Very small modular nuclear fission reactors for military and space applications

The Defense Science Board has a 99 page report which proposes that the US military fund the development of very small nuclear reactors for forward remote operating bases.

The Task Force reviewed several nuclear reactor concepts that differ in size and technology from conventional commercial reactors and the small modular reactor (SMR) concepts currently under development for commercial use. Some of these reactors, very small modular reactors (vSMRs) with an output less than 10 MWe (megawatts-electric), may be transportable and deployable in FOB, ROB, and expeditionary force situations, and could eliminate the need for logistics fuel otherwise dedicated to producing electrical power.

In Iraq and Afghanistan, between 70%7 and 90% of the volume of goods delivered to forward bases and expeditionary forces were accounted for by fuel and (to a lesser extent) water.

Costs of up to $400 per gallon of fuel have been reported in the media for air-dropped fuel, though the FBCE of truck-delivered fuel during combat is more typically reported to be between $10 and $50 per gallon.

The Task Force found two of the concepts more technically mature than the others. The first is LANL’s MegaPower Reactor System and the other is Filippone and Associates LLC’s “Holos” Gas-cooled Hardened Micro Modular Reactor.

One vSMR concept being developed by Los Alamos National Laboratory (LANL), which the Task Force reviewed, is the “MegaPower” reactor [Patent No. US 20160027536 A1].

Mobile heat pipe cooled fast reactor system US 20160027536 A1

A mobile heat pipe cooled fast nuclear reactor may be configured for transportation to remote locations and may be able to provide 0.5 to 2 megawatts of power. The mobile heat pipe cooled fast reactor may contain a plurality of heat pipes that are proximate to a plurality of fuel pins inside the reactor. The plurality of heat pipes may extend out of the reactor. The reactor may be configured to be placed in a standard shipping container, and may further be configured to be contained within a cask and attached to a skid for easier transportation.

In this concept, the nuclear fuel is uranium oxide enriched up to 19.5% in uranium 235. This level of low enrichment is considered “non-weapons grade” from a proliferation standpoint. The large mass of fuel is encapsulated in a solid steel monolith to form a sub-critical nuclear core which is surrounded by a material that reflects decay neutrons emanating from the uranium metal core back into the core, in a controlled way, causing a sustained nuclear reaction (a “critical reaction”). The thermal energy created by the fission reactions is removed from the uranium metal core by heat pipes, which in turn produce electrical energy via open-air Brayton or supercritical carbon dioxide Stirling engines. This concept is designed to provide 2 MW of electricity and another 2 MW of process heat for 12 years of continuous operation, weighs about 35 metric tons, and is transportable by air and highway. Funding from NASA and Laboratory Directed Research and Development programs is being leveraged to mature MegaPower. The system could be connected to the generators and operated within 72 hours upon arrival.

The reactor system can be shut down, cooled, disconnected, and “wheeled out” in less than seven days. The reactor core and all other critical equipment are housed in special armor, which protects the reactor systems from beyond the design basis attack, and also shields personnel and environment from the core radiation during operation and transport. The design is mature, but would require additional investment for demonstration. Every component has technology readiness level (TRL) of six 40 or better, with integration of the components into system prototypes the major remaining work to be done. A projection has been made that a unit could be available for concept demonstration in five years.

Lessons learned from the kiloPower development program (for NASA and possible Mars usage) are being leveraged to develop a Mega Watt class of reactors termed MegaPower reactors. These concepts all contain intrinsic safety features similar to those in kiloPower, including reactor self-regulation, low reactor core power density and the use of heat pipes for reactor core heat removal. The use of these higher power reactors is for terrestrial applications, such as power in remote locations, or to power larger human planetary colonies. The MegaPower reactor concept produces approximately two megawatts of electric power. The reactor would be attached to an open air Brayton cycle power conversion system. A Brayton power cycle uses air as the working fluid and as the means of ultimate heat removal.

MegaPower design and development process will rely on advanced manufacturing technology to fabricate the reactor core, reactor fuels and other structural elements. Research has also devised methods for fabricating and characterizing high temperature moderators that could enhance fuel utilization and thus reduce fuel enrichment levels.

Holos

This concept features a “plug-and-play” system with effective full-power days (EFPDs) capability corresponding to approximately 13 years with 8% core enrichment as determined by an independent study and a privately funded study. The core sub-assemblies and shields can be transported with current FOB and ROB lifting capabilities. Only when all subassemblies are coupled via exoskeleton structure in an armored and shielded ISO transport container, the core becomes whole and coupled neutronics enables electricity production. The core sub-assemblies fit in storage canisters commercially utilized for waste/spent fuel temporary and permanent disposal to minimize decommissioning cost. If required, each subassembly may be loaded with different fissile and fertile isotopic compositions. Holos integrates modular power conversion systems within each sealed core-sub-assemblies and does not require balance of plant or equipment outside the armored ISO transport container. The Holos core is formed by universal cartridges which can be loaded by various types of fuels and moderators, including ceramic melt-resistant fuels, and other advanced fuels proposed by various national laboratories.

Holos is a nuclear powered electric generator concept designed to address and satisfy the requirements of transportability and encapsulation. The reactor is distributable and can be configured to supply from 3 megawatt-electric (MWe) up to 81MWe of load-following electricity.

The developers believe Holos systems could achieve 5 to 6 cents per kilowatt hour.

Diverging from LWR and Generation IV 4 designs approach, Holos thermal-hydraulic, turbo machinery and electricity producing components are fully integrated and sealed within the subcritical power modules all together with the fuel cartridge. While Brayton cycle conversion to electricity is often executed through gear reductions to match the turbine rotational speed with the generator’s speed, Holos integral PCU is directly driven. The turbine-generator assembly is directly coupled.

The Holos Reactor: A Distributable Power Generator with Transportable Subcritical Power Modules Public

Description: Holos is a distributable modular nuclear power generator with enhanced safety features. Holos design objectives include production of affordable pollutant-free electricity and process heat with the safest melt-tolerant and proliferation resistant fuel. The design leverages commercial technologies utilized for the conversion of thermal energy into conditioned electricity. Holos can operate as a stand-alone electric island at sites with no power grid infrastructure and can be scaled-up or clustered to meet local electric demands. Specialized configurations of Holos generators can be airlifted and timey deployed to supply emergency electricity and process heat to disaster areas and to inaccessible remote locations. The proposed distributable electric generator is comprised within dimensions and weight requirements compatible with International Standard Organization (ISO) transport containers, and is formed by subcritical power modules protected from shock stressors during transport. Holos coupled core becomes critical and enables power generation only when multiple subcritical power modules are positioned near one another. Cooling of Holos’ fuel relies only on environmental air during operations with decay-heat removal executed passively. Depending on configurations, Holos fuel cycle is 12-20 years, with 8%-15% enriched nuclear fuel sealed at all times and contained within replaceable fuel cartridges. At the end of the fuel cycle, the fuel cartridges fit within licensed transport and storage canisters for long term storage with low decommissioning cost. Holos power conversion components can be reconditioned when fuel cartridges are replaced at the end of their fuel cycles and the generator can be re-licensed to resume operation for a total generator life-span of 60 years. In this design, the thermodynamic cycle utilized to convert the core thermal energy into electricity is based on the Brayton power cycle. In some configurations, the design integrates and couples a bottoming Rankine power cycle operating with organic fluids to enhance efficiency, convert decay thermal energy into electricity and support process heat applications. Holos’ waste heat recovery and conversion feature also relaxes thermal loading requirements at underground spent fuel repositories. The power conversion components utilized in this design are off-the-shelf, with power ratings comparable to those forming aviation jet engines and gas turbines worldwide commercially available. This approach simplifies the design and enables factory certification following the regulatory and quality assurance programs applied to aviation systems. Holos innovative architecture provides the means to support a distributable power source satisfying various applications’ requirements with enhanced safety and substantial cost reductions, thus making Holos generators competitive when compared to various electricity producing technologies, and synergetic with technology sourced on renewable energy.

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