Monday, May 24, 2021

Reactors Built Like Cars in a Factory

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Innovative Technologies Could Reduce Nuclear Reactor Production Costs by 40%; Commercialization Possible in the Next Decade

When David Gandy envisions the future of nuclear power, he sees reactors being made in a similar way as automobiles. “Our goal is to get to a point where reactors can be produced on an assembly line in a factory,” said Gandy, who is an EPRI senior technical executive. “Steel or other raw materials come in one end and out comes a reactor on the other end.”

Since 2016, Gandy has been working toward this vision. With the support and sponsorship of the U.S. Department of Energy (DOE), EPRI is investigating advanced manufacturing and fabrication technologies with potential to dramatically reduce the time and costs required to build a nuclear plant’s reactor pressure vessel. Gandy expects that welding time can be reduced by up to 90%—and that overall costs can be cut by 40%.

Researchers are testing the technologies for constructing small modular reactors (SMRs). Collaborators include the United Kingdom–based Nuclear Advanced Manufacturing Research Center (Nuclear AMRC) and Oregon-based reactor manufacturer NuScale Power. The work focuses on producing the upper and lower assemblies of the reactor pressure vessel of NuScale’s 60-megawatt SMR.

One technology under investigation is powder metallurgy/hot isostatic pressing, which involves atomizing metal alloys into a powder, placing the powder into a metal mold, and using high temperatures and pressures to consolidate the powder into solid components.

Relative to traditional forging, this process produces near net shape parts with much less material wasted during machining. Production of components can be accomplished in as little as four to six months—just a fraction of the two to five years often required with forging.

The team has successfully produced a 3,650-pound reactor head at 44% scale with good strength and dimensional quality, which means that the size of the components doesn’t change during production. The team has produced components as heavy as 7,000 pounds.

Fabrication has required addressing challenges associated with oxygen absorption. “When fine powder absorbs oxygen, the oxygen can react with silicon and manganese to form oxides, which reduces the toughness of the components,” said Gandy. “Working together with DOE and our collaborators, we have developed new processing methods to create components with excellent toughness and tensile strength.”

Researchers also are investigating electron beam welding, which fuses two sections of metal by focusing a high-intensity energy beam on the junction. The process occurs in a vacuum chamber. Unlike traditional welding, it does not require the use of filler material and can be completed in one pass.

Nuclear AMRC has demonstrated for two-thirds-scale SMR components that electron beam welding can be completed much faster than traditional welding.

“These welds are about 4-3/8 inches thick, and we demonstrated that you can complete a weld in one pass of the beam in 47 minutes,” said Matthew Cusworth, who manages welding and materials engineering at Nuclear AMRC. “By comparison, traditional welding can take days, weeks, or months for one weld.”

The goal is to complete a 10-foot diameter weld in about 90 minutes, which Gandy believes can be achieved. That would reduce total welding time for an SMR by up to 90%. If electron beam welding—coupled with an appropriate heat treatment—can produce components with uniform microstructures and material properties, it might eliminate the need for in-service inspections, which could save millions of dollars over the life of a nuclear power plant.

Next Steps: Building and Welding Larger Components

Over the next two years, researchers will use electron beam welding to join two-thirds-scale reactor components, some fabricated using conventional forging and others with powder metallurgy and hot isostatic pressing.

If successful, EPRI plans to transfer the technologies to other reactor manufacturers. Gandy believes that manufacturers could be able to use powder metallurgy and electron beam welding in about seven years, though the timeline depends on approvals from the U.S. Nuclear Regulatory Commission and ASME.

In a new project, also supported by DOE, researchers plan to use electron beam welding to assemble a full-size reactor pressure vessel. A primary challenge is to overcome the need to construct a 40-foot-plus long vacuum chamber necessary to accommodate the 35-foot-long vessel. This would be cost-prohibitive.

In previous research, a much smaller vacuum chamber has been sufficient to fit the relatively small reactor assemblies. “The chamber is large enough to easily assemble 6-foot-diameter components inside,” said Gandy. “But it’s not large enough for full-scale reactor vessel components, which are about 10 feet in diameter.”

As an alternative to the large vacuum chamber, researchers are testing a new modular approach: As the vessel’s components are stacked and welded together, modular vacuum chamber sections are moved or added to enclose each weld, making the process significantly faster and cheaper.

“Applied together, these new manufacturing and fabrication technologies could be game changers for manufacturing nuclear plant components,” said Gandy.

Key EPRI Technical Experts:

David Gandy
For more information, contact techexpert@eprijournal.com.

Artwork by David Foster Graphics


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