Design and Development of EM²

The principal design objectives for EM² are to achieve an economically competitive power source that improves resource utilization, reduces waste and meets a self-imposed high standard of safety. In order to meet this challenge, EM² departs from traditional nuclear technologies and embraces technical advances in materials, physics design, power conversion, control and passive safety methods. EM² is a modular helium-cooled fast reactor with a 265MWe net output. It uses a combined Brayton-Rankine cycle to achieve a net conversion efficiency of 53%. The core design is predicated on the convert-and-burn principle in which fertile material is converted to fissile and burned in situ. This allows the core to achieve a 30 year life without refueling or reshuffling. The combination of high efficiency and convert-and-burn reduces the rate of once-through high-level waste production by 80% relative to an LWR. This principle also enables the core to be multi-fuel capable including LEU, natural and depleted U, Th and spent LWR fuel. The base fuel is in the form of UC pellets with SiC composite cladding. These materials allow a high power density and a core outlet temperature of 850°C for high efficiency. The core outlet helium goes directly to a variable speed turbo-compressor within the primary coolant system. The direct Brayton cycle eliminates costly steam generators and large, steam-condensate system components. The bottoming cycle is a self-contained Organic Rankine cycle (ORC). General Atomics (GA) has a bench-scale fuel fabrication facility for making both EM² fuel pellets and cladding. GA cladding materials have been irradiated in ORNL’s HFIR to demonstrate the desired irradiation saturation behavior. The design is highly modularized not only reduce cost but also the risks associated with construction cost and schedule.