United States Nuclear Regulatory Commission - Protecting People and the Environment

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 168E. 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, November 12, 2013