Transient characteristics of typical design basis accidents in integrated small reactor NHR200-II using RELAP5 model

The development of advanced integrated small reactors is one of the most important trends in nuclear engineering nowadays, the NHR200-II reactor proposed by Tsinghua university has also undergone several iterations of improvement. The increased thermal–hydraulic parameters mean that the design-basis accidents need to be reanalyzed, of which three typical scenarios are chosen as benchmarks and simulated with the complete RELAP5-model. The small break loss-of-coolant accident, the pump-shaft-stuck accident and the heat-transfer-tube-rupture in main heat exchanger accident were assessed systematically and showed good agreement with previous research. The characteristics like the transient flow rate at the break, the moment of inertia of circuit pump and the position of the main heat exchanger were examined, different control variables mainly affect the sequence of trigger actions rather than overall thermal–hydraulic parameters. The results demonstrate that the reactor core can be cooled sufficiently throughout all transient conditions and be flooded with coolant.