Analysis of Fission Gas-Fuel Particle Dispersion in a Voided Triangular Channel Under Sustained PCM Conditions

The release and axial dispersion of fission gas-fragmented fuel particle mixture through the voided coolant channel following the fuel pin rupture in sodium fast reactor under severe accident condition is investigated. The motion of fuel particles released from the ruptured fuel pin is evaluated using Euler–Lagrangian approach. The fission gas velocity in the triangular voided coolant channel is described using an exponentially decaying pressure gradient. The decaying pressure gradient has a characteristic time typical of fuel pin rupture resultant fission gas release process. A parametric analysis for gas-particle flow in the range of 50 and 1000 μm diameter fuel particles is carried out. Results show that the fuel particle velocity and displacement for particles of diameter 1000 μm and above are negligible and not expected to participate in the fuel particle dispersion following the pin rupture. Also, dispersion behavior of fuel particles less than 100 μm is identical to that of fission gas. The result brings out the influence of pressure decay time constant and the fuel particle relaxation time on the behavior of fission gas-fuel particle mixture following the fuel pin rupture. It contributes to the evaluation of in-vessel radiological source term due to refractory material under severe accident condition in sodium fast reactor.