ML20136D621

Forwards Case Study Rept on DHR Problems at Us Pwrs.Rept Makes Several Recommendations Based Upon Significance of loss-of-DHR Events.W/O Encl

ML20136D621
Person / Time
Issue date:	12/23/1985
From:	Heltemes C NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD)
To:	Rossin D NUCLEAR SAFETY ANALYSIS CENTER
References
REF-GTECI-A-45, REF-GTECI-DC, TASK-A-45, TASK-OR NUDOCS 8601060221
Download: ML20136D621 (2)

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" , !$E Dr. David Rossin, Director Nuclear Safety Analysis Center 3412 Hillview Avenue P.O. Box 10412 Palo Alto, California 94303

SUBJECT:

CASE STUDY REPORT -- DECAY HEAT REMOVAL PROBLEMS AT U.S. PRESSURIZED WATER REACTORS Following resolution of peer review comments, we have completed the enclosed case study report on decay heat raroval problems at U.S. pressurized water reactors. Between 1976 and 1983, 130 loss-of-DHR events were reported to have occurred during approximately 500 reactor years of operation. Total loss of the DHR systems under certain conditions could lead to core uncovery, and resultant fuel damage. The results of scoping analyses of total loss-of-DHR scenarios presented in the study indicate that for certain postulated events, unless timely corrective actions are taken, core uncovery could result on the order of one to three hours. To date, no serious damage has resulted from the loss-of-DHR system events that have occurred at U.S. PWRs. However, many of the events which have occurred thus far may serve as important precursors 'to more serious events.

AE0D's analysis of operating data indicates that the underlying or root causes of most of the loss-of-DHR system events are human factors deficiencies involving procedural inadequacies and personnel errar. Most of the errors were comitted during maintenance, testing and repair operations.

The leading category of loss-of-DHR events (37 of 130) was the automatic closure of the suction / isolation valves, most of which resulted from human errors.

The report nakes several recommendations based upon the potential safety significance of loss-of-DHR events. Implementation of those recommerdations should significantly improve DHR system reliability and availability. The recommendations include: improving human factors by upgrading coordination, planning, and administrative control of surveillance, maintenance, and testing operations which are performed during shutdown; providing operator aids to assist in determining time available for DHR recovery and to assist operators in trending parameters during loss-of-DHR events; upgrading the training and qualification requirements for operations and maintenance staff; requiring the use of reliable, well-analyzed methods for neasuring reactor vessel level during shutdown modes; modifying plant design to remove autoclosure interlocks jO,l and/or power to the DHR suction / isolation valves during periods which do not f jh 8601060221 8512P3 PDR GTECI GDCA ,

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Dr. David Rossin require valve motion; and clarifying plant technical specifications to elimi-nate ambiguities associated with operating mode definitions.

The report acknowledges NRC's ongoing efforts to address shutdown decay heat removal requirements (Unresolved Safety Issue A-45). The AE0D recommenda-tions are applicable to A_45, ard should be considered in the resolution of this generic issue.

As you may know, AE0D reports do not represent an official NRC position or the position of the responsible NRC program office. Our reports are one input to an ongoing review and evaluation process, and any recommendation contained in our final report will be considered and perhaps rodified or eliminated by the responsible NRC office.

A copy of the case study report and this letter are being placed in the Public Document Room at 1717 H Street, N.W., Washington, D.C. 20555.

If you have any questions regarding this study, please feel free to contact Dr. Hal Orrstein at (301)492_4439.

Sincerely, Or!Ein'! -!cred by:

C. J. iiti t c;es , Jr.

C. J. Heltenes, Jr. , Director Office for Analysis and Evaluation of Operational Data

Enclosure:

As stated cc w/ enclosure:

Mr. G. Vine, NSAC Distribution PDR AE00 CF POAB CF ROAB SF H0rnstein KBlack WLanning TIppolito CHeltemes KSeyfrit __

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