Optimization of seed-blanket type fuel assembly for reduced-moderation water reactor

Shelley, A.; Shimada, Shoichiro*; Kugo, Teruhiko ; Okubo, Tsutomu; Iwamura, Takamichi

Parametric studies have been done for a PWR-type reduced-moderation water reactor (RMWR) with seed-blanket fuel assembles to achieve a high conversion ratio, negative void reactivity coefficient and a high burnup. It was found that 50 to 60% of seed in a seed-blanket assembly has higher conversion ratio. The number of seed-blanket layers is 20, in which the number of seed layers is 15 and blanket layers is 5. The fuel assembly with the height of seed of 1000mm2, internal blanket of 150 mm and axial blanket of 400mm2 is recommended. The conversion ratio is 1.0 and the average burnup in core region is 38.2 GWd/t. The enrichment of fissile Pu is 14.6 wt%. The void coefficient is +21.8 pcm/% void, however, it is expected that the void coefficient will be negative if the radial neutron leakage is taken into account. It is also possible to use this fuel assembly for a high core averaged burnup of 45GWd/t, however, the height of seed must be 500mm2 to improve the void coefficient. The conversion ratio is 0.97 and void coefficient is +20.8 pcm/%void.