Nuclear fuel assembly

Purpose: To increase the maximum allowable thermal power of nuclear fuel assemblies than usual in BWR type reactors. Constitution: A plurality of spacers are disposed to a fuel rod at a predetermined interval in the direction of the fuel rods, in which the flow of the coolants is resisted to worsen the cooling effect, as well as the thermal power exceeds the cooling performance near the upstream of the spacers to rise the temperature of the cladding tube till the burning damage may possibly be resulted. In view of the above, hollow fuel pellets are charged to a portion of the fuel rod from 98.5 to 100.5 % length assuming the distance from the lower surface of the fuel pellet charged at the lowermost end of the fuel rod to the upper end of each of the spacers as 100 %. In this way, since the hollow fuel pellets with a lower thermal power are disposed near the upper side of the spacers, the burning accident to the cladding tube at this portion can be avoided. Accordingly, the maximum allowable thermal power of the nuclear fuel assembly can be increased. (Kawakami, Y.)