| 摘要 |
PROBLEM TO BE SOLVED: To eliminate the possibility of damaging fuel rods by enhancing cooling efficiency. SOLUTION: A fuel unit 1 of a fuel group, in which a plurality of fuel units 1 assemble, is constituted of a fuel body 2 extending in a fixed specified direction and a pipe 3 surrounding the periphery of the fuel body 2. A gap is formed between the fuel body 2 and the pipe 3 by spacers 4. The spacer 4 has an excitation face, for exciting a steam flow flowing with a component in a specified direction (a) in the gap to an inclination direction which is inclined in a specified direction (a). The excitation face applies a centrifugal force to the two phase flow. Steam flows 7 and 8 containing moistures as the two phase flow form a centrifugal flow in a gap between the fuel body 2 and a plurality of pipes 3, cooling inner faces of the pipes with a high efficiency to be heat exchanged and furthermore vaporized.
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