United States Nuclear Regulatory Commission - Protecting People and the Environment

RELAP5 Analysis of Mitigation Strategy for Extended Blackout Power Condition in PWR (NUREG/IA-0467)

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Publication Information

Manuscript Completed: November 2015
Date Published: May 2016

Prepared by:
Andrej Prošek, Andrija Volkanovski

Jožef Stefan Institute
Jamova cesta 39
Sl-1000 Ljubljana, Slovenia

K. Tien, NRC Project Manager

Division of Systems Analysis
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Prepared as part of:
Prepared as part of The Agreement on Research Participation and Technical Exchange Under the Thermal-Hydraulic Code Applications and Maintenance Program (CAMP)

Published by:
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Availability Notice


A set of measures have been proposed and currently implemented in response of the accident at the Fukushima Daiichi nuclear power plant. Those measures include diverse and flexible mitigation strategies that increase the defense-in-depth for beyond-design-basis scenarios. Mitigation strategies are based on the utilization of the portable equipment to provide power and water to the nuclear power plants in order to maintain or restore key safety functions. The verification of the proposed measures with the plant specific safety analyses is endorsed in the mitigation strategies. The purpose of the study was to investigate the application of the deterministic safety analysis for mitigation strategy of the extended station blackout (SBO). A methodology for the assessment of flowrates for steam generator makeup using portable pump is proposed. The aim is to fill steam generator without available information on level in such a way that makeup is sufficient and that at the same time the steam generators are not overfilled. The RELAP5/MOD3.3 computer code and input model of a two-loop pressurized water reactor is used for analyses, assuming different injection start times, flowrates and reactor coolant system losses. The calculated results show effectiveness of the proposed extended SBO mitigation strategy. The applicability of the developed method on operational power plant is validated.

Page Last Reviewed/Updated Thursday, May 19, 2016