First-Ever Additively Manufactured Debris-Filtering Bottom Nozzles Installed at Farley Nuclear Plant

Southern Nuclear, a subsidiary of Southern Company and operator of more than 8.2 GW of nuclear power capacity, said it has completed the installation of lead test assemblies with additively manufactured debris-filtering bottom nozzles (AMBN) at Alabama Power’s Joseph M. Farley Nuclear Plant. The AMBN assemblies are a new technology manufactured by Westinghouse Electric Co. that is designed to improve debris capturing, ultimately improving fuel endurance.

“Over the past decade, Southern Nuclear has led the industry in the development and implementation of new technologies that improve fuel resiliency,” Southern Nuclear President Pete Sena said in a statement announcing the accomplishment. “The existing nuclear power fleet is the backbone of our country’s clean energy supply, and we are innovating nuclear fuel today to be more robust in order to deliver safer, more affordable, and more reliable carbon-free clean nuclear power for decades to come.”

Westinghouse says debris-wearing action on fuel rod cladding, known as debris fretting, is the primary source of leaks in pressurized-water reactor (PWR) fuel assemblies. The company claims additive manufacturing (AM) technology (often referred to as 3D printing) “offers significant improvements in debris filtering thanks to enhanced design freedom.” This was the first time Westinghouse has used AM to fabricate bottom nozzles for installation in an operational nuclear power plant.

The AMBN design (Figure 1) reduces the diameter of debris that can enter into the reactor compared to previous designs. Based on testing, Westinghouse said the additively manufactured components significantly increase bottom nozzle debris resistance from 65% to 96%.

1. Image of a Westinghouse fuel assembly bottom nozzle fabricated using additive manufacturing. Courtesy: Southern Nuclear

“Our additive manufacturing technology is allowing us to achieve breakthrough performance with an immediate positive impact for our customers,” Tarik Choho, president of Nuclear Fuel with Westinghouse, said in a statement. “This significant technology innovation for PWR reactors mitigates the risk of leakage in the fuel rods due to the accumulation of debris, strengthening the safety and efficiency of our customers’ operations.”

Westinghouse has long been conducting research on cutting-edge solutions using AM techniques. In 2015, the company led the first-ever material irradiation study of 3D printed nuclear components. In 2020, Westinghouse installed the first-ever safety-related AM component—a thimble plugging device—into an operating commercial reactor. And, earlier this year, the company produced the 1,000th AM component for Russian-designed VVER-440 fuel.

Meanwhile, Westinghouse has also been working for years to improve debris protection in commercial nuclear fuel. In 2021, the company announced the successful implementation at an undisclosed nuclear plant of an advanced debris filter bottom nozzle that utilized innovative side skirt filters on fuel assemblies. The design reportedly provided “a revolutionary defense against debris that could otherwise escape between fuel assemblies and cause leaking fuel rods by fretting in peripheral rods.” The innovative bottom nozzle was a feature added to Westinghouse’s PRIME fuel package, which is comprised of optimized enhancements to help utilities improve fuel performance and enable improved fuel cycle economics. The PRIME package includes the bottom nozzle, reinforced dashpots, and Low Tin ZIRLO grids.

Now, the AMBN design presumably takes debris protection a step further. Southern Nuclear explained that among the many redundant safety systems at a nuclear power plant, each nuclear fuel pellet is encased by fuel cladding and resides within the nuclear coolant system inside of the nuclear containment structure, which collectively serve as a fission-product barrier for nuclear fuel. AMBNs are designed to capture debris that could enter the reactor coolant system and damage fuel cladding.

Westinghouse fabricated and delivered the four lead test assemblies with AMBN to Plant Farley in the first quarter of 2024. Improved fuel resiliency is expected to produce fuel cost efficiencies and improve long-term plant reliability.

Southern Nuclear operates eight nuclear power units: two at Plant Farley near Dothan, Alabama; two at the Edwin I. Hatch Nuclear Plant near Baxley, Georgia; and four at the Alvin W. Vogtle Electric Generating Plant near Waynesboro, Georgia. The company touts itself as “a recognized leader within the commercial nuclear industry in fuel innovation.” It claims to have been the first company to deploy accident tolerant fuel (ATF), and says it has won more than 10 consecutive Top Innovative Practice Awards and eight EPRI awards.

In late September last year, Southern Nuclear announced that it had received “first-of-a-kind approval” from the Nuclear Regulatory Commission to use advanced ATF exceeding 5% enrichment of uranium-235 (U-235) in Plant Vogtle Unit 2. The fuel is expected to be loaded in 2025 and will have enrichments up to 6 weight % U-235. At the time, the company said the milestone “underscores the industry’s effort to optimize fuel, enabling increased fuel efficiency and long-term affordability for nuclear power plants.” Higher-uranium-enriched fuels could extend the length of time between refueling outages, making nuclear power an even more reliable source for the grid, Southern Nuclear said. The AMBN design could help ensure reliable operation of units during these extended runtimes.

Aaron Larson is POWER’s executive editor (@POWERmagazine).

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