Design of a PWR for long cycle and direct recycling of spent fuel

Abstract

In a previous work, a new design was proposed for the Pressurized Water Reactor (PWR) fuel assembly for direct use of the PWR spent fuel without processing. The proposed assembly has four zircaloy-4 tubes contains a number of 61-element CANDU fuel bundles (8 bundles per tube) stacked end to end. The space between the tubes contains 44 lower enriched UO2 fuel rods and 12 guide tubes. In this paper, this assembly is used to build a single batch loading 36-month PWR and the spent CANDU bundles are recycled in the on power refueling CANDU reactors. The Advanced PWR (APWR) is considered as a reference design. The average enrichment in the core is 4.76%w U-235. IFBA and Gd2O3 as burnable poisons are used for controlling the excess reactivity and to flatten the power distribution.The calculations using MCNPX showed that the PWR will discharge the fuel with average burnup of 31.8MWd/kgU after 1000 effective full power days. Assuming a 95 days plant outage, 36 calendar months can be achieved with a capacity factor of 91.3%. Good power distribution in the core is obtained during the cycle and the required critical boron concentration is less than 1750ppm. Recycling of the discharged CANDU fuel bundles that represents 85% of the fuel in the assembly, in CANDU-6 or in 700MWe Advanced CANDU Reactor (ACR-700), an additional burnup of about 31 or 26MWd/kgU burnup can be achieved, respectively. Averaging the fuel burnup on the all fuel in the PWR assembly, 58 or 54MWd/kgU burnup of the fuel can be achieved, respectively. Comparing this fuel cycle strategy with that of the advanced pressurized water reactors such as AP-1000 and EPR, we find that almost the same burnup can be achieved with longer core cycle: 36 months versus 18 months for these reactors.Recycling these fuel bundles in CANDU-6 reactors requires minimizing the lattice pitch to 22cm. In order to keep the coolant void reactivity of the ACR-700 slightly negative, the calandria tube should be increased from 7.8cm to 8.2cm to decrease the moderator to fuel volume ratio.