Sodium cooled reactor

A plug is rotatably mounted on the vessel of a sodium cooled type reactor to close the upper opening of the vessel while leaving an annular gap formed between the side wall of the plug and the inner wall of the upper portion of the vessel which contains liquid sodium. This gap communicates with the interior of the vessel through a narrow passage formed between a cooling plate fixed to the lower end face of the plug and another cooling plate fixed to the vessel. A cooling pipe is attached to each plate and a coolant flows through the pipe to cool the cooling plate. Sodium evaporated from the liquid sodium surface is solidified by the cooled plates while passing through the passage therebetween to clog the passage before the arrival of the sodium at the annular gap. Devices located adjacent to the gap are not imperilled by the solidification of the sodium coming into the gap, and the plug is readily removed to permit the exchange of reactor fuels. (Ohno, Y.)