Cooling device for dry well

A water injecting pipeline passes through between a lower dry well disposed below a reactor pressure vessel and a water source, and a water injecting valve is intervened in the lower dry well. A valve driving device is disposed to the water injection valve. The valve driving device comprises a temperature sensor secured at one end thereof and a shape memory alloy. On the other end of the shape memory alloy is connected with a link mechanism and a rack pinion mechanism. If high temperature debris should melt and fall from the reactor pressure vessel due to a state of a severe accident, the temperature in the lower dry well is raised. Then the shape memory alloy is deformed and a driving force due to the deformation is transmitted to the rack pinion mechanism by way of the link mechanism, and the water injection valve opens. Cooling water is injected from the water source into the lower dry well by way of the water injection pipeline and the water injection valve. The debris are cooled by the cooling water, to lower the temperature in the lower dry well. (I.N.)