| abstract |
(57) [Summary] [PROBLEMS] To reduce the types of Pu enrichment in a MOX fuel assembly and increase the amount of Pu loaded, and at the same time, to flatten the power distribution in the height direction of the core and burnable poisons at the end of the operation cycle. Eliminating unburned fuel increases fuel design flexibility and fuel economy. SOLUTION: A fuel rod G including a burnable poison at an axial portion thereof and surrounding the axial portion with a substance not containing a burnable poison. i is arranged in the outermost peripheral region of the fuel assembly. The diameter of the axis of Gi is larger in the order of G1, G2 and G4, and G3 is larger. Is the same as G2 in the upper half and G4 in the lower half. This G3 is also arranged at a position facing the water rod. In other places, the fuel rods M containing no burnable poisons Place. |