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As fossil fuels increasingly become unsustainable energy sources and renewable energies face their own challenges, nuclear energy (nuclear power) is re-emerging as one of the most practical and clean energy sources available to mankind today. New technologies are moving in two main directions: by making spent fuel easier to deal with in next-generation reactors, and by making reactors easier and cheaper to build. A nuclear microreactor is of the second type: it is a factory-built 1 to 20 megawatt nuclear reactor that could benefit significantly from AM as a means of production (see infographic).
Last year, ORNL researchers demonstrated a 3D printed microreactor core. The lab aims to have the first reactor of its kind on stream by 2023. The program has maintained its aggressive schedule during the COVID-19 pandemic and is using remote work to continue design and analysis efforts. The TCR program completed several groundbreaking experiments, including the selection of a core design and a three-month “sprint” that demonstrated the agility of additive manufacturing technology to rapidly manufacture a prototype reactor core.
ORNL scientists selected and optimized a design for printing over a three-month period to demonstrate the ability to rapidly manufacture a prototype reactor core. Photo credit: Brittany Cramer / Oak Ridge National Laboratory, US Department of Energy
With the TCR program, ORNL is looking for a solution to a worrying trend. Although nuclear power plants provide nearly 20 percent of US electricity, more than half of US reactors will be decommissioned within 20 years, based on current license expiration dates. “The TCR program will provide a new model for the accelerated deployment of advanced nuclear power systems,” said Zacharia. “If costs and construction times are not addressed in the near future, the United States will eventually lose its single largest source of zero-emission electricity.”
Smaller is better
Today nuclear energy is getting smaller and opening up great opportunities for industry. A handful of microreactor designs are under development in the United States and could be ready for adoption within the next decade. These compact reactors will be small enough to be transported by truck and could help solve energy challenges in a number of areas, from remote commercial or residential locations to military bases.
Microreactors are not defined by their fuel shape or coolant. Instead, they have three main characteristics. The first, and the reason why AM could play a significant role, is that they are manufactured in the factory: all the components of a microreactor would be fully assembled in a factory and shipped to the site. This eliminates difficulties associated with large-scale construction, lowers capital costs, and would help get the reactor up and running quickly.
Another feature is that they are portable. This would make it easier for suppliers to ship the entire reactor by truck, ship, plane or railcar. They are also self-regulating, which means that microreactors adapt themselves through simple and responsive design concepts (which will certainly be iterated a lot over 3D printing). They do not require a large number of specialized operators and would use passive safety systems that prevent any possible overheating or reactor meltdown.
Small size, big punch
Microreactor designs vary, but most could generate 1-20 megawatts of thermal energy that could be used directly as heat or converted to electrical energy. They can be used to generate clean and reliable electricity for commercial use or for non-electrical applications such as district heating, water desalination and hydrogen generation.
In addition to seamless integration with renewable energies within microgrids, microreactors can also be used for emergency response to restore power to areas affected by natural disasters. They will also have a longer core life and operate for up to 10 years without refueling. Most designs require fuel with a higher concentration of uranium-235, which is not currently used in today’s reactors, although some could benefit from the use of high temperature moderator materials that would reduce fuel enrichment requirements while maintaining the small system size would.
The US 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 focusing on gas and heat pipe cooled designs that could hit the market as early as the mid-2020s.
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