| 摘要 |
PROBLEM TO BE SOLVED: To obtain a fuel assembly in which the leak of neutrons from the upper part of a fuel body is suppressed, in which an irregularity in the pressure force of a presser bar spring in a uranium and plutonium mixed oxide (MOX) fuel rod is suppressed and in which the soundness of the presser bar spring is ensured by providing a member between a pellet and the presser bar spring only in the fuel rod. SOLUTION: This fuel assembly is provided with a member 11a between a MOX pellet 1a and a presser bar spring 9 only in a MOX fuel rod 2a. At this time, since the member 11a is provided in the same position as the lower end of a natural uranium region 12 in an adjacent uranium fuel rod 2b, the member 11a absorbs or reflects neutrons which come out from the lower side. As a result, the amount of neutrons which are leaked to the outside from the upper part of a fuel body can be suppressed. In the uranium fuel rod 2b, the natural uranium region 12 is provided with a neutron- leak suppression effect, the member 11a is not filled, and the cost of the fuel assembly can be reduced. In addition, on the basis of the heat insulating effect of the member 11a, heat which is transmitted to the presser bar spring 9 from the MOX pellet 1a is suppressed, an irregularity in the pressure force of the presser bar spring 9 is suppressed, and the soundness of the presser bar spring 9 itself can be ensured.
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