Possibly (and literally) one of the hottest segments for AM adoption is the civil nuclear industry. Ever since Siemens successfully installed a 3D printed part—a metallic 108 millimeter (mm) diameter impeller for a fire protection pump—in the Krško nuclear power plant in Slovenia, AM in the nuclear industry has seen several new applications in development. With the proper materials, including ceramics and refractory metals, AM can be used for obsolete parts which are no longer available, allowing old power plants to safely continue their operations. Radiation shielding materials such as boron carbide are now available as powders for binder jetting on ExOne systems. And last year, Swedish 3D printing companies Additive Composite and Add North 3D released a new boron carbide composite filament suitable for radiation shielding applications in the nuclear industry.
Two studies that 3dpbm just received, co-authored by Iurii Bilobrov and first published several years ago, explore how AM can be used to make titanium parts that can better resist neutron and proton irradiation. As AM becomes an increasingly adopted production method in both the nuclear and the space industries, these papers now carry new significance.
The studies focus on how heavy work conditions require a successful composition for structural alloys. Specifically, they look at powder sintered composite Ti-6Al-4V/LaB6 (the typical titanium used in AM with the addition of lanthanum hexaboride) created for the nuclear industry, using dehydrogenation and sintering compacts in vacuum technology, has reached the level of cast Ti-6Al-4V alloy. The porosity problem is solved by filling the pores with LaBxOy and TiB chemical compounds. These materials can also hinder the growth of the grains of the alloy. This is an important feature for both cast alloys and powder metallurgy, as well as for welds and products created by additive manufacturing methods.
A key finding of the papers is that the addition of 0.08 weight % boron (in the form of lanthanum hexaboride) in 3D printed titanium parts may be an effective hardening method, without loss of ductility, resulting in better irradiation resistance.
Proton irradiation of solar wind on satellites in space
A long-term rational approach is to leverage the large and free vacuum of space for in-orbit additive manufacturing opportunities. In this case the ability of the printed materials to resist solar irradiation will become necessary. Extremely low values of residual pressure outside a spaceship eliminate several factors, which limit the dimensions of vacuum chambers of research instruments. Most bulky vacuum pumps and very thick walls are unnecessary for outside vacuum chambers.
The increased dimensions may allow keeping in a vacuum a large number of samples prepared for space additive manufacturing. Space 3D printing in a vacuum aboard a spaceship allows the creation of a metal product without an oxide film on the surface. This simplifies the acoustic emission signal processing, by reducing the amount of information coming from the sensors. The absence overlay of signals from the oxide film cracking and the base metal destruction enhances the capabilities of non-destructive testing of metal parts. The ideal solution is Ti-6Al-4V/LaB6 wire serving as a raw material for microgravity rapid prototyping (and eventually for serial parts as well).
Neutron impact in nuclear reactors on Earth
Severe conditions of radiation hardening with embrittlement in nuclear reactors require that materials have a plasticity reserve. Intricate parts made by AM have many vulnerable areas. Most of the damage occurs in the areas with maximum brittleness. The specific requirements of the nuclear industry can be met by combining the technologies for modernization of the existing alloys, which are time-proved, with the use of new materials both separately and in combination with the existing ones.
Combining methods of mechanical reduction of grain size by Friction Stir or high-temperature deformation, using TiH2 instead of titanium powder, modification by lanthanum hexaboride, chromium plating or laser cleaning of the surfaces before joining, employment of vacuum instead of inert atmosphere and post heat treatment can allow the production of the alloys without the trade-off of strength against plasticity.
This study discusses the metallurgical aspects of the modification of titanium alloys for use in the nuclear industry. Irradiation leads to hardening, plastic instability and reduction in fracture toughness in Ti alloys. Sintered compositions Ti–6Al–4V, Ti–6Al–4V/LaB6 have shown methods to reduce embrittlement.
Residual porosity may serve as temporary storage of products of nuclear decay H and He. High uniformity of the element distribution reduces the number of places predisposed to defect cluster formation. The plasticity reserve of Ti–6Al–4V/LaB6, in comparison with international standards, is ≈10%. The boron compounds to the partial absorption of neutrons fill the volume of residual pores in the material without degrading the properties of the matrix Ti–6Al–4V/LaB6 alloy.
Earlier uses of AM in the Nuclear industry
Advanced research on the use of 3D printed replacements and spare parts for nuclear reactors began officially in 2016 when the U.S. Department of Energy (DOE) has announced that GE Hitachi Nuclear Energy (GEH) had been selected 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 are now being used by GEH to support the deployment of 3D printed parts for fuels, services and new plant applications.
In February 2018, Russia’s state-owned nuclear power utility, Rosatom, established a company for the development of additive manufacturing technologies. It has already developed a pre-production prototype of a Gen II 3D printer to be used for both metal and composite AM parts in nuclear energy generation activities.
The new company, RusAT (Rusatom – Additive Technologies, an enterprise of TVEL Fuel Company), is an integrator of the nuclear industry in the field of additive technologies (three-dimensional printing). The company’s activities are focused on four key areas: the production of a line of 3D printers and their components, the creation of materials and metal powders for 3D printing, the development of integrated software for additive systems, as well as the provision of services for 3D printing and the introduction of additive technologies into production (including, in terms of the organization of production centers).
RusAT supervised a project by specialists of All-Russia Research Institute of Technical Physics (VNIITF)to develop and manufacture prototypes of lasers with a power of 200, 400, 700 and 1000 W to be used in SLM printers. The model range of laser sources will undergo a set of tests at RFNC-VNIIEF, after which they will be sent to RusAT’s Additive Technologies Center at the site of the Moscow Polymetal Plant for further testing on RusMelt 300M and RusMelt 600M 3D printers.
By the end of 2021, the organization plans to carry out a full cycle of tests of laser sources in accordance with the requirements of State Standards and prepare the line for serial production..
Latest nuclear developments for AM
More recently, 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. R&D is also ongoing to identify more applications of 3D printing in the nuclear industry.
One of these, supported by DOE’s Office of Nuclear Energy, is the Transformational Challenge Reactor (TCR) Demonstration Program, an unprecedented approach to develop a 3D printed reactor core by 2023. 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 the 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.
Things are now moving really fast in the nuclear industry—a big change from the past—especially on the front of SMR (small modular reactors) which are scaled-down versions of nuclear reactors including both current and IV generation (fast neutron) technology. As recently as May 15th 2020, the U.S. Department of Energy awarded grants to GE Research and the Massachusetts Institute of Technology (MIT) for research projects to develop digital twin technology for advanced nuclear reactors using artificial intelligence and advanced modelling controls. The research projects will use a digital twin of the company’s BWRX-300 small modular reactor as a reference design.
In 2021, French nuclear industry leader Framatome manufactured the world’s first uranium-molybdenum and uranium-silicon objects using 3D printing technology. The objects were manufactured at the CERCA Research and Innovation Lab (CRIL). This technological leap advances the development and production of metallic uranium fuel plates for research reactors and irradiation targets for medical isotopes widely used by hospitals for the diagnosis of cancer.
The uranium-molybdenum and uranium-silicon objects were 3D printed, layer by layer, using laser beam melting (laser PBF) equipment. This equipment is nuclear compliant and operates in a glove box under an inert argon gas atmosphere. The manufacturing project was developed by Framatome R&D experts working in close collaboration with the University of Technology of Belfort Montbéliard. Framatome continues to advance 3D printing technology for the production of irradiation targets and other components such as fuel plates for research reactors. Research efforts at CRIL can also be applied to prototyping or to small series production of innovative fuels for fourth-generation advanced reactors.