Information Notice No. 81-31: Failure of Safety Injection Valves to Operate Against Differential Pressure
SSINS No.: 6835
Accession No.:
8107230032
IN 81-31
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
October 8, 1981
INFORMATION NOTICE NO. 81-31: FAILURE OF SAFETY INJECTION VALVES TO OPERATE
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).
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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
required.
If you have questions regarding this matter, please contact the Director of
the appropriate Regional Office.
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