Heat transfer and fluid flow aspects of fuel-coolant interactions

A major portion of the safety analysis effort for the liquid metal fast breeder reactor is involved in assessing the consequences of a hypothetical core disruptive accident (HCDA). The thermal interaction of the hot fuel and the sodium coolant during the HCDA was investigated in two areas. A postulated loss of flow transient may produce a two-phase fuel at high pressures. The thermal interaction phenomena between fuel and coolant as the fuel is ejected into the upper plenum were investigated. A postulated transient overpower accident may produce molten fuel being released into sodium coolant in the core region. An energetic coolant vapor explosion for these reactor materials does not seem likely. However, experiments using other materials (e.g., Freon/water, tin/water) demonstrated the possibility of this phenomenon.