United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 81-10: Inadvertent Containment Spray Due to Personnel Error


                                                            SSINS No.:  6835
                                                            Accession No.: 
                                                            8011040273 
                                                            IN 81-10 

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                          WASHINGTON, D.C.   20555

                               March 25, 1981

Information Notice No. 81-10:  INADVERTENT CONTAINMENT SPRAY DUE TO 
                                  PERSONNEL ERROR 

Description of Circumstances: 

On February 11, 1981 while in mode 5 (cold shutdown), an auxiliary unit 
operator at Sequoyah Unit 1 misunderstood a verbal instruction and opened a 
single valve in the residual heat removal (RHR) system.  The opened valve 
created direct flow path through the RHR system from the primary coolant 
system to the RHR containment spray header.  A rapid primary system 
depressurization to the atmospheric pressure resulted, and a total of about 
110,000 gallons of water was sprayed into the containment from the primary 
system and from the refueling water storage tank (RWST). 

Licensees and applicants should be aware of the following aspects of this 
event and should take appropriate steps to prevent a recurrence a their 
plant. 

The auxiliary unit operator did not have adequate training or orientation at
the particular duty station involved.  A single valve at that station is 
part of the primary coolant system pressure boundary when using the residual 
heat removal (RHR) system for shutdown cooling.  Thus, 
personnel/administrative problems and a plant design feature combined to 
cause the event. 

Design of the control room annunciators contributed to prolonging the event. 
The panel indicating emergency core cooling system (ECCS) valve positions is
designed to warn when the ECCS is not properly aligned for the injection 
(safety) mode.  When the first valve misalignment occurs, one light comes on
in an otherwise dark field of indicators, and an alarm sounds and flashes. 
However, in the shutdown cooling mode, several valves are not in their 
injection mode position.  Therefore, in the event at Sequoyah, the alarm 
light had already been on continuously for some time, the annunciator was 
not supposed to operate, and one more light coming "on" in a valve-position-
indicating field with several lights already "on" was easily missed.  The 
operators thus failed to detect the presence of the inadvertently opened 
valve for at least 35 minutes.  

Lack of an ECCS initiation procedure for use in the shutdown cooling mode 
did not significantly delay recovery from this event, but potentially could 
have done so had the primary system been at a higher pressure.  To provide 
injection flow for pressurizer level recovery, the operators opened the RHR 
system suction valve from the RWST, but they neglected to close the RHR 
system suction valves from the reactor coolant system (RCS).  A proper 
procedure would require those latter valves to be closed to prevent reactor 
pressure    
.

                                                            IN 81-10 
                                                            March 25, 1981 
                                                            Page 2 of 2 


from seating a check valve in the RWST suction line, which would prevent the
injection mode for the low-pressure (RHR) pumps from being effective and 
delay recovery from the event. 

A similar problem with the borated water storage tank (BWST) check valve 
occurred at Crystal River 3 on July 16, 1980 while the unit was in Mode 5 
with the decay heat system in use for shutdown cooling.  Improper valve 
alignment on the decay heat system heat exchangers caused a rapid cooldown 
of the RCS which resulted in a loss of pressurizer level.  When recovery was 
attempted by realigning the decay heat system suction to the BWST, injection 
flow could not be established until RCS pressure approached atmospheric 
conditions since the RCS suction valves remained open. 

This problem would be particularly significant under a LOCA condition with 
the RCS temperature above boiling (Mode 4). 

The information herein is being provided as an early notification of a 
possibly significant matter that is still under review by the NRC staff. 
Recipients should review the information for possible applicability to their
facilities.  If NRC evaluation so indicates, further licensee actions may be
requested. 

No written response to this information notice is required.  If you need 
additional information regarding is matter, contact the Director of the 
appropriate NRC Regional Office. 

Attachment: Recently issued IE Information Notices. 

Page Last Reviewed/Updated Tuesday, November 12, 2013