[en] The SOPHT code was assessed against Bruce Nuclear Generating Station B commissioning data from a heat transport system rapid cooldown. It was found that (a) under a rapid upstream depressurization, the steam relief valves, like orifices, had a lower discharge coefficient than the corresponding steadystate value and (b) the flashing of water in the steam generators during depressurization causes the at-power boiling heat transfer correlations to overpredict the steam generator heat transfer