ML20050Z880
| ML20050Z880 | |
| Person / Time | |
|---|---|
| Site: | 05000000, San Onofre |
| Issue date: | 03/23/1981 |
| From: | ORGANIZATION FOR ECONOMIC COOPERATION & DEVELOPMENT |
| To: | |
| Shared Package | |
| ML19240B432 | List: |
| References | |
| FOIA-81-380 NUDOCS 8204150229 | |
| Download: ML20050Z880 (4) | |
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-P MAR 2 31981 No. IRS 29 RESTRICTED DlFFUSlOIJ ltESTREIllTE Date of Receipt 12th March,1981 Date de Reception Name of nuclear power station San Onofre 1 (US)
Nom de la centrale Date of incident 10th March,1980 Date de l' incident Type of reactor PWR Type de r6acteur Authorized electrical power Niv'cau de puissance 61ectrique 456 Icte autoris6 First commercial operation January 1968*
Date de mise en service x added by OECD/NEA Secretariat 8204150229 811109 PDR FOIA CONNOR 81-380 PDR
3 e
Failure of Salt Water Coolino System Date and Place - On March 10, 1980, San Onofre Unit 1, a 456-MWe pressurized water reactor that is operated by Southern California Edison Company in San Diego County, experienced the failure of the Salt Water Cooling System (SWCS).
Nature and Probable Consecuences - The Salt Water Cooling System is a safety-related system snat supplies cooling water to safety equipment such as heat exchangers and necessary auxiliary safety-related equipment.
The SWCS is required for normal operation and safe shutdown of _the plant under certain tran,sient and accident conditions. Therefore, if the system is inop'erable, the reactor is required to be shut down. This event involved the loss of two redundant safety grade. pumps; the loss of a third pump which was a safety-I related pump in the Salt Water Cooling System; and the failure of the plant staff to shut down the plant as required by the plant technical specifications and the plant operating procedures.
During this event, there was no associated accident or radioactivity releases.
The temperature in the Component Cooling '
Water System (CCWS), which is cooled by the Salt Water Cooling System, increased 16*F but was within normal operating parameters.
The sequence of events was as follows: While the plant was operating'at 100%
power, the shaft on the south salt water cooling pump failed and the pump stopped pumping.
The redundant north pump automatically started, but qid not supply salt water cooling to the component cooling system since its isolation valve failed to automatically open.
Subsequently, the plant operators attempted l
to start the auxiliary salt water cooling pump, but there was insufficient prim-ing and the pump was stopped.
After about fifteen minutes, the operators, fol-1 lowing plant emergency procedures, supplied a source of water for component cooling by aligning the screen wash pumps to the salt water cooling system, a manual operation.
About twenty minutes later, the auxiliary salt water pump
0 2
was adequately primed and placed in service, and about two and one-half hours later one of the main salt water cooling pumps was made operable when its isolation valve was opened.
The plant Technical Specifications require that the reactor not be maintained critical unless two salt water cooling pumps are operable, or one salt water cooling pump and the auxiliary salt water cooling pump are operable. The existing plant emergency procedure required a reactor trip..Although a plant shutdown was initiated about 45 minutes af ter the initial loss of the salt water cooling system, it was terminated after a power reduction of about three megawatts following consultation with offsite plant management.
As stated, the decision to continue operations was contrary to the plant license conditions stated in the Technical Specifications and contrary to established emergency operating procedures; the intent,of both is to require that the plant be placed in a safe shutdown condition upon the complete loss of an important safety system and that a safety evaluation be made prior to restart.
In this case, the decision to terminate the shutdown included consideration of the effects of perturbing stable plant operating conditions including increasing the heat load on the component cooling water system, manning the control room while shutting down and simultaneously working on returning the SWCS to opera-tion, and the indications of adequate interim cooling from the screen wash pumps and the auxiliary SWC pump which were supplying saltwater flow.
- However, the cooling capacity of the screen wash pump in this mode was heretofore untested, unanalyzed, and unproven under full power operation or maximum CCWS heat load conditions.
Subsequent analysis has confirmed that either during normal shutdown while on residual heat removal (RHR) cooling with a large decay heat load or under cer-tain steam line break conditions, the loss of the SCWS could result in serious degradation of safety functions if prompt corrective actions are not taken.
The timing and details of these actions were not fully known prior to the event.
Detailed engineering analysis that was conducted after the event indicated that component cooling water temperatures could exceed cooling limits on pump bearings in the charging system (high head Emergency Core Cooling System, ECCS), the RHR system, and the reactor cooling system.
Significant damage to the pumps in these vital systems could have therefore resulted. The complete loss of the SWCS and the adequacy of alternative cooling pathways hac not been thoroughly analyzed prior to the event.
Further, the licensing process has traditionally not required analyses of the loss of complete safety systems caused by such interactions.
In addition to the loss of the SWCS, the plant was also being operated with the instrument air system contaminated with desiccant particles.
The desiccant problem had contributed to at least one previously reported safety related valve failure (failure to operate) and was suspected to be a cause for other valve problems such as sluggish operation.
Contamination in the instrument air system can affect performance, causing multiple failures.
It is thought that the desiccant may have contributed to the failure of the isolation valve to open on one of the SWCS pumps.
o.
3 Analysis also indicated that the equipment failures might have been prevented if adequate preventive maintenance programs existed.
Deficiencies in the licensee's preventive maintenance program and noncompliance with requirements for pump testing and for inservice testing of pumps and valves were identified to the licensee as a result of a February 1979 inspection by the NRC (Ref. 2).
The NRC considers the multiple equipment failures, the failure to shut down the plant according to the Technical Specifications and plant procedures, and the uncorrected deficiencies in the preventive maintenance program to be indicative of deficiencies in management and procedural controls.
Cause or causes - The equipment failure causes were:
one SWCS pump shaft failed oue to apparent excessive vibration (a worn bushing in the pump had been previ-ously noted); the other SWCS pump isolation valve failed to open due to a dete-riorated 0-ring in a solenoid valve on the valve operator; and the auxiliary SWCS pump failed to prime due to an air leak into the priming system (this situation had occurred previously).
Other potential contributing factors are deficiencies previously noted in the licensee's preventive maintenance program and the existence of some desiccant in the plant's service air lines.
The plant staff did not shut down the facility as required due to apparent misunderstandings of the Technical Specification requirements and the technical basis for the requirements.
Actions Taken to Prevent Recurrence Licensee - The licensee has taken, or will take, action as follows:
(1) The equipment that failed was, or will be, repaired and returned to service.
System redesign and changes to the preventive maintenance program will be
. implemented to improve system reliability.
(2) Desiccant was being flushed from the plant service air system during the summer refueling outage.
The licensee is preparing a report on the extent of the desiccant contamination and associated problems.
(3) Management has taken action to improve the plant staff's knowledge of the Technical Specifications and their basis.
Tighter controls were also placed on the administrative process for changing procedures.
Clari ficatio. s are also being made to the Technical Specifications.
l (4) A review is being made of the capability of the plant to withstand.postu-lated accidents if the SWCS and/or its alternative cooling pathways are unavailable.
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