PURPOSE: To simplify the structure of a cold trap for impurities in liquid Na by providing an inner tube, as the support structure of the impurities capturing part, communicating with the Na outlet of the capturing part and having a Na discharge hole.

CONSTITUTION: Inner structure 4 including a capturing part 6 for impurities in liquid Na is supported with inner tube 28. The lower part of tube 28 communicates with the Na outlet of part 6, and Na outlet nozzle 29 is attached to the upper part. Na is introduced into distributor 22 from inlet 21 and cooled with cooling fins 24 while falling through annulus part 23. Impurities in the Na flow into lower body 25 in a supersatd. state and flow down the space between the outer frame of na pass guide structure 4 and body 25. The flowing Na reverses at lowermost end plate 31 and passes through mesh 12 of part 6 to filter the impurities. The impurities-free Na turns to a rising stream in center pipe 30, rises through tube 28 as an economizer, and is discharged from nozzle 20.