Robert W. Schleicher

A Compact Gas-Cooled Fast Reactor with an Ultra-Long Fuel Cycle

In an attempt to allow nuclear power to reach its full economic potential, General Atomics is developing the Energy Multiplier Module (EM2), which is a compact gas-cooled fast reactor (GFR). The EM2 augments its fissile fuel load with fertile materials to enhance an ultra-long fuel cycle based on a “convert-and-burn” core design which converts fertile material to fissile fuel and burns it in situ over a 30-year core life without fuel supplementation or shuffling. A series of reactor physics trade studies were conducted and a baseline core was developed under the specific physics design requirements of the long-life small reactor. The EM2 core performance was assessed for operation time, fuel burnup, excess reactivity, peak power density, uranium utilization, etc., and it was confirmed that an ultra-long fuel cycle core is feasible if the conversion is enough to produce fissile material and maintain criticality, the amount of matrix material is minimized not to soften the neutron spectrum, and the reactor core size is optimized to minimize the neutron loss. This study has shown the feasibility, from the reactor physics standpoint, of a compact GFR that can meet the objectives of ultra-long fuel cycle, factory-fabrication, and excellent fuel utilization.

The Energy Multiplier Module (EM2): Status of Conceptual Design

Abstract The Energy Multiplier Module (EM2) is a helium-cooled fast reactor with a core outlet temperature of 850°C. It is designed as a modular, grid-capable power source with a net unit output of 265 MWe. The reactor employs a convert-and-burn core design that converts fertile isotopes to fissile and burns them in situ over a 30-year core life. The reactor is sited in a below-grade sealed containment. It uses passive safety methods for heat removal and reactivity control to protect the integrity of the fuel, reactor vessel, and containment. The plant also incorporates a below-grade, passively cooled spent fuel storage facility with capacity for 60 years of full-power operation. EM2 employs a direct closed-cycle gas turbine power conversion unit (PCU) with an organic Rankine bottoming cycle for 53% net power conversion efficiency assuming evaporative cooling. The high-power conversion efficiency and long-burn fuel cycle reduce the electricity cost by 35% when compared with the conventional light water reactor. The conceptual design has been conducted for the EM2 plant with focus on the reactor, fuel, and safety system designs. A detailed model of the passive direct reactor auxiliary cooling system was created to demonstrate functionality for selected design-basis accidents. The bench-scale fuel development campaign demonstrated high-quality uranium carbide pellet fabrication as well as β-SiC composite cladding and SiC-joining technologies. Irradiation tests of reactor materials are also being conducted. The PCU variable-speed generator mechanical design was validated with operational testing of its novel rotor at speeds >13 000 rpm. The design of the turbo-compressor with active magnetic bearings continues. A large cost database and financial model have been constructed for use as a key driver for the design to be economically competitive with competing generating technologies after 2030.

Design risk analysis comparison between low-activation composite and aluminum alloy target chamber for the national ignition facility

The baseline design for the target chamber for the National Ignition Facility (NIF) consists of an aluminum alloy spherical shell. A low-activation composite chamber (e.g., carbon fiber/epoxy) has important advantages such as enhanced environmental and safety characteristics, improved chamber accessibility due to reduced neutron-induced radioactivity, and elimination of the concrete shield. However, it is critical to determine the design and manufacturing risk for the first application. The replacement of such a critical component requires a detailed development risk assessment. A semiquantitative approach to risk assessment has been applied to this problem based on failure modes, effects, and criticality analysis. This analysis consists of a systematic method for organizing the collective judgment of the designers to identify failure modes, estimate probabilities, judge the severity of the consequence, and illustrate risk in a matrix representation. The results of the analyses indicate that the composite chamber has a reasonably high probability of success in the NIF application. The aluminum alloy chamber, however, represents a lower risk, partially based on a more mature technology. 8 refs., 4 figs., 5 tabs.

Physics Analysis of Alternative Fuel Options for HTGR

The modular high-temperature gas-cooled reactor (MHTGR) is known to be inherently safe because the fuel cannot fail even if all engineered safety systems, including decay heat removal and reactivity control, fail. In the event of a loss of cooling accident, even with failure of passive convective systems, core afterheat will safely be conducted to ground. However, it is also known that the MHTGR core is physically big when compared with current commercial reactors, the tri-isotropic (TRISO)-coated particle fuel is expensive and limits the uranium loading, and the reactor vessel is very large despite modest power output. Earlier economic evaluations indicate the truly inherently safe MHTGR has a weakness as a commercial product due to high cost. This study investigates the neutronic feasibility of a fuel alternative similar to the conventional pellet-type fuel, which can simplify the fuel fabrication process and reduce the enrichment of the fuel, while maintaining the accident-tolerant fuel (ATF) features. The neutronics performance of such a fuel concept has been evaluated for the amount of fuel loading, excess reactivity, and fuel cycle length, followed by thermal–mechanical performance and inherent safety analyses of such a design. The preliminary investigations have shown that it is feasible to construct a fuel cycle using uranium carbide (UC) fuel of ~5 wt% enrichment.

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.Copyright