Technology Highlight: HolosGen

I think about it all the time: “How can we build a power system that can be deployed globally, help people everywhere, is safe, and cost effective?”

In my search, I keep coming back to the high temperature gas reactor design developed by HolosGen (referred to throughout this article simply as Holos). It may as well be the definition of pure genius built on decades of intense engineering work.

The advantages are many and simple:

  • Minimize number of components to keep the system as simple as possible.
  • Make it small – small enough to fit in a shipping container.
  • Make it powerful – powerful enough to power remote industrial operations, large transport vessels, or even the grid.
  • Solve all of the nuclear “problems” – proliferation resistant, accident tolerant fuels, low source term with virtually zero chance of meltdown and escape of radionuclides, and ultimate cooled by air
  • Make it modular – modular enough to be able to be air lifted, transported on a truck, and assembled incredibly quickly.

HolosGen’s power systems do all these things. They have two versions which are essentially scaled versions of each other to provide optionality in power requirements, capital cost, and footprint.

I’ve known about the HolosGen system for years, but I’ve procrastinated on learning more about it. There are so many other systems in the news all the time (NuScale, Oklo, Kairos, X-Energy, TerraPower, Terrestrial Energy, Ultra Safe Nuclear Corporation, BWXT, etc.) that I’ve generally assumed Holos isn’t making any progress and the design isn’t likely to succeed. Why aren’t they doing more podcasts? Why aren’t they showing the world all they’ve accomplished?

That generally changed this week after I did a deep dive into Rod Adams’ Atomic Insights blog archives. Obsessed with the simplicity and inherent advantages of a turbo-machinery style design, I’m re-energized to learn everything I can about these systems. Adams started a company, Adams Engines, in the ’90’s to solve the problem of developing a new micro reactor with the same underlying principles in mind: go small, use a high temperature gas reactor design, and utilize the compressor/turbine system developed in the ’60’s for the aviation industry. 

In his story, he uses prose to outline his personal journey of attempting to start a small business to develop a new nuclear engine. The story is inspiring, but he leaves it short by the end of the blog not alluding to why he stopped working on the technology seemingly before it was fully developed. Over 20 years later, I had the opportunity to sit down with him over video chat (and beers) to get the rest of the story. The project was eventually shelved indefinitely when the conjuncture of the 2008 financial crisis, the shale revolution, and the widespread adoption of natural gas as a base load power source transformed the cost of electricity in America. Developing new technology is hard. It can be even more difficult if you’re competing with a global commodity which doesn’t play by all the same rules.

It’s become obvious why HolosGen hasn’t been public about the work they’re doing. The short answer is somewhat of a Catch 22: they’ve been too busy developing, testing, and iterating on the design to need to go fundraise externally; and, because they don’t have outside funding, they need to work all the time to develop, test, and iterate on their technology to bring it to fruition as quickly as possible. Their founder, Claudio Fillipone, is an accomplished engineer with decades of experience. He understands the fundamentals behind nuclear power plants, and he’s chased the problem to its core to develop the world’s best nuclear power plant system.

What is publicly available is a phenomenal report outlining their technology, the market, and the opportunity in great detail. To the ignorant observer, it appears the Holos Team has thought of nearly everything. Here’s a brief overview.

Show me the money! Where’s the market?

In section 4, they identify the most relevant item for the survival of their technology: immediate and high demand market applications for the technology. They walk through the advantages and deployment for:

  • Coal and nuclear power plant replacements
    • Closing a coal or nuclear power plant and don’t want to replace it with wind or solar, but also want to combat climate change? No problem. Clustering Holos’ Titan design can quickly and easily replace coal or nuclear power plants and leverage the same electrical infrastructure necessary to bring power to the grid.
  • Disaster preparedness – from Hurricanes to Tsunamis
    • These things work underwater. They are transported easily via air or truck. And they can be hooked up to AC, 3-phase grids quickly and easily. Imagine being able to truck in 5 MWe to a hospital, hook it up to a substation, or air lift it onto a hurricane devastated island? These machines can do that.
  • Diesel engines replacement in industrial applications and in the shipping industry
    • In their two case studies, they walk through why replacing power generation via burning diesel with their reactors in remote mining industries and on shipping vessels is a great idea. Short answer: diesel is ridiculously expensive ($200/MWh up to $350/MWh), and their technology is much, much cheaper (~$50/MWh). I can envision leveraging their technology in the oil and gas industry to frac for less than the cost of diesel or even natural gas. 
  • Large reactor support and enhancement
    • Through several sections they outline how they can support existing nuclear power plants. Emergency preparedness: because there’s no need for diesel refueling or consuming air, they are the perfect technology selection for power backup at existing nuclear power plants. Why not back up the best energy generation source with… the best energy generation source! They tout that the core meltdown at Fukushima would not have occurred had a technology with their capabilities been installed. No need to maintain a fuel supply. No risk of damaging engines by ingesting air, water, or debris in the system. 

How does it work?

  • Core design
    • The utilization and innovations around how Holos utilizes nuclear fuel is one of the core tenants of their design (pun intended). They use a fuel cartridge with a honeycomb geometry which can be loaded with a variety of fuels or moderators to create the desired reactivity. The nuclear fuel is mechanically isolated from the primary working power fluid, which is really genius. Why touch the nuclear fuel if you don’t have to?
    • The core is essentially split into four equal quadrants which are all designed to be subcritical in the absence of three other fuel cartridges. Once they’re all close enough together, the reactivity of the nuclear fuel is capable of going critical, and heat is generated for the generator.
Fuel Cartridge Example
  • Holos Design Features unique to Holos
    • The design uses three working fluids:
      • Primary working fluid is He or CO2
      • Secondary is organic in Organic Rankine Cycle (ORC) system which rejects heat to Ultimate Heat Sink (UHS)
      • A third fluid can be utilized to send thermal energy to process heat applications.
    • Radionuclides can’t be transferred to process heat equipment. They’re mechanically isolated from the working fluids, won’t melt down, and can’t escape their silicon carbide coating layers.
    • These machines are designed to load follow.
    • The source term (i.e. the nuclear fuel) is much smaller, so the emergency planning zone (EPZ) can be smaller.
    • The entire footprint for Titan configuration is 90’ x 32’ x 20’, which is just a 2880 square feet footprint. Think about that. 10 MW on 2880 square feet. THAT’S INCREDIBLE! For context, if you wanted to have a solar farm with an equivalent power rating, you would need 98 MILLION times more space. 🤯
    • Balance of Plant elimination: there’s no networks of piping, valves, fittings, electric conduit, multiple buildings, containment for those buildings, etc. By eliminating all of these components, the cost is lowered significantly, and the system reliability, robustness, and safety performance increases.
  • Fuel Elements Thermally Coupled while Physically Isolated
    • The fuel brick has the fuel ingrained in it (in the form of TRISO marbles) which are “thermally coupled” i.e. touch the fuel brick and transfer heat to it. The primary working fluid flows through holes or tubes in the fuel brick and moves the heat away from the fuel brick. Several key points here:
      • Fuel can be operated at atmospheric pressure. 
      • Working fluid can be operated at higher pressure to increase thermodynamic efficiency of the system.
    • Fuel bricks are sealed inside the fuel cartridge with tubes running through them. The tubes are what allow the power fluid to move through the fuel cartridge and transfer heat from the fuel cartridge to the turbine and compressor. It’s operating at “high pressure” because the gas pressure increases as it’s heated up, which then allows it to transfer energy to the turbine as it expands and moves the blades of the turbine. The turbine then turns a generator and creates electricity.
  • Brayton Cycle Intercooler and Precooler Coupled to ORC
    • This part needs more explanation for me. It looks great on paper… but I don’t really understand how big it is, how efficient the intercooler is, etc. But it’s fascinating.
Holos Fuel Brick

Robust Design Features 

The level of detail in this report is frankly astonishing. Try finding another report which gives specific dimensions and drawings for key components of the system. You won’t. These guys aren’t afraid of anyone replicating their engineering work. They’re simply too far ahead. It’s impressive to say the least.

They outline each of the following components and potential hazards of the system:

  • Power cycle
    • They walk through the thermal-hydraulics of power conversion
    • Thermodynamic efficiency is ~45%. 
    • Cool fluid (He or CO2) enters the compressor, is compressed (and heated) to a minimum pressure to move it through the fuel cartridge; fuel cartridge heats it up even more (by like, 700 C), and then it’s pushed across the turbine. Then the process heat cools it down, and it’s recycled through the system again.
  • Core
    • Tables with real metrics and geometry of core are listed including number of fuel channels, number of coolant channels, number of TRISO pellets required, etc. 
  • Radiation Risk
    • It’s real and present, but they’ve quantified it and have a good understanding of what’s needed to work with it.
  • Loss of coolant accident
    • Max temp reached in the middle of the core (according to computer simulations) remains below the 1600 C max temp to melt the casings of the TRISO fuel pellets. It’s thus deemed Inherently safe.
    • They verified this by comparing it against data from testing of the Modular High Temperature Gas-Cooled Reactor (F. Reitsma, “The Path Towards a Germane Safety and Licensing Approach for Modular High Temperature Gas-Cooled Reactors,” in Proceedings of the European Nuclear Society – TopSafe, Vienna, Austria, 2017.)
  • Shielding: shields do all of the following:
    • Neutron reflection
    • Heat transfer to ORC working fluid without physical contact between primary working fluid and the fuel-moderator elements
    • Heat transfer to UHS (ISO container surrounding air)
    • Radiation shielding
    • Ballistic shielding
    • Structural support
    • Need ~65 cm of steel to shield at full dose… and ~48 cm of steel thickness after 1 day after shut down.
  • Inherent safety features
    • Core/fuel cartridge remains below melting point for TRISO fuel under many (all?) design basis.  
    • Heat sink is walls of ISO container.
    • Negative temperature coefficients of reactivity. Temperature increases, reactive decreases and reactor shuts down.
    • Working fluid isn’t mixed and doesn’t touch anything outside of the fuel cartridges. 
    • Fuel cartridges fit into standard fuel casks for spent fuel disposal.
    • Simpler probabilistic risk assessment (PRA) because there are fewer safety systems.
    • Capable of withstanding several forms of attacks.

So what? Why do we care?

HolosGen is creating something truly remarkable. A system like this has the capability to change the world. It’s small enough that it stands a chance to be developed and deployed quickly. Additionally, because it’s smaller, it’s likely to be cheaper; and because it’s cheaper, it has a chance to be iterated and improved on over time. This is a key competitive advantage over almost every other nuclear power system currently in development.

If it can be iterated and improved on over time, then it stands a chance at replacing all other energy generation systems on the planet. We won’t need hydroelectric dams. We won’t need millions of oil and gas wells all over the planet. We won’t need windmills on mountain tops, solar panels on every roof, or the millions of square miles of ecological damage associated with creating those technologies. Instead, we’ll have abundant, cheap, reliable, safe, and awesome energy for humans everywhere.

Additional Questions:

I always have more questions when looking at new technologies. Hopefully I’ll be able to ask HolosGen these someday.

  1. How do you get the power modules out of the system container safely?
  2. What happens if there’s a leak in the power module?
  3. Where is the core manufactured? How is it manufactured? Is it cast?
  4. If these turbines are off the shelf, which ones are they?
  5. How are TRISO particles capable of being subcritical and then going critical when more are presented around them? I.e. what’s the heat pipe scenario?
  6. How is the process heat cooled from 620C to 58 C across the “Process heat” and “Intercooler HEXs”? What are those components? Seems… too good to be true.
  7. Still don’t understand why it’s critical when you bring 4 together and not before.
  8. What are their next steps? When can we expect to see these for sale?
  9. I believe HolosGen also applied to the PELE program, but they weren’t awarded it. Why not? Was their system not developed enough? Did they not have a big enough team? There’s very little public information about it.

If you’d like to dig in more, here’s the full report and a link to HolosGen’s website!

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