Reactor design strategy to support spectral variability within a sodium-cooled fast spectrum materials testing reactor

A concept of a sodium cooled fast spectrum materials testing reactor is presented as one of the potential design configurations to achieve the performance versatility with respect to supporting a range of testing environments from current thermal-spectrum LWRs to Generation IV advanced fast-spectrum reactors. The objective is accomplished by designing a core with region-wise varying neutron spectra. This paper presents the design details and explores spectral variability examining feasibility to maintain thermal and fast energy spectra in the system. The core assemblies are designed using the EBR-II assembly as a prototype while implementing certain design modifications to meet performance needs. The fuel is 19.9%-enriched U-10Zr. Compare to EBR-II, the proposed core has larger pins, a taller active core, and thick reflector instead of depleted uranium breeding blankets. The MgO pins are analyzed as the reflector material to meet the needed versatility requirements. The design effort successfully concluded yielding a feasible 600 MWth-configuration with sufficient neutron fluxes in material testing locations. A fast flux greater than 5.6E15 n/cm2-s is maintained over the core lifetime in the central irradiation position. The volume of 63,000 cm3 with a fast flux of ∼ 4.2E15 n/cm2-s or greater is provided for materials irradiation options. The core has regions of high magnitude thermal flux in a large graphite region at the core periphery. Spectral variability, design choices and reactor physics characteristics are discussed to demonstrate the concept viability.