United States Nuclear Regulatory Commission - Protecting People and the Environment

GSI-191 Technical Assessment:  Parametric Evaluations for Pressurized Water Reactor Recirculation Sump Performance (NUREG/CR-6762, Volume 1)

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Publication Information

Manuscript Completed: August 2001
Date Published: August 2002

Prepared by:
D. V. Rao, B. C. Letellier, C. Shaffer*
S. Ashbaugh, L. S. Bartlein

Los Alamos National Laboratory
Los Alamos, NM 87545

Subcontractors:
*ARES Corporation
851 University Blvd. S.E.
Albuquerque, NM 87106

M. L. Marshall, NRC Project Manager

Prepared for:
Division of Engineering Technology
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code Y6041

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Abstract

This report documents a parametric evaluation of operating U. S. pressurized water reactors (PWR) plants that was conducted, as part of the resolution of the Nudear Regulatory Commission (NRC) Generic-Safety-Issue (GSI) 191, to access whether or not Emergency Core Cooling Systems (ECCS) recirculation sump failure is a plausible concern. The purpose of the GSI-191 study is to determine if the transport and accumulation of debris in a containment following a loss-of-coolant accident (LOCA) will impede the operation of the ECCS in operating PWRs. In the event of a LOCA within the containment of a PWR, thermal insulation and other materials in the vicinity of the break will be damaged and dislodged. A fraction of this material would be transported to the recirculation (or emergency) sump and accumulate on the screen thereby forming a debris bed. Excessive head loss across this bed could prevent or impede the flow of water into the core or containment.

The parametric evaluation identified a range of conditions in which PWR ECCS could fail in the recirculation mode of operation; thereby forming a credible technical basis for making a determination that sump blockage is a generic concern for PWRs. However, the likelihood that sufficient quantities could transport and accumulate on the recirculation sump screen to severely impede recirculation flow is plant specific. The primary limitation of the parametric evaluation was a general lack of plant specific data. A review of PWR plant design features and limited plant specific data did, however, indicate that adverse conditions exist in several plants.

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