United States Nuclear Regulatory Commission - Protecting People and the Environment

BWR Anticipated Transients Without Scram in the MELLLA+ Expanded Operating Domain, Part 4: Sensitivity Studies for Events Leading to Emergency Depressurization (NUREG/CR-7182)

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Publication Information

Manuscript Completed: April 2014
Date Published: June 2015

Prepared by:
Lap-Yan Cheng, Joo Seok Baek, Arantxa Cuadra, Arnold Aronson,
David Diamond, and Peter Yarsky*

Nuclear Science and Technology Department
Brookhaven National Laboratory

*U.S. Nuclear Regulatory Commission

Tarek Zaki, NRC Project Manager

NRC Job CodesV6150 and F6018

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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Abstract

This is the fourth in a series of reports on the response of a boiling water reactor (BWR) to anticipated transients without reactor scram (ATWS) when operating in the expanded operating domain “MELLLA+.” In this report, we analyze the ATWS events initiated by the closure of main steam isolation valves and requiring emergency depressurization (ED). The analysis is done at the beginning-of-cycle and end-of-full-power-life. Our objective is to understand the sensitivity of ATWS-ED events to the initial operating core flow and to the spectrally corrected moderator density history (void history). We also consider different strategies for controlling the water level.

We simulate the ATWS events for 2500 seconds, a sufficiently long time for us to identify and understand the response of key components and the potential for damaging the fuel or causing the containment to fail. These events lead to the automatic trip of recirculation pumps, and to the operator actions to manually activate the automatic depressurization system when the wetwell (suppression pool) has reached the heat capacity temperature limit, and to regulate power by controlling the water level and injecting soluble boron.

The simulations were carried out using the TRACE/PARCS code system and the models we developed for a previous study with all relevant BWR systems.

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