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(ITERP2/09) Thermal-Hydraulic Characteristics during Ingress-of-Coolant and Loss-of-Vacuum Events in Fusion Reactors

K. Takase¹, T. Kunugi², Y. Seki³, H. Akimoto¹

Department of Energy System Research, Tokai Research Establishment,
¹ Tokai Research Establishment, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki-ken
² Faculty of Engineering, Tokai University, Hiratsuka-shi,Kanagawa-ken,
³ Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Naka-machi, Ibaraki-ken
Japan

Abstract.  The thermal-hydraulic characteristics in a vacuum vessel (VV) of a fusion reactor under an ingress-of-coolant event (ICE) and loss-of-vacuum event (LOVA) were investigated quantitatively using preliminary experimental apparatuses.

In the ICE experiments, pressure rise characteristics in the VV were clarified for experimental parameters of the wall temperature, water temperature and with/without a blowdown tank. Furthermore, the functional performance of a blowdown with/without a water cooling system was examined and it was confirmed that the blowdown tank with the water cooling system is effective to suppress the pressure rise during the ICE event.

In the LOVA experiments, the saturation time in the VV from vacuum to atmosphere was investigated for various breach sizes and it was found that the saturation time is in inverse proportion to the breach size. In addition, the exchange flow characteristics through breaches were clarified for the different breach positions on the VV. It was proven from the experimental results that the exchange flow becomes a counter-current flow when the breach was positioned at the roof on the VV and a stratified flow when it is formed at the side of the VV, and then the flow exchange under the stratified flow condition is smoother than that under the counter-current flow. Based on these, the severest breach condition in ITER was changed from the top-break case to the side-break case.

In addition, to predict with high accuracy the thermal-hydraulic characteristics during the ICE and LOVA events under the ITER condition, the necessity of a large-scale test facility was mentioned. The current conceptual design of the combined ICE/LOVA test facility with a scaling factor of 1/1000 in comparison with the ITER volume was expressed.

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