After decades of being focused on the GT-MHR and its variants, General Atomics recently introduced a new gas-cooled SMR called the Energy Multiplier Module (EM2). Although leveraging some of the GT-MHR technologies, the design is a significant departure from the thermal-spectrum GT-MHR. The EM2 is a fast spectrum reactor with its primary purpose to be a consumer of spent nuclear fuel. Specifically, it is a ‘breed and burn’ type reactor that converts fertile elements contained within the special fuel assemblies into fissile elements to sustain the process, while also consuming minor actinides produced in precursor once-through reactors such as LWRs. The reactor core uses uranium-carbide fuel clad in silicon-carbon composite material. The fuel is in the form of porous annular pellets and stacked within SiC-SiC tubes to form pins. The first reactor is loaded with nearly equal portions of low-enriched uranium fuel (approximately 6% 235U average enrichment) and discharged LWR

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Figure 2.19 EM2 (United States) — General Atomics (GA).

fuel. Subsequent EM2 reactors are loaded entirely with the fuel discharged from preceding EM2 reactors. The nearly 50% power conversion efficiency is achieved by operating with an outlet helium temperature of 850 °C and by using a vertically mounted, variable-speed direct Brayton-cycle power conversion unit.

It is expected that the reactor will operate for 30 years without refueling or fuel shuffling. After 30 years, the core will be replaced with a fresh load of recycled used fuel and the discharged fuel will be processed using a dry oxidation process to produce feedstock for subsequent reactors. Units are expected to be deployed in twin-unit plants with up to four plants per site. Fuel development and qualification tests are underway but are expected to be the longest lead challenge for eventual deployment. Despite the longer-term deployment schedule for the EM2, it is included in this survey because of the significant level of commercial investment by General Atomics. Key parameters and a representative graphic for the EM2 design are given in Figure 2.19. [17]