[en] It was found that U-Ti and U-Zr alloys show the high resistance to pulverizing at the time of hydrogenation, and also the temperature at which the hydrogen dissociation pressure of 1 atm. is shown rises. Similarly in Th-Ti and Th-Zr systems without intermetallic compound, the ternary hydrides of Laves phase structure were found. U-ZrHx alloy has been already used widely and practically as the fuel for TRIGA reactors, and it possesses the very high peculiar safety. In order to obtain the basic data for developing the hydride fuel possessing the peculiar safety, the research on the hydrogen absorption property of the alloy containing U-Th has been advanced. The features of U-ZrHx fuel such as the negative temperature coefficient of reactivity, the property of holding fission products and others are explained. The restricting condition to the reactor design and the specification of an actual reactor possessing the peculiar safety, that is TRIGA power system are described. The characteristics of hydrogen absorption of intermetallic compound U₂Ti, U-Ti alloy, U-Th-Ti-Zr alloy and U-Th-Zr alloy are reported. (K.I.)