Molten fuel moderator interaction experiments for PHWRs

One of the very-low probability events considered for CANDU PHWRs is a reduction in coolant flow to a single fuel channel. If the reduction inflow is severe, the fuel in the affected channel will rapidly overheat, leading to failure of the fuel channel and ejection of molten material into the surrounding heavy water moderator. AECL is implementing an experimental program to determine the nature of the interaction between the forcibly ejected molten material and moderator. A Molten Fuel Moderator Interaction (MFMI) facility has been constructed at Chalk River Laboratories for the experiments. To date, two non-corium tests - one with adjacent channels simulating a 3 × 2 channel matrix of the reactor core and the other without adjacent channels - have been performed in the MFMI facility. These tests have confirmed the experimental procedure, tested the facility instrumentation and provided base-line data for interpreting future tests to be conducted with corium ejection. The actual molten-fuel moderator-interaction experiments will consist of igniting the thermite mixture inside a 1.14-m long insulated pressure tube. Once the molten material has reached the desired temperature of ∼2400°C, the pressure inside the tube will be increased (to ∼10 MPa) until the pressure tube fails at a pre-machined flaw, ejecting the molten material into the surrounding tank of water.