• NuGen launches self-funded entrepreneurial effort to develop a 20 MWe mini reactor with an eye on its potential use to power landing sites on the Moon and Mars. It also has plans for terrestrial applications.
• URENCO U-Battery takes next step in Canadian National Lab SMR program. U-Battery is a 4 MWe high-temperature gas-cooled micro nuclear reactor
• OKLO is engaged with NRC in pre-licensing meetings. The firm is developing a 2 MWe fast reactor using U-Zr metal fuel (HALEU) based on the fuel in EBR-II

While the mainstream and nuclear trade press, including this blog, have spent considerable time reporting on the progress of various developers of small modular reactors (SMRS), another group of entrepreneurial efforts are underway to develop mini reactors. These units are easily transported by truck or train and come in sizes of 1-10 MWe.

While there is overlap among the types of applications deployed by SMRs and mini-or-micro reactors, the smaller footprint, weight, and power ratings of these pint size power stations make them suitable for remote off-the-grid sites on earth and in outer space for keeping astronauts homesteads lit and warm on the Moon and Mars.

The costs of micro reactors are still a work in progress, but developers are banking on being able to produce power well below the cost of diesel powered generators and closer to the cost of natural gas than full size units.

All three firms profiled here forecast having operational units in the hands of customers by the end of the 2020s or sooner. A roadmap on paths to market for micro reactors, published in 2018 by the Nuclear Energy Institute (NEI), estimates that once a micro reactor design enters the licensing process at NRC, a customer has signed on, and construction begins, the time to entry to revenue service is about 7-10 years.

Here are three reports on progress for mini-reactors.

NuGen Engine is at Start of Development Cycle

NuGen’s self-funded startup is developing  the NuGen Engine [tm] which is a high temperature gas cooled reactor (HTGR) in a small package.  Steve Rhyne, CEO of the firm, (NuGen) participated in an email interview with this blog on August 3, 2019, about the reactor which could have power ratings of up to 20 MWe for remote site terrestrial applications.  (Slide deck PDF File) Some details of the reactor core and fuel remain proprietary information at this time.

NB: What is the NuGen reactor?

Rhyne: The microreactor called the NuGen Engine has a patented revolutionary helical fuel core, which results in a shorter fuel core and higher efficiency.  The helical fuel core and other components are fully integrated and enclosed in a single module.

It is a direct-cycle gas-cooled microreactor enclosed in a single module. Using a direct-cycle concept eliminates the “balance of plant” infrastructure, such as the secondary loop, allowing for a simpler design. The firm is focusing on the simplicity of its design to minimize licensing costs, operational requirements, maintenance costs and the risk of damage during transportation and siting.

NB: What are some of the intended uses of the micro reactor?

Rhyne: The design is adaptable for space applications. It could serve as a lunar reactor at a permanent outpost or habitat on the moon and provide heat and electricity for in situ resource utilization (e.g., for water extraction, fuel production and 3-D printing).   It could also serve as the electricity generator to power an electric propulsion rocket for travel to Mars.

Concept – NuGen Engine on Mars. Image: NuGen

Terrestrial uses include being sited at remote locations, such as in Alaska and northern Canada, which are dependent on expensive diesel generators and high transportation costs for fuel and at mining sites that are also dependent on expensive diesel generators. Additional uses include 24/7 secure off-grid electricity for critical infrastructure, such as military bases, data centers and financial institutions, desalination, and for deployment in emergency response scenarios, such as in the aftermath of hurricanes.

Description of the Reactor

Key Elements of NuGen Reactor.  Image: NuGen

The gas propulsion chamber is in the center and houses the helical fuel core. The helical passageways provide two key physical advantages. First the longer helical contact paths for the gas allow for a shorter core length. Second, the helical passageways support the enhanced gas transport. A drive shaft runs through the center of the fuel core.

The streamlined turbine and simplex compressor are coupled to the drive shaft, as is the electrical generator and, if needed, a circulation fan. After the gas leaves the outlet it is cooled by a variety of mechanisms, including: high-temperature heat exchanger; expansion of the gas in the containment vessel, mixing with the relatively cooler gas that bypasses the propulsion chamber, cooling pipes and other cooling features.

NB: Is the primary use of the microreactor for static power or is it also intended for propulsion and power in deep space?

Rhyne: We view the most likely first use of the NuGen Engine™ to be as a lunar microreactor to provide power on the surface since we believe that will be the first actual deployment of a space nuclear fission system.

The NuGen Engine™is adaptable for electric propulsion for deep space, and our preliminary scoping has indicated that it would meet the output, size and weight requirements for such use based on the parameters we have been advised of by NASA. Defense applications in earth orbit also come to mind.

Side note to readers – nuclear propulsion systems aren’t used to get a payload off the launch pad. Once in low earth orbit, the systems are turned on by remote or on-board commands and using the on-board guidance systems, take over from the depleted chemical propulsion rockets to speed their cargo and/or crew to their destination.

Safety in the event of a failed launch requires significant attention to design elements that will insure a reactor survives a catastrophic failure during the chemical powered phase of ascent. All of NASA’s radioisotope thermonuclear generators (RTGs) over the years have these safety-related design elements incorporated into their fabrication.

NB: What is your most recent development milestone, interest from a customer or collaboration of another firm, university, or national lab?

Rhyne: At the GAIN Microreactor Workshop held at INL in June 2019, NuGen publicly disclosed for the first time its revolutionary patented helical nuclear fuel core.

NB: Funding? Seed, SERIES A first round, venture, anything you can disclose? DOE funding?

Rhyne: Currently funded by the founder.  DOE funding is being considered.

NB: Partnerships in development?

Rhyne: NuGen’s team includes professors in three Texas A&M University Departments (Nuclear Engineering, Aerospace and Mechanical Engineering).  NuGen is open to, and will be seeking, partnerships based on specific opportunities, as well as advancing its technology generally.

U-Battery SMR Moves to Next Stage of Canadian Lab Assessment

(WNN) The Urenco-led U-Battery consortium has completed the first stage of Canadian Nuclear Laboratories’ (CNL) invitation to site a first-of-a-kind small modular reactor (SMR) at the Chalk River site. It is the fourth reactor design to do so.

As a result the U-Battery consortium has been invited by CNL to enter the Due Diligence stage – the second of CNL’s four-stage process – in which CNL will evaluate the proposed design, assess its financial viability and review the necessary national security and integrity requirements. The reactor is also progressing through the UK’s Advanced Modular Reactor Program.

U-Battery General Manager Steve Threlfall said the consortium was a “step closer” to establishing a first-of-a-kind SMR at Chalk River.  (Slide Deck PDF file)

“We are entering the energy sector at a critical time in Canada’s energy transformation, and U-Battery has the potential to drive significant regional economic benefits across Canada while addressing urgent climate change needs,” he said.

U-Battery is a 4 MWe high-temperature gas-cooled micro nuclear reactor which will be able to produce local power and heat for a range of energy needs.

The project was initiated by Urenco in 2008 and the concept design was developed by the Universities of Manchester and Dalton Institute in the UK and Technology University of Delft in the Netherlands.

U-Battery Specifications

• Twin unit – each unit has an output of 4MW electric, 10MW thermal.  Multiple modules can be installed at a single site.
• Gas cooled – helium in primary circuit, nitrogen in secondary circuit (no water).
• TRISO fuel – absence of water eliminates need for multiple back-up safety systems.
• Heat and power source – 750°C process heat.

Market for Remote Power in Canada

Canada has a population of roughly 37.3 million and 80% of it is located within 200 miles of the U.S. border. Vast areas of the counry have population densities of as little as 4 people per square mile. Also, the arctic regions are inhospitable to modern urban life and infrastructure.  Many small towns and villages rely on diesel power for generating electricity on a local grid with very high costs mostly related to getting the fuel to the site.

Canada’s interior regions suport mining including coal, tar sands oil, and uranium. Power for all of these operations comes from fossil fuels. A nuclear battery could be a solution for these remote off-the-grid communities and the mine operations.

Population density in Canada. Image: Statistics Canada

A recent CNL study found that the potential market for off-grid SMRs in Canada consists of over 600 power plants, with a total power demand of 35 GWe. Reference: “Potential Off-Grid Markets for SMRS in Canada”; D. Wojtaszek

TRISO Fuel Fabrication

The U-Batery consortium says the reactor technology, which uses high-integrity TRISO fuel, aims to replace diesel power with clean, safe, and cost-effective energy for a variety of applications, including remote communities and other off-grid locations such as mining operations.

TRISO fuel is constructed by triple coating spherical particles of uranium fuel. A uranium centre is coated in a layer of carbon, which in turn is coated in silicon carbide, with a further outer layer of carbon. (U.S. Department of Energy resource page on TRISO fuel)

TRISO Fuel for U-Battery. Image: URENCO

See prior coverage on this blog: TRISO Fuel Drives Global Development of Advanced Reactors

Urenco says U-Battery can help address a number of challenges related to the need to develop a low carbon economy.  Planned uses include;

• Produce both power and heat for heavy industrial locations.
• Could be used as a back-up support for large scale nuclear generating sites instead of diesel.
• Be deployed in remote locations.
• Provide solutions to water scarce areas through desalination
• Generate hydrogen for hydrogen-powered vehicles.

Status of Three Other SMR Firms in CNL Process

CNL aims to site an SMR at one of its locations by 2026, under a long term strategy in which it aims to become a global hub for SMR development. It launched its staged invitation process after a 2017 request for expressions of interest received responses from 19 technology developers interested in building a prototype or demonstration reactor at a CNL site.

WNN reports that the other proponents engaged in the CNL invitation process that have made the most progress are two SMRs and a micro reactor.

• StarCore Nuclear, with a proposed 14 MWe high-temperature gas reactor;
• Terrestrial Energy, with its 190 MWe integral molten salt reactor  (IMSR-400), and
• Global First Power, with a 5 MWe high-temperature gas reactor.

All three have completed the first phase of the process. Global First Power’s design has entered the third phase, which includes preliminary discussions on land arrangements, project risk management and contractual terms. The fourth and final project execution phase includes construction, testing, commissioning, operation and finally decommissioning of an SMR unit.

All the projects are subject to regulatory requirements and CNL’s invitation and evaluations are independent of the Canadian Nuclear Safety Commission’s (CNSC) licensing process.

Global First Power submitted an application to the CNSC earlier this year to prepare a site at Chalk River, the first licence application for an SMR to be received by the Canadian regulator. An environmental assessment of the project is now under way.

See prior coverage on this blog – Canadian National Lab Advances Three SMR Designs

OKLO Mini Reactor in Prelicensing Discussions with NRC

One of the earlier efforts to devlop a mini reactor is the Oklo micro-reactor. Oklo (formerly UPower). It is a Californian company founded in 2013. The firm is developing a 2 MWe fast reactor using U-Zr metal fuel based on the fuel in EBR-II, but with lower burn-up.

Oklo is developing a compact 2 MWe fast spectrum reactor. The reactor operates purely on natural physical forces, with very few moving parts. It is designed to operate for 12 years before refueling.

The Idaho National Laboratory (INL) is working with the company on fuel development and qualification. OKLO is a partner with the INL on a DOE ARPE-E $1.8 million award of federal funding. INL and its partners are proposing a next generation metal fuel in support of a megawatt-scale compact fast reactor – being developed by Oklo Inc – that is uniquely sized for off-grid applications.

The team seeks to develop a fuel with a demonstrated production process and validated performance that incorporates engineered porosity to absorb and retain produced gasses, allowing for higher operating temperatures, as well as a diffusion barrier between the fuel alloy and the cladding to avoid material degradation, which removes the need for the complicated-to-manufacture sodium bond between fuel and cladding.

Since November 2016, the staff of the U.S. Nuclear Regulatory Commission (NRC) has been engaged in pre-application activities with Oklo. The docket number 99902046  in the NRC ADAMS system, which contains OKLO’s pre-application documents, indicates that the most substantive parts of the exchanges with the agency are closed to public access due to the proprietary nature of the data being shared with the NRC.

Unlike a few other SMR and nuclear battery developers, who have published significant information on the technical specifications of their designs, OKLO has kept most of its development information closely held.  For more information, readers are referred to the following patent: Passive inherent reactivity coefficient control in nuclear reactors (November 2017)

In May 2016 in congressional testimony to the Senate Committee on Energy and Natural Resources, CEO and founder Jacob DeWitt, said this about the design.

“It is sized appropriately to open up new opportunities for clean and safe nuclear power in remote, rural, and native communities, as well as industrial and military sites in areas that have previously been too small to support larger reactors. This system has the potential to reduce these customer’s energy bills by up to 90%.”

“Furthermore, our reactor is up to 300 times more fuel efficient than current reactors, and can consume the used fuel from today’s reactors, as well as the depleted uranium stockpiles around the nation.”

“In fact, our reactors, and others like it, could power the world for 500 years with the global inventory of used fuel and depleted uranium, all while reducing the radioactive lifetime of those materials. Our reactors can also assist with plutonium disposition by consuming excess cold war era materials and turning them into clean, peaceful energy.”

The Energy Policy Center Columbia University in New York has this information about the Oklo design (Pages 89-90 PDF file –A Comparison of Advanced Nuclear Technologies)

“The plant is designed to be a metal block containing uranium based metallic fuel in a heat pipe configuration that uses liquid sodium. The power conversion system is not final, but consideration is being given to organic Rankine cycle, steam, or super-critical CO2. There is insufficient technical information available publicly to put together a table of key parameters.”

“The design is such that the nuclear plant can ft into a standard shipping container. Two additional containers would house the power conversion system. With mass manufacturing of these small modules, designers claim they can produce electricity for $0.03/kWh. While the design is only in very preliminary stages, they have received venture capital funding to move the design forward.”

Note to readers: The above description indicates that the Oklo design would be using high assay low enriched fuel (HALEU) which is enriched to greater than 5% U235 but less than 20% U235.

See prior coverage on this blog –

• DOE Takes Divergent Paths to Fabrication of High Assay Fuels
• Advanced Nuclear Fuel Projects Set the Stage for New Reactors

Oklo has been working with the Alaska Center for Microgrid Technologies Commercialization.  In May 2018 the firm received an award of 125 hours of technical consultation and analysis.

ACEP, was launched in August 2015 with funding through the U.S. Economic Development Administration, the Office of Naval Research and the University of Alaska. The Center focuses on providing technical and business assistance to accelerate a market of new microgrids and improve the affordability and reliability of microgrid energy systems.

Oklo has a minimalist web page and can also be found on Linkedin and  Facebook.

Reference Design – Solid Core Sodium Cooled Concept

Readers interested in the historical and conceptual basis for a solid core, sodium cooled nuclear battery are referred to the following technical paper which is open source data through DOE’s OSTI website.

Solid-Core Heat-Pipe Nuclear Battery Type Reactor
Award Number: DE-FC07-05ID14706 – Summary Report; September 30, 2008
University of California, Department of Nuclear Engineering, Berkeley, CA 94720
https://www.osti.gov/servlets/purl/940911

Ehud Greenspan;  https://nuc.berkeley.edu/people/ehud-greenspan/;
email:  gehud@nuc.berkeley.edu

Key Highlights of the Abstract

This project was devoted to a preliminary assessment of the feasibility of designing an Encapsulated Nuclear Heat Source (ENHS) reactor to have a solid core from which heat is removed by liquid-metal heat pipes (HP).

The HP-ENHS is designed to have a 20 year operation without refueling, very small excess reactivity throughout life, natural circulation cooling, walkaway passive safety, and robust proliferation resistance. The HP-ENHS reactor offers a number of advantageous features including:

• (1) significantly enhanced passive decay heat removal capability;
• (2) no positive void reactivity coefficients;
• (3) relatively lower corrosion of the cladding
• (4) a core that is more robust for transportation;
• (5) higher temperature potentially offering higher efficiency and hydrogen production capability.

This preliminary study focuses on five areas: material compatibility analysis,

• HP performance analysis,
• neutronic analysis,
• thermal-hydraulic analysis and
• safety analysis.

Of the four high temperature structural materials evaluated, Mo TZM alloy is the preferred choice; its upper estimated feasible operating temperature is 1350 K. (1077 C).

Sodium is the preferred working fluid and the HP working temperature can be as high as 1300 K. (1027 C)

The preferred design utilizes nitride fuel made of natural nitrogen and loaded with depleted uranium and TRU from LWR spent fuel cooled for approximately 30 years. The preferred intermediate coolant is LiF- 2 BeF2; its average outlet temperature is ~ 1040K.

The required reactor vessel height is 9m. The vessel diameter is 4m

The resulting HP-ENHS reactor concept is unique in offering sustainable proliferation-resistant nuclear energy that can be delivered at very high temperatures. A number
of outstanding issues need be addressed, though, before the practicality of the HP design concept could be asserted. Included among these issues are:

• More thorough reactor safety analysis, including transient analysis
• Fuel-cladding chemical compatibility
• Ability to manufacture the design
• Maximization of the specific power by optimization of fuel/HP diameter and core length
• Economic feasibility analysis

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