LOFA Analysis for US ITER Solid Breeder Blanket

Abstract

This paper addresses the thermal transport issues associated with a loss of flow accident (LOFA) for US ITER solid breeder blanket. Two LOFA scenarios were considered. For a LOFA due to a simultaneous catastrophic pump failure, the coolant temperature reaches its boiling point within only about 15 – 20 seconds. This scenario appears extremely unlikely and should be better characterized through a probability risk assessment study in order to determine to what extent corrective actions such as the use of backup pump should be taken. For a LOFA due to loss of power to the coolant pumps, the resulting flow transient is characterized by considering the effect of fluid inertia and pump inertia. Once a determination of the flow coastdown has been made, the temperature histories of blanket elements and coolant are analyzed using lumped parameter techniques. The results of the analyses indicate that the rate of coolant temperature rise due to the heat (generated and/or stored) transferred from the solid breeder area is strongly dependent on the transient flow behavior. If the coolant pump can be designed with a sufficiently large pump inertia (with an inertia time constants of about 1.5 s or more), the coolant temperature can stay under its boiling point for several minutes to allow for corrective action to be implemented. As an added safety measure, it seems prudent to include in the design a system of expansion volumes and/or safety valves for accommodating coolant pressure transients.