ML20136D883

Forwards Case Study Rept AEOD/C503, DHR Removal Problems at Us Pwrs. Rept Makes Several Recommendations Based Upon Potential Safety Significance of loss-of-DHR Events

ML20136D883
Person / Time
Issue date:	12/23/1985
From:	Heltemes C NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD)
To:	Pate Z INSTITUTE OF NUCLEAR POWER OPERATIONS
Shared Package
ML20136D889	List: ML20136D883 ML20136D900
References
REF-GTECI-A-45, REF-GTECI-DC, TASK-A-45, TASK-OR NUDOCS 8601060310
Download: ML20136D883 (4)

Text

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nec a 3 mm Dr. Zack.Pate, President

~ Institute of Nuclear Power Operations 1100 Circle 75 Parkway, Suite 1500 Atlanta, Georgia 30339

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 stu: y report on decay heat removal 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 morelseriousevents.

AE00'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 errer. Most of.the errors 3

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.were committed.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

errogs.

The report makes several recommendations based upon the potential safety significance of loss-of-DHR events.

Implementation of those recommendations

~

?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 measuring reactor vessel-level e

during shutdown modes; modifying plant design to remove autoclosure interlocks-and/or power to the DHR suction / isolation valves during periods which do not

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Dr. Zack Pate 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, and 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 modified 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 Ornstein at (301)492-4439.

Sincerely, Original Signed by:

C. J. Holte es, Jr.

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

Enclosure:

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• Mr. R. Crouse, Chairman Mr. C. McNeill, Jr.

B & W Owners' Group Vice President, Nuclear Toledo Edison Company Public Service Electric & Gas Co.

Edison Plaza P.O. Box 236 300 Madison Avenue Hancocks Bridge, N.J. 08038 i

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