Scientists from the U.S. Department of Energy’s Argonne National Laboratory have used 3D printing to create a new method of reusing nuclear waste, which could allow up to 97 percent to be recycled.
The novel process could increase the percentage of fuel that scientists are able to reuse from 95 percent under existing processes, to 97 percent. While this may not initially appear to represent major progress, it could significantly reduce the amount of used fuel that needs to be stored, and the time it remains hazardous for.
“Rather than store five percent for hundreds of thousands of years, the remaining three percent needs to be stored at a maximum of about one thousand years,” said Andrew Breshears, an Argonne nuclear chemist, and co-author. “In other words, this additional step may reduce the length of storage almost one thousandfold.”
How 3D printing can reduce nuclear waste
While nuclear energy is an established and reliable source of electrical power, one barrier to expansion is the management and disposal of the radioactive by-products of nuclear fission. If the spent fuel discharge rate remains at its current level, the 98 operating commercial nuclear power reactors in the United States, will need to store 126,000 metric tons of used nuclear fuel (UNF) by 2040.
Argonne scientists found that 97 percent of the fissionable content of this fuel could be recovered and reused. To achieve this, they extended the existing Actinide Lanthanide Separation Process (ALSEP) which was introduced in 2013, in order to separate the so-called minor actinides (MA), including neptunium (Np), americium (Am), and curium (Cm).
Using a liquid to liquid extraction method due to their speed and compatibility benefits, the new process is designed to be the most simple, standardized method possible, based on minimum adjustments and producing maximum stability. 3D printing is utilized in the process to create a bank of 1.25 cm centrifugal contactors. Once connected, the contactors enable a continuous reprocessing loop.
The more efficient ALSEP process
The new method begins at the end of the existing Plutonium Uranium Reduction Extraction (PUREX) process, with nuclear fuel from which uranium, plutonium, and neptunium have been extracted. This liquid mixture is introduced into one side of a row of 20 3D printed contactors, and a blend of industrial chemicals that were designed to separate the actinides are inserted into the other. The centrifuges are then spun to create an outward (or centrifugal) force that separates the substances inside.
During tests carried out at Argonne’s research laboratories, americium and Cm were separated from the lanthanides with over 99.9 percent completion. The sum of the impurities of the Am/Cm product stream using simulated raffinate was found to be 3.2 × 10−3 g/L. In addition, separation factors of nearly 100 for 154Eu over 241Am were achieved, indicating that the process was scalable on an engineering scale.
The centrifugal contactors were critical to the process, and 3D printing allowed the complex fluid devices to be manufactured with internal channels, and as a single component. In addition, multiple contactor stages were integrated into single multi-stage modules, reducing the effort required for installation, and eliminating potential failure points.
Not only does using 3D printing to produce the contactors accelerate the process, but the design of the devices offer an added layer of protection against nuclear proliferation. The tubes connecting the 20 contactors run inside each device making it difficult to access and divert the radioactive materials to non-civil nuclear practices.
Following a 36 phase blueprint, and taking over 20 hours to complete the separation, the method is still in its early stages of development. The researchers are continuing to explore new ways to reduce the size of the process and achieve greater separation.
Argonne National Laboratory and 3D printing
The Argonne research team has been developing and experimenting with new applications of 3D printing technology for some time and announced in March 2020 that they had successfully scaled up the recycling of the molybdenum-99 isotope using 3D printed parts. Using the new apparatus, they expect to increase the efficiency of the recycling process, allowing producers to yield more Mo-99 from their expensive enriched molybdenum reserves.
Working with scientists from Carnegie Mellon University in February last year, Argonne researchers used high-speed x-ray imaging to study the keyhole effect in powder-based metal 3D printing. The research helped 3D printing manufacturers to better understand how pores develop in metals during the printing process and deliver end-use products that are less prone to cracking and general weakness.
Similarly, working with the U.S. Department of Energy, researchers from Argonne National Laboratory produced a ‘deep dive’ into the laser melting that takes place inside metal 3D printers. The study contributed to a body of research seeking to improve the additive manufacturing process and increase adoption in industries around the world.
The researchers’ findings are detailed in their paper titled “Closing the Nuclear Fuel Cycle with a Simplified Minor Actinide Lanthanide Separation Process (ALSEP) and Additive Manufacturing,” which was published in the Scientific Reports journal in September 2019. The paper was co-authored by Artem V. Gelis, Peter Kozak, Andrew T. Breshears, M. Alex Brown, Cari Launiere, Emily L. Campbell, Gabriel B. Hall, Tatiana G. Levitskaia, Vanessa E. Holfeltz, and Gregg J. Lumetta.
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Feature image 3D printed contactor. Photo via Argonne National Laboratory.