As fossil fuels become increasingly unsustainable energy sources and renewable energy meets with its own challenges, nuclear (fission) energy is again emerging as one of the most viable and clean energy sources humanity can access today. New technologies are moving in two main directions: by enabling next-gen reactors to deal more easily with spent fuels and by making reactors easier and cheaper to build. A nuclear microreactor belongs to the second kind: they are factory-built 1-to-20-megawatt nuclear reactors that could significantly benefit from AM as a means of production (see the infographic).
Last year, researchers at ORNL demonstrated a 3D printed microreactor core. The lab aims to turn on the first-of-its-kind reactor by 2023. The program has maintained its aggressive timeline during the COVID-19 pandemic, using remote work to continue design and analysis efforts. The TCR program has completed several foundational experiments including the selection of a core design, and a three-month “sprint” that demonstrated the agility of the additive manufacturing technology to quickly produce a prototype reactor core.
Through the TCR program, ORNL is seeking a solution to a troubling trend. Although nuclear power plants provide nearly 20 percent of U.S. electricity, more than half of U.S. reactors will be retired within 20 years, based on current license expiration dates. “The TCR program will provide a new model for accelerated deployment of advanced nuclear energy systems,” Zacharia said. “If cost and construction times are not addressed in the very near future, the United States will eventually lose its single largest source of emissions-free power.”
Smaller is better
Today nuclear is getting smaller and it’s opening up some big opportunities for the industry. A handful of microreactor designs are under development in the United States, and they could be ready to roll out within the next decade. These compact reactors will be small enough to transport by truck and could help solve energy challenges in a number of areas, ranging from remote commercial or residential locations to military bases.
Microreactors are not defined by their fuel form or coolant. Instead, they are characterized by three main features. The first, and the reason why AM could come significantly into play, is that they are factory-fabricated: all components of a microreactor would be fully assembled in a factory and shipped out to the location. This eliminates difficulties associated with large-scale construction, reduces capital costs and would help get the reactor up and running quickly.
Another feature is that they are transportable. This would make it easy for vendors to ship the entire reactor by truck, shipping vessel, airplane or railcar. Thye are also self-adjusting, which means that via simple and responsive design concepts (which will certainly be heavily iterated via 3D printing) will allow microreactors to self-adjust. They won’t require a large number of specialized operators and would utilize passive safety systems that prevent any potential for overheating or reactor meltdown.
Small size, big punch
Microreactor designs vary, but most would be able to produce 1-20 megawatts of thermal energy that could be used directly as heat or converted to electric power. They can be used to generate clean and reliable electricity for commercial use or for non-electric applications such as district heating, water desalination and hydrogen fuel production.
Besides seamless integration with renewables within microgrids, Microreactors can also be used for an emergency response to help restore power to areas hit by natural disasters.They will also have a longer core life, operating for up to 10 years without refueling. Most designs will require fuel with a higher concentration of uranium-235 that’s not currently used in today’s reactors, although some may benefit from use of high temperature moderating materials that would reduce fuel enrichment requirements while maintaining the small system size.
The U.S. Department of Energy supports a variety of advanced reactor designs, including gas, liquid metal, molten salt and heat pipe-cooled concepts. American microreactor developers are currently focused on gas and heat pipe-cooled designs that could debut as early as the mid-2020s.