Assessment of Channel Coolant Voiding in RD-14M Test Facility using TRACE (NUREG/IA-0446)

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Publication Information

Manuscript Completed: December 2013
Date Published: August 2014

Prepared by:
Andrew Oussoren
Aleksandar Delja

Canadian Nuclear Safety Commission
280 Slater Street
P.O. Box 1046 Station B
Ottawa, Ontario, Canada
K1P 5S9

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

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Abstract

Coolant voiding in fuel channels of CANDU reactors during a Loss of Coolant Accident (LOCA) is important to reactor behaviour due to the power pulse arising from positive void reactivity. The prediction of voiding in fuel channels is therefore of fundamental importance to LOCA safety analysis. The CNSC is evaluating the applicability of the TRACE thermal hydraulics code to CANDU reactor simulation.

In this study, inlet header LOCA test B0106 from AECL’s RD-14M thermal hydraulic test facility was modeled using TRACE. RD-14M is a scaled CANDU heat transport system containing 10 electrically heated fuel channels and full elevation feeders and boilers. In this test, a break in an inlet header is simulated using a fast opening valve. The size of the break is such that it creates near stagnation flow in the affected loop. A neutron scatterometer installed on one of the test channels measures void fraction in the channel during the transient.

The TRACE code was capable of predicting channel voiding trends with good accuracy, while the extent of voiding was generally over predicted. System pressure is predicted very well over the first several seconds of the transient; however pressure is under-predicted later in the transient. This under-prediction can be corrected through modifying the multiplying coefficients in the TRACE critical flow model. Fuel sheath temperature was under predicted for most of the test; this is due to limitations in the ability to represent a horizontal fuel channel in TRACE.