| 摘要 |
PROBLEM TO BE SOLVED: To reduce the number of uranium fuel rods containing burnable poison, to enhance a MOX charge rate, to properly maintain thermal allowance and to reduce an influence to a neutron instrumentation, in a MOX fuel assembly. SOLUTION: This fuel assembly is concerned in a fuel assembly charged into a boiling water reactor, in particular, relates to a fuel assembly having a fuel rod mixed with plutonium. Uranium fuel rods containing a burnable poison are arranged in positions in the outermost peripheral fuel rod layer of the fuel assembly or positions in the vicinity of the center, and the uranium fuel rods containing the burnable poison are arranged in positions separated from the corner positions opposite to a control rod insertion side by one or two fuel rod pitches in the outermost peripheral fuel rod layer, degradated uranium fuels rod or natural uranium fuel rods are arranged in the corner positions, and degradated uranium or natural uranium is used as a base material of the uranium fuel rod containing the burnable poison, in this fuel rod assembly. The number of the uranium fuel rods containing the burnable poison is reduced thereby, the MOX charge rate is enhanced thereby, the thermal allowance is maintained properly thereby, and the influence to the neutron instrumentation is reduced thereby.
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