Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
April 20, 1989
Information Notice No. 89-41: OPERATOR RESPONSE TO PRESSURIZATION
OF LOW-PRESSURE INTERFACING SYSTEMS
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is being provided to alert addressees to potential
problems that may arise from the lack of proper procedures to deal with un-
expected pressurization of systems designed for low operating pressure such
as the residual heat removal (RHR) system. 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.
Description of Circumstances:
On March 9, 1989, when Vogtle Unit 2 was in Mode 3 preparing for initial
criticality, the reactor coolant system (RCS) leakage exceeded Technical
Specification limits. The leakage was observed during a surveillance test
on a cold-leg swing check valve that acts as the inboard pressure isolation
boundary between the RCS and the low-pressure RHR system. The RHR system
had been taken out of service, but the pressure in it did not reduce to the
expected level. To relieve the RHR system pressure, operators opened two
normally locked-closed valves that connect the RHR system to the refueling
water storage tank (RWST), thereby venting RCS coolant to the tank, and from
there, to the atmosphere. The action they took to depressurize the RHR system
was inappropriate and taken without the benefit of proper procedures.
Subsequent investigations determined that the inboard cold-leg check valve in
question had experienced abnormal wear. The operators appear to have
considered possible leakage into the RHR system, such as leakage through check
valves and through isolation valves from the chemical and volume control
system. However, the action taken did not reflect an awareness of the
potential seriousness of such leakage.
8904140042
.. IN 89-41
April 20, 1989
Page 2 of 2
Discussion:
During this event, public safety was not adversely affected at Vogtle Unit 2
because there was no fission product inventory in the reactor. Also, the
potential for damage to the RHR system was minimal because the leakage was
well within the relieving capacity of the system. However, leakage of RCS
coolant into systems such as the RHR system and responses to such events by
operators have been sources of longstanding concern because of the potential
for the so-called "Event V" or the "interfacing system loss-of-coolant ac-
cident." It is important that licensees have proper procedures that will
enable operators to take only appropriate actions to respond to unexpected
or unexplained pressurization of systems such as the RHR system.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: N. Prasad Kadambi, NRR
(301) 492-1153
Attachment: List of Recently Issued NRC Information Notices
.. Attachment
IN 89-41
April 20, 1989
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
88-75, Disabling of Diesel 4/17/89 All holders of OLs
Supplement 1 Generator Output Circuit or CPs for nuclear
Breakers by Anti-Pump power reactors.
Circuitry
89-40 Unsatisfactory Operator Test 4/14/89 All holders of OLs
Results and Their Effect on or CPs for nuclear
the Requalification Program power reactors.
89-39 List of Parties Excluded 4/5/89 All holders of OLs
from Federal Procurement or CPs for nuclear
or Non-Procurement Programs power reactors.
89-38 Atmospheric Dump Valve 4/5/89 All holders of OLs
Failures at Palo Verde or CPs for nuclear
Units 1, 2, and 3 power reactors.
89-37 Proposed Amendments to 4/4/89 All U.S. NRC
40 CFR Part 61, Air licensees.
Emission Standards
for Radionuclides
89-36 Excessive Temperatures 4/4/89 All holders of OLs
in Emergency Core Cooling or CPs for nuclear
System Piping Located power reactors.
Outside Containment
88-86, Operating with Multiple 3/31/89 All holders of OLs
Supp. 1 Grounds in Direct Current or CPs for nuclear
Distribution Systems power reactors.
89-35 Loss and Theft of Un- 3/30/89 All U.S. NRC
secured Licensed Material byproduct, source
and special
nuclear material
licensees.
89-34 Disposal of Americium 3/30/89 All holders of an
Well-Logging Sources NRC specific
license
authorizing
well-logging
activities.
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
..
