NRC Generic Letter 1986-07
UNITED STATES NUCLEAR REGULATORY
COMMISSION
WASHINGTON, D. C. 20555 A 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).8@<)ijvf0
Wh&7/t?P>A~c >OSDOOOoOf March 20, 1986-2-On February 4, 1986, the Executive Director for Operations (EDO) identified and assigned responsibility for 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-Offic of Nuclear Reactor Regulation Enclosures:e>l6,O> ( ) A 1. NUREG-1190
2. EDO Memorandum of February 4, 1986 3. List of Generic Letters STAFF ACTIONS RESULTING
FROM THE INVESTIGATION
OF THE NOVEMBER 21 SONGS-1 EVENT (Reference:
1. Item: Adequacy of feedwater check valves to perform safety function.(References:
Commission briefing, Sections 6.2.4, 6.4, 6.7, and Principal Finding)Action Responsible Office Category Implement and coordinate the staff and industry actions necessary to assure the reliability of safety-related check valves.Other offices to assist as requested.
Areas to be evaluated include: IE Plant-specific Generic-licensee's engineering report on root cause analysis and proposed corrective actions-adequacy of check valve design for this applica-tion-adequacy of Inservice Testing (IST) Program and procedures to detect degraded and failed valves-adequacy of check valves (and related testing programs)
in other systems such as RHR system 2. Item: Completeness of resolved USI A-1, (References:
Finding numbers 1, 2, 3, 8 Action Responsiblf Assess the need to re- NRI evaluate USI A-1 to specifically address the potential for and prevention of condensation-induced water hammers in feedwater piping (assume the issue concerning check valve integrity will be resolved in item 1)."Water Hammer".and 9)* Office Category Generic
-2 -3. Item: Adequacy of San Onofre (Commission briefing, Finding Action Implemert and coordinate the staff's actions to re-evaluate the following San Onofre design features: Unit 1 design.numbers 11 and 13)Responsible Office NRR Category Plant-specific manual loading of the diesel generators follow-ing a loss of power event manual actuation of steam line isolation valves and assurance of steam generator availability to remove decay heat lack of steam generator blowdown status in control room adequacy of the licensee's design change to eliminate spurious SI indication on loss of ower 4. Item: Ade'cy of post-trip review.(References:
Sections 6.6 and 7.2.2.4 and Finding number 17)Category-Action Responsible Office a. Evaluate NRC require-ments for ensuring that sufficient event data are retrievable to accurately reconstruct the event following a loss of offsite power.NRR Generic b. Evaluate the licensee's process for post-trip review and evaluation, including the thoroughness of review and oversight provided by the onsite and offsite nuclear safety review groups.Region V Plant-specific
_ 3 -5. Item: Adequacy of licensee's recordkeeping practices.(References:
Section 6.5 and Finding number 20)Action Evaluate the adequacy of the licensee's maintenance records.Responsible Office Region V Category Plant-s pecific 6. Item: Adequacy of operator training and/or procedures.(References:
Section 7 and Finding numbers 14, 15 and 16)Action Responsible Office Category Review the implementation of the training program regarding operator under-standing and actions in the area of electrical systems, and invoking technical specification action statements.
Region V Plant-specific response.Category 7. Item: Adequacy of emergency notifications and NRC (References:
Section 7.3 and Finding number 22)Action Responsible Office a. Verify the adequacy of the licensee's procedures and training for reporting of events to NRC Operations Center.b. Evaluate the need for changes in NRC policy or guidance regarding:
the use of the ENS line; the use of NRC personnel as ENS communicators;
and possible approaches to improve the ability to determine the overall plant status.Region V Plant-specific IE Generic
-4 -8. Item: Significance of backlog of license amendments.(Reference:
Commission briefing)Action Responsible Office Evaluate whether a backlog of license amendments and technical specification changes contributed to delays in approving the licensee's.
IST program.Ca tegoty Plant-specific NRR
List of Recently Issued Generic Letters Generic Letter No.Subject Date of Issue Issued To 86-06 To be Issued To be Issued 86-05 86-04 86-03 86-02 86-01 85-22 Policy Statement on Engineering Expertise on Shift Applications for License Amendments Technical Resolution of Generic Issue B-19 -Thermal Hydraulic Stability Safety Concerns Associated with Pipe Breaks in the BWR Scram System Potential for Loss of Post -LOCA Recirculation Capability Due to Insulation Debris Blockage 02/13/86 02/10/86 01/23/86 01/03/86 12/03/85 All Power Reactor Licensees and Applicants for Power Reactor Licenses All Power Reactor Licensees and OL Applicants All Licensees of Operating BWRs All BWR Applicants and Licensees All Licensees of Operating Reactors, Applicants for OLs and Holders of CPs 85-21 Not Issued 85-20 Resolution of Generic Issue 69: High Pressure Injection/
Make-up Nozzle Cracking in Babcock and Wilcox Plants 10/30/85 All Licensees with Babcock and Wilcox Operating Reactors