Comparison between RELAP5 Mod3.2 and Mod3.3 in Simulating a Large Break LOCA in Low Power RRs

The assessment of reactor safety during the beyond design basis accident is oneof the lessons learned from Fukushima Daiichiaccident. In this article a total break ofone of the Neutron Beam Tubes (NBT) in a low powerpool type Research Reactor(RR) is analyzed. Two modes of RELAP5 thermal hydraulic system code, Mod3.2 and Mod3.3, are used in the analysis.In addition to the assessment of RR safety, the purpose from using two modes of RELAP5 is to assess Mod3.3 comparing with Mod 3.2 which is widely used in the analysis of RR’s safety. The RR is typically nodalized and a unique input dick is prepared for the two modes. The results showed that, the reactor coolant was rapidly drained and the core was partially uncovered. On the long term transient, the clad temperature in the un-covered region was continuously increased with time. Therefore, additional measures should be implemented to overcome the consequences of the accident. On the other hand, the comparison shows, in general, good agreement between the predictions of the two modes and demonstrates the capability of MOD3.3 in the analysis of RR safety.