Transmittal of NUREG-1190 Regarding the San Onofre Unit 1 Loss of Power and Water Hammer Event (Generic Letter No. 86-07)
UNITED STATES
NUCLEAR REGULATORY COMMISSION
WASHINGTON, D. C. 20555
March 20, 1986
TO ALL REACTOR LICENSEES AND APPLICANTS
Gentlemen:
SUBJECT: TRANSMITTAL OF NUREG-1190 REGARDING THE SAN ONOFRE UNIT 1 LOSS OF
POWER AND WATER HAMMER EVENT (GENERIC LETTER 86-07)
On November 21, 1985, while operating at 60% power, Southern California
Edison Company's San Onofre Unit 1 Nuclear Power Plant experienced a loss of
ac electrical power followed by a severe water hammer in the secondary
system which caused a steam leak and damaged plant equipment. Shortly after
the event, the NRC Executive Director for Operations directed that an NRC
Team be sent to San Onofre, in conformance with the recently established
Incident Investigation Program, to investigate the circumstances of this
event. The NRC Team has now completed its investigation and has documented
the factual information and their findings and conclusions associated with
the event (see enclosed NUREG-1190, entitled "Loss of Power and Water Hammer
Event at San Onofre Unit 1, on, November 21, 1985").
In this report, the team has concluded that the event was significant
because (a) all inplant ac power was lost for 4 minutes; (b) all steam
generator feedwater was lost for 3 minutes; (c) a severe water hammer caused
by check valve failures was experienced in the feedwater system which caused
a leak, damaged plant equipment and challenged the integrity of the
auxiliary feedwater system; (d) all indicated steam generator water levels
dropped below scale; and (e) the reactor coolant system experienced an
acceptable but unnecessary cooldown transient. In the team's view the most
significant aspect of the event was that five safety-related feedwater
system check valves degraded to the point of inoperability during a period
of less than a year, without detection, and that their failure jeopardized
the integrity of safety-related feedwater piping. The cause of the feedwater
system check valve failures has been preliminarily identified by SCE as
partial or complete separation of the check valve disc assemblies due to
fluid flow conditions. Information submitted to the staff on this subject is
currently under review.
You should review the information in the enclosed report for applicability
to your facility. In addition, you should ensure that the information in
NUREG-1190 is made available to your plant staff as part of your training
program in connection with the Feedback of Operating Experience to Plant
Staff (TMI Action Plan Item I.C.5).
8603210334
March 20, 1986
- 2 -
On February 4, 1986, the Executive Director for Operations (EDO) identified
and assigned responsibility or generic and plant-specific actions resulting
from the investigation of the San Onofre event. Some of the generic actions
may be applicable to your facility. A copy of the EDO memorandum is included
for your information.
This generic letter is provided for information only, and does not involve
any reporting requirements. Therefore, no clearance from the Office of
Management and Budget is required. The enclosed report is currently under
NRC review.
Any generic requirements stemming from the report will be transmitted at a
later date following completion of the appropriate procedural steps.
Sincerely,
Harold R. Denton, Director
Office of Nuclear Reactor Regulation
Enclosures:
1. NUREG-1190
2. EDO Memorandum of February 4, 1986
3. List of Generic Letters
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