Information Notice No. 81-31: Failure of Safety Injection Valves to Operate Against Differential Pressure

                                                           SSINS No.: 6835 
                                                           Accession No.: 
                                                           IN 81-31 

                               UNITED STATES 
                          WASHINGTON, D.C.  20555 
                              October 8, 1981 

                              AGAINST DIFFERENTIAL PRESSURE 

Description of Circumstances: 

Both trains of the San Onofre Unit 1 safety injection system were found to 
be inoperable when challenged under actual operating conditions on September
3, 1981.  Following manual reactor trip from 88% power due to steam 
generator flow and level oscillations caused by a regulated power supply 
failure, low primary system pressure caused a safety injection initiation 
signal.  The licensee reported that operators dispatched to the auxiliary 
building following the safety injection initiation signal found that neither 
of the safety injection valves, located in the discharge of both trains of 
the safety injection pumps, had opened as required.  There were no adverse 
consequences in this particular event since there was no loss of coolant 
accident.  The reactor pressure remained above the safety injection pump's 
shutoff head and therefore no actual injection of water would have occurred 
if the valves had opened.  However, had reactor pressure decreased and 
actual injection been required, injection flow would not have been 
automatically available as designed. 

The valves which failed to open are 14-inch Anchor Darling, Series 600, 
stainless steel, Part No. SI-50-WDD valves using Greer Hydraulics No. 832210
actuators.  Tests were conducted on these valves in the as-found condition 
following this event and both valves failed to open against the 1,200 psi 
differential pressure which would normally exist across the valves following
a safety injection signal.  Pressure was lowered until one valve opened with
a 520 psid and the other at 80 psid.  Subsequent tests were performed after 
readjusting the valve packing to determine the cause of the failure.  These 
tests also failed to provide consistent opening against a 1,200 psid.  
System modifications and further testing is under way to provide the 
necessary reliability for the safety injection system. 

These valves had been regularly tested at each refueling outage, but the 
tests were not required to be performed with differential pressure across 
these valves.  There may be systems and components at other facilities that 
are not periodically tested under the differential pressure conditions at 
which they are designed to operate.  Consequently, we suggest that 
recipients of this notice take appropriate steps to determine whether or not 
situations similar to the above could exist at the recipients' plant(s). 

                                                           IN 81-31 
                                                           October 8, 1981 
                                                           Page 2 of 2 

This information notice is provided as an early notification of a 
significant safety matter that is still under review by the NRC staff.  If 
it is determined that actions are required, such as additional periodic 
tests with differential pressure or other actions, you will be notified in 
an appropriate manner.  In the meantime, no response to this notice is 

If you have questions regarding this matter, please contact the Director of 
the appropriate Regional Office. 

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