Station Blackout Transient Analyses for VTT’s SMR Design LDR-50

VTT Technical Research Centre of Finland is developing a small district heating reactor that operates at low temperature and pressure with natural convection. The design features an innovative passive decay heat removal function that works without any mechanical moving parts. This paper presents variations of station blackout transient analyses done with Apros simulation software. The station blackout transient sets boundary conditions for the design. The variations include a normal case, in which the reactor trip is successful, and two cases in which the scram fails: at the beginning and end of cycle. The pool, which functions as the final heat sink, was assumed to contain spent nuclear fuel as additional heat source. The transients were calculated until the pool reached boiling point. During the station blackout transients, both primary temperature and pressure remained at safe levels and the containment removed decay heat efficiently. The pool reached 100 °C in 22 days in the case with scram and 12 days in the cases without scram. The primary pressure and temperature peaked at the highest in the case without scram at the end of cycle.