Hermes 2 by Kairos Power: status and timeline

Hermes 2

Hermes 2 is a 50 MWe demonstration of Kairos's fluoride salt-cooled high-temperature reactor, delivering power to TVA grid for Google data centers. First commercial KP-FHR deployment.

PilotStage 3 of 5

Groundbreaking April 2026. Samsung $100M partnership Sep 2026. TVA delivery 2030.

Updated 20d agoChecked 10 Oct0 updates this week

Milestones

Next · Power delivery to TVA grid

NRC Environmental Review signed off30 Aug 2024Complete.
Construction permit issued by NRC21 Nov 2024Complete.
Groundbreaking at Oak Ridge17 Apr 2026Complete.
Samsung C&T strategic partnership and investment agreement21 Sep 2026Complete.
Power delivery to TVA gridTarget 2030Not yet reached.

Most important updates

Upcoming

2026First commercial-scale TRISO fuel production at BWXT (next)
2030Power delivery to TVA grid

Current obstacles

First-of-a-kind construction complexityBuilding the first commercial KP-FHR at scale introduces untested design and construction challenges unique to molten-salt systems.
Materials qualification for molten saltConfirming that structural materials survive years of exposure to hot corrosive molten salt requires long-term testing.
Supply chain maturityTRISO fuel and specialized components for molten-salt reactors are not yet produced at commercial scale.

Physics limits

Materials compatibilityMolten salt is corrosive; all components must be chosen carefully and inspected frequently, limiting material choices and raising maintenance costs.
Demonstrating passive safetyProving decay heat removal works over the reactor's operating lifetime requires years of performance data the field does not yet have.

How it works

4 parts

TRISO fuel

Coated fuel particles

Ceramic-coated uranium fuel particles retain fission products even at extreme temperatures, enabling higher efficiency than conventional reactors.

Molten salt cooling

Liquid heat removal

Flibe molten salt circulates through the core and remains liquid across wide temperature ranges, so the reactor operates at atmospheric pressure.

High temperature operation

Efficient power conversion

Operating at higher temperatures than light-water reactors (700+ degrees Celsius) allows better thermodynamic efficiency when converting heat to electricity.

Passive safety

Decay heat cooling

If circulation stops, decay heat naturally convects from the core; no active cooling is required.

Spec sheet

Spec	Hermes 2
Electrical output	50 MWe^R (reported)
Thermal power	~110 MWt^E (estimated)
Coolant	Flibe molten fluoride salt^R (reported)
Fuel type	TRISO coated particle fuel^R (reported)

^R reported by the company · ^E our estimate

Update log

4 updates

About Kairos Power

The team behind Hermes 2

Kairos Power

Fluoride salt-cooled reactor, TRISO pebbles, Hermes

California company building a high-temperature reactor cooled by molten salt (FLiBe) and fuelled by TRISO pebbles. It is building Hermes test reactors in Oak Ridge, Tennessee, and has a deal with Google for up to 500 MW.

Hermes got the first US permit in 50+ years for a reactor not cooled by ordinary water (Dec 2023).
Google agreed in October 2024 to buy power from up to 500 MW of Kairos reactors.
Builds non-nuclear test units in-house first, learning step by step before the nuclear reactor.

kairospower.com (opens kairospower.com)Company profile →

Founded: 201610 yrs
Headquarters: United States
Status: Private
Valuation: private
Works in: EnergyFission
Coverage: 2 programs · 14 updateslatest 19d agochecked 25 Sep
People: Mike Laufer (opens kairospower.com)Co-founder & CEO

Spec

Hermes 2

Electrical output

50 MWe^R (reported)

Thermal power

~110 MWt^E (estimated)

Coolant

Flibe molten fluoride salt^R (reported)

Fuel type

TRISO coated particle fuel^R (reported)

Hermes 2

Milestones

Most important updates

Upcoming

Current obstacles

Physics limits

How it works

Coated fuel particles

Liquid heat removal

Efficient power conversion

Decay heat cooling

Spec sheet

Update log

Mon 21 Sep

Fri 4 Sep

Fri 17 Apr

Mon 18 Aug 2025

About Kairos Power

Current obstacles

Physics limits

How it works

Coated fuel particles

Liquid heat removal

Efficient power conversion

Decay heat cooling

Spec sheet

Update log

Mon 21 Sep

Fri 4 Sep

Fri 17 Apr

Mon 18 Aug 2025

About Kairos Power