Neutron shielding studies on an advanced molten salt fast reactor design

The molten salt reactor technology has gained some new interest, but the current projects are based on designing a molten salt fast reactor. Thus the shielding becomes more challenging than in historic concepts. One very interesting and innovative result of the EVOL project is the fluid flow optimized design of the inner reactor vessel using curved blanket walls. The developed structure leads to a very uniform flow distribution. The design avoids all internal structures. Based on this new geometry a model for neutron physics calculation is presented. The major steps are: the modeling of the curved geometry in the unstructured mesh neutron transport code HELIOS and the determination of the real neutron lfux and power distribution for this new geometry. The developed model is then used for the determination of the neutron fluences in the inner and outer wall of the system and for developing an optimized shielding strategy for the molten salt fast reactor to keep the fluence in the safety related outer vessel below the limit values. A lifetime of 80 years can be assured, but the size of the core/blanket system will be comparable to a sodium cooled fast reactor.