Large break loss-of-coolant accidents analysis using the TUF code

The TUF (Two-Unequal-Fluids) computer code has been developed by Ontario Hydro as a state-of-the-art system thermal-hydraulics code for the transient response of the CANDU nuclear generating stations. The TUF code is employed for the simulation of the heat transport system (HTS) response following large break loss-of-coolant accidents (LOCAs) to provide boundary conditions for the assessment of shutdown system effectiveness, radiological consequence and emergency coolant injection effectiveness and for pressure tube integrity. This paper provides an overview of large break LOCAs methodology during the early blowdown and refill phases, with particular emphasis on the thermal-mechanical response of channels. Bruce Nuclear Generating Station A is selected for the application of the new methodology. The following tasks are performed in the course of the analysis: identify the critical break which results in the most degraded cooling conditions in the core; determine the HTS response; and determine the extent and timing of the pressure tube ballooning into contact with the calandria tube and heat load to moderator. (author). 8 refs., 3 tabs., 12 figs