To support tritium in a state of being confined in sufficient retention volume up to a recovery process without leaking it by providing a tritium transmission preventing layer constituted of a porous ceramics layer coating the whole surface of a core grain and a non-porous ceramics layer coating the whole surface of the grain on the outer layer side.

The surface of a core grain 1 made of lithium titanate is coated with a porous ceramics layer 2 made of aluminum oxide, and further on the outer layer, a non-porous ceramics layer 3 made of an aluminum oxide. A tritium transmission preventing layer is formed out of the porous ceramics layer 2 and the non-porous ceramics layer 3. Hereby, under the temperature condition from neutron irradiation in the blanket of a unclear fusion reactor up to a recovery device, tritium generated in the interior can be held in a state of almost perfectly being confined. thereafter in the recovery device, heating process at about 1400 K and cover about 25 days is executed and tritium is recovered.