Minor Actinide Transmutation in Supercritical-CO₂-Cooled and Sodium-Cooled Fast Reactors with Low Burnup Reactivity Swings

This paper presents the investigation of minor actinide (MA) transmutation in supercritical CO₂-cooled and sodium-cooled fast reactors (S-CO₂-FR and SFR) with the thermal output of 600 MW(thermal) for simultaneously attaining low burnup reactivity swings and reducing long-life radioactive waste. Minor actinides are loaded uniformly in the fuel of the cores, and the MA contents are determined to minimize the burnup reactivity swings. In the S-CO₂-FR, the burnup reactivity swing is minimized to 0.11% ∆k/kk’ when the MA content is 6.0 wt%. In the SFR, the MA content was determined to reduce the burnup reactivity swing while maintaining sodium void reactivity under a design limitation of 5 $. The burnup reactivity swing of the SFR is reduced to 1.94% ∆k/kk’, whereas sodium void reactivity is about 4.7 $ when 10.0 wt% MAs are loaded. The low burnup reactivity swing enables minimization of control rod operation during fuel burnup. The number of control rods in the two reactors is reduced to ten, which is half of a typical sodium-cooled mixed-oxide fuel MONJU reactor without MA loading. The MA transmutation rates in the S-CO₂-FR and SFR are 42.2 and 52.2 kg/year, respectively, which are equivalent to the production rates in seven and nine light water reactors of the same electrical output.