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Can 3D printing build a better, cheaper reactor faster?

OAK RIDGE, Tenn. — A 3D-printed nuclear reactor, if built and demonstrated, could open a path to advanced commercial nuclear power stations that produce carbon-free electricity at a cost competitive with natural gas turbine power plants.

That’s the hope of Kurt Terrani, director of the Transformational Challenge Reactor Demonstration Program at Oak Ridge National Laboratory. At a recent Zoom meeting of Friends of ORNL, he described the progress the program has made so far toward building a possible 14th reactor at ORNL by 2023.

Unlike other industries, Terrani argued, “The nuclear industry is a dinosaur industry that has failed to adopt any new technologies partly because the United States hasn’t built any advanced reactors for 40 years.”

These new technologies include additive manufacturing (3D printing of parts by building them layer by layer in shapes directed by a computer program) and artificial intelligence (providing a computer with data and training it to identify trends and make predictions based on the data).

Kurt Terrani spoke to Friends of ORNL (FORNL) about the 3D printed advanced reactor project at the Lab.

“Advances made in nuclear fuels, materials, manufacturing and computational sciences in the past 40 years could be applied to the design and construction of an advanced nuclear reactor,” Terrani said.

The TCR program’s researchers, he noted, are refining their design of a 3D-printed nuclear reactor core, scaling up the additive manufacturing process necessary to build it and developing methods using Artificial Intelligence (AI) to confirm the consistency and reliability of its printed components.

As part of the program’s research, three facilities at ORNL — the Spallation Neutron Source, High Flux Isotope Reactor (ORNL’s only operating research reactor) and Summit supercomputer — are being used. The work is being funded by the Department of Energy’s Office of Nuclear Energy.

“With AM (additive manufacturing) we have the freedom to make metallic and ceramic components that have complex geometries and use new materials. We can embed sensors—thermocouples and optical fibers—into the structures to monitor the health of the reactor system and enable autonomous operation.

“We want autonomous operation to reduce the staff needed to operate a nuclear power plant because it is competing with a gas turbine power plant, which has seven staff members versus 400 for the nuclear plant,” Terrani said. “We are trying to remove human workers from the process to make it cheaper.”

Nuclear power plants with light-water reactors take 10 years to build and are expensive to construct and operate. Only one nuclear power plant has been built in the U.S. in the past 20 years, and more than half of U.S. reactors will be retired within 20 years, based on current license expiration dates. The goal of the TCR program, Terrani asserted, is to show that by using modern technologies, a better and cheaper reactor can be built faster.

Citing ORNL’s 77-year history in nuclear reactor reserarch and development (R&D), Terrani noted that the Graphite Reactor, the world’s first continuously operated reactor, was built in nine months. Most of the world’s 400 nuclear power plants today have pressurized-water reactors (PWR) based on former ORNL Director Alvin Weinberg’s concept of using pressurized water as a coolant and moderator (to slow the neutrons) for a reactor using uranium slightly enriched in U-235.

Hearing in 1946 about Weinberg’s pressurized-water reactor concept from a mutual acquaintance, Navy Capt. Hyman Rickover decided to build a PWR to power the first nuclear submarine, whose development he spearheaded. He also oversaw the construction of the first land-based, electricity-producing PWR in Shippingport, Pa., launching the U.S. nuclear power industry, which supplies 20% of the nation’s electricity and is the single largest source of emissions-free power. Both the nuclear submarine Nautilus and atomic power plant began operation in the 1950s.

ORNL researchers have shown that a pressure vessel made of stainless steel can be 3D printed rapidly, along with the nuclear fuel assemblies that make up the reactor core.

The reactor will be two-and-a-half feet tall.

“We have said the TCR is the size of a large trash can, but we don’t call it the trash can reactor — we named it the Transformational Challenge Reactor,” noted Terrani, who also calls it a microreactor.

The demonstration microreactor will be passively safe and reliable and will produce three megawatts of heat, he said. It will be cooled by helium gas, and yttrium hydride will be used as the moderator. The nuclear fuel will be uranium nitride TRISO (tri-structural isotropic) fuel particles, each the size of a poppy seed and each able to retain fission products; Terrani called the fuel “high assay low enriched uranium,” meaning that the uranium will be enriched between 5% to 20% U-235. Developed at ORNL, the fuel will be incorporated in 3D-printed silicon carbide fuel blocks.