United States Nuclear Regulatory Commission - Protecting People and the Environment

Loss of Decay Heat Removal - 10 CFR 50.54(f) (Generic Letter No. 88-17)


October 17, 1988



Loss of decay heat removal (DHR) during nonpower operation and the consequences of such a loss have been of increasing concern for years. Numerous industry and NRC publications have addressed the subject. The Diablo Canyon event of April 10, 1987, and ensuing work by both the staff and industry organizations have provided additional insight. Yet the problems continue, as illustrated by (1) the inadequacies demonstrated by many licensees in their response to Generic Letter (GL) 87-12; (2) the event at Waterford on May 12, 1988; (3) the event at Sequoyah on May 23, 1988; (4) the DHR perturbations due to inadequate level at San Onofre on July 7, 1988; and (5) the apparent lack of a complete industry understanding of the potential seriousness of such events.

The report of the Diablo Canyon event, NUREG-1269, stated that operating a plant with a reduced reactor coolant system (RCS) inventory was a particularly sensitive condition and identified many generic weaknesses in DHR. GL 87-12, which requested information from all PWR licensees, provided additional insight, and NUREG-1269 was transmitted with the generic letter to ensure that licensees had the latest information. Despite this, many of the responders to GL 87-12 demonstrated that they did not understand the identified problems.

Deficiencies exist in procedures, hardware, and training in the areas of (1)prevention of accident initiation, (2) mitigation of accidents before they potentially progress to core damage, and (3) control of radioactive materialif a core damage accident should occur. Although deficiencies exist in all PWRs, certain design features make initiation and the time available for mitigation in the Westinghouse and Combustion Engineering designs of more concern than in the nuclear steam supply systems (NSSSs) designed by Babcockand Wilcox. Nevertheless, we believe expeditious actions are necessary at all PWRs to rectify these deficiencies. These should be paralleled by programmed enhancements which supplement, add to, or replace the expeditious actions to accomplish a more comprehensive improvement. Recommendations covering these items are summarized in the attachment, and additional Information and guidance are provided in the three enclosures.

Pursuant to 10 CFR 50.54(f), we request your response regarding your plans with respect to each of the recommendations as related to operation following placement of the NSSS on shutdown cooling, or following the attainment of NSSS conditions under which shutdown cooling would normally be initiated. Your response is to include the following:

(1)  A description of the actions you have taken to implement each of the eight recommended expeditious actions identified in the attachment. Your reply shall be submitted to us within 60 days of receipt of this letter.

(2)  A description of enhancements, specific plans, and a schedule for implementation for each of the six programed enhancement recommendations identified in the attachment. Your reply shall be provided to us within 90 days of receipt of this letter.

Individual deviations from the recommendations will be considered on a case by case basis provided compensatory measures are provided which will achieve a comparable level of protection.

No further responses are required to GL 87-12 and licensees or construction permit holders need not provide any supplemental information in a response to GL 87-12 to which they previously committed.

We will accept documents such as technical reports, action plans, and schedules prepared by industry groups when accompanied by commitments from participating licensees in lieu of individual documents from those licensees. Alternatively, such industry group documents may be incorporated by reference in licensee documentation. We encourage your participation in cooperative efforts to effectively resolve these issues.

Your written response shall be submitted under oath or affirmation under the provisions of Section 182a, Atomic Energy Act of 1954, as amended. Your written response is needed to determine whether actions to modify, suspend, or revoke your license are necessary. An analysis as required by 10 CFR 50.109 has been performed regarding this request.

The original copy of your written response shall be transmitted to the U. S. Nuclear Regulatory Commission, Document Control Desk, Washington, D.C. 20555 for reproduction and distribution.

This request is covered by Office of Management and Budget Clearance Number 3150-0011 which expires December 31, 1989. The estimated average burden hours is 200 person-hours per licensee response, including assessment of the new requirements, searching data sources, gathering and analyzing the data, and preparing the required reports. Comments on the accuracy of this estimate and suggestions to reduce the burden may be directed to the Office of Management and Budget, Room 3208, New Executive Office Building, Washington, D.C. 20503, and to the U. S. Nuclear Regulatory Commission, Records and Reports Management Branch, Office of Administration and Resources Management, Washington, D.C. 20555.

If you have technical questions regarding this matter please contact Wayne Hodges at 301-492-0895. Other questions may be directed to the NRR Project Manager assigned to this issue, Charles M. Trammell (301-492-3121) or to theProject Manager assigned to your plant.

  Dennis M. Crutchfield
Acting Associate Director for Projects
Office of Nuclear Reactor Regulation

[See PDF (1.98 MB) for Attachment and Enclosures]

Attachment:  Recommended Actions

Enclosures: 1.  Overview and Background Information Pertinent to Generic Letter 88-17
2.  Guidance for Meeting Generic Letter 88-17
3.  Abbreviations and Definitions

(NUDOCS Accession Number 8810180350)
Page Last Reviewed/Updated Thursday, June 27, 2013