Fuel assembly

The axial length of a natural uranium pellet charged in natural uranium regions at upper and lower axial ends of a fuel assembly, where the linear power density is relatively low, is made longer than the axial length of a uranium pellet charged in other axial regions of the fuel assembly. The upper limit for the axial length of the natural uranium pellet is defined as I/d = 30 (in which I represents the axial length and d represents the diameter of the natural uranium pellet). In view of the above, the number of the natural uranium pellets required for one fuel assembly can be reduced than usual and they can be discriminated at once visually due to the difference of the length. Accordingly, it is possible to facilitate the production management, suppress the occurrence of inferior concentration distribution, prevent the loss of the production efficiency and reduce the production cost. (T.M.)