NRC Accepts Application for Kairos Pebble-Bed Reactor Construction Permit

The Nuclear Regulatory Commission (NRC) will review Kairos Power's construction permit application (CPA) for its Hermes non-power demonstration reactor, which the firm has proposed to build at the East Tennessee Technology Park Heritage Center site, in Oak Ridge, and begin operating by 2026.

The NRC formally accepted the CPA for review on Nov. 30, noting Kairos had submitted the first portion of the application, a preliminary safety analysis report (PSAR), on Sept. 29, and the remainder, comprising an environmental report, on Oct. 31. While the NRC's acceptance of the CPA marks a formal docketing" of its review, it stems from a lengthy process that involved extensive pre-application discussions and activities that began in March 2018. The NRC said this week that barring unforeseen delays," it expects to complete its environmental and safety reviews within a tight 21-month schedule, by September 2023.

As Kairos's CPA enclosures show, the company had urged the NRC to complete its review and approve the Hermes construction permit by April 2023 so construction of safety-related structures, systems, and components could begin in mid-2023. Because the firm bagged a $303 million federal award under the Department of Energy's (DOE's) Advanced Reactor Demonstration Program (ARDP) risk reduction pathway, it is targeting initial operations by mid-2026. Given these objectives, the earliest start date for construction is expected April 2023; the earliest projected date for completion of construction is the latter half of 2025, and the latest projected date for completion is December 2026," the company told the NRC.

The acceptance milestone is nonetheless a notable achievement for Oak Ridge-based Kairos Power, which was established in 2016. The Kairos Hermes demonstration will test a 50-MWth reactor based on the Kairos Power Fluoride Salt-Cooled High-Temperature Reactor (KP-FHR) design as part of a cost- and risk reduction-focused development pathway that ultimately envisions commercial deployment of a 140-MWe KP-X" plant. The NRC refers to the Hermes test reactor as a non-power" reactor, though Kairos in press materials calls it a low-power" reactor.

The KP-FHR test reactor is essentially a graphite moderated, randomly packed" pebblebed reactor with molten fluoride salt coolant (a chemically stable molten fluoride salt mixture of 2LiF:BeF2 [Flibe] enriched in Li7), operating at high temperature and nearatmospheric pressure. The fuel in the KP-FHR is based on tri-structural ISOtropic (TRISO) particle fuel in pebble form with a carbonaceousmatrix coated particle design. The fuel kernel and some of the coatings on the particle fuel provide retention of fission products. TRISO particles are dispersed within the graphite matrix of fuel pebble's fuel layer," the company said.

The Kairos Power FHR (KP-FHR) is a novel advanced reactor technology that leverages TRISO fuel in pebble form combined with a low-pressure fluoride salt coolant. Courtesy: Kairos

The KPFHR fuel pebbles are buoyant in reactor coolant under steady-state and postulated events." The reactor coolant also provides retention of fission products that escape from any fuel defects. The design also includes a pebble handling and storage system (PHSS) that continuously inserts pebbles at the bottom of the reactor core and extracts them from the top of the reactor vessel during normal operations. Pebbles will be examined for burnup and damage, and are either returned to the vessel or directed to storage, Kairos said.

This May, the company garnered engineering, operations, and licensing backing from the Tennessee Valley Authority (TVA), a federal corporate agency, under a cooperative development agreement for its demonstration at the East Tennessee Technology Park (ETTP). The 2,200-acre ETTP site hosted a complex of federally owned facilities that enriched uranium for 40 years before the Department of Energy terminated its uranium enrichment operations. (The area has now begun a major environmental site cleanup and it seeks to convert the ETTP into a private industrial park called Heritage Center Industrial Park.)

In a statement on Tuesday, Mike Laufer, Kairos Power co-founder and CEO, highlighted the quick turnaround that led to the NRC's acceptance of the CPA for review. This licensing milestone represents a significant achievement, concluding a tremendous cross-functional effort by the Kairos Power team to complete the application just 18 months after the decision to build the Hermes reactor was made," he said.

Since 2018, Kairos Power has submitted 11 topical reports that have been approved or are under review and a number of technical reports, which will contribute to future applications," the company noted. Additionally, the lessons learned from Hermes will inform the licensing process for future reactors, consistent with Kairos Power's rapid iterative development approach," noted Peter Hastings, vice president of Regulatory Affairs & Quality with Kairos.

The NRC's acceptance of review of Kairos's application marks the second advanced nuclear reactor application in recent years. The first came in June 2020, when the NRC announced it had accepted for formal review a first-of-its-kind combined license application (COL) from Oklo Power to build and operate the company's 1.5-MW Aurora fast microreactor at the Idaho National Laboratory (INL) site in Idaho. The speed at which the NRC accepted the application that Oklo submitted in March 2020 is remarkable, especially because it was the first COL application submitted of any type since 2009.

The NRC said Kairos submitted its CPA pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Part 50. NRC regulations typically fall within 10 CFR, explains the Nuclear Innovation Alliance (NIA), a think tank that works to enable and deploy advanced nuclear power, in a September 2021 technology primer. All operating commercial reactors were licensed under 10 CFR Part 50, which is a historical two-step process involving a construction permit and an operating license as the plant approaches completion," it said.

In the 1990s, the NRC approved a second pathway, 10 CFR Part 52, which allowed an applicant to receive a combined license for construction and operation, with optional steps such as a reactor vendor applying for approval of a reactor design or builders applying for a site permit," the group said. The NRC staff approved the NuScale SMR design under Part 52, but the NRC had to determine which parts of its rules were applicable to the NuScale design."

Separately, as directed by the 2018-enacted Nuclear Energy Innovation and Modernization Act (NEIMA), the NRC is developing 10 CFR Part 53. Part 53 is intended to simplify the licensing of advanced reactors by setting safety performance standards as opposed to prescriptive rules and letting applicants demonstrate how they achieve the safety standards," NIA said. Part 53 is better suited for advanced reactors than the existing Part 50 or Part 52, which are prescriptive systems tailored to conventional light-water reactors."

-Sonal Patelis a POWER senior associate editor (@sonalcpatel,@POWERmagazine).

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