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Information Notice No. 83-55: Misapplication of Valves by Throttling Beyond Design Range
SSINS No.: 6835 IN 83-55 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 August 22, 1983 Information Notice No. 83-55: MISAPPLICATION OF VALVES BY THROTTLING BEYOND DESIGN RANGE Addressees: All nuclear power facilities holding an operating license (OL) or a construction permit (CP). Purpose: This information notice is provided to alert licensees to a potentially generic problem regarding the throttling of valves outside the design limits of these valves. No new requirements are imposed in this notice but licensees should review this notice for applicability to their facilities. Discussion: Pressurized Water Reactors Based on analysis of the Crystal River Unit 3 (CR-3) plant by Babcock and Wilcox (B&W), Florida Power Corporation reported by letter addressed to NRC Region II dated July 27, 1983, that throttling of the high pressure injection (HPI) valves as described in the emergency operating procedure guidelines for small-break LOCA could result in unacceptable valve damage. The emergency operating procedures require the throttling of coolant flow through the HPI valve in order to prevent overcooling and pressurized thermal shock. The HPI valves at CR-3, manufactured by the Walworth Company, are not designed for throttling and such activity could result in damage to the valve from cavitation, high velocity erosion of seat, and/or excessive vibration of valve stem and plug. Degradation of the integrity of these valves would impose a significant safety hazard. B&W believes that CR-3 is the only B&W plant that uses the Walworth valve as an HPI valve. It is our understanding that Westinghouse plants do not throttle the safety injection valves but rather vary the flow with the safety injection pumps. However, some Combustion Engineering (CE) plants do throttle and could be susceptible to the same problems encountered in the B&W plant. The requirement for restricting safety injection flow was not imposed until after most operating plants were designed and constructed. Thus, it is possible that plants constructed before the requirements for throttling contain valves 8308040032 . IN 83-65 August 22, 1983 Page 2 of 3 that are not specifically designed for these purposes. Throttling of valves not designed for throttling could also be a problem in other systems in addition to the high pressure safety injection systems. Boiling Water Reactors On February 18, 1983, while in the shutdown mode of operation at Susquehanna Station, a local operator discovered a low pressure coolant injection (LPCI) valve in the "B" loop of the RHR system severely vibrating. Upon further inspection the valve was found to have lost its packing, the valve position indicator had vibrated off, and the adjacent saddle-type pipe hanger had broken welds. At the time of the discovery, the valve was being used to control the shutdown cooling flow to the vessel. This loop of the LPCI was immediately declared inoperable and the "A" loop was put into service for shutdown cooling. On June 9, 1983, at Susquehanna Station, shift personnel noticed that the keep fill system pressure in the RHR system was less than normal on the upsteam side of the LPCI throttle valve. The loss of pressure indicated possible blockage at this normally open valve. Further investigation showed that the throttle valve disc to skirt nut tack welds were broken and the skirt nut had separated from the valve disc. This allowed the disc to separate from the stem block the keep fill system flow, and render the "B" loop of LPCI inoperable. It is suspected that the skirt nut tack welds broke as a result of high vibrational loadings during testing and normal operation early in 1983. Following the February 18 event it was concluded that the shutdown cooling flow rates were outside the optimum throttling range of the LPCI throttle valve causing severe valve vibration. The system was being operated in this manner to afford finer control of reactor coolant temperatures. The operating procedures were subsequently changed to operate the system intermittently at higher flow rates. The separation of the throttle valve disc and stem by June 9 was also attributed to severe valve vibration experienced before the February 18 event, but it was not until June 9 that the skirt nut had finally worked itself free. Similar problems occurred during startup and the early operational phase at Browns Ferry 1 (circa 1975). In order to adjust cooldown rates, the residual heat removal (RHR) service water valves were throttled. Severe vibration occurred which caused extensive damage to valve internals. When the RHR 24-inch angle valves were used to throttle RHR flow, these valves also vibrated excessively and similar damage occurred. TVA consulted with the valve manufacturer, the Walworth Company, and was advised that the disc characteristics were improper for the throttling that was necessary for controlling the cooldown rate. A "fluted flow-disc" was installed in each of the angle valves and the system has provided satisfactory service since then. Operating personnel should be made aware of the operating characteristics of throttle valves, and procedures should be provided to limit valve operation outside the optimum throttling range. . IN 83-55 August 22, 1983 Page 3 of 3 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: P. R. Farron, IE 492-4766 Attachment: List of Recently Issued IE Information Notices .
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