United States Nuclear Regulatory Commission - Protecting People and the Environment

BWR Anticipated Transients Without Scram in the MELLLA+ Expanded Operating Domain, Part 3: Events Leading to Emergency Depressurization (NUREG/CR-7181)

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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 third in a series of reports on the response of a BWR/5 boiling water reactor to anticipated transients without reactor scram (ATWS) when operating in the expanded operating domain “MELLLA+.” In this report ATWS events initiated by the closure of main steam isolation valves are analyzed. The objectives were to improve the ability to model such events with the TRACE/PARCS code package, and to simulate them for a sufficiently long time (2500 s) to understand the response of key components and also the potential for fuel damage or damage to the wetwell (suppression pool). These events automatically trip the recirculation pumps. The operator’s responses are to activate the emergency depressurization system when the wetwell has reached the heat capacity temperature limit, and to control power through controlling water level and injecting soluble boron.

Models were developed for three different statepoints in the fuel cycle: beginning-of-cycle, peak-hot-excess-reactivity, and end-of-full-power-life. Eleven cases were assessed to determine the effect of three different strategies for controlling water level, two initial flowrates, two different locations for injecting boron, and two different numerical schemes. In all cases, the event is mitigated successfully in terms of minimizing the degree of damage to the fuel, and assuring the ability of the containment to fulfill its function.

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