The US Nuclear Regulatory Commission (NRC) has approved a request by Kairos Power, submitted on 24 March, to extend the latest date for completion of the construction of the Hermes test reactor facility (Hermes 1) from 31 December 2026 to 30 April 2029. Kairos performed a review of the Hermes 1 construction schedule and determined that construction would not be completed by the end of 2026 – latest date for completion of construction prescribed in Construction Permit CPTR–6 issued by NRC.
Kairos attributed the delays to two factors. First, Kairos stated in its amendment request that it had performed non-nuclear demonstrations of first-of-a-kind construction techniques and design features prior to performing them on the Hermes nuclear facility for the purpose of identifying construction challenges and lessons learned in the construction processes for the Hermes test reactor facility. Performing these non-nuclear demonstration activities had extended the construction timeline.
Second, Kairos said site preparation work, including removal of legacy structures from the Hermes test reactor footprint, required extensive coordination with other organisations such as the Department of Energy (DOE) and required significantly more work than originally planned.
Kairos now expects construction of the Hermes test reactor facility to be completed in 2028. To accommodate this construction schedule and to incorporate conservatism, Kairos asked to extend the latest date for completion of construction to 2029.
NRC states that “upon good cause shown, the Commission will extend the completion date for a reasonable period of time” and that the it will recognise, among other things, “developmental problems attributable to the experimental nature of the facility or fire, flood, explosion, strike, sabotage, domestic violence, enemy action, an act of the elements, and other acts beyond the control of the permit holder,’’ as a basis for extending the completion date.
Hermes 1 is a molten salt-cooled demonstration reactor being built at the Heritage Center Industrial Park in Oak Ridge, Tennessee. It was the first non-water-cooled reactor to be approved for construction in the USA in more than 50 years. Kairos Power broke ground on the facility in July 2024, and excavation works were completed the following October. Safety-related construction activities, which are subject to NRC oversight, began on 1 May 2025, with the start of work on the piers that will form part of the building’s foundation.
Hermes 1 will be a 35 MW (thermal) non-power version of the company’s fluoride salt-cooled high temperature reactor, the KP-HFR. Kairos Power submitted a construction permit application in July 2023 for Hermes 2, a proposed two-unit demonstration plant that would build on experience from Hermes 1 and would demonstrate the complete architecture of future commercial plants.
NRC approved the permit for Hermes 2 in November 2024 and Kairos Power broke on the facility earlier in April. Hermes 2 is Kairos Power’s first deployment under a 2024 agreement with Google to develop an advanced reactor fleet. It is intended to supply up to 50 MWe to the Tennessee Valley Authority grid to support Google data centres in Tennessee and Alabama.
