| 摘要 |
PURPOSE:To contrive the reduction of mechanical correlation of a fuel element bundle, a wrapper tube and the like by applying the difference of working temperatures of coating tubes and the wrapper tube to use materials different in temperature dependency of swelling respectively. CONSTITUTION:A fuel assembly is formed so that many coating tubes 2 composed of the materials (cold working AISI 316 SS-Ti) in which titanium is added to cold working material 316 SS which is filled with fuel pellets 5 composed of mixing oxide of uranium and plutonium are bundled and covered by a wrapper tube 1 of a cold working material AISI 316. Thereby, since there is a peak of swelling at about 450 deg.C in the cold working material 316 SS-Ti and the swelling is suddenly lessened at the temperature equal to or more than said temperature, the maximum value of the swelling of the coating tubes is about 1/2, as compared with the case where the cold working material AISI 316 is used for both the coating tubes and the wrapper tube and the maximum value of the swelling of the wrapper tube is about 1/2, as compared with the case where the cold working material 316 SS-Ti is used for both the coating tubes and the wrapper tube.
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