Neutronics of a sub-critical system burning non-recycled LWR waste

We have investigated neutronic properties of a subcritical system designed for transmutation of non-recycled TRU discharges from commercial light water reactors. Burnable absorbers (BA) and depleted uranium in variable concentrations are introduced in order to maximize fission to absorption ratios, and to minimize power peaking as well as reactivity losses. The use of nitride fuel raises linear power ratings to 60-110 kW/m while keeping fuel center line temperatures below 1400 K after gap closure. A comparatively small power peaking of 1.5 at a subcriticality level of 0.97 allows for a total core power of 1200 MWth with a corresponding proton beam power of 20 MW at BOL. Core averaged fission to absorption ratios for Np and Am as high as 0.5 are achieved using 10B enriched B4C as BA. Hence, both Pu and minor actinide inventories are reduced during burnup in the here proposed system, mitigating swelling problems arising due to high-activity in MA-based fuels. Disadvantages following BA introduction, such as increase of void coefficients and decrease of negative doppler feedback in conjunction with small values of βeff, are addressed by setting the BOL subcriticality level to 0.97. (author)