Information Notice No. 89-41: Operator Response to Pressurization of Low-Pressure Interfacing Systems

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C.  20555

                                 April 20, 1989

                                   OF LOW-PRESSURE INTERFACING SYSTEMS


All holders of operating licenses or construction permits for nuclear power 


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.  

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                                                            April 20, 1989
                                                            Page 2 of 2


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

                                   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.

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

89-34          Disposal of Americium         3/30/89        All holders of an
               Well-Logging Sources                         NRC specific 

OL = Operating License
CP = Construction Permit 

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