GSI-191: Thermal-Hydraulic Response of PWR Reactor Coolant System & Containments to Selected Accident Sequences (NUREG/CR-6770)

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Publication Information

Manuscript Completed: January 2002
Date Published: August 2002

Prepared by:
D. V. Rao, K. W. Ross*
S. G. Ashbaugh

Los Alamos National Laboratory
Los Alamos, NM 87545

Subcontractors:
*OMICRON
2500 Louisiana, N.E.
Albuquerque, NM 87110

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 the results of calculations performed, as part of the resolution of the Nuclear Regulatory Commission (NRC) GenericSafety-Issue (GSI) 191, to simulate reactor coolant system (RCS) and containment thermalhydraulic response to a number of accidents that could potentially cause insulation debris to be collected on the sump screen. The purpose of the GSI-1 91 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 calculations were performed using the NRC-approved computer codes RELAP5 and MELCOR. These calculations identified important RCS and containment thermalhydraulic parameters that influence the generation and/or transport of debris in PWR containments. The calculations determined the time-dependent system response parameters. The system responses were used to construct accident progression sequences that form the basis for strainer blockage evaluations and probabilistic risk evaluations.