Simultaneous Evaluation of the Effects of ²³²U and ²³⁶U on Uranium Recycling in Boiling Water Reactors

The effects of ²³²U and ²³⁶U on uranium recycling in boiling water reactors are studied with the two-dimensional lattice physics code TGBLA. A simple analytic expression is proposed for reactivity compensation factor K, taking into account the self-shielding effect of resonance absorption in ²³⁶U: K = a + b/ (1 + ce₆)^1/2, where e₆ denotes the ²³⁶U concentration. To output the same energy as the 3.0 wt% enrichment fuel free from ²³⁶U, the constants are determined to be a = 0.06, b = 0.23, and c = 1.9. The introduction of 1 ppb ²³²U increases the surface dose rate of the fuel assembly by 60% over the aged enriched natural uranium. Lead time is as important as cooling time in ²³²U production because of the presence of the chain that originates from the alpha decay of naturally occurring ²³⁴U. The natural uranium feed and the separative work requirement are evaluated on these bases, introducing typical recycling strategies, and it appears that uranium recycling saves 17 to 19% of the natural uranium but increases the separative work by 0 to 2%. The front-end cost analysis reveals the benefit of a concentrated utilization of reprocessed uranium, which results from the self-shielding effect of ²³⁶U and the assumption of a linear dependence of the front-end penalty on ²³²U concentration. Also studied are plutonium composition in irradiated fuels and the effects of extended burnup.