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Information Notice No. 89-86: Type HK Circuit Breakers Missing Close Latch Anti-Shock Springs
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 December 15, 1989 Information Notice No. 89-86: TYPE HK CIRCUIT BREAKERS MISSING CLOSE LATCH ANTI-SHOCK SPRINGS Addressees: All holders of operating licenses or construction permits for nuclear power reactors. Purpose: Information Notice No. 87-41, "Failures of Certain Brown Boveri Electric Circuit Breakers" (IN 87-41) was issued August 31, 1987. This information notice is intended to alert addressees of additional information regarding Type HK circuit breakers that may have been manufactured without a close latch anti-shock spring. 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: Type HK circuit breakers utilize a charging spring motor to charge (compress) the charging springs. At the end of the charging cycle, a close latch is engaged to hold the charging springs in the charged (compressed) position. The circuit breaker can then be closed (by spring force) on demand. IN 87-41 highlighted instances at Limerick Unit 1 and Beaver Valley Unit 2 where Type HK circuit breakers inadvertently closed following completion of the charging cycle. Subsequent to the occurrence at Limerick Unit 1, the manufacturer indicated that this condition can be corrected by adding an anti-shock spring to the close latch. The manufacturer also indicated that this anti-shock spring was not included in Type HK circuit breakers manufactured prior to 1973 and from June 1975 to June 1977. Description of Circumstances: During the recent refueling outage at Fermi Unit 2, the licensee inspected both safety-related and non-safety-related Type HK circuit breakers. The close latch anti-shock springs were observed to be missing in approximately 40 safety-related Type HK circuit breakers that had been manufactured outside of the previously identified timeframes. (The identified circuit breakers 8912110174 . IN 89-86 December 15, 1989 Page 2 of 2 were manufactured in 1974.) Thus, the timeframes previously identified by the manufacturer (prior to 1973 and from June 1975 to June 1977) may not be totally inclusive. In addition, because of changes in corporate name, mergers, etc., Type HK circuit breakers may indicate manufacture by ITE, ITE Imperial, Gould, Brown Boveri, or a combination thereof. The current name of the manufacturer is ASEA Brown Boveri. Recipients may need to be cognizant of this when determining whether they utilize potentially affected equipment. Discussion of Safety Significance: Failure to close on demand or inadvertent closure of a Type HK circuit breaker could result in a circuit breaker not performing its intended function. This, in turn, could result in the loss of a power supply. For example, inadvertent closure of a Type HK circuit breaker onto a vital bus supplied by an emergency diesel generator, such as during load sequencing, could result in overloading the emergency diesel generator. This could occur at the end of a spring charging cycle on a Type HK circuit breaker which was tripped by a loss-of-offsite power signal, as typically happens just prior to load sequencing. This information notice requires no specific action or written response. If you have any questions about the information in this notice, 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: Jack Ramsey, NRR (301) 492-1167 Attachment: List of Recently Issued NRC Information Notices .
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