With a significant increase in the rate of adoption over the past five years, additive manufacturing has found applications in different sectors of the power generation and energy industry, both in building prototypes and in mainstream production, leading to process simplification and greater operational efficiency. Very few energy sectors stand to benefit from AM more than the relaunched nuclear fission industry, along with great hopes for a nuclear fusion-powered future.
In the nuclear energy industry, additive manufacturing plays a crucial role in the production of complex components and prototypes. It enables the rapid fabrication of intricate designs, reducing lead times and costs associated with traditional manufacturing methods. This technology allows for the creation of specialized parts with enhanced durability and precision, which are essential for ensuring the safety and reliability of nuclear power plants. Additionally, 3D printing can be used to produce radiation-resistant materials and tools for maintenance and repair in radioactive environments.
AM for current fission reactors
The civil nuclear industry is one of the hottest segments for the energy-related applications of additive manufacturing. Ever since Siemens successfully installed a 3D printed part—a metallic 108-millimeter-diameter impeller for a fire protection pump—in the Krško nuclear power plant in Slovenia, new AM applications for nuclear power plants have been in development. With the proper materials, including ceramics and refractory metals, AM can be used for obsolete parts that are no longer available, allowing old power plants to continue their operations, while new AM materials are being qualified for radiation shielding via binder jetting and extrusion technologies, along with metal PBF.
Advanced research on the use of 3D printed replacements and spare parts for nuclear reactors began in 2016 when the U.S. Department of Energy (DOE) selected GE Hitachi Nuclear Energy (GEH) to lead a $2 million additive manufacturing research project. The project is part of a more than $80 million investment in advanced nuclear technology. GEH led the project by producing sample replacement parts for nuclear power plants. The samples were 3D printed in metal at the GE Power Advanced Manufacturing Works facility in Greenville, SC, and then shipped to the Idaho National Laboratory (INL). Once irradiated in INL’s Advanced Test Reactor, the samples were tested and compared to an analysis of unirradiated material conducted by GEH. The results were used by GEH to support the deployment of 3D printed parts for fuels, services and new plant applications.
More recent examples of functional parts include four first-of-their-kind 3D printed fuel assembly brackets, produced in 2021 at the Department of Energy’s Manufacturing Demonstration Facility at Oak Ridge National Laboratory. These have been installed and are now under routine operating conditions at the Tennessee Valley Authority’s Browns Ferry Nuclear Plant Unit 2 in Athens, Alabama.
The components were developed in collaboration with TVA, Framatome and the DOE Office of Nuclear Energy-funded Transformational Challenge Reactor, or TCR, a program based at ORNL. 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.
The current focus of the TCR program is to further mature and demonstrate industry-ready technology informed by advanced manufacturing, artificial intelligence, integrated sensing, and deployment of a digital platform for informed certification of components.
Now AM operations are starting to scale. In 2022, Westinghouse Electric Company installed a 3D printed component into a commercial nuclear reactor at Exelon’s Byron Unit 1 nuclear plant during its spring refueling outage. Westinghouse operates powder bed fusion metal AM, as well as hot wire laser welding (HWLW), as part of its advanced manufacturing offering. 430 nuclear reactors operate around the world using Westinghouse technology.
Also in 2022, Westinghouse installed its StrongHold AM 3D printed nuclear fuel debris filters in two Nordic Boiling Water Reactor (BWR) units—Olkiluoto 2 in Finland, and Oskarshamn 3 in Sweden—to further improve the plants’ operational reliability. Westinghouse created the StrongHold AM filter in close cooperation with plant operators Teollisuuden Voima Oyj (TVO) and OKG. The StrongHold AM filters are fully manufactured through 3D printing techniques and offer enhanced capture features to prevent debris from entering the fuel assembly and potentially damaging the cladding, which could cause unplanned and expensive outages.
R&D is also ongoing to identify more applications of 3D printing in the nuclear industry. One of these, supported by the Department of Energy’s Office of Nuclear Energy, is the previously mentioned Transformational Challenge Reactor (TCR) Demonstration Program. As part of deploying a 3D printed nuclear reactor, the program will create a digital platform that will help in handing off the technology to industry for the rapid adoption of additively manufactured nuclear energy technology. Through the TCR program, ORNL is seeking a solution to a troubling trend: although nuclear power plants provide nearly 20% of U.S. electricity, more than half of U.S. reactors will be retired within 20 years, based on current license expiration dates.
A similar situation is taking place in France, where by mid-August 2022, more than half of the 56 nuclear reactors in France were offline. The reasons for this were safety-relevant damage in the safety injection system, along with scheduled shutdowns. Serious stress corrosion cracking in the stainless steel safety system piping was discovered in 2021, requiring shutdowns for inspections and repair. All these parts will need to be replaced and additive manufacturing will have to play a role, especially where the original molds are no longer available.
With this in mind, the French nuclear energy services and parts provider Framatome completed the installation of the first 3D printed, stainless steel fuel component at the Forsmark Nuclear Power Plant, operated by Vattenfall in Sweden. In collaboration with KSB SE & Co. KgaA, the ATRIUM 11 upper tie plate grids were designed, manufactured, and installed in Forsmark Unit 3 for a multi-year irradiation program.
Located at the top of the ATRIUM 11 fuel assembly, the upper tie plate grid is a non-structural weight-bearing component that secures fuel rods and retains larger debris from entering the fuel assembly from the top. Upper tie plate grids are easily inspected, and samples are accessible for qualifying this new manufacturing process for in-reactor use as needed. During the conventional manufacturing process, upper tie plate grids are laser welded using stamped comb-like sheets that require additional manufacturing steps and operator oversight. Additive manufacturing streamlines the manufacturing process and increases design options for enhanced functionality and improved performance.
Framatome’s initiative to introduce additive manufacturing to nuclear fuel, which began in 2015, is focused on stainless steel and nickel-based alloy fuel assembly components. In 2021, the first 3D printed stainless steel fuel assembly channel fastener created by Framatome in collaboration with Oak Ridge National Laboratory (ORNL) was loaded in a U.S. commercial BWR nuclear power plant. Framatome fuel experts in France, Germany and the U.S. developed this technology in close collaboration with customers worldwide.
AM for next-gen nuclear fission
Things are now moving a little bit faster in the nuclear industry—a big change from the past—especially on the front of small modular reactors (SMR), which are scaled-down versions of nuclear reactors including both current and IV generation (fast neutron) technology.
A handful of microreactor designs are under development in the United States, and they could be ready to roll out within this decade. These compact reactors will be small enough to transport by truck and could help solve energy challenges in several 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 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. They are also self-adjusting, which means that simple and responsive design concepts 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.
Microreactor designs vary, SMRs are defined as producing up to 300 megawatts (MW) of power, while Very Small Modular Reactors (vSMRs) or microreactors produce up to 20 MWs of power per module. 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. However, some may benefit from the 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-made microreactor developers are currently focused on gas and heat pipe-cooled designs that could debut as early as the mid-2020s.
Ultra Safe Nuclear Corporation (USNC), a wholly U.S.-controlled corporation headquartered in Seattle, is a global leader in the deployment of micro reactors, and a vertical integrator of nuclear power technologies. The company is committed to bringing safe, commercially competitive, clean and reliable nuclear energy to power markets throughout the world.
USNC is demonstrating MMR Energy Systems at the Canadian Nuclear Laboratories in partnership with Ontario Power Generation and at the University of Illinois, and has started new projects to further deploy its technology in the United States, Canada and Europe. The company adheres to strict inherent and intrinsic safety principles through technological innovation in fuels, materials, and design.
More than a dozen countries around the world are now collaborating in a global race toward Generation IV—next-generation concepts in nuclear energy seen as vital to supplying carbon-free energy to a world with ever-increasing demands for electricity.
While renewable sources such as solar and wind continue to grow, conventional wisdom has taken root in energy circles that nuclear stands alone as a reliable baseload energy source, one that operates continuously to meet the minimum level of power demand 24/7 without negative environmental consequences. In this environment, Seattle-based USNC is leading the way by leveraging new 3D printing methods to deliver all-new designs that deliver optimal performance in unique materials.
The USNC’s approach is centered around the use of Fully Ceramic Micro-encapsulated (FCM) fuel. To produce this fuel, the company utilizes Desktop Metal‘s X-Series binder jetting 3D printers. These printers are capable of 3D printing ceramic particles that are heat-resistant and can encase a standard type of nuclear fuel particle.
The application of binder jetting is a crucial part of USNC’s fuel manufacturing process, which is vital for the organization’s innovation. This approach is gaining momentum as testing of USNC’s FCM fuel is currently underway by the Nuclear Research & Consultancy Group in the Netherlands (NRG Petten). Additionally, through its joint venture Global First Power, USNC is working towards deploying its first-of-a-kind MMR at Chalk River Laboratories, a site owned by Atomic Energy of Canada Limited and managed by Canadian Nuclear Laboratories. Efforts are being made to obtain a License to Prepare Site from the Canadian Nuclear Safety Commission (CSNC).
Building upon a technology that originated in the 1960s, Ultra Safe Nuclear produces smaller-scale coated fuel particles, known as TRISO in the industry. TRISO is a tristructural isotropic particle fuel that is experiencing a resurgence in the development of Generation IV nuclear reactors. These fuel microspheres are typically placed in a soft graphitic matrix. However, this matrix lacked structural strength and failed to effectively prevent the release of radionuclides.
To address this, USNC replaced the graphitic matrix with a refractory ceramic material called silicon carbide (SiC). SiC is a technical ceramic material known for its exceptional environmental stability and is commonly used in aerospace, armor, plasma shield, and high-temperature applications. The conditions inside a nuclear reactor are extremely harsh, but SiC does not shrink or excessively swell like the traditional graphitic matrix. It also exhibits high resistance to oxidation and corrosion, making it highly stable under the demanding conditions of a nuclear reactor core.
However, manufacturing or forming SiC into complex parts has always presented challenges. For many years, despite the industry’s interest in utilizing silicon carbide, there was no viable or cost-effective manufacturing process to transform highly pure, crystalline, nuclear-grade SiC into the required shapes and forms for nuclear applications. That is, until the advent of 3D printers.
By employing 3D printing technology, USNC can create SiC fuel forms with complex geometries that serve as shells for the nuclear fuel particles. Silicon carbide is often infiltrated with silicon or other matrices to increase its density, but this is not feasible in a nuclear environment. To maintain material uniformity and homogeneity, USNC combines binder jetting with chemical vapor infiltration. This process fills the porous SiC structure with high-purity crystalline silicon carbide, enabling the realization of highly complex, near-net shapes without the need for sintering the SiC material, applying pressure, or introducing secondary phases.
In addition to its production efficiencies, USNC’s manufacturing strategy with binder jet 3D printing allows reactor performance optimization by capitalizing on the design freedom provided by 3D printing. Previously, the team was limited to a single design that was produced in large quantities using hard tooling. Due to the expensive nature of the tooling and the long lead times for making changes, designers aimed to create a generic yet efficient design. However, with the ability to create unique designs in large quantities using 3D printing, USNC can enhance the quality assurance of its mission to provide safe and responsible nuclear energy.
