AbstractActive cooling components have to be employed in the divertor of a fusion reactor to handle the large power flow from the core plasma. An extremely large thermal stress and electromagnetic force acting on these components may cause cracking of the cooling pipe. Since the inner wall and the vacuum vessel will be significantly damaged by this loss of coolant accident (LOCA), control schemes have to be considered. The process of in-vessel LOCA and ex-vessel LOCA were investigated, and several control schemes are suggested such as the use of an expansion chamber and the use of a shielding shutter. In addition, the pressure rise in vacuum chamber due to a water leak was analyzed for the scheme using the expansion chamber.