Post-test analysis of the BTF-104 severe-fuel-damage experiment using the CATHENA thermalhydraulics code

In the BTF-104 (Blowdown Test Facility) experiment a single fully-instrumented, CANDU-type fuel element was subjected to conditions representative of a Loss-Of-Coolant Accident (LOCA) with additional Loss-Of-Emergency-Coolant Injection (LOECI). Depressurization was followed by a period of degraded steam cooling achieving fuel temperatures of the order of 1800-1900 °C. Material and coolant temperatures, and fission-product releases were monitored. The principal objective of the BTF-104 experiment was to determine the timing and amount of short-lived fission-product release from the fuel element at the target fuel temperature. Information generated from BTF experiments is used by the CANDU Owners Group (a consortium of AECL and Canadian nuclear utilities) for validating computer codes used in licensing CANDU reactors. Simulations of the BTF-104 experiment were conducted using the CATHENA code (Canadian Algorithm for THErmalhydraulic Network Analysis) to provide a better understanding of the thermalhydraulic phenomena observed in the experiment. This paper summarizes the major events and conditions of the BTF-104 experiment, describes the CATHENA idealization of the BTF-104 fuel stringer and BTF loop, and discusses important results obtained by these simulations.