| 摘要 |
PROBLEM TO BE SOLVED: To further raise burnup of fuel assembly realizing average takeout burnup of 45 GWd/t by raising fuel assembly enrichment of 5.0 wt.% or less in maximum enrichment without lowering the integrity of uranium fuel rods having burnable absorber inside and by setting uranium enrichment distribution in axial direction. SOLUTION: An assembly is constituted to have maximum pellet enrichment (a) of fuel rods 2 being a <=5% and average fuel assembly uranium enrichment is 4% or more and pellets to which gadolinia of 1% or more is added in uranium are charged in fuel rods 2 with gadolinia (sign G) except for the upper and lower ends so as to be the uranium enrichment c<a. Fuel rods 2 without gadolinia (sign 1, 2 and 3) are constituted to be a/b<=1.16 except for the upper and lower ends, where (b) wt.% is a cross sectional average uranium enrichment. The fuel rods 2 (sign G) have uranium enrichment distribution not decreasing from the lower part to the upper part except for the upper and lower ends.
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