Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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
