RELAP5 and TRACE Simulation of BETHSY 4.1a TC Test (NUREG/IA-0560)

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Publication Information

Manuscript Completed: December 2025
Date Published: March 2026

Prepared by:
Andrej Prošek

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

Albert Hsieh, 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

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Abstract

The objective of the 4.1a TC (counter-part test) test carried out on the Boucle d`Etudes Thermohydraulique Systeme (BETHSY) facility was at different states to study the behaviour of the primary system under single phase natural circulation, two-phase natural circulation and reflux condenser mode, as well as transitions from one mode to another. The purpose of the present study was to assess the TRACE calculation of BETHSY 4.1a TC test against experimental data and RELAP5 calculation. BETHSY facility was a 3-loop replica of a 900–MW electrical power Framatome pressurized water reactor (PWR). The TRACE input deck was semi-converted from the legacy RELAP5 input deck using Symbolic Nuclear Analysis Package (SNAP). During the test the sequence of withdrawal of a predetermined quantity of primary coolant was repeated 14 times. Corresponding to these 14 draining phases, 3the test covers 15 stages from 100 % to 38 % of reactor coolant mass inventory, where term "stage" characterizes the period between two "draining phases". The results showed that the RELAP5 and TRACE computer codes are shown to reasonably simulate single-phase natural circulation, two-phase natural circulation, and reflux condensation.