How Fuel is Used in MMR

Fuel Based Safety

Fully Ceramic Microencapsulated (FCM®) fuel provides a new approach to inherent reactor safety by providing an ultimately safe fuel. Industry standard TRISO fuel, which contains the radioactive byproducts of fission within layered ceramic coatings, are encased within a fully dense silicon carbide matrix. This combination provides an extremely rugged and stable fuel with extraordinary high temperature stability.

Fuel Kernel

The fuel packaging starts with a Uranium Fuel Kernel measuring less than 1 mm across.

TRISO Particle Fuel

The kernel is coated with special layers designed like tiny pressure vessels. The layers contain fission products inside and ensure mechanical and chemical stability during irradiation and temperature changes. This is called a TRISO Particle. Developed in the 1960’s for gas-cooled reactors, TRISO has enjoyed continued international development resulting in an excellent starting point for the Ultra Safe reactor.

FCM® Fuel

Ultra Safe Nuclear’s breakthrough is encasing the TRISO Particles within a dense Silicon Carbide matrix, which we call Fully Ceramic Micro-Encapsulated Fuel, or FCM® Fuel.

Pellet Stacks

FCM® Fuel Pellets are stacked…

Graphite Blocks

…and placed into Graphite Blocks. Graphite is the moderator which slows down neutrons and increases the likelihood that neutrons will cause fission reactions in the fuel. Cooling channels are built into the Graphite Blocks. Cold helium flows through the cooling channels and picks up heat.

Reactor Core Cartridge

The Reactor Core is made up of several hundred such Graphite Blocks with a few tons of fuel. Various openings and channels are used for control rods and coolant flow.

Benefits of Intrinsic Safety

The Core is placed inside the vessel of the Micro Modular Reactor (MMR®). The FCM® fuel unlocks a number of system benefits including fission product isolation that improves worker and plant safety, enhanced proliferation resistance, and minimized emergency planning zones.

The Micro Modular Reactor (MMR®) system is a 4th Generation nuclear energy system that delivers safe, clean, and cost-effective electricity and heat to remote mines, industry, and communities. It is the leading SMR project in Canada and the first so called "fission battery" concept worldwide.

Reactor Pressure Vessel
Thermal Power
45 MWth
Electrical Power
15 MWe
Power Density
1.23 W/cm3
Helium Circulator
Outlet Temp
630° C
Flow Rate
8.8 kg/sec
3.0 MPa
Passively cools in all scenarios
No active safety systems needed
No water or power needed

Reactor Core

Predictable Power

The buried reactor core consists of hexagonal graphite blocks containing stacks of Ultra Safe’s FCM® fuel pellets. The MMR® reactor core has a low power density and a high heat capacity resulting in very slow and predictable temperature changes.

Helium Coolant

The Most Benign Cooling Medium Available

Helium gas is the MMR® reactor’s primary coolant. The helium passes through the nuclear core and is heated by the controlled nuclear fission process. The helium then transports the heat away from the core to the Molten Salt System.

The MMR® reactor uses helium as it is an inert gas; a radiologically transparent, single-phase gas with no flashing or boiling possible. Helium does not react chemically with the fuel or reactor core components. It is easy to accurately measure and control the helium pressure in the reactor.

The FCM® fuel ensures the helium is clean and free of fission products.

Ultra Safe

Genuine Safety Margin

The MMR® reactor is a walk-away safe reactor. In the case of an accident, the MMR® reactor cannot melt down, as all heat dissipates passively into the environment, no matter the scenario.

The plant has no need for active systems to remove heat. Additionally, the plant does not need any outside services, including electrical power, to operate safely.

The fuel safety margin is so large that fission product retention is accomplished entirely by the fuel; no other containment is needed. There are no sudden temperature rises – the reactor shuts down naturally in all accident conditions.

Typical MMR® Layout

The MMR® Energy System consists of two plants, the nuclear plant and the adjacent power plant. The nuclear plant contains the MMR® reactors including all the equipment required to transport the heat to the adjacent plant. The adjacent power plant contains the equipment that converts heat to electricity or process heat as required.

Site Area
5 acres
Assembly Time
Molten Salt Storage Tanks
Load Compliance
Cartridge (optional)
20 years
District Heating Aqua Farms Electricity Green Houses Process Heat

Molten Salt Loop

Fully Dispatchable Nuclear Heat

The MMR® Energy System is simple to operate, and flexible in its outputs. The use of molten salt thermal storage allows for significant flexibility in the supply of both electricity and process heat. While the MMR reactor operates at constant power, electricity and heat are delivered on-demand from the power plant.

No Refueling

Operations are simple with minimal maintenance requirements, and no on-site fuel storage, handling, or processing. The MMR® reactor is fueled once for its lifetime. A fuel cartridge is rated at 20 years of full power. If operation of the Energy System is desired beyond 20 years, a cartridge replacement can be performed.

Useful Heat

The MMR®’s high temperature heat has many uses beyond generation of electricity. District heating, desalination, and process heat are all possible with the MMR®.


The MMR® facility uses standardized modules. The modules are to be assembled, tested, and commissioned at our factories.

Easy to Transport

Modules will be sized for standard International Standards Organization shipping containers; this means they can be transported easily by ship, rail or road. This includes ice roads.

Quick to Build

The modules are transported to the site, and then assembled. The construction of the MMR® plant is quick, simple, and scalable.

Scalable and Adaptable

Multiple MMR® reactors can be linked together to provide as much power as needed. The modules can also be combined in different ways for different sites and needs including integration with renewable micro grids.

Total Environmental Protection

The MMR Energy System uses no water. There is no risk of spills with environmental impacts during accidents. The nuclear fission products are locked inside the FCM fuel form during and after power production permanently.

Total Non-Proliferation

FCM® fuel cannot be re-processed using currently available reprocessing schemes. The MMR® fuel cartridge is sealed at the factory– the fuel cannot be accessed.


The MMR® Energy System can operate as a stand-alone off-grid plant to deliver fully dispatchable and resilient power. Or can be connected to existing grids.

Download Table Top MMR®

Learn more about the MMR® with Table Top MMR®.  This interactive augmented reality app will let you explore a few of the components of the MMR® energy system from your smart phone.

Available on:

Get it on Google Play