Fast Spectrum Material’s Testing Reactor with Variable Energy Spectra to Support Advanced Reactors Program and Light Water Reactor Sustainability Program R&D

The current US fleet of LWR’s are approaching the end of their original 40 year licenses. Most of these have applied for and been granted 20 year license extensions. Further increases in license length require more materials research into, amongst other things, neutron damage and stress corrosion cracking. In addition to the Light Water Reactor Sustainability program, the US maintains an Advanced Reactor program and Next Generation Nuclear Plant program. All three programs require extensive materials research, especially into fast neutron damage of core materials. A sodium cooled fast reactor based on EBR-II was designed in accordance with requirements generated by a Nuclear Energy Advisor Commission subcommittee released in November 2014. The reactor operates at 600 MWth and has sections of epithermal and thermal flux within the outer reflector. LEU metallic fuel was used without any plutonium. The active core is 1 meter tall and has an effective diameter of 1.13 meters. Magnesium Oxide was used as a reflector. The fast flux within the core depends on the enrichment of the core. Many different fuel loadings were investigated. Peak fast fluxes within the central irradiation positions vary from 5E15 to 7.5E15 n/cm^2s. Higher fluxes are associated with longer core lifetimes, which vary from greater than one year to approximately 100 days. Shuffling schemes were not analyzed, but simple refueling schemes were analyzed. The recommended driver irradiation locations provide more space at higher fluxes than comparable research reactors from around the world. The moderating region, which is composed of graphite, is highly versatile. While the size of the region was constant throughout the investigation, a wide range of configurations were studied. It is possible to irradiate materials within the reactor at fission powers and neutrons spectra typical of PWR’s and VHTR’s. Transient testing flux traps are located in the outer reflector, away from the moderating region and driver. Assemblies can be subjected to transients at constant reactor power. Both control drums and control rods can be used to control reactivity. The use of rods versus drums depends on initial keff and the degree of acceptable flux perturbation within the driver and reflector