Molten salt cooled

Kairos Power Is developing a truly new nuclear fission power technology. Their KP-FHR (Kairos Power – Fluoride Salt Cooled, High Temperature Reactor) combines the solid fuel form usually associated with gas-cooled reactors with the fluoride molten salt often associated with fluid-fuel reactors.

For Atomic Show #288, my guest was Dr. Per Peterson, Kairos Power’s chief nuclear officer (CNO). Per explained the technical logic leading his company to make its ground-breaking choices.

Before describing process of making technical choices, Per provided a brief summary of the KP-FHR technological development history. The FHR originated in a conversation with MIT’s Dr. Charles Forsberg and later became the subject of an integrated research program between MIT, University of Wisconsin, and Dr. Peterson’s academic home at University of California’s Berkeley campus.

As Per was careful to point out, the program was primarily funded with Department of Energy (DOE) academic research grants and involved a number of both graduate and undergraduate research students from each of the participating institutions.

This type of project grant program is aimed at giving students practical design experience and providing purpose for experiments, equipment design and testing. Sometimes, as in the case of the FHR, members of the research team recognize that they have a product that can be commercialized because it has characteristics that are superior to similar products in the market.

Three members of the FHR integrated research project team, Per Peterson, Ed Blandford, and Mike Laufer founded Kairos Power in 2016 as a venture-funded Silicon Valley company to refine their ideas and commercialize the technology they had helped to develop within the academic setting.

In 2018, I talked with Ed Blandford and Per about Kairos Power, this show is part of my promise to provide updates on an intermittent basis.

Brief description of the KP-FHR

The nuclear fission heart of the KP-FHR is a pebble-bed reactor with 4 cm diameter fuel elements that each contain thousands of TRISO fuel particles in a graphite matrix. Fission heat generated in the reactor is moved by a pumped flow of fluoride salts through a heat exchanger that transfers the fission heat into nitrate salts similar to those used in concentrated solar thermal power systems.

The nitrate salt is pumped through a second heat exchanger (steam generator) that functions as a water boiler to produce steam with temperature of 585 ℃ and pressure of 19 MPa. As Per explained, that combination of temperature and pressure is equal to the most modern coal fired steam plants.

In fluoride salt the fuel elements have a slight positive buoyancy. To provide long operating periods without a large amount of excess reactivity at the beginning of core life, the KP-FHR includes an online fueling system that removes pebbles at the top of the core and replaces them with fresh or slightly used pebbles at the bottom.

The pebbles move slowly and have very low frictional contact with each other in the bath of molten salt. The reactor operating temperature is approximately 1000 ℃ lower than the temperature at which the TRISO fuel particles would begin releasing even small quantities of fission products, giving the reactor a broad thermal margin. As Per described it, the pebbles are so relaxed that they are almost meditating during their residence time in the molten salt.

What happened to the gas turbine concept?

Some listeners might remember that Kairos Power initially planned to use a Brayton cycle heat conversion system with the potential for using natural gas co-firing to produce peak power. Like many academic ideas, the system that looked good on paper or on computer screens turned out to be more complex and difficult to develop than expected. The current design is the result of numerous studies done with both technical and market parameters included.

Per provides a more complete version of the story and also shares the excitement that comes from working with a large, growing team of talented and motivated technologists.

What is Kairos Power’s near term plan?

One of the more exciting developments that Per shared was the fact that Kairos has been selected as a recipient for a grant under the DOE’s Advanced Demonstration Reactor Program (ADRP). Kairos will be filing a construction permit application in approximately one year to build a reduced scale version of its KP-FHR that it calls the Hermes project.

The project will be constructed on a site at the East Tennessee Technology Park near the Oak Ridge national laboratory.

DOE has promised to provide a little more than $300 million over a five year period (subject to future appropriations); Kairos will provide at least a 1:1 match of that DOE money for a project total of a about $600 million.

As might be expected, Kairos hiring and will continue to expand as it moves past laboratory scale and into a nuclear construction project.

I hope you enjoy the show. As always, comments are welcome. The conversations here often stimulate new ideas and thinking.

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