Thermal-hydraulic design of high conversion type core of FLWR

Kobayashi, Noboru; Onuki, Akira; Uchikawa, Sadao; Okubo, Tsutomu

A thermal-hydraulic design of the high-conversion (HC) type core of the innovative water reactor for flexible fuel cycle (FLWR) was constructed under the natural circulation core cooling, in order to achieve that HC-FLWR core can be converted to a breeder type one. The criteria on the thermal-hydraulic design of HC-FLWR were that the average void fractions in the core was smaller than 50%, and that the critical power ratio was larger than 1.3. The criterion on void fractions was determined from the nuclear design of HC-FLWR. The length of the chimney and the settings of the inlet orifice are common in both types of cores. The coefficient of the lower tie-plate of the HC-FLWR core and the temperature of the feed water were parametrically changed. Consequently, the design criteria were satisfied by adopting the setting of the form loss coefficients of the lower tie-plate comparable to those of the current BWRs and by lowering the feed water temperature to 505 K.