Analysis of minor actinides incineration adopting an innovative fast reactor concept

The specific characteristics of fast spectrum reactors allow loading of fuels containing minor actinides (MA) and implementing closed (or partially closed) fuel cycles thus providing an option for MA transmutation and incineration. However, advantages in terms of fuel cycle sustainability should not lead to a lower safety level of the systems. Within the Collaborative Project on European sodium fast reactor, CP-ESFR, reference designs for cores with oxide and carbide fuels were proposed by CEA (France). Both systems show a positive sodium void reactivity effect (SVRE) at Beginning of Life (BOL). In order to reduce the SVRE, measures have been considered for improving neutron leakage under voided conditions. This paper refers to the modified configuration as CONF2 where a larger Na plenum close to the core, an absorber layer above the Na plenum and a lower fertile blanket have been introduced compared to the reference design. The low SVRE in CONF2 (about 2$ less than the reference configuration) offers an opportunity for introducing MA into the core and the lower axial blanket. Several options with homogeneous and heterogeneous MA loadings have been considered showing a good flexible behavior of the system. The reference and the modified configurations have been compared also in terms of fuel cycles. A simplified reference scenario characterised by a constant nuclear energy production in the period 2020-2200 has been defined. The transition from pressurised water reactors (PWRs) based fleet to fast reactors (FRs) fleet has been studied. Only Pu and MA produced in the cycle have been considered focusing on the characteristics of the fast reactor transmuting its own waste (and the ones accumulated by the thermal fleet) while reaching an equilibrium condition. The results have shown that the introduction of MA in the lower fertile blanket (10-20 pc) is sufficient for stabilising the MA inventory in the cycle without any impacts on safety coefficients of the system. Further studies are needed to investigate the feasibility of this type of fuel and the impact on fabrication and reprocessing plants. (authors)