Recent expressions of support by the US and UK governments have highlighted a new class of very small nuclear power reactors.
Microreactors, sometimes defined as reactors of less than 15 MW, have been identified as potential recipients of development funds by the UK government as part of its search for an "advanced modular reactor" for near-term deployment, while the US Congress passed legislation in July asking the Department of Energy to develop a report on the potential deployment of such units at military or energy facilities.
Small modular reactors have received attention in recent years as a potential solution for the problems of small grids and remote locations while benefiting from faster factory-like manufacturing. Advocates for microreactors say their diminutive size allows for an expanded range of siting options and functions.
Critics wonder, however, whether the tiny reactors have much of a market outside a few remote Arctic communities, as well as highly specialized defense and resource extraction facilities.
Some established and newcomer reactor vendors have developed such designs, initially in secret, and report growing interest for the product category. Westinghouse is looking to build a demonstration unit of its eVinci reactor, while US start-up Oklo has engaged for more than a year with NRC on fuel and licensing plans for its design. The UK's U-Battery is developing a microreactor design, as are other global companies.
The units could be small enough to fit inside a standard 40-foot shipping container, vendors have said.
“In terms of their role in the nuclear industry, they would be broadening the range of applications for which nuclear technology can be applied,” said Jonathan Cobb, a senior analyst with the World Nuclear Association. “Some microreactors also have the ability to load-follow, which could have applications in balancing supply,” he noted in an email.
Art Wharton, vice president of market development for Studsvik Scandpower, said there are “potentially attractive economics” for locating microreactors in isolated communities, noting remote communities in Alaska and Canada are paying $1 per kilowatt-hour for electricity produced by diesel generators. By comparison, he said, customers in US and Canadian cities and towns, where electricity is produced by large coal, gas or nuclear plants, pay 6–9 cents per kWh.
Another consideration that favors microreactors in such locations, Wharton said in an interview, “is their ability to operate off the grid in these areas, where building transmission lines” to connect to a regional grid would be prohibitively expensive.
Everett Redmond, the Nuclear Energy Institute’s senior technical advisor for new reactors and advanced technology, said that a key attribute of microreactors is their “ability to offer resilience and reliability.”
“In remote locations, the bottom line is that if the electricity goes out they are in serious trouble and in a life-threatening situation,” Redmond said.
Microreactors could be useful for a variety of industrial applications, he said, and could be downsized to the point they become portable – enabling them to displace diesel generators that are brought to industrial or work sites for specific periods of time.
Studsvik’s Wharton said that the heat, rather than electricity, generated by microreactors could be a cost-effective product of the units. The reactors would substitute for other generating sources, such as natural gas, to produce heat for chemical processes, the extraction of oil from tar sands, and sea water desalination or district heating in towns and cities. Such reactors could be the primary source of electricity generation in small African towns, he said.
However, Stephen Thomas, an energy professor at the University of Greenwich in London, is skeptical about the need for new nuclear construction, said in an email that “after 40 years of observing the nuclear industry, my gut-feel is this is just the latest nuclear technology rabbit out of a hat that will lead nowhere but might attract a little public funding and will give hope to nuclear enthusiasts that the industry has a future.”
Some microreactors could be unstaffed, with operators monitoring them remotely, vendors have said. The WNA’s Cobb said the use of microreactors in certain settings would “require a different regulatory regime to that to which the current large nuclear reactors are subject.”
The NEI’s Redmond said he “does not see barriers” at NRC for staff to review microreactor design approval applications, noting the agency “is doing a lot of work to educate staff on various advanced technologies, such as high-temperature gas-cooled, molten salt and liquid metal” reactor design concepts.
Some advanced reactor developers believe the standards for microreactors may be more comparable to those for nuclear materials licensees, which use radioactive sources for industrial and medical purposes.
William Reckley, a senior project manager in NRC's Office of New Reactors, said during a meeting to discuss advanced reactor licensing July 26 that the agency is considering whether additional regulatory options are needed for microreactors. Even the new framework being considered by NRC to streamline the licensing of advanced reactors and small modular reactors – those under 300 MW of capacity – still might not be suitable for the unique features of microreactors.
“We’re looking to say, do you reach a point where it is so fundamentally different — and I’ll get in trouble for this — but at some point does a reactor even though it’s commercial power, look more like a radiographer than a Vogtle? Obviously that’s an exaggeration,” Reckley said.
The expansion of Georgia Power's Vogtle plant in the US features two 1,150-MW AP1000 units.
“At some point, is it so fundamentally different that we need to totally change how we’re viewing it in terms of how it should be regulated based on the potential consequences and risks associated with the machine?” he asked.
Fuel, enrichment issues
To achieve efficient, cost-effective generation, Studsvik’s Wharton said microreactors would use high-assay, low-enriched uranium, meaning levels from 5% U-235 enrichment to just below 20%. Almost all existing power reactors use fuel enriched to below 5% U-235.
However, he said a common element shared by microreactors is “they have smaller thermal loads and less decay heat that needs to be dealt with.”
Wharton said he could not estimate the cost to license and build a microreactor, noting the first prototype unit could be built by the late 2020s at a US national laboratory site.
Technological and cost-efficiency improvements “will be made by engineers in the next few decades,” he said. “Twenty years from now,” Wharton said, it is likely “we’ll see some of these [microreactors] available for substantially lower costs,” although he could not estimate a dollar amount.
Edwin Lyman, senior scientist, global security, with the Union of Concerned Scientists, was more skeptical about the economic viability, security and demand for microreactors. Noting that the idea of installing small-size nuclear reactors on military bases has been “discussed and dismissed” for many years, Lyman said microreactor developers “are going after the same remote communities in the Arctic and how big a market is this, realistically?”
“We’ll see a dozen companies all chasing after a tiny market segment with a product that is looking for a use,” he said.
Although he could not estimate any electricity production cost for microreactors, Lyman said, “the one thing you can say [about] the economics is that the smaller the plant, the more expensive the cost of electricity will be," because of economies of scale. "That’s why reactors, which started off small, have consistently become larger,” he added.
Lyman took issue with comments by microreactor proponents such as Wharton, who said “the concept is that you can push the on-button and walk away for 10 to 12 years before having to refuel” the reactor.
“If something goes wrong,” Lyman said, “you will have to have a team of nuclear engineers on site to fix the problem.” In addition, he said “novel reactor designs will raise safety concerns,” especially since these systems will use high-assay LEU.
Procuring this material likely will be a problem, he said. There is no commercial supply of high-assay LEU, Lyman said, noting that “DOE has about 1.5 tons” of the material that it makes available each year “for research reactors around the world.”
He noted that Urenco’s New Mexico uranium enrichment facility could make high-assay LEU, but “it would need a license amendment to do this, requiring much research.” Existing centrifuges would have to be reconfigured, he said. “On a commercial basis, [no enricher] would do this unless it knows the demand will be there, but demand is greatly uncertain, and so you have a chicken-and-egg situation.”
Nonetheless, Oklo, Urenco and Westinghouse are pressing ahead with their microreactor designs. Other companies working on microreactors include Ultra Safe Nuclear Corp., LeadCold Nuclear and StarCore Nuclear. All have engaged with the Canadian Nuclear Safety Commission about reviewing their designs.