New ²³⁷Np Burning Strategy in a Supercritical CO₂-Cooled Fast Reactor Core Attaining Zero Burnup Reactivity Loss

A new ²³⁷Np burning strategy in a supercritical CO₂-cooled fast reactor core has been proposed: consuming ²³⁷Np as fuel and burnable poison to attain zero burnup reactivity loss. Addition of ²³⁷Np at content of 6.5 wt% in fuel engenders nearly zero burnup reactivity loss of 0.02% k/k during 10 yr. The burning rate of ²³⁷Np in the core is ~69 kg/yr, which is equivalent to the quantity produced in a year from about 20 light water reactors of equivalent electrical output. The zero burnup reactivity loss enables reduction of the control rod number to half that of a typical sodium-cooled mixed-oxide fuel MONJU core without added ²³⁷Np and no need for rod operation with fuel burning to compensate for the burnup reactivity loss. Void reactivity is 0.72% k/kk', which is three-fourths that of a typical Na-cooled core, although ²³⁷Np is added and the active core length is elongated to 1.2 m. The power density is reduced to ~20% of that in a Na-cooled core. The hot-spot temperature of cladding is below its maximum permissible temperature of 700°C.