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Information Notice No. 83-70: Vibration-Induced Valve Failures
SSINS No.: 6835 IN 83-70 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 October 25, 1983 Information Notice No. 83-70: VIBRATION-INDUCED VALVE FAILURES Addressees: All nuclear reactor facilities holding an operating license (OL) or construction permit (CP). Purpose: This information notice is provided as a notification of events that resulted in valve failures and system inoperability as a result of normal operational vibration. It is expected that recipients will review the information for applicability to their facilities. No specific action or response is required at this time. Description of Circumstances: A review of recent Construction Deficiency Reports and License Event Reports indicates that there have been a number of vibration-induced valve failures. Discussions with General Electric indicate that some of these failures may be generic to a specific valve type. The following is a brief account of some of these events. On October 22, 1982, at Quad Cities Station Unit 2, it was decided to cycle the 2A recirculation pump discharge valve during the current maintenance outage. The valve had exhibited problems in opening and closing in the past and the licensee wanted to verify proper operation while the reactor was shut down. When the valve was given a close signal, it would not fully close. An inspection of the valve in the Unit 2 drywell revealed that two of the four valve yoke-to-bonnet holddown studs and nuts were missing and the valve motor operator had pulled the yoke away from the valve. Further investigation revealed that the valve stem was bent and would have to be replaced. Apparently the valve studs and nuts had loosened and fallen out from normal system vibration. On June 21, 1983, at Quad Cities Station Unit 1, the maintenance department was investigating a position indication problem on a suppression pool return valve in the B loop of the residual heat removal (RHR) system. An inspection of the valve revealed that two of the four bolts that hold the valve yoke to the bonnet had vibrated loose. This allowed the yoke to separate from the bonnet causing the valve stem to bind excessively and finally bend. The B loop of the RHR containment cooling system was declared inoperable until the valve could be manually opened. 8308310030 . IN 83-70 October 25, 1983 Page 2 of 3 On January 14, 1983, at Browns Ferry Station Unit 3, during routine testing of the RHR valves, a low pressure coolant injection (LPCI) valve failed to operate properly. An inspection of the valve revealed that the stud and nut combination that retains the yoke collar device had loosened. This allowed the motor operator to turn (with the yoke) around the valve stem causing motor and valve damage. An inspection of other RHR and LPCI valves indicated, that 50% of these valves had loose collar devices. The loosened devices were attributed to vibrational loading of the yoke-to-bonnet interface. The affected valves are gate valves manufactured by the Walworth Company. Locking devices were installed on the studs and nuts of the collar device to prevent future instances of vibrational loosening. At Shoreham Station Unit 1, during valve testing, it was discovered that a stem clamp was missing on an RHR globe valve. Although this was considered an isolated event, the appropriate startup procedure was revised to include a check to ensure that each stem clamp was properly oriented on the stem, with the clamp key and setscrew properly tightened. Following this event, another globe valve failed to stroke while being tested. The valve stem clamp setscrew loosened, allowing the clamp to slide along the stem and the clamp key to fall from its keyway. This allowed the motor operator to rotate the stem without moving the valve disc. It is believed that the setscrew in the stem clamp loosened because of normal system vibration. Stone & Webster performed a review of the safety-related valves at Shoreham and has determined that only globe valves manufactured by the Anchor Darling Co. are susceptible to vibrational failures of this type. Following these events at Shoreham Station, General Electric notified the NRC that similar failures of this type were experienced in the high pressure core spray (HPCS) system at Zimmer Station. The valves were Anchor Darling globe valves specified by General Electric for HPCS systems in the test return line of all BWR/5s and BWR/6s. To preclude the possibility of future failures, both Anchor Darling and General Electric have provided recommendations on how to secure the stem clamp setscrews. The valve failure at Shoreham Station was especially significant because the remote valve position indication was from limit switches on the motor operator, so the valve appeared to be opening and closing normally when in fact the valve had not moved. Station personnel should be aware of the potential for vibrational loosening of valve components and may want to emphasize this aspect in valve preventive maintenance. Other recently issued IE generic communications addressing valve locking devices include, Information Notice No. 81-33, "Locking Devices Inadequately Installed on Main Steam Isolation Valves," IE Circular No. 80-04, "Securing of Threaded Locking Devices on Safety-Related Equipment," and IE Circular No. 79-04 "Loose Locking Nut on Limitorque Valve Operators." . IN 83-70 October 25, 1983 Page 3 of 3 No written response to this notice is required. If you have any questions 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: Paul R. Farron (301) 492-4766 Attachment: List of Recently Issued IE Information Notices .
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