Computational Fluid Dynamic Studies of the MEGAPIE Spallation Source Target and Safety Vessel

In this paper, we describe some numerical investigations that have been undertaken in demonstrating the cooling principle of the MEGAPIE liquid-metal neutron spallation source target using computational fluid dynamics (CFD). Simultaneously, stresses in the structural components have been examined using finite element method (FEM) techniques, with an in-house CFD/FEM interface program employed to ensure full consistency of data at the local level. Results for steady-state operation of the target show that the critical lower target components are adequately cooled tinder normal operating conditions, and that stresses and displacements are well within tolerances. With unexpected overfocusing of the beam, there is the potential for structure failure of the target window. Detailed analysis has shown that 35% overfocusing call be tolerated, and that even if the target window is breached, the D2O-cooled safety vessel positioned around the target will remain intact, even with 100% beam overfocusing. Transient analysis of a thermal shock incident is also described in which a jet of cold D2O is imagined to impinge on the target window following rupture of the nearby Water Circuit. Results indicate that the margin of error to ductile-brittle transition is large enough for the integrity of the window not to be at risk from this incident.