PURPOSE: To utilize effectively a demister layer, and to increase the impurity collection capacity of the titled apparatus by providing a perforated riser tube to a demister so that Na may be capable of flowing into the demister from two passages on the outer side surface and on the inner side surface of the demister.

CONSTITUTION: In an impurity removing apparatus for removing continuously impurities in Na used as a coolant of a fast breeder reactor, the Na introduced from an Na inlet nozzle 19 is cooled to about 140°C by a cooling gas 27 flowing in a cooling tube 25 while Na flows down in the annular part 23 of an Na drum 16. A part of the deposited impurity of sodium oxide is separated and accumulated on a lower partition plate 18, and the Na flows up in an internal drum body 22, passing through a demister layer 28 from the outside to the inside to remove the impurity, and is discharged from a valve 31 and a nozzle 36 through a central passage 30. When the pressure of the Na flow is increased due to the deposition of the impurities on the demister layer 28, a passage opening device 32 is opened. Then the Na flows into the demister layer 28 from the inside, entering a riser tube 33 provided in the demister layer 28, flowing upward, and is discharged through a ring header 34 and a valve 35.