ML20214M538
| ML20214M538 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 08/31/1986 |
| From: | SOUTHERN CALIFORNIA EDISON CO. |
| To: | |
| Shared Package | |
| ML20214M527 | List: |
| References | |
| NUDOCS 8609110161 | |
| Download: ML20214M538 (4) | |
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SCE PLANS FOR INDUSTRY HIDE DISSEMINATION OF LESSONS LEARNED FROM THE HATER HAMMER EVENT OF NC.VEMBER 21, 1985 SAN ON0FRE NUCLEAR GENERATING STATION UNIT 1
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SUMMARY
REPORT August 1986 i
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INTRODUCTION The loss of offsite power and water hammer event which occurred on November 21, 1985 required that SCE perform a large scale investigation to determine the causes of the event and to institute corrective measures to prevent incidents of this type from reoccurring.
The base report which documents these investigations was provided to the NRC by letter dated April 8, 1986. The lessons learned from the event may have some generic application at other nuclear facilities.
Therefore, SCE will participate in exchanges of information to review the lessons learned with other industry representatives during several upcoming opportunities.
The discussion of lessons learned which follows emphasizes the generic aspects of our conclusions.
LESSONS LEARNED 1.
Check Valve Failure a.
Findings - The concurrent failure of five feedwater check valves was caused by cyclic loading which resulted from a marginal design application.
The design problem was complicated by the non-integral disk / swing arm construction of the check valves.
b.
SCE Action - SCE reviewed all swing check valve design applications and instituted corrective measures as required. The feedwater check valves were replaced with check valves of an integral design.
c.
Generic Implications - The use of check valves in certain applications may not have received sufficient consideration to assure reliable operation.
2.
Cable Fai' lure a.
Findings - The cable failure which initiated the loss of offsite power transient was caused by the overheating of the cable insulation due to the existence of a localized heat source at the point of failure, b.
SCE Action - A cable evaluation task force was established to investigate and analyze the cable failure and all other cable in the plant.
The task force efforts were made part of the Material Condition Review Program (MCRP) and the Area Monitoring Program (AMP) as described in item 4 below. Corrective measures were instituted as required.
c.
Generic Implications - Plant conditions must be monitored to assure continued maintenance of desired standards of performance.
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Water Hammer Event a.
Findings - Condensation induced water hammer in main feedwater line 8 resulted when the check valve failures allowed the line to-i void thereby creating conditions conducive to water hammer, b.
SCE Action - The water hammer phenomenon was reviewed to establish the conditions which led to the feedwater piping damage.
The low flow condensation induced water hammer was identified as th mechanism for slug formation which occurred. Corrective measures to j
minimize the probability of line voiding were instituted.
c.
Generic Implications - Systems susceptible to steam / water interaction should include sufficient design measures to minimize j
the probability of line voiding.
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Material Condition a.
Findings - The material failures which. caused the event also led to challenges to safety systems. The material condition of plant equipment is therefore an important contributor to the occurrence of challenges to safety systems and should be monitored throughout the i
life of the plant.
b.
SCE Action - Two administrative programs were instituted, the Material Condition Review Program (MCRP) and the Area Monitoring i
Program (AMP).
c.
Generic Implications - Monitoring of plant conditions using an 4
approach similar.to the MCRP (older plants) and the AMP (all plants) can result in improved reliability and minimize challenges to safety systems.
l EFFORTS TO DISSEMINATE LESSONS LEARNED 1
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SCE considers the water hammer event of November 21, 1985 to be very significant since it has identified several issues which may have generic j
implications.
Efforts have been and are being made to share the information gained regarding these issues with other utilities and other interested parties during several upcomming opportunities. A summary of our plans in 4
this regard is provided below.
o A presentation was made at the McGraw Hill Nuclear Services Conference in i_
May 1986.
The presentation discussed the lessons learned from the water hammer event related to the MCRP.
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o SCE representatives participated in the NRC IIT training session at Harper's Ferry in June 1986. The water hammer event was discussed during this meeting.
o A presentation was made at the American Nuclear Society Summer Meeting in June 1986.
This presentation covered the root causes of the condensation induced water hammer and the check valve failure.
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.. o A presentation was made at the MIT Reactor Safety Course in July 1986.
The presentation covered the methods available for prevention of flow induced vibrations in check valves and to minimize the probability and consequence of condensation induced water hammer.
o A presentation was made at the EPRI Hater Hammer Horkshop in July 1986.
i This presentation covered the lessons learned from the condensation induced water hammer event and also discussed their applicability to other types of water hammer.
o As part of SCE's participation in the Combustion Engineering and Westinghouse Owner's Groups, information has been provided to the group members regarding the lessons learned from the water hammer event.
Presentations on the Material Condition Review Program were made in June 1986. An additional presentation is scheduled for the Combustion Engineering Owner's Group Annual Meeting in October 1986.
o The INP0 Check-Valve Workshop will take place in October 1986. SCE is planning a presentation for this workshop which will emphasize the near and long term corrective actions associated with the check valve failures related to the water hammer event.
o A presentation is scheduled for the Atomic Industrial Forum Annual l
Meeting in November 1986. The presentation will emphasize the MCRP related corrective measures instituted by SCE.
4 o
A presentation is scheduled for the American Nuclear Society Winter Meeting in November 1986. A paper entitled, "In Search of Excellence; the Problems of Material Aging and Reliability in an Old Nuclear Unit at the Southern California Edison Company," will be presented.
This paper discusses the water hammer event and the corrective measures instituted by SCE following our investigations with emphasis on the MCRP.
o The American Nuclear Society International Meeting on " Anticipated and Abnormal Transients in Nuclear Power Plants" will taken place in April 1987. SCE is planning to present two invited papers on the water hammer event.
The first paper addressing the details of the event will be presented at the Operational Transient Experience Session.
The second paper addressing the root causes of the event will be presented at the Root Causes of Transients Session.
o Presentations are also under consideration for upcoming forums which l
include the INP0 CEO Workshop in November 1986, the INP0 Plant Managers Horkshop in early 1987, the LIS seminar in Spring 1987, and an
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appropriate EEI forum such as the Nuclear Operations Task Force.
I In addition to the items referenced above, the lessons learned from the o
l water hammer event have been discussed during informal exchanges of l
various industry organizations and personal contacts.
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