PURPOSE: To prolong the service life of the titled device and enhance the removing efficiency by prodiving a trap for low-melting metal and a metallic filter on the outlet side of a soildification-type vapor remover, in the titled device used for sodium- cooled fast breeder reacter.

CONSTITUTION: The space 3 in a sodium tank 1 is communicated with the solidification-type vapor remover 5 through the first pipe 4 for detdcting a specified gas. In addition, the vapor remover 5 is communicated with a low-melting metal container 8 storing a low-melting metal 9 such as Na, K, etc. so that the metallic vapors contained in the flowing gas are completely removed. Further, since the container 8 is connected to the metallic filter 11 through the third pipe 10, the metal 9 is prevented from being carried by the flowing gas when the gas is passed through the metal 9 in the container 8.