Simulations with trace of a BWR/4 steam line break under 'hot standby' conditions

Simulations have been performed with TRACE (V5.0P1) to predict the behavior of a BWR/4 plant under 'Hot-standby' conditions and subjected to a steam line break in the turbine building, which has no provision for radioactivity barriers. Two break sizes were considered, a 10% and 200% ('guillotine') break, along with two main steam isolation valve closure durations, 5 seconds and 20 seconds. Thus, three transients embodying a combination of these conditions have been simulated. The transients initiated from a system pressure P=68 bars and 5% core power, while the water level was at +1.15 m. The results yielded a total discharged mass of water and steam bounded between 1380 kg and 6730 kg for the limiting cases of the 10% break with 5 seconds closure time and the 200% break with 10 seconds closure time, respectively. The worst-case scenario result is consistent with the conservative (SAR) value of 7575 kg. (author)