Validation of the SAMPSON/MCRA Code against CORA-18 Experiment

The Fukushima-Daiichi nuclear accident has highlighted the importance of analyzing the meltdown of a Boiling Water Reactor (BWR). The core melting in a nuclear reactor is affected by different phenomena, whose the most substantial are the chemical reactions and the interactions between the core materials; these can lead to a temperature escalation and bring forward the melt progression. Moreover it has to be considered that the geometry of a BWR complicates the core modeling. The existence of channel boxes and control blades represents a significant challenge for the heat transfer calculation, in particular as regards the thermal radiation. The CORA-18 has been selected as the validation test to provide information on the damage progression of a BWR fuel element. A model has been built in SAMPSON/MCRA and a simulation of CORA-18 experiment has been performed. The zirconium oxidation assumes noteworthy importance after the temperature has reached values close to 1300 K and leads to a considerable heat release. The temperature trends appear to be similar to those in the experiment CORA-18; the hydrogen production, however, is approximately the double of the experimental data. The melting of the structures occurs at the end of the computed transient and portions of the debris are deposited on the rods under the form of crust