A moderated target design for minor actinide transmutation in sodium-cooled fast reactor

This paper presents a moderated target assembly design study for minor actinide (MA) transmutation in the first-stage sodium-cooled fast reactor (FR) to reduce the amount of MA to be sent to the second-stage accelerator driven system (ADS) in a two-stage FR/ADS fuel cycle option. In order to minimize the local power peaking problem induced by moderated target assemblies, the target assemblies were loaded in the reflector region. Using MA-40Zr target composition and ZrH1.6 moderator, an optimum MA target assembly design was developed to maximize the MA destruction within the practical thermal design limits on the cladding inner wall temperature. Long-lived fission product pins were used as thermal neutron filters to reduce the local power peaking in the adjacent fuel assemblies due to the thermal neutron leakage from the moderated target assembly. The performance characteristics of the FR with moderated target assemblies were evaluated by performing detailed neutronics and thermal-hydraulics analyses. Analysis results showed that the use of MA target assemblies reduces the amount of MA to be sent to ADS by a factor of six without deteriorating safety characteristics. As a result, the electricity sharing of ADS in a nuclear park composed of FRs and ADSs was reduced to 0.3% from 1.9%.