United States Nuclear Regulatory Commission - Protecting People and the Environment

GSI-191 Technical Assessment: Development of Debris Transport Fractions In Support of the Parametric Evaluation (NUREG/CR-6762, Volume 4)

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Publication Information

Manuscript Completed: October 2001
Date Published: August 2002

Prepared by:
S. G. Ashbaugh, D. V. Rao

Los Alamos National Laboratory
Los Alamos, NM 87545

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 debris transport analysis that supported a parametric evaluation of operating U. S. pressurized water reactors (PWR) plants to access whether or not Emergency Core Cooling Systems (ECCS) recirculation sump failure is a plausible concern. This evaluation was part of the Nuclear Regulatory Commission (NRC) Generic-Safety-Issue (GSI) 191 study tasked 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. The parametric evaluation identified a range of conditions in which PWR ECCS could fail in the recirculation mode of operation. These conditions stem from the destruction and transport of piping insulation materials, containment surface coatings (paint), and particulate matter (e.g., dirt) by the steam/water jet emerging from a postulated break in reactor coolant piping. The methodology used to estimate quantities of insulation debris transported to the recirculation sump screen was an essential part of the parametric evaluation. This report documents the methodology, assumptions, and data used to determine the fractions of debris generated that subsequently transported to the sump screen that were used in the parametric evaluation.

The transport fractions estimated were based on available experimental and analytical data and were focused on fibrous insulation debris. Both favorable and unfavorable transport fractions were estimated for small LOCAs with the sprays active and inactive, and for medium and large LOCAs. The transport fractions considered the size of the debris generated, the depressurization driven air and steam flow transport, the subsequent containment spray washdown transport, and the sump pool debris transport. Substantial uncertainty associated with the debris transport estimates is inherent due to the complexity of the analysis and the availability of appropriate data. Due to limitations of information, these estimates are not considered best-estimate plant-specific values. Instead, they represent a plausible range of debris transport estimates for the industry as a whole.

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