Patent Number: 
Section: claims

1. A water injection device that injects water into a reactor containment vessel, the device comprising:a flow path through which cooling water is supplied;a disk that closes the flow path;a swing arm that is connected to the disk and performs closing and opening of the flow path by the disk; anda weight that is connected to the swing arm via a swing lever, whereinthe weight is supported by a support member made of a low melting point alloy,the swing arm has one end which is rotatably supported by a body of the water injection device and another end which is rotatably connected to the swing lever,an end portion of a side opposite to an end portion which is connected to the swing arm of the swing lever is connected to the weight via a wire, andthe low melting point alloy is an alloy that is in a solid state at a temperature lower than 200° C. and is in a liquid state at 260° C. 2. The water injection device according to claim 1,wherein the flow path is closed by the disk by a connection portion between the swing arm and the swing lever being supported by an arm rotatably provided with respect to the body of the water injection device. 3. The water injection device according to claim 1,wherein the disk is seal welded to a body of the water injection device using a metal material having a melting point lower than that of the low melting point alloy constituting the support member. 4. The water injection device according to claim 1, wherein the support member melts due to the temperature rise of the surrounding environment of the water injection device, the weight falls, the disk is released due to the fall of the weight, and water is injected into the reactor containment vessel. 5. The water injection device according to claim 1, wherein the low melting point alloy constituting the support member is an alloy including Sb: 8.0 mass % to 12.5 mass %, Ag: 0 to 6.0 mass %, and Cu: 0 to 1.5 mass %. 6. The water injection device according to claim 5, wherein the low melting point alloy constituting the support member is an alloy further including Sn.