The future of (sustainable) safe nuclear energy is 3D printed at ORNL
How TRISO fuels and 3D printing of refractory metals are shaping the new generation of safer and more economical nuclear reactors
BWX Technologies, (NYSE: BWXT) has just been awarded a $4.9 million contract amendment by Battelle Energy Alliance LLC to manufacture TRISO nuclear fuel. BEA manages Idaho National Laboratory on behalf of the Department of Energy. Under the terms of the amendment, BWXT subsidiary Nuclear Operations Group, Inc. will manufacture a quantity of natural uranium TRISO particles that will be used to power next-gen microreactors, to provide accessible and safe nuclear energy, such as those in development at ORNL.
“We are excited and confident about the growing market for TRISO and specialty fuels, and with our third TRISO fuel production contract since the spring of 2020, we believe that confidence is being validated,” said Joel Duling, BWXT Nuclear Operations Group president. “We are uniquely positioned to capture additional work in fueling, designing and manufacturing microreactors.”
But what are TRISO fuels and what do they have to do with additive manufacturing? Apparently, a lot, as AM is emerging as a key technology for manufacturing the small, fast next-gen reactors that will be using TRISO fuels.
TRISO refers to a specific design of uranium nuclear reactor fuel. TRISO is a shortened form of the term TRIstructural-ISOtropic. TRIstructural refers to the layers of coatings surrounding the uranium fuel, and ISOtropic refers to the coatings having uniform materials characteristics in all directions so that fission products are retained.
The particles are incredibly small (about the size of a poppy seed) and very robust. They can be fabricated into cylindrical pellets or billiard ball-sized spheres called “pebbles” for use in either high-temperature gas or molten salt-cooled reactors. TRISO fuels are structurally more resistant to neutron irradiation, corrosion, oxidation and high temperatures (the factors that most impact fuel performance) than traditional reactor fuels. Each particle acts as its own containment system thanks to its triple-coated layers. This allows them to retain fission products under all reactor conditions. Simply put, TRISO particles cannot melt in a reactor and can withstand extreme temperatures that are well beyond the threshold of current nuclear fuels.
TRISO fuel testing is gaining a lot of interest from the advanced reactor community. Some reactor vendors such as X-energy and Kairos Power, along with the Department of Defense, are planning to use TRISO fuel for their designs—including some small modular and micro-reactor concept
BWXT is the only U.S. company to manufacture irradiation-tested uranium oxycarbide TRISO fuel using production-scale equipment. Its TRISO production facility is currently licensed to produce this type of High Assay Low Enriched Uranium (HALEU) fuel, which is undergoing validation in a series of experiments. BWXT is also designing TRISO-fueled microreactors using previously announced funding from the Department of Energy and DoD. And that is where 3D printing first came in.
TRISO fuel for a 3D printed reactor
Back in March 2020, BWXT Nuclear Operations Group, Inc (NOG) was awarded a contract from the US Department of Energy’s Oak Ridge National Laboratory (ORNL) to manufacture TRISO nuclear fuel to support the continued development of the Transformational Challenge Reactor (TCR). The TCR project aims to build an additively manufactured microreactor, with a demonstration unit planned to be operational by 2024.
NOG is the BWXT subsidiary that began manufacturing TRISO fuel at its Lynchburg (VA) facility in late 2019. “This contract award is strategically significant given our stated intention to find new markets for our advanced nuclear technologies,” BWXT NOG President Joel Duling said. “We are exceedingly pleased with this award and look forward to working with Oak Ridge National Laboratory and the Department of Energy to demonstrate safe and clean nuclear power generation with a novel, low-cost, additively manufactured nuclear reactor.”
The scope of the contract includes the fabrication and delivery of uranium kernels, TRISO coated surrogate materials, and TRISO coated uranium kernels. ORNL will use these materials as it continues the development and prototyping of the reactor’s design and advanced manufacturing process.
Faster, safer and more economical nuclear energy
The TCR – which will be the 14th nuclear reactor to be built at ORNL – will use a core of uranium nitride-coated fuel particles within an advanced manufactured silicon carbide structure. This will be housed inside a conventionally manufactured, qualified stainless steel vessel. Fuel blocks will be interspersed with yttrium hydride moderator elements. The reactor system will be housed inside a vented containment within an ORNL building.
“The nuclear industry is still constrained in thinking about the way we design, build and deploy nuclear energy technology,” ORNL Director Thomas Zacharia said. “DOE launched this program to seek a new approach to rapidly and economically develop transformational energy solutions that deliver reliable, clean energy.”
Reactor development and deployment have traditionally relied on materials, fuels and technology pioneered in the 1950s and ’60s, and high costs and decades-long construction times have limited the United States to building only one new nuclear power plant in the last 20 years. TCR introduces new, advanced materials and uses integrated sensors and controls, providing a highly optimized, efficient system that reduces cost, relying on scientific advances with the potential to shape a new path in reactor design, manufacturing, licensing and operation.
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.
“We have been aggressively developing the capability to make this program a reality over the last several months, and our effort has proven that this technology is ready to demonstrate a 3D printed nuclear reactor core,” said Kurt Terrani, the TCR technical director. “The current situation for nuclear is dire. This is a foundational effort that can open the floodgates to rapid innovation for the nuclear community.”
Nuclear industry benefits
As part of deploying a 3D printed nuclear reactor, the program is also creating a digital platform to help in handing off the technology to industry for rapid adoption of additively manufactured nuclear energy technology.
“The entire TCR concept is made possible because of the significant advances in additive manufacturing process technology,” Terrani said. “By using 3D printing, we can use technology and materials that the nuclear community has been unable to capitalize on in the last several decades. This includes sensors for near-autonomous control and a library of data and a new and accelerated approach to a qualification that will benefit the entire nuclear community.”
But TCR’s end goal is bigger than a single reactor: it’s to revolutionize manufacturing in the nuclear industry — and in other industries, too. That means outside companies are already benefitting from what ORNL is learning from the TCR program.
“As we’re developing this framework for TCR, we are also engaging companies that can benefit from additive manufacturing and data analytics technologies for producing components,” said ORNL’s Ryan Dehoff, group leader for Deposition Science and Technology. “We’ve shown them the benefits 3D printing can provide — especially in the nuclear industry — and now we’re working with them to start to realize some of those advantages.”
One example is Kairos Power. Because of the same technology employed in the Transformational Challenge Reactor Program, ORNL can use additive manufacturing to continually adjust the prototype, producing a series of parts in rapid order for testing. California-based Kairos is also looking to develop innovative nuclear technology on a tight timeline, which led the company to partner with ORNL to produce a specific part for its own reactor prototype.
The part is a closed pump impeller, part of a heat exchanger loop designed to move molten salt through a heat source. It needs to withstand temperatures up to 600 degrees Celsius, and it needs to perfectly fit with the rest of the prototype so that there’s no variance in the way that it works. It needs to have exactly the right shape, exactly the right dimensions, and exactly the right surfaces.
With next-day turnaround in manufacturing, the ORNL team worked with Kairos engineers to adjust their design for additive manufacturing without compromising the component’s performance. “What TCR is doing is really important for changing the paradigm for nuclear energy,” said Per Peterson, Chief Nuclear Officer of Kairos and elected member of the National Academy of Engineering. “But I think TCR is also changing the paradigm for our national labs to return them back to what were their most important competencies — a bar they were already hitting 50 years ago.”
With additive manufacturing technologies, ORNL can take a computer-aided design, or CAD, file, 3D-print a scaled-down prototype and give it to a company for testing in their environments relevant for their specific application. If modifications are required, no matter how slight, the CAD file can be adjusted, printed again, and then tested, modified, and printed again and again, in agile fashion, until optimal specifications are met.
“Instead of getting to try two designs, we might get to try 20,” Dehoff said. “It makes for a very rapid design iteration, to final design and then full-scale production.”
TCR is the first to develop and demonstrate an expansive digital platform that combines continuous monitoring of the print and data analytics to certify the quality of the additively manufactured components that demanding nuclear applications require. Companies receive not only the part, but also digital data associated with every aspect of the part. As test results come in, engineers can correlate performance with manufacturing data from embedded monitoring.
“Having a relationship with ORNL strengthens our technology development program for Kairos Power’s advanced reactor, specifically in advanced manufacturing,” said Dr. Edward Blandford, Kairos’ co-founder and chief technology officer. “This partnership creates flexibility and competency, allowing us to build smarter and faster through our iterative development approach.”
Solving supply-chain issues
Good luck finding a casting company willing to make a mold and manufacture such a small number – and even if one is willing, the cost is likely to be prohibitive. “Where additive manufacturing excels is in low-quantity production with high quality, rigorous requirements where there’s difficulty in the supply chain,” such as having to wait for a large enough order to justify producing a batch, said ORNL researcher Fred List of Deposition Science and Technology. “The turnaround is days, rather than weeks to months.”
Best of all, because of its ability to consider literally a thousand different variables and then make sense of them, advanced manufacturing can produce items that are already “qualified” — that is, it’s possible to already know exactly how they will perform. For the tightly regulated nuclear industry, where such details are crucial, Dehoff said that this new way of producing components can be a game-changer.
“For TCR, we’re using this digital platform to certify components inside a nuclear reactor, so this rapid design iteration is very important,” Dehoff said. “We could never do that with a traditional project.”
AM parts at TVA nuclear reactor
Four 3D printed fuel assembly channel fasteners have been installed and are now under routine operating conditions at unit 2 of the Tennessee Valley Authority’s (TVA’s) Browns Ferry nuclear power plant in Alabama. The components were produced at the US DoE’s Manufacturing Demonstration Facility at the ORNL, under the TCR program
The components installed at Browns Ferry 2 were printed at ORNL using additive manufacturing techniques – also known as 3D printing – in which material is deposited in layers, following a computer-designed model, to form precise shapes without the need for later carving or machining. “The channel fasteners’ straightforward, though non-symmetric, geometry was a good match for a first-ever additive manufacturing application for use in a nuclear reactor,” ORNL said.
The parts were installed on Atrium 10XM boiling water reactor fuel assemblies at Framatome’s nuclear fuel manufacturing facility in Richland, Washington. These were installed within Browns Ferry 2 during a planned outage which ended on 22 April. The fasteners will remain in the reactor for six years with regular inspections during that period.
Deploying 3D-printed components in a reactor application is a great milestone,” said Ben Betzler, ORNL’s TCR program director. “It shows that it is possible to deliver qualified components in a highly regulated environment. This programme bridges basic and applied science and technology to deliver tangible solutions that show how advanced manufacturing can transform reactor technology and components.”
“Collaborating with TVA and ORNL allows us to deploy innovative technologies and explore emerging 3D printing markets that will benefit the nuclear energy industry,” said John Strumpell, manager of North America Fuel R&D at Framatome. “This project provides the foundation for designing and manufacturing a variety of 3D-printed parts that will contribute to creating a clean energy future.”
Refractory metals for advanced reactors
The development of advanced nuclear reactors is continuing at a rapid pace, but issues still remain working with some special materials that are important to these reactors. Teamed with the Oak Ridge National Laboratory, engineers and designers at BWX Technologies, Inc. (BWXT) have developed new additive manufacturing technologies for the design and manufacture of reactor components made from high-temperature alloys and refractory metals.
Advanced reactors are designed to operate at very high temperatures, and the ability to additively manufacture parts from these alloys and metals can further speed development. Specifically, BWXT has demonstrated the ability to additively manufacture nickel-based superalloys and refractory-metal-based alloys for use in nuclear components. The company also accomplished component-level qualifications, leading to a more efficient certification of nuclear materials configured in complex geometries. BWXT validated this technology during the successful execution of an advanced nuclear technology development cost-share program awarded by the U.S. Department of Energy.
“We have a uniquely talented group of engineers and designers at BWXT,” said Ken Camplin, president of the Nuclear Services Group. “Their work will make it far easier for advanced reactor developers to move forward in dealing with a number of critical technical challenges inherent in many of these designs.”
With refractory metal alloy-based core components, it is conceivable that an advanced reactor can reach core exit temperatures of 2,700°F and overall plant efficiencies of approximately 50%. Additionally, these material developments could have an immediate impact on the current commercial reactor fleet and the goal of achieving an accident-tolerant fuel design.
BWXT plans to use its unique design expertise and advanced manufacturing capability to reduce the costs of advanced nuclear energy systems. Specifically, BWXT’s designs and manufacturing methods will enhance the power output and longevity of a reactor while maintaining affordable costs to manufacture. BWXT expects to reduce manufacturing risk over time as outlined in its proposal to the Department of Energy’s Advanced Reactor Development Program (ARDP).
In January 2022 Ultra Safe Nuclear Corporation (USNC) licensed the ORNL method to 3D print highly resistant components for use in nuclear reactor designs. USNC Executive Vice President Kurt Terrani, formerly of ORNL, said the novel method will allow the company to make parts with desired complex shapes more efficiently.
The novel method to 3D print components for nuclear reactors, developed by the Department of Energy’s Oak Ridge National Laboratory, uses a sophisticated additive manufacturing technique to print refractory materials, which are highly resistant to extreme heat and degradation, into components with complex shapes needed for advanced nuclear reactor designs. USNC will incorporate this method to boost their mission to develop and deploy nuclear-based, energy-generating equipment that is safe, commercially competitive and simple to use.
“It’s rewarding to see the transition from basic concept to a more mature technology that is actively being developed and deployed by our industry partners,” said Jeremy Busby, director of ORNL’s Nuclear Energy and Fuel Cycle division. “This is exactly the sort of impact that ORNL strives to make for our energy portfolio.”