United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 90-55: Recent Operating Experience on Loss of Reactor Coolant Inventory While In a Shutdown Condition

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C. 20555

                               AUGUST 31, 1990


Information Notice No.  90-55:  RECENT OPERATING EXPERIENCE ON LOSS OF
                                    REACTOR COOLANT INVENTORY WHILE IN A  
                                    SHUTDOWN CONDITION


Addressees:

All holders of operating licenses or construction permits for nuclear power
reactors.

Purpose:

This information notice is being provided to alert addressees to recent 
operating experience involving losses of reactor coolant inventory caused by 
deficiencies in human performance while in a shutdown condition.  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.

Background:

A number of NRC generic communications have been written describing events 
at operating reactor facilities involving inadvertent loss of reactor 
coolant inventory while in shutdown conditions (e.g., IN 84-81, "Inadvertent 
Reduction In Primary Coolant Inventory In Boiling Water Reactors During 
Shutdown and Startup" and IN 86-74, "Reduction of Reactor Coolant Inventory 
Because of Misalignment of RHR Valves").  IN 90-25, "Loss Of Vital AC Power 
With Subsequent Reactor Coolant System Heat-up" describes a March 20, 1990 
event at Vogtle Unit 1 in which a significant event occurred during shutdown 
conditions in which human performance played an important role.  Generic 
Letter 88-17, "Loss Of Decay Heat Removal", stated that these types of 
events indicated an apparent lack of a complete industry understanding of 
the potential seriousness of such events with the reactor in a shutdown 
condition.

Description of Circumstances:

The following are examples of recent events that were caused or initiated by 
deficiencies in human performance with the reactor in a shutdown condition.

CATAWBA 1, 6/11/90

     At Catawba Unit 1, on June 11, 1990, 5000 gallons of water from the 
     reactor coolant system (RCS) were transferred inadvertently to the 


9008270047 
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                                                            IN 90-55 
                                                            August 31, 1990 
                                                            Page 2 of 3


     refueling water storage tank (RWST).  This coolant was transferred 
     because the reactor operator ordered isolation valves to be opened 
     while performing Residual Heat Removal (RHR) check valve testing before 
     ensuring that the manual isolation valve to the RWST was closed.  The 
     loss of RCS inventory occurred over a 30 second period while a 
     motor-operated cross-tie RHR isolation valve was partially open. 


MAINE YANKEE, 6/4/90

     While performing the RCS fill and vent procedure with the reactor in 
     cold shutdown, the licensee inadvertently transferred 6000 gallons of 
     coolant to the RWST.  The RCS was being pressurized with nitrogen for 
     venting of the reactor coolant pumps and loops.  Pressurizer level was 
     being monitored by means of one cold- and two hot-calibrated level 
     instruments. As the RCS pressure increased, the hot- and 
     cold-calibrated level instruments were not in agreement.  The operators 
     requested that a calibration be performed on the pressurizer level 
     instruments while continuing to fill the pressurizer.  With the 
     hot-calibrated level instruments indicating 67 percent, the operators 
     decided to reduce the level to 25 percent by draining to the RWST.  
     Because the hot-calibrated level instruments were not reading 
     correctly, the actual RCS level was below the bottom of the pressurizer 
     for 3 hours.

BRAIDWOOD 2, 3/20/90

     While performing activities for defueling with the reactor in cold 
     shutdown, the reactor operators inadvertently transferred about 9500 
     gallons of reactor coolant to the RWST while preparing to switch 
     operation of the RHR trains.  RHR train B was in operation with train A 
     operating in the recirculation mode to the RWST.  A licensed operator 
     inadvertently opened the RHR train A hot leg suction valve in 
     preparation for shifting from train B operation to train A operation.  
     Opening this valve established a flow path from the RCS to the RWST.  
     The operator immediately recognized the error and started to close the 
     hot leg suction valve.  However, the valve takes 4 minutes to close.  
     About 9500 gallons of reactor coolant were transferred to the RWST.  In 
     addition, this error allowed a rapid reduction in pressurizer level and 
     RCS pressure to occur, resulting in the pressurizer exceeding its 
     technical specification limit on the pressurizer cooldown rate 
     (200 degrees F/hour).


Discussion:

The events described above are examples where RCS inventory was 
inadvertently reduced as a result of deficiencies in human performance with 
the reactor in a shutdown condition.  These types of events are of concern 
because with the reactor in a shutdown condition, many pieces of ESF 
equipment can be removed from service at the same time unusual valve lineups 
are performed.  Human performance then becomes a major factor in maintaining 
safety and system configuration control during shutdown conditions.  
.

                                                            IN 90-55 
                                                            August 31, 1990 
                                                            Page 3 of 3


This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
the technical contact listed below or the appropriate NRR project manager.




                                Charles E. Rossi, Director
                                Division of Operational Events Assessment
                                Office of Nuclear Reactor Regulation

Technical Contact:  John Thompson, NRR
                    (301) 492-1171

Attachment:  List of Recently Issued NRC Information Notices
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