A Feasibility Study of a Molten Salt Fast Reactor with Moderated Blanket for Long-Lived Fission Product Transmutation

A conceptual design study has been performed for a 300–megawatt thermal (MWt) fast spectrum molten chloride salt reactor coupled with an external moderated blanket for transmutation of long-lived fission products (LLFPs) Tc-99, I-129, and Se-79, which supplies electricity to a proton accelerator of the spallation neutron transmuter for transmutation of other LLFPs of Zr-93, Sn-126, and Cs-135. The design involves a cylindrical flowing fuel core and an external D2O-moderated target blanket in which LLFPs are loaded in elemental forms with no isotopic separation as technetium metal pins, cladded selenium pins, and MgI2 diluted in the heavy water. Design parameters were determined via a series of parametric studies including LLFP loading pattern optimization, addition of a technetium thermal neutron filter, enrichment of the chloride salt with Cl-37, and increase in core height-to-diameter ratio to increase radial neutron leakage to the blanket. Several reactor design metrics, such as reactivity feedback coefficients, reactor shutdown margin, precursor drift effect, and material thermal margins, were analyzed to ensure satisfaction of design constraints. The resulting net transmutation rates are 31.55 kg/yr of Tc-99, 12.28 kg/yr of I-129, and 0.77 kg/yr of Se-79. Other LLFPs that experience net production in the fuel salt will be treated with the spallation neutron transmuter to fully transmute the priority LLFPs. The proposed 300-MWt molten salt reactor (MSR) transmuter can effectively transmute the Tc-99, Se-79, and I-129 LLFPs from a 3500-MWt pressurized water reactor and produces energy for driving complementary transmutation technologies.