Nuclear Power Startups Are Heating up in Southern California, with Radiant's Ultra-Portable Microreactors a Major Player

Los Angeles Times

20-07-2025

What if you could deliver a megawatt of energy anywhere in the world a cargo container could be shipped? For an El Segundo-based company, this sci-fi-sounding dream may be much more 'next Tuesday' than 'next planet.'
Radiant, a startup that is repackaging and refining traditional nuclear technology into a portable microreactor, is on the home stretch to development and testing of its prototype reactor following a $165 million Series C funding round (bringing total raised capital to $225 million) and the hiring of key executives, including Dr. Rita Baranwal, former U.S. Assistant Secretary for Nuclear Energy. Baranwal serves as Radiant's chief nuclear officer, and most recently worked at Westinghouse on their modular reactor program. The company also hired Mike Starrett as its first chief revenue officer.
In fact, the company recently signed an agreement to build 26 microreactors, including 20 units for an as-yet-undisclosed customer.
'Our focus is on the portability of nuclear power because then you could put a reactor in a place where you would have never imagined possible in the past,' said Doug Bernauer, chief executive and founder of Radiant. 'We have ceramic-coated, poppy-seed-size fuel and helium coolant. That combination means you can't have a leak and you can't damage the environment – you can give people the option of picking a nuclear reactor generator over a diesel generator.'
The company is on track to be the first to to develop and test its 1 megawatt (MW) Kaleidos microreactor at the U.S. Department of Energy's Idaho National Laboratory, which is scheduled for next year. The research design and its construction is being conducted by a team that has grown to about 100 employees.
Radiant is among five nuclear developers that were announced as recipients of high-assay, low-enriched uranium to fuel reactor demonstrations. These companies, and a handful of others, are racing to be first to market with nuclear microreactors, which offer a clean energy source that can be deployed for a variety of uses that typically rely on diesel generators. They produce about 100 to 1,000 times less electricity than conventional reactors and can operate independent of an electric grid. Use cases include backup generators at infrastructure sites, like hospitals to remote power needs in off-grid areas such as military bases, data centers, ships, desalinization plants and specific industrial facilities.
The company expects its nuclear microreactor to be competitive with diesel generators where diesel fuel is priced at $6.50 per gallon. That price is above the average price for diesel in the United States, but it can be well below pricing for fuel in other countries and distant areas that rely on generators for power. Microreactors can provide a steady energy source at a consistent price and will include enough fuel for several years. Nuclear fuel can be replenished in a portable manner. More importantly, the design has a passive cooling system that uses helium gas rather than water to cool the reactor. It is meltdown-proof and leak-safe, ensuring protection of people and the surrounding environment.
'We needed to make sufficient design progress to show the Department of Energy that this small startup in Southern California deserves its portion of this precious material it holds for the industry,' said Tori Shivanandan, Radiant chief operating officer. 'Now we have the funding, we have fuel, and we have the team. We're finalizing the design and getting parts on order. I like to say we have our shot on goal.'
That design has been years in the making. The company moved into its current building in El Segundo, a former Hughes Aerospace warehouse, about three years ago, vacating a former dance studio that it used as an office. Leveling up in square footage was essential, as the company was rapidly growing and needed space for hardware to be delivered and the team to expand.
The new location was great because it offered access to Southern California's vast talent pool of engineers, but it was in rough shape. Early employees sat in the dark as they worked through building renovations that added heating and air conditioning. Even now, the company temporarily ran out of desks for additional staff and Shivanandan said that she planned to sit in the kitchen for several days until new desks arrived.
The genesis of the company was from the desire to explore space and inhabit Mars. Bernauer moved to California in 2007 to work as an engineer at SpaceX. The company was headquartered in El Segundo at the time, and he worked on the Falcon 1 rocket, Falcon 9 rocket and other projects promoted by Elon Musk, such as Hyperloop and the Boring Company, before pivoting to Mars colonization plans. He investigated ways to power development on our neighbor planet, and nuclear power generation compared favorably to other power sources, like solar. However, there were no companies that provided an off-the-shelf solution to launch a small nuclear reactor into space. He originally tried to develop a nuclear program within SpaceX but eventually decided to create Radiant in 2019.
'I started researching nuclear on nights and weekends, looking at Wikipedia, and my curiosity lead down the path of who can do nuclear now, how quickly can they do it and what does it cost?' said Bernauer, who provided some of the initial company funding himself. 'I was fully committed to making this thing happen.'
Radiant is on target to construct its nuclear reactor and test it in 2026. With its recent round of funding, it anticipates that it has raised enough to carry it through construction of a prototype and testing in 2026 as well as the establishment of a larger scale manufacturing facility to ramp up production. At full capacity, the company expects to build about 50 microreactors per year.
'I was blown away by their capability and vision. The nuclear industry needed people from other sectors to come into nuclear because nuclear hadn't built anything new for a long time,' said Dr. Rachel Slaybaugh, partner at DCVC, the Palo Alto-based venture capital firm that led the Series C round. Slaybaugh is a trained nuclear scientist who taught at the University of California, Berkeley and previously served as an independent board member. 'Radiant has gone very fast with not very many resources.'
There is a flurry of activity from established companies and startups looking to repackage nuclear energy at a variety of reactor sizes. At the smallest level, both startups and established nuclear companies are developing microreactors, which can be packaged and transported in a shipping container on a truck or even in an aircraft and deployed in a relatively short amount of time.
Many of these companies are working with the U.S. Department of Energy's Idaho National Laboratory, which is where they will demonstrate and test microreactor designs. They are designed to use low-enriched uranium with higher concentrations of uranium-235 than the fuel used in conventional reactors.
Companies developing microreactors include Torrance-based Antares, which opened a new 128,000-square-foot factory this year for research and development, component manufacturing, and assembly of its first microreactors.
The company is targeting testing by 2027. It raised $30 million in Series A financing last year, co-led by Alt Cap and existing lead seed investor Caffeinated Capital, with participation from Rogue, Uncommon Capital, Shrug, Banter Capital, Box Group and Shine Capital.
On a larger scale, small modular reactors are typically designed to be connected to an electric grid while providing 50 to 300 MW. TerraPower, a small modular reactor company that was founded by Bill Gates, is developing Natrium, a next-generation nuclear power plant. The Natrium reactor uses liquid sodium as a coolant rather than a traditional water-cooled reactor. Its first plant is a 345 MW facility that is currently under construction in Kemmerer, Wy., and includes a storage system that can boost output to 500 MW. It is being developed as part of a public-private partnership with the U.S. Department of Energy's Advanced Reactor Demonstration Program.
In June, TerraPower announced that it raised an additional $650 million in funding from both new investors, including NVentures, the venture capital arm of NVIDIA, and current investors, including founder Bill Gates and HD Hyundai, an industry leader in shipbuilding. Gates has invested $1 billion in the company.
Not to be outdone, tech giants such as Microsoft, Google and Amazon have also signed agreements to explore advanced nuclear technology.
While this technology is expanding and the next-generation plants are exploring safer ways to cool reactors, conventional reactors have been phased out in California, and there have been very few new reactors built nationwide, primarily due to the Three Mile Island accident in 1979 and changing economics.
In California, the San Onofre Nuclear Generating Station was permanently closed in 2013 due to issues with its steam generators. Diablo Canyon Power Plant, which is operated by PG&E, is the only conventional nuclear power plant in California and was in the process of being decommissioned, but a state decision to extend operations through at least 2030 is in place with the possibility of further extensions.
Public perception is changing due to increased power demands and the fragile electric grid in the United States. In June, New York Governor Kathy Hochul directed the state's public electric utility to develop and construct an advanced nuclear power plant in Upstate New York with a capacity of one gigawatt of electricity.
Furthermore, the nuclear industry has received boosts from the Trump administration, which signed several executive orders to advance nuclear power. Some Army installations could be powered by nuclear microreactors under a May 2025 executive order calling for deploying advanced nuclear reactor technologies. The order, citing national security concerns, directs the Army to establish a program utilizing the technology and requires operation of a nuclear reactor at a domestic military base or installation by Sept. 30, 2028.
It is one of a series of orders that seeks to increase the amount of nuclear energy produced in the United States, which is estimated to produce only about 20% of its energy usage currently from nuclear sources. Those orders build on earlier projects. In 2022, the Defense Department awarded a $300-million contract to Lynchburg, Virginia-based BWX Technologies to develop a microreactor that could be transported by a C-17 cargo plane and set up to power a military base for several years before refueling.
The U.S. military is a strong customer base for many aerospace and defense startups – and Radiant was selected as a finalist by the Defense Innovation Unit for a potential contract to have its reactor on a U.S. military base – Bernauer still has his eye towards the sky.
'What we have to do is get reactors operating for about five years and then take the thing apart and inspect it to see what's breaking and what's working well. From there, we can make extremely reliable reactors that can operate anywhere,' said Bernauer. 'I want to be able to eventually make the space reactor for Elon (Musk), but to do that, you need something highly reliable and transportable.'