The U.S. Nuclear Regulatory Commission last month (Nov. 20) granted non-power construction permits to Kairos Power for the second of its two Hermes “advanced” small modular reactor projects. The construction permit for the two-reactor test project Hermes 2 came just 11 months after NRC granted a construction permit for an earlier single reactor test project, Hermes 1.
Neither Hermes 1 nor Hermes 2 are designed as commercial endeavors, and both permits are “non-power” licenses, although Kairos intends to add generating equipment later after applying for an operating license for Hermes 2.
The NRC said, “The Hermes 2 facility would include the two reactors and a shared power generation system. The facility is intended to provide operational data to support the development of a larger version for commercial electricity production. The NRC would need to review and approve a future application from Kairos before operating licenses for the Hermes 2 facility could be issued.”
Both projects are sited on federal government land in Oak Ridge, Tenn., that was originally site of the Department of Energy’s K-25 nuclear weapons complex. It appears that Kairos will continue with the first permit to build the first reactor to generate a small amount of thermal energy, about 35 MW(t). Then add two more, with power generation tacked on.
According to the NRC, “Hermes 2 will consist of two test reactors powering a common turbine generator set to produce approximately 20 megawatts electric (MWe). Each Hermes 2 unit would use an intermediate heat transport system (IHTS) to transport heat from the primary coolant salt to a common power generation system (PGS). Each unit would have its own reactor protection system and reactivity controls and no safety-related systems would be shared between the two units. Hermes 2 will have the same core design and safety-related SSCs as Hermes 1. The proposed operational lifetime of Hermes 2 is 11 years, as compared to the 4-year operational lifetime of Hermes 1.”
The Hermes project is built around a reactor cooled by molten fluoride salt, which maintains a high outlet temperature (650°C), at low, near atmospheric, pressure using TRISO fuel “in pebble form” with 19.75% enriched uranium. The fuel encases the uranium in a ceramic medium that can withstand high temperatures and irradiation, eliminating the need for an external containment structure. The design also includes online refueling.
While the Hermes reactors are advanced in terms of being a major departure from conventional and commercial light water cooled and moderated reactors that dominate the world of nuclear power, there is a long U.S. history with the technology. The late nuclear power pioneer Alvin Weinberg (1915-2006), who was the first to term nuclear power as a “Faustian bargain,” was an early champion of the technology as the long-time director of the Oak Ridge National Laboratory.
He commissioned the construction of a molten salt cooled reactor, under the direction of another nuclear pioneer, H.G. MacPherson. In Weinberg’s 1997 memoir “The First Nuclear Era,” he recounted the experience at Oak Ridge: “The molten-salt reactor began operation in 1966 and achieved its maximum power (limited by the size of the air-cooled ultimate heat exchanger) of 7,500 kilowatts in March of that year. It continued to operate remarkably smoothly, though with interruptions for maintenance, until December 1969, when its operation was terminated….”
While Oak Ridge continued its interest in molten salt technology, the governing Atomic Energy Commission decided to put all of its technology eggs into liquid sodium cooled fast breeder reactors. Weinberg noted ruefully that “the earliest ideas about commercial nuclear power were dominated by the mistaken belief that uranium was very scarce.”
California-based and privately-held Kairos has received strong support from the Department of Energy and is also engaged in advanced marketing of its yet-unproven technology, which has become common among new reactor venders.
In February, DOE awarded Kairos a contract, called a “technology investment agreement,” to support design, construction, and commissioning of the Hermes project. According to Kairos, “DOE will provide up to $303 million to Kairos Power using a performance-based, fixed-price milestone approach, wherein the company will receive fixed payments upon demonstrating the achievement of significant project milestones.”
Kairos and Google also have a speculative deal based on future success for the Kairos reactors. Under the terms of the deal, Google would have power purchase agreements for up to 500 MW of “energy, ancillary services, and environmental attributes” to be located “in relevant service territories to supply clean electricity to Google data centers, with the first deployment by 2030….” Google has a long history of interest in and support for nuclear power, including creating an internal group, the “Nuclear Energy R&D Group,” known internally as, appropriately, NERD.
While Kairos is getting a lot of positive publicity, unanswered questions remain. In an email to The Quad Report, nuclear physicist Edwin Lyman of the Union of Concerned Scientists wrote, “The weird thing – or maybe not so weird – is that Kairos now has two construction permits but there is no sign that it is planning anytime soon to submit an operating license application for Hermes 1. You would think that in a logical sequence of development, the company would operate its first test reactor to inform the design of its second test reactor. But that didn’t happen.”
Lyman added, “I do not think the company has any credible plan to obtain the HALEU it needs and to fabricate the fuel, which is a unique type of TRISO. There has only been limited irradiation testing of a small sample of the Kairos-type fuel and it apparently turned up some problems.”
He concludes with another possible showstopper: “Moreover, the reactor is going to leak large quantities of tritium like a sieve. The company has proposed a tritium retention system but as far as I can tell it is still just a paper design that has never been tested.”
–Kennedy Maize
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