Converting the VVÉR-440 to enhanced-enrichment fuel

Originally, the fuel cycle for the standard W~R-440 was designed for use with fuel of enrichment 2.4 and 3.6%, with each reload involving approximately one-third of the core, which consists of 312 standard assemblies and 37 control ones. With a mean enrichment for the incoming fuel of 3.25% and the fuel moving from the edge to the center, the reactor could operate at full power between reloads for 7000 h, average burnup in the spent fuel about 29 MW'days/kg. The fuel utilization can be increased substantially by increasing the enrichment of the incoming fuel and reducing the number of assemblies changed during reloading. With a quarter of the core renewed and enrichment 3.6%, the same mode of migration can raise the mean burnup to 36.5 MW-days/kg. However, the effective interval between reloads in that case is reduced to about 6500 h. Raising the enrichment to 4.4% with four reloads in a cycle increases the burnup by a further 25% and prolongs the interval between reloads to about 8000 h.