Thermal hydraulic characteristics during ingress of coolant and loss of vacuum events in fusion reactors

The thermal hydraulic characteristics in the vacuum vessel (VV) of a fusion reactor under an ingress of coolant event (ICE) and a loss of vacuum event (LOVA) were investigated quantitatively using preliminary experimental app aratuses. In the ICE experiments, pressure rise characteristics in the VV w ere clarified for experimental parameters of the wall temperature and water temperature and for cases with and without a blowdown tank. In addition, t he functional performance of a blowdown tank with and without a water cooli ng system was examined and it was confirmed that the blowdown tank with a w ater cooling system is effective for suppressing the pressure rise during t he ICE. In the LOVA experiments, the saturation time in the VV from vacuum to atmosphere was investigated for various breach sizes and it was found th at the saturation time is in inverse proportion to the breach size. In addi tion, the characteristics of exchange flow through breaches were clarified for the different breach positions on the VV. It was proven from the experi mental results that the exchange flow became a counter-current flow when th e breach was positioned on the top of the VV and a stratified flow when it was formed on the side wall of the VV, and that the exchange flow under the stratified flow condition was smoother than that of counter-current flow. On the basis of these results, the severest breach condition in ITER was ch anged from the top-break case to the side-break case. To predict with high accuracy the thermal hydraulic characteristics during ICEs and LOVAs under ITER conditions, a large scale test facility will be necessary. The current conceptual design of the combined ICE-LOVA test facility with a scaling fa ctor of 1/1000 in comparison with the ITER volume is presented.