RELAP5 Simulation of Total Loss of Feedwater in Two-Loop PWR (NUREG/IA-0536)

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Publication Information

Manuscript Completed: November 2022
Date Published: February 2023

Prepared by:
Andrej Prošek

Jožef Stefan Institute
Jamova cesta 39
SI-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:
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


In Europe the design extension conditions (DEC) were introduced after the Fukushima Dai-ichi accident as preferred method for giving due consideration to the complex sequences and severe accidents without including them in the design basis conditions. The purpose of the study is to determine available elapsed time before core degradation and needed DEC safety features to prevent total loss of all feedwater (TLOFW) in a two-loop pressurized water reactor. In its documents, both WENRA (Western European Association of Nuclear Regulators) and the International Atomic Energy Agency (IAEA) present TLOFW initiating event as a possible DEC for existing nuclear power plants.

For simulations six U.S. Nuclear Regulatory Commission RELAP5 computer code versions were used to study the possible impact of code version on the results. The initiating event for TLOFW are multiple failures in which, besides the loss of main feedwater also auxiliary feedwater is lost. It is assumed that both high pressure and low pressure safety injection trains and batteries are available. Four different scenarios of TLOFW have been studied. The results section shows the comparison of calculated results obtained by several RELAP5 versions. Finally, the simulated results of total loss of feedwater with DEC safety feature available are shown.

Page Last Reviewed/Updated Thursday, March 02, 2023