Long-Term Validation of the Molten Fuel-Moderator Interactions Model

Pressurized heavy water reactors of the CANDU design may be susceptible to a partial or a complete blockage of the flow of coolant to some of the pressure tubes. This event, although very rare, would result from the presence of debris in the heat transport conduits. In the case of an extreme event where the coolant flow is blocked completely, in addition to failure to scram the reactor, an accident scenario may prevail. Coolant trapped in the pressure tube is expected to boil off; the fuel rods would overheat and partially melt with the melt accumulating at the bottom of the pressure tube. This degraded situation, along with the high pressure involved under normal operation conditions, would lead to a rupture of the pressure tube. The pressure signature at the rupture site predicted from a lumped parameter phenomenological model is used as an input to a three-dimensional ANSYS model to assess the pressure signature at the inner walls of the tank in response to the pressure tube rupture. The pressure predicted by the ANSYS model is benchmarked against experimental data from the literature.