Episode 441 of The VentureFizz Podcast features Assil Halimi, CEO & Co-Founder of Apollo Atomics.
Today we are diving into a topic that is way outside my typical comfort zone: nuclear energy. While fossil fuels still account for roughly 85% of global energy, nuclear power offers incredible energy density, yet conventional reactors take over a decade and billions to build.
Apollo Atomics is changing that. Through his research at MIT, Assil realized that existing designs for nuclear haven’t evolved in decades and he set out to change that with a breakthrough approach.
Apollo Atomics is an advanced reactor company developing compact pressurized water reactors designed to accelerate nuclear deployment. The company’s core breakthrough is a proprietary compact steam supply system that delivers approximately an order of magnitude higher power density than conventional designs, allowing Apollo to dramatically shrink the reactor while maintaining the same power output.
The key benefits for all of this is time and money. The resulting reactor platforms are designed to be factory built, transported by truck, and deployed in less than two years using commercially available fuel, established supply chains, and existing regulatory pathways.
The company recently announced an oversubscribed $31 million seed round of funding led by FCVC, with participation from Y Combinator, Alumni Ventures, Robinhood Ventures, and notable angels including Paul Graham.
In this episode, we cover:
- Advice on how to shift from academic research to an entrepreneurial mindset, plus advice on pitching Hardtech startups.
- Assil’s background story and how his interest in nuclear power originated.
- His time as an MIT Research Scientist and his process for working on this problem.
- How he met his co-founder, Drew Walker, and the origin story of Apollo Atomics.
- The breakthrough moment and all the details on how their technology works.
- Why nuclear is the safest way of making electricity.
- Their experience at Y Combinator, including a funny story about smoke in the parking lot.
- And, so much more!
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Podcast Transcript
Host: Keith Cline
Guest: Assil Halimi, CEO & Co-Founder of Apollo Atomics
Keith Cline:
Assil, thanks so much for joining us.
Assil Halimi:
Thank you for having me.
Keith Cline:
I’m excited to talk to you. This podcast has been going on for about eight years now, and I cover different lanes—tech, software, and AI, of course. But I like to stretch myself. Great people like Rob Biederman, who runs an accelerator called TNT, have been introducing me to really extraordinary entrepreneurs that are way outside my comfort level.
We’re going to talk about a modern nuclear power company and mini nuclear power plants—topics that are way outside my pay grade! If I fumble on any of the concepts, please pick me up, because I’m here to absorb and learn.
Before we get into Apollo Atomics, you’ve gone through an intense journey of PhD research. There comes a point in time where you ask, Is there a commercial opportunity here that we can actually create a company around? That can be a struggle for scientists and researchers who want to pursue an entrepreneurial path. What advice would you give to someone who has been working on research for years and wants to evaluate the commercial potential?
Assil Halimi:
First, you have to identify whether you actually want to build stuff versus purely loving research. I know many people who just want to do fundamental research, solve mathematical problems, or theorize about phenomena in the universe without needing to prove it during their lifetime—and they’re completely fine with that.
For me, that was not the case. I wanted to solve hard problems and see the results to confirm my assumptions within my lifetime.
If you are more of a builder and want to disrupt a highly capital-intensive industry, you need a credible path to de-risk the technology. In our case, we focused on one single innovation within an existing, highly mature technology called Pressurized Water Reactors (PWRs). We said, “If we can disrupt this one component, we can disrupt the entire deployment model of nuclear power plants.” That allowed us to start small and scale later.
If your thesis requires disrupting everything at once, you need massive capital from day one. During my PhD, when I first wanted to build new reactors, I started with the final vision. I remember my first investor meeting where I said, “This is what I want to build, it’s better than any other reactor, and I need $300 million.” They looked at me like, No way!
You then have two choices: either go back to pure science or figure out a staircase approach to risk. You start small, de-risk, and show that at a smaller scale, you can achieve at least a 10x gain. It shouldn’t be an incremental change—if it’s incremental, you should do it as R&D inside an existing company or license the patent. But if it offers a 10x, 100x, or greater impact, there’s a venture story to tell. Step one is building a small prototype with pre-seed or seed capital.
Keith Cline:
How do you navigate the mindset shift from deep research to pitching venture capitalists, building a team, managing lawyers, and building a company?
Assil Halimi:
That’s a great point. As a scientist, you want to go as granular as possible and analyze every scenario. An investor says, “I have 30 seconds. Tell me what you do and why it’s a good idea.”
It’s a funnel approach. On one end, you must know every technical detail inside and out; on the other end, you must articulate the value proposition in 20 seconds.
You break down what you’re building while establishing clear differentiation. For us, we make the most compact nuclear reactors, deployable in less than 24 months, with the highest uptime.
Those three statements cover:
- Highest power density: A technical feature enabling compact design.
- Under 24-month deployment: Solving the market’s urgent need for fast energy.
- Highest uptime: Focusing on reliability, which data centers critically require.
You need technical mastery on one side and simple, compelling statements on the other that investors instantly grasp.
Keith Cline:
Pitching requires practice and feedback. How long did it take you to refine your pitch into a conversational flow?
Assil Halimi:
I have a non-conventional approach. First, you must convince yourself that it’s worth it—especially in hard-tech. With software, you can start with a story and pivot along the way. In hard-tech, you must build deep conviction around the product and where the industry needs to go.
From there, the pitch should be tailored to the specific investor. General advice says to have one fixed pitch deck. When we raised our Seed round, we used just four or five slides.
Because we had questioned our own assumptions and analyzed every point of potential failure, we were prepared for completely different questions from different investors—whether about regulations, capital intensity, or safety. We could address how nuclear safety has evolved over the past 15 years to be an order of magnitude safer than legacy operating plants.
In academia, you present a paper for 10 minutes with slides and answer questions for 10 minutes. Investor pitches shouldn’t be lectures; the best pitches are collaborative conversations.
Keith Cline:
How did you structure those four or five slides?
Assil Halimi:
We led with the team—our backgrounds and why we are qualified.
Next was the product before and after: how nuclear plants are built today, what is different with our design, and why it’s valuable.
Then we showed something tangible: our test reactor running out of MIT to show we’ve built real hardware.
The last slide was our timeline: where we are today and our milestones over the next 1 to 3 years.
We kept backup slides for business models, project financing, regulatory pathways, and supply chains, but leaving the floor open for investors to guide the conversation worked extremely well.
Keith Cline:
That’s fantastic advice—keep it simple and lead with the team.
Let’s rewind the clock. Where did you grow up, and what were you like as a child?
Assil Halimi:
I grew up in Algeria, North Africa. As a child, I was intensely curious and read about politics, literature, and science. My father was an engineer who was passionate about technology, and my mother was a judge who focused on social sciences—she used to tell me that humans are the most complex machines! I had a balance of exposure to technology and human systems.
I wanted to be an astrophysicist when I was young, but I realized that in astrophysics, you might theorize something and someone proves it 200 years after you’re dead. I wanted the satisfaction of conceptualizing a theory, building it, testing it, and seeing the results. That led me to engineering and energy.
I studied electrical engineering alongside economics because if you want to commercialize a physical product, you must understand finance, economics, and how products are bought and sold.
Later, during an internship working on electrically propelled aircraft, I was reviewing a NASA roadmap comparing energy sources. Uranium stood out by far as having the highest energy density in nature—a million times more dense than fossil fuels! From a physics perspective, the potential was immense. I asked myself: Why isn’t this the cheapest, most dominant source of energy on Earth? That sparked my deep focus on nuclear power, and I moved to France after high school.
Keith Cline:
What eventually brought you to MIT for your PhD?
Assil Halimi:
I first came to MIT as an intern, and that’s when I found the problem I wanted to dedicate my life to solving. At MIT, you feel like you are standing on the edge of current knowledge, looking at the next step for human progress.
Before starting my PhD, I wanted practical operational experience. I returned to Europe and worked on reactor operations, specifically fuel reloads for Belgium’s nuclear fleet—which supplied 50% of the country’s electricity. Experiencing critical infrastructure operations firsthand was invaluable. After that, I moved back to the U.S. to start my PhD at MIT.
Keith Cline:
What was your PhD program like?
Assil Halimi:
It was very entrepreneurial. At MIT, there are no limits—the only limit is yourself. Most research scientists work on one project, but I was so excited that I worked on four simultaneously. I collaborated with leading nuclear reactor manufacturers and utilities across Europe and the U.S.
That exposure showed me how legacy nuclear engineers think, what matters, and what doesn’t. I began theorizing how a next-generation nuclear power plant should be built—integrating material science, fuel design, thermal hydraulics, and project finance.
Keith Cline:
How did you bridge all those disciplines?
Assil Halimi:
To be a designer, you must be humble enough to admit you aren’t the sole expert in every field. My core technical specialty is nuclear fuel. For thermal hydraulics or materials, I relied on world-class experts.
For finance, I took corporate finance classes at MIT Sloan. MIT allows you to challenge design assumptions against world authority figures in nuclear radiation, material science, and project finance within a single environment.
Keith Cline:
Let’s talk about Apollo Atomics. What is the current global landscape for energy?
Assil Halimi:
Fossil fuels account for roughly 85% of global primary energy consumption today. Projections show that 30 years from now, that share will still be around 82% to 83%. We haven’t seen a fundamental shift; overall energy demand is growing, so we are adding renewables while simultaneously adding more oil, gas, and coal.
Historically, France proved that rapid decarbonization is possible. During the 1973 oil crisis, Prime Minister Pierre Messmer launched a national fleet build of nuclear reactors. Within 15 years, France reduced oil and gas in its electricity mix from 90% down to 20%.
Nuclear is scalable, clean, and non-intermittent—it doesn’t depend on weather or solar irradiation.
However, conventional nuclear power plants have two major drawbacks:
- Speed to deployment: They take 10+ years to build, compared to 18 months for a natural gas plant.
- Cost: They have become hyper-complex, on-site construction projects costing up to $17 billion per plant.
On the flip side, nuclear offers carbon-free energy at a 95%+ capacity factor.
Apollo’s thesis isn’t to reinvent the entire reactor—with unproven fuels, coolants, or moderators. Instead, we start with proven Pressurized Water Reactor (PWR) technology and introduce one single design breakthrough: dramatically shrinking the footprint of the largest physical component—the steam generator—by 10 to 20x.
That reduction allows us to fully assemble the reactor inside a factory rather than on a construction site, while maintaining high power output. Size represents cost, while power represents revenue. By building high-power, compact reactors in a factory, we deliver high quality assurance, predictable timelines, and truck-transportable modules that connect directly to a steam turbine on site.
Keith Cline:
Nuclear fuel contains one million times more energy density than coal. What was your specific technological breakthrough to extract that energy compactly?
Assil Halimi:
Every thermal power plant converts heat into steam, which turns a turbine generator to produce electricity. The component converting heat into steam is the steam generator.
In the 1950s, when civil nuclear energy began, engineers took legacy steam converters designed for coal and natural gas plants and attached them to uranium fuel. You had fuel with a million times higher energy density paired with a mediocre, massive converter.
We designed the right converter—a compact steam supply system engineered specifically to extract intense energy density safely and efficiently. If you don’t remove that heat effectively, energy remains trapped in the fuel, leading to core meltdown risks. Our technology safely extracts that energy to generate continuous power for AI, industrial manufacturing, and communities.
Keith Cline:
How do you address safety concerns with the public and investors?
Assil Halimi:
There is perception of risk, and there are actual numbers. Statistically, nuclear is the safest form of electricity generation. Factoring in every historical accident since the 1950s, casualties per unit of energy produced are lower than coal, natural gas, solar, or wind.
Furthermore, energy consumption correlates directly with human life expectancy. Providing clean, abundant energy extends and saves lives.
Modern reactor designs are an order of magnitude safer than the technology used 30 to 40 years ago during Three Mile Island or Chernobyl.
Keith Cline:
How did you meet your co-founder, Drew Walker?
Assil Halimi:
I raised our pre-seed round as a solo founder. I then sought a co-founder with complementary operational experience in scaling companies.
A friend at Tesla introduced me to Drew, who had built two previous startups and had recently moved to New England. We worked together for a few months, hit it off, and he joined as co-founder.
Keith Cline:
Where is Apollo Atomics today in terms of product development and commercialization?
Assil Halimi:
We built a working mini-reactor demonstrator at MIT, proving an order-of-magnitude reduction in footprint from fuel to condenser.
We recently closed our Seed round to build a 20x more powerful commercial-scale facility outside of MIT to demonstrate megawatt-range output.
Commercially, we have over 20 gigawatts in signed Letters of Intent (LOIs), are finalizing contracts, and are progressing on state and federal regulatory permitting. Our goal is to deploy the first commercial, factory-built advanced nuclear reactor from a startup in the U.S.
Keith Cline:
How do your reactor platforms address different market demands, including AI data centers?
Assil Halimi:
We offer scalable, factory-built reactor platforms at 10 MW, 50 MW, and 300 MW (which can be combined for gigawatt-scale campuses).
The 10 MW module is ideal for remote locations or “behind-the-meter” data center applications. Right now, the electrical grid faces massive interconnection backlogs. Hyperscalers and AI data centers need dedicated, off-grid power generation that can be deployed rapidly without waiting years for grid connection. Multiple 10 MW or 50 MW modular units provide redundancy so power stays continuous.
Keith Cline:
What was your experience going through Y Combinator?
Assil Halimi:
Y Combinator was one of the best decisions we made. Before joining, people questioned whether YC was right for a hard-tech nuclear company. But YC partners connected us with hard-tech alumni, and YC actually funds more hard-tech startups per year than almost any other fund. The network and peer community are extraordinary.
We also had a funny moment during a fireside chat with Paul Graham and Jessica Livingston. We had brought our unfueled reactor demonstrator to the YC parking lot to show the setup. During the chat, Jessica noticed smoke rising outside. Five minutes later, as the smoke got thicker, someone shouted, “Isn’t there a nuclear company in this batch with a demo in the parking lot?!” Everyone turned around, and I had to stand up and reassure them, “It’s not fueled, it’s not operating, it’s not us!” It turned out to be unrelated, but it was great PR!
Keith Cline:
That is hilarious! What do you enjoy doing for fun outside of building Apollo Atomics?
Assil Halimi:
Building a hard-tech company is a marathon, so I prioritize exercise, healthy eating, and sleep. I play soccer occasionally. I used to do amateur astronomy and astrophotography, which I’ll get back to after our Series B or C! For now, I’m giving every minute to building Apollo Atomics.
Keith Cline:
Assil, thank you so much for taking us through your journey, your pitch advice, and the incredible mission at Apollo Atomics.
Assil Halimi:
Awesome! It was great talking to you, Keith. Thank you!
