The thermalhydraulic behavior of CANDU 600 reactor core fuelled with SEU 43

CANDU 600 nuclear reactors are usually fuelled with Standard 37 rods fuel bundles, and natural uranium (NU) dioxide (UO2) is used as fuel composition. A new fuel bundle geometry is proposed with 43 rods and slightly enriched uranium fuel (SEU 43 with 0.96% enrichment of 235U). In this paper a comparative analysis of the behavior of the primary circuit during a LOCA 35% RIH accident is performed for two core types (normal core 37 pin/bundles and a 43 pin/bundles proposed core). This kind of accident is considered to be a severe accident for CANDU type fuel elements. This analysis uses FIREBIRD code coupled with bipoint kinetics module. The bipoint kinetics module includes the models for the neutronic measurement instrumentation (the platinum detectors and the ion chambers) and the RRS (Reactor Regulating System) module. For the large LOCA, the RRS is of no effect, therefore the RRS option was not used for this analysis. The main conclusions of the analysis are the following: in this case of 35% RIH, LOCA, the thermalhydraulic behavior of the 43 pin/bundles core is better than the normal core. while the fuel and the sheath temperature reached not the melting point. (authors)