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Modelling Guidelines for CCFL Representation During IBLOCA Scenarios of PWR Reactors (NUREG/IA-0550)

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Publication Information

Manuscript Completed: February 2024
Date Published: October 2024

Prepared by:
J. Freixa, V. Martínez-Quiroga, K. Martin-Gil and F. Reventós

Advanced Nuclear Technologies
Universitat Politècnica de Catalunya
Av. Diagonal 647
Barcelona, 08028 Spain

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

Abstract

Studies on pipe integrity have pointed out the relevance of Intermediate break LOCA. These scenarios are more dynamic than small break LOCA due to a faster depressurization and a stronger force exerted by the break leading to a stronger counter current flow limitation (CCFL). The OECD/NEA ROSA-2 project conducted three IBLOCA experiments at the ROSA/large-scale test facility (LSTF) of the Japan Atomic Energy Agency. These three experiments have been analyzed with the US-NRC system code RELAP5. The attention has been focused on the representation of the CCFL phenomenology occurring simultaneously in different parts of the reactor. The post-test calculations have shown the adequate capabilities of RELAP to reproduce this type of scenarios, given that certain modelling guidelines are followed: (1) the three-dimensional representation of the core and upper plenum region (2) the correct configuration of the break nozzle and (3) the CCFL set up of locations and parameters. These three elements showed to be essential to reproduce correctly the phenomenology. The analysis has shown that it is not feasible to approach the CCFL configuration conservatively. Therefore, it is recommended to use the most realistic parameters, preferably obtained by simulating separate effect experiments, and then combine them with uncertainty analysis.

Page Last Reviewed/Updated Tuesday, November 05, 2024