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Natrium nuclear plant coming to Wyoming may not improve on existing water-cooled reactors

Bill Gates, founder of TerraPower, in a recorded announcement that a new Natrium nuclear reactor will be built in Wyoming. (Screenshot from Wyoming PBS, Youtube)

CASPER, Wyo. — When Governor Mark Gordon announced this June that Wyoming has been selected for the construction of a new “advanced” nuclear reactor, he said it would be “game-changing and monumental” for Wyoming.

The system that would be built at one of four sites in Wyoming is called the “Natrium” reactor. It was co-developed by TerraPower, founded by Bill Gates and GE Hitachi Nuclear Energy.

The U.S. Department of Energy has awarded TerraPower $80 million in initial funding to demonstrate the Natrium technology, technology TerraPower claims can offer “improved reactor economics, greater fuel efficiency, enhanced safety and lower volumes of waste.”

The Union of Concerned Scientists has expressed some hesitation in regard to the rosy picture TerraPower and other players in the field of new nuclear technology have been painting.

In a March 2021 report titled “‘Advanced’ Isn’t Always Better: Assessing the Safety, Security, and Environmental Impacts of Non-Light-Water Nuclear Reactors” the Union of Concerned Scientists point to a number of potential problems in regard to claims about new “advanced” nuclear technology.

First, what is different about the “Natrium” technology compared with existing nuclear plants?

The majority of operating nuclear reactors are known as “light water reactors” (LWR) because they use ordinary water to cool their radioactive cores. The heat from the core is produced through the process of fission which occurs when a neutron hits an atom and splits it into two smaller atoms, as explained in “Here’s How a Nuclear Reactor Actually Works” by the National Energy Institute (NEI).

“When a reactor starts, the uranium atoms in the reactor core split, releasing neutrons and heat, and kick off an ongoing chain reaction that generates more neutrons and heat,” the NEI article explains. “The reactor core (where uranium atoms are splitting) is immersed in water. As the chain reaction happens, the heat generated is used to create steam.”

The majority of the nuclear reactors in the United States are pressurized water reactors and the remaining are boiling water reactors.

“In both types of reactors, the steam spins the turbine, which drives the generator that produces electricity,” the NEI article adds. “This mechanism is the same as the turbine used to generate wind power; the only difference is that steam causes the nuclear reactor’s turbine to spin, not wind. After the steam is used, it gets condensed to water so it can be recycled and reused.”

While most existing nuclear plants are “light water reactors” (LWR), using water to cool their cores, many of the “advanced” reactors that are being developed are cooled by other substances such as liquid sodium, helium gas or molten salts, the Union of Concerned Scientists explain.

The Natrium reactor is a sodium-cooled fast reactor (SFR).

“These reactors are known as ‘fast reactors’ because, unlike LWRs or other
reactors that use lower-energy (or ‘thermal’) neutrons, the liquid sodium coolant does not moderate (slow down) the high-energy (or ‘fast’) neutrons produced when nuclear fuel undergoes fission.” the Union of Concerned Scientists’ report explains. “The characteristics and design features of these reactors differ significantly from those of LWRs, stemming from the properties of fast neutrons and the chemical nature of liquid sodium.”

The Union for Concerned Scientists say that some people see flaws in the traditional water-cooled nuclear reactors: “In addition to its high cost and long construction time, critics point to—among other things— the LWR’s susceptibility to severe accidents (such as the meltdowns at Fukushima), their inefficient use of uranium, and the long-lived nuclear wastes they generate.”

That’s where companies like TerraPower step in and claim that technology they have developed can address those concerns. But the Union of Concerned Scientists say that the so-called “advanced” reactor designs might not in fact be able to deliver on those claims.

First, they point out in the report that exploring the use of substances other than water to cool reactor cores is not new: “At least one NLWR concept, the liquid metal–cooled fast reactor, even predates the LWR.”

“Nevertheless, NLWR designers claim such reactors have innovative features that could disrupt the nuclear power industry and solve its problems,” the Union of Concerned Scientists add. “They state variously that their designs could lower costs, be built quickly, reduce the accumulation of nuclear waste, use uranium more efficiently, improve safety, and reduce the risk of nuclear proliferation.”

“Are these claims justified? How can we identify genuine innovations and recognize those that are likely unattainable? As with any technology, an independent reality check is needed.”

The Union for Concerned Scientists say that almost all of the non-light water reactors on the table, including the Natrium reactor, “fail to provide significant enough improvements over LWRs to justify their considerable risks.”

While the Natrium reactor, like traditional reactors, would also rely on uranium rather than other elements like plutonium, it is would be more enriched.

The Union for Concerned Scientists say that water-cooled reactors in operation use uranium-based nuclear fuel that contains less than 5% of the isotope uranium-235.

“This fuel is produced from natural (mined) uranium, which has a uranium-235 content of less than 1 percent, in a complex industrial process called uranium enrichment,” the reports states.

Fuel enriched to under 20% uranium-235 is considered “low-enriched uranium (LEU).” The Union of Concerned Scientists say that low-enriched uranium is considered to be “a far less attractive material for nuclear weapons development than ‘highly enriched uranium’ (HEU), with a U-235 content of at least 20 percent.”

The Natrium reactor as well as the Xe-100 demonstration reactor, which have both received funding from the DOE, would rely on “high-assay low enriched uranium” which is uranium enriched to 10-20% uranium-235.

“While HALEU is considered impractical for direct use in a nuclear weapon, it is more attractive for nuclear weapons development than the LEU
used in LWRs,” the Union for Concerned Scientists’ report states.

Not only is such HALEU fuel potentially more attractive to a non-state actor looking to develop a nuclear weapon, but both the Natrium and Xe-100 would need large quantities of uranium for this fuel.

“HALEU is a material that is in very short supply and not commercially available,” the Union of Concerned Scientists states. “Even a single small reactor could require tons of HALEU per year…far more than the current available supply.”

“The Nuclear Energy Institute has estimated that it would take a minimum
of seven to nine years to establish a domestic fuel-cycle infrastructure to support a significant level of HALEU production, assuming full funding is available.”

While TerraPower announced a partnership with Ohio-based Centrus to produce HALEU for the Natrium reactor, the Union of Concerned Scientists express skepticism that the Centrus centrifuge plant will be able to produce as much HALEU as the natrium reactor will need for its initial core if the project is to happen as scheduled.

Rocky Mountain Power is partnering with TerraPower to bring the Natrium demonstration reactor to Wyoming, replacing either their Dave Johnston coal plant in Glenrock, their Jim Bridger plant in Point of Rocks, their Wyodak Plant near Gillette or the Naughton Plant near Kemmerer.

President and CEO Gary Hoogeveen said during the June 2 press conference announcing that Wyoming would be home to the Natrium reactor that it should be operational in seven years.

But the Union of Concerned Scientists says that the Centrus facility will need to be “quickly scaled up by a factor of three or more in order to produce the 15–20 MT of HALEU needed for the reactor’s initial core by 2027” if the schedule is the be kept without relying on foreign producers like Russia and China.

“In the absence of sufficient domestic HALEU production, fast reactors in the United States may become dependent on foreign producers, such as Russia and China, raising issues of reliability of supply,” the Union of Concerned Scientists states.

Another point of skepticism expressed in the ‘Advanced’ Isn’t Always Better report is that fast reactors such as the Natrium are “significantly more expensive to build and operate” than light-water reactors.

The Union of Concerned Scientists say that in theory, fast reactors can offer more sustainability in terms of using uranium more efficiently or in terms of reducing the quantity of “transuranic” waste elements.

“This is the only clear advantage of fast reactors compared with LWRs,” the report states. “However, once-through fast reactors such as the Natrium…would be less uranium-efficient than LWRs.”

“To significantly increase sustainability, most fast reactors would require spent fuel reprocessing and recycling, and the reactors and associated fuel cycle facilities would need to operate continuously at extremely high levels of performance for many hundreds or even thousands of years. Neither government nor industry can guarantee that future generations will continue to operate and replace these facilities indefinitely. The enormous capital investment needed today to build such a system would only result in minor sustainability benefits over a reasonable timeframe.”

Another concern about the sodium fast-cooled rectors like the Natrium is what could happen in an accident. The Union of Concerned Scientists say that a “type of fast reactor accident known as the unprotected transient overpower event, in which a control rod is ejected and the reactor fails to shut down, could also be very severe.”

“An Argonne National Laboratory analysis found that such an event at a relatively small SFR (380 MWe, similar to the Natrium) could cause large-scale fuel melting within 10 seconds, and dangerously high radiation doses to the offsite public (hundreds of rem at a 200-meter site boundary)
(Grabaskas et al. 2016).”

The report notes that the radiation levels that could occur in such an accidents would not be lower than radiation levels in the event of the melt-down of a large scale water-cooled reactor.

“How likely is it that the sodium would boil during an accident?” the Union of Concerned Scientists ask. “Fast reactor developers argue that such an event would be extremely unlikely because there is a significant margin between the normal operating temperature of the reactor (around 500ºC) and the sodium boiling point (around 900ºC).”

“Nevertheless, the likelihood of a rapidly developing sodium boiling event is design-dependent, highly uncertain, and not so easily dismissed. There is very little information about the temperature limits of metal fast reactor fuel and how much time would be available before fuel damage would occur if cooling were lost.”

The Union of Concerned Scientists add that the Nuclear Regulatory Commission conducted an analysis and report in 1994 which found that in the instance of an overpower event “large-scale sodium boiling would begin after about 14 seconds, leading to a power increase after 25 seconds.”

“By 26 seconds, the power level would have increased by a factor of three, and the temperature at the centers of the fuel pins would have exceeded 1300°C, which is greater than their melting point,” the Union of Concerned Scientists state. “The NRC terminated the calculation at 26 seconds because there was little doubt where things were headed after that.”

“The NRC report dryly states that ‘assuming that the prediction of the sodium flow rate through the core . . . is correct, this is clearly an event
that must be avoided.'”

The Union of Concerned Scientists adds that the Natrium reactor technology is based on a General Electric-Hitachi (GEH) PRISM sodium-cooled,
metal alloy–fueled design.

“[T]he PRISM design has never had a full-scale performance demonstration: the VTR and the Natrium will serve as the first large-scale demonstrations of PRISM technology,” the report states. “It is far from clear that prior fast reactor experience has provided adequate supporting evidence that full-scale PRISM reactors can be operated safely or reliably.”

“Thus proceeding with construction of the VTR and the Natrium without conducting prototype testing could pose unacceptable risks to public health, safety, and security, as well as to the success of either project.”

The Union of Concerned Scientists notes that TerraPower was initially founded to develop “once-through traveling-wave ‘breed-and-burn'” reactors but that the Natrium reactor is more conventional that the traveling-wave technology, which could potentially bring greater sustainability benefits.

“Initially, the company has planned to build a 600 MWe reduced-scale prototype traveling-wave reactor in China by as soon as 2022, although it would not have been capable of breed-and-burn operation because some of the necessary technologies—including ultra-high burnup fuels—have not yet been developed,” the Union of Concerned Scientists say in their report. “TerraPower has now rebranded this more conventional design as the Natrium, which the DOE has selected for deployment by 2027.”

The Union of Concerned Scientists note that the DOE in a 2017 study of advanced demonstration and test reactor options identified sodium-cooled fast rectors like the Natrium as the more mature of the potential new technologies and estimated “it would cost $4 billion and take 13 to 15 years to build and start up a commercial scale demonstration reactor.”

The Union for Concerned Scientists full ‘Advanced’ Isn’t Always Better report contains further information about both the Natrium design and other nuclear technology that is being discussed.