Description of Circumstances: Browns Ferry Unit 1 Event Following a reactor scram on February 5, 1983 at Browns Ferry Unit 1, three safety relief valves (SRVs), each with a capacity of approximately 865,000 lb/hr, cycled to control pressure. One SRV stayed partially open, after which, unidentified leakage in the drywell increased to greater than 5 gpm. The primary system was depressurized at a slow rate and a cold shutdown was initiated. During the cooldown the unidentified leak was traced to a vacuum breaker (10" GPE check valve) on the discharge line of the leaking SRV. The vacuum breaker hinge pin appeared to be damaged, causing the vacuum breaker to stick partially open. The licensee replaced the solenoid and pilot cartridge on the SRV and replaced the leaking vacuum breaker. The licensee then inspected all the SRV vacuum breakers and found that four others were damaged and these were also replaced. All three SRVs that actuated following the scram were scheduled to be cycled during the forthcoming startup at 250 psig to ensure proper operation. On February 8, 1983 with Unit 1 heating up at 178 psig and prior to the planned testing of the SRVs, the previously failed SRV again started to leak (Information Notice No. 83-22). The drywell unidentified leakage again increased to greater than 5 gpm. After cooling down it was discovered that the SRV discharge line vacuum breaker was again damaged. Peach Bottom Unit 2 Event During a startup on October 24, 1982 with the reactor pressure at 832 psig, relief valve 71J with a capacity of approximately 830,000 lb/hr opened. The 8303040028 . IN 83-26 May 3, 1983 Page 2 of 2 resulting vessel level swell tripped the operating reactor feed pump on a high level signal and the unit subsequently scrammed on a low level signal because the loss of feedwater. The relief valve remained open until the reactor pressure dropped to 80 psig. During an inspection of the relief valve discharge line piping it was discovered that the vacuum breakers (8" Anderson Greenwood check valves) for this valve and a second relief valve that was actuated during the transient were damaged. Both vacuum breakers showed some binding on the hinge pin such that the normal spring pressure was insufficient to close them. The two vacuum breakers were replaced. The 10" vacuum breakers on the SRV discharge lines at Browns Ferry Unit 1 were installed during the previous refueling outage for relief valve second-pop transient protection. The 8" vacuum breakers on the relief valve discharge lines at Peach Bottom Unit 2 were installed in July 1980. These vacuum breakers were also installed for relief valve second-pop transient protection. This transient in the relief valve discharge line is postulated to result from a failure of the previously installed small vacuum breakers to quickly equalize pressure in the relief valve discharge lines during the closing and rapid reopening (typically at 15 seconds) of the relief valves. Some recently licensed plants are using the low-low set point relief function in lieu of vacuum breakers for second-pop protection. No written response to this information notice is required. If you need additional information regarding this matter, please contact the appropriate NRC Regional Office or this office. Edward L. Jordan, Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Contact: P. R. Farron (301) 492-4766 Attachment: List of Recently Issued Information Notices .
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