PURPOSE: To convert gases such as hydrogen and tritium into a state easy to hold without discharging them to the atmosphere, in the titled apparatus as the secondary cooling system of a fast breeder reactor, by burning gas formed during the regeneration of a cold trap into an aqueous state.

CONSTITUTION: During the regeneration of a plugged cold trap 10, inlet and outlet valves 15, 18 are closed, line valves 21, 22 are opened, and liquid Na is circulated between the trap 10 and a degassing pot 23 by an electromagnetic pump 16. Hereon, by heating the trap 10 with a heater 13, hydrogen and tritium captured by a mesh 11 are transferred to the pot 23 with the liquid Na as a carrier. Then, the pot 23 is decompressed with a vacuum pump 29, hydrogen and tritium in Na are transferred to gas and discharged through a degassing pipe 25, and the vapor and mist of Na are removed in traps 26, 27. Thereafter, the exhaust gas is mixed with air from a blower 33 and reacted with O2 in a catalytic oxidizing device 35. The resulting steam-contg. gas is disharged through a gas- water separator 42 to the atmosphere, after most of steam is separated as water from it by a cooler 37.