A simple analytical method to evaluate transient behaviours of metal fueled fast reactors

Through our experiences in transient calculations using a general purpose transient system analysis code, the thermal hydraulic and nuclear responses of a typical metal fueled fast reactor core against unprotected transient overpower accidents (UTOP) and unprotected loss of flow accidents (ULOF) are found to be approximated by quasi-steady state representation. With these observations transient fuel and coolant temperature distributions in the core are given by simple algebraic expressions. The influences of temperature dependence of material properties are discussed. With these temperature predictions under typical ATWS conditions, effective reactivity changes due to sodium coolant and fuel temperature changes are found to have a unique linear relationship under the extreme conditions of sodium boiling as well as fuel failures. On the basis of these limiting relations, passive shutdown or power stabilization capabilities of metal fueled large fast reactors in case of accidents are discussed. (author)