Fuel assembly for reactor

In a fuel assembly in which n x n fuel rods are arranged in a lattice-like configuration, assuming fuel rods at the corner on the side of control rod insertion as at (1,1) coordinate, and fuel rods on the opposite side with respect to a diagonal line as at (n,n) coordinate, fuel rods at (1,1) coordinate or (1,1), (1,2), (2,1), (1,n), (n,1) coordinates are composed of uranium fuel rods. Further, remaining fuel rods are composed of MOX fuel rods, except for burnable poison-incorporated fuel rods. That is, the number of the MOX fuel rods having lower Pu enrichment degree can be decreased based on the distribution curve for the number of MOX fuel rods and the quantity ratio of the Pu enrichment degree. In addition, since the product (quantity ratio) of the Pu enrichment degree and the number of the MOX fuel rods is small, the MOX fuel rods having lower Pu enrichment degree can be substituted with easily handlable uranium fuel rods. As a result, the kinds of Pu enrichment degree can be decreased, thereby enabling to facilitate the production and improve economical property without greatly reducing the amount of plutonium per one fuel assembly. (N.H.)