Recommendations for an MSFR demonstrator pre-conceptual design

The present deliverable introduces the need for several demonstration tools before reaching the final levels of a zero power demonstrator and subsequently a power demonstrator from which an industrial prototype may be defined. Safety consideration by safety authorities should be addressed all along the demonstration process, and this should take time, more than that needed previously for older concepts. This is essential for an innovative reactor concept that has a potentially high level of intrinsic safety. Two designs have been presented for the final step of the power demonstrator. For the MSFR-like demonstrator, a rather small reactor would both fit the needs for a demonstrator and be the base for modular reactors (300MWth) with less than 2 cubic meters of fuel salt. A simplified version of such a small reactor would be a burner only reaching fissile regeneration with an additional fertile blanket. It may be the simplest prototype to build and operate. An alternative spherical core shape design has been also introduced, taking into account the strongly-coupled behavior of the reactor neutronics and thermal fluid dynamics. It is characterized by an arrangement of the fuel circuit that would still ensure good neutron economy and breeding performance, limit hot spots at walls and reduce the overall temperature of structural materials, improve the effectiveness of natural circulation under pump blockage accidents, and keep the design as simple as possible. Preliminary analyses of the pre-conceptual spherical core shape design have demonstrated such potentialities, it could be further investigated. At this point, several design and fuel composition options are still open after the EVOL-MARS collaboration. This is an illustration of the high flexibility of this concept both in terms of size and fuel composition. Proceeding further in the definition of the most suitable common demonstrator for all the foreseeable application of this concept, with priority to simplicity and compliance to the safety authority requirements will be an important next step of future international collaborations.