Simulation With Trace of a BWR/4 Steam Line Break Under "Hot Standby" Conditions

Abstract

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 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 worse-case scenario result is consistent with the conservative (SAR) value of 7575 kg.