NRC Generic Letter 80-88, Seismic Qualification of Auxiliary Feedwater Systems

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(GL 80-88)

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555

October 21, 1980

ALL OPERATING PRESSURIZED WATER REACTOR LICENSEES

SUBJECT: SEISMIC QUALIFICATION OF AUXILIARY FEEDWATER SYSTEMS

After the accident at Three Mile Island (TMI), a large amount of our attention focused on the capability of plants to reliably remove shutdown decay heat. The NRC Action Plan (NUREG-0660,Section II.E) identifies post-TMI actions that are underway concerning this general subject. While we recognize that alternate ways may be available for removing decay heat following anticipated transients or accidents, removal of heat through the steam generators would be the first choice for accomplishing a safe plan, shutdown. For this reason, the design of auxiliary feedwater (AFW) systems should satisfy the same standards applied to other safety related systems in the plant. Accordingly, the current acceptance criteria for AFW systems which are applied to construction permit and operating license reviews are contained in Section 10.4.9 of the NRC's Standard Review Plan (SRP), which treats the AFW system as an engineered safety feature. However, only the recently licensed facilities have been reviewed against this section of the SRP. A copy of that SRP Section is attached as Enclosure 1. The purpose of this letter is to identify our generic concerns related to the seismic design capabilities of AFW systems in operating PWRs and to describe a program which we intend to undertake in reviewing the capability of operating PWRs to remove decay heat following an earthquake.

Since the accident at TMI, we have been reviewing AFW systems for all operating PWRs to assess the need to backfit design and procedural modifications. Our review has been based on a deterministic evaluation, primarily against the SRP, in conjunction with a reliability study utilizing event and fault tree analyses to determine dominant failure modes. During the course of these reviews, we have informally questioned licensees regarding seismic capabilities of AFW system piping and components but our interest has been specific to the potential for seismically induced damage to the system water source and subsequent damage to the pumps due to loss of suction. Our concern now has turned to the capability of the entire system. Attached as Enclosure 2 is a table listing some of the information informally received from licensees which describes the capability of systems to perform, in the event of an earthquake.

We have recently conducted a preliminary probabilistic assessment of seismically induced loss of decay heat removal for plants which are considered not to have seismically qualified AFW systems. The results of the study are contained in an NRC memorandum dated August 8, 1980 a copy of which is attached as Enclosure 3. We intend to complete a more detailed evaluation within the next several months to determine whether there is sufficient safety justification for long term operation until any required plant modifications have been completed. . October 21, 1980


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The evaluation program developed by the staff will include a site visit to a few plants to better define the scope and depth of our continuing review. Following the site visits, within the next few weeks, we will request of each PWR licensee information on the capability of each plant to satisfactorily remove decay heat following an earthquake. The primary purpose of our evaluation program is to develop consistent and balanced criteria for making backfit decisions should they prove necessary. This technical issue, including our evaluation program, was recently discussed with our Advisory Committee on Reactor Safeguards. Their letter which resulted from the meeting is attached as Enclosure 4.

Although the NRC evaluation effort is continuing, we strongly encourage you to promptly re-examine your plants capability to remove decay heat following an earthquake. If your review should identify any modifications necessary to ensure this capability, you should begin to plan for such activities.

Sincerely,

Darrell G. Eisenhut, Director Division of Licensing

Enclosures:

1. SRP Section 10.4.9
2. Table of Seismic Capabilities
3. 8/8/80 Memo: Mattson to Eisenhut
4. ACRS Letter

. Enclosure 2

SEISMIC QUALIFICATION OF AFW SYSTEMS

X indicates that the licensee has not analyzed the component(s) for the SSE

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