Emergency cooling system for nuclear reactors

In the cooling system of a pressurized water cooled reactor, an emergency cooling water feed pipe is connected to a lower header communicated with a steam drum by way of fine tubes passing through the reactor core. Cooling water flows from the header to the drum and is returned to the header through a recycling pump. According to this invention, the header is either directly connected to the drum through a fine tube or to a steam discharge pool or gas bomb through a check valve. If one of the tubes for connecting the header to the drum disposed at a level higher than that of the header is broken and water for emergency cooling is fed into the header through the feed pipe to increase the internal pressure of the header due to the condensation of the steam, a high temperature steam or incompressible gas flows into the header from the drum or gas bomb to prevent a vacuum from forming in the header while checking the formation of a siphoning effect. The coolant flowing in the unbroken tubes is thus prevented from flowing out and the emergency coolant is effectively fed to cool the reactor core. (Ohno, Y.)