Simulation of CANFLEX thermal hydraulics during a SBLOCA in a CANDU reactor

Thermalhydraulic behavior of an advanced CANDU fuel, CANFLEX (CANdu FLEXible), has been described with CATHENA(Canadian Algorithm for THermal-hydraulic Network Analysis). A CATHENA CANFLEX circuit and channel simulation for a 2.5 % RIH (Reactor Inlet Header) LOCA case has been made to assess the relative safety of CANFLEX over the reference fuel. A key design improvement of CANFLEX is a flatter radial power shape over the reference fuel. The operational margin can be increased by decreasing the outer fuel center temperature to 278 .deg. C, which is from 1443 .deg. C to 1165 .deg. C. However, the inner fuel center temperature increased to 154 .deg. C due to the flatter radial power profile. A better safety margin with CANFLEX may be obtained in the outer sheath temperature without experiencing a fuel heatup. The other transients indicated that CANFLEX relative safety can be achieved for this 2.5 % RIH LOCA scenario in a typical CANDU 600 plant