FUEL ASSEMBLY

摘要

A fuel assembly comprising a plurality of first fuel rods, a plurality of second fuel rods having a length smaller than that of the first fuel rods and not provided in the outermost layer of a fuel rod array, and two water rods provided in a region in which eight fuel rods can be arranged, the fuel assembly being formed so as to satisfy the relation shown by the following expressions in which Awr represents the sum of cross-sectional areas of the water rods, Ach a cross-sectional area of a coolant flow passage in a lower portion of the fuel assembly, Lf an effective fuel length of the first fuel rods, n and Lp the number and an effective fuel length respectively of the second fuel rods, and B(Gwd/t) an average burn-up. B>/=60; 15n is an integer); Awr/Ach/=(3.00 x 10<-4>x n<2>+ 6.00 x 10<-4> x n - 1.2 x 10<-2>) x (Lp/Lf - 1) + 1.75 x 10<-1>; Awr/Ach x n<2> - 6.09 x 10<-2> x n + 1.33 x 10<-1>) x (Lp/Lf - 8.32 x 10<-1>).