Abstract: Horizontal partition wall 10 is disposed between ceiling slab 9 and floor slab 8. A plurality of storage tubes 6 each accomodating canister 2 are hanging from ceiling slab 9, and penetrate horizontal wall 10 to extend towards floor slab 8. Cooling passages are formed between horizontal partition wall 10 and ceiling slab 9 and between horizontal partition wall 10 and floor slab 8. Cooling air flowing through each of the cooling passages cools down storage tubes 6.

Abstract: A reactor core of a fast breeder reactor is supported by a core support within a reactor vessel. The reactor vessel is provided with a first or lower sodium chamber for accommodating low temperature sodium, a second or intermediate sodium chamber for accommodating low temperature sodium and a third or upper sodium chamber for accommodating high temperature sodium heated by passage of the low temperature sodium through the reactor core into the third sodium chamber. Low temperature sodium is introduced into the second sodium chamber arranged between the first and third sodium chamber for cooling the core support.

Abstract: A pad of a fuel assembly with a wrapper tube is pressed out from the interior of the wrapper tube to provide a band-like pad. The pad is reinforced by a reinforcing member fitted in a hollow portion of the pad. The pad is joint to the reinforcing member, or made so that swelling of the pad does not exceed that of the reinforcing material.