Information Notice No. 81-09: Degradation of Residual Heat Removal (RHR) System
SSINS No.: 6835 Accession No.: 8011040280 IN 81-09 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 March 26, 1981 Information Notice No. 81-09: DEGRADATION OF RESIDUAL HEAT REMOVAL (RHR) SYSTEM Description of Circumstances: Recent, repeated expressions of serious concern have been made regarding loss of shutdown cooling capability (IEB 80-12 and IN 80-20). Nevertheless, an additional instance has occurred in which proper attention was not given to assure reliability of the shutdown cooling function. On March 5, 1981 during a shutdown at Beaver Valley, residual heat removal (RHR) flow was severely degraded while the water level was near the hot leg midpoint. During the 54 minutes needed to vent both RHR pumps and add approximately 600 gallons of water to the primary system, primary coolant temperature increased from 102E to 168 E. The event occurred when water was slowly lost from the reference leg of a temporary (tygon tubing) differential pressure system installed to measure water level in the primary system. There were no required surveillance procedures to check proper operation of the water level instrument. Consequently, the reference leg water loss was not detected until the actual primary system water level decreased to about 6" below the indicated level, sufficiently low to allow air entrainment in the RHR suction line, which air-bound both RHR pumps. Loss of shutdown cooling capability is a potentially significant contributor to the total risk associated with nuclear power (Reactor Safety Study, WASH - 1400, pg. 135.) It is expected that licensees will review the circumstances of this event and take appropriate actions to assure shutdown cooling system operability. This notification, in conjunction with IEB 80-12 and IN 80-20, is intended to convey the seriousness of NRC concern with failures to maintain adequate decay heat removal provisions. No written response to this information notice is required. If you require additional information with regard to this subject please contact the appropriate NRC Regional Office. Attachment: Recently issued IE Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021