GSI-191: Thermal-Hydraulic Response of PWR Reactor Coolant System & Containments to Selected Accident Sequences (NUREG/CR-6770)
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Manuscript Completed: January 2002
Date Published: August 2002
D. V. Rao, K. W. Ross*
S. G. Ashbaugh
Los Alamos National Laboratory
Los Alamos, NM 87545
2500 Louisiana, N.E.
Albuquerque, NM 87110
M. L. Marshall, NRC Project Manager
Division of Engineering Technology
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
NRC Job Code Y6041
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.