PURPOSE: To prevent tritium from accumulating in sodium by absorbing the tritium adsorbed in a liquid sodium used as a heat medium for a high speed breeder reactor with Ca.

CONSTITUTION: When liquid metal sodium is used as a heat energy medium for a high speed breeder reactor, tritium, one of hydrogen radioative isotopes, is dissolved therein. With the actuation of a pump 2, the liquid sodium is introduced into a Ca dissolution tank 3; a part thereof is proceeded into an inner tank 4 through a valve 6 so that dissolve Ca 16 is dissolved therein upto the concentration for full saturation. The liquid sodium and the Ca-saturated sodium are quantitatively regulated respectively with valves 7 and 8 and mixed together to form a liquid sodium containing calcium of a specified concentration. The calcium contained therein combines with the tritium to form a hydride of calcium. After passing through an inner tank 12 in a precooling tank 11, the liquid sodium is introduced into an inner tank 14 in a tank 13 to deposit the Ca hydride. Subsequently, the liquid sodium is preceeded to a tank 15 to deposit Ca. Then, the liquid sodium is returned to a main Na passage 1 through a valve 9. When being recovered, the Ca flows to a Ca recovery system through a valve 10. The tritium is otherwise recovered.