| 摘要 |
PURPOSE:To make flattening of fuel rod output distribution and to reduce ineffective neutron absorption by a gadolinia. CONSTITUTION:In a region such as the outermost layer of a fuel assembly, where neutron energy spectrum is very soft and thermal neutron flux is fairly large, fuel rods 2 and 3 into which a burnable poison with comparatively small neurton absorption cross-section, such as a boron and the like, is mixed, are arranged. In other regions of average neutron energy spectrum, fuel rods 11 into which a burnable poison with comparatively large neutron absorption cross-section, such as a gadolinium and the like, is mixed, and fuel rods 1 without mixing any burnable poison, both are arranged respectively. Even though distribution of uranium enrichment factor is made to be almost uniform, fuel rod output distribution can be made to be of flat one whole through the fuel life. Consequently, high burn-up of the fuel can be attained and also fuel cycle cost can be saved.
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