Jeff Green raises $7M for Fluxnium's seawater uranium bet

Why it matters

Fluxnium is betting that the nuclear buildout's hardest bottleneck shifts upstream to fuel. A utility investor helps, but field-level cost data will decide whether seawater can compete with mines.

Jeff Green, the repeat founder who previously commercialized desalination membranes and direct-air-capture projects, brought Fluxnium out of stealth on September 16th with $7 million to extract uranium from seawater. TechCrunch reported that Congruent Ventures led the seed round, with Active Impact Investments and nuclear operator Constellation Energy participating.

A Fluxnium securities filing confirms that the Santa Monica-based company sold $6,999,998 of equity to three investors. The offering recorded its first sale on May 5th, and Green signed the filing as CEO on May 11th. Fluxnium did not disclose a valuation.

The investor lineup matters as much as the check. Congruent Ventures and Active Impact Investments are climate-focused funds. Constellation Energy operates the largest U.S. nuclear fleet, placing a prospective customer from the existing fuel supply chain on Fluxnium's cap table. The disclosed transaction gives Fluxnium utility-side validation without proving that a reactor operator has agreed to buy its output.

Green returns to materials science

Green founded Fluxnium with James AC "Jim" McDermott, his business partner dating back to the launch of Stamps.com in 1996. The pair later built Rusheen Capital Management, a Santa Monica investment group focused on low-carbon energy, water and carbon capture.

Green's career has moved from software toward the harder work of commercializing engineered materials. He founded NanoH2O in 2005 around nanocomposite reverse-osmosis membranes. According to Green's Rusheen biography, NanoH2O reached more than 300 installations in 40 countries within three years of launch before LG Chem acquired it in 2014. He later helped launch carbon-removal developer 1PointFive and serves as executive chairman of water-treatment business Moleaer.

Fluxnium follows the same operating pattern: take laboratory chemistry, redesign it for mass production and build an industrial deployment system around it. Green is entering uranium with a clear supply thesis. He told TechCrunch that projected reactor demand could leave Western buyers "structurally short" because production is concentrated across countries including Kazakhstan, Uzbekistan, Russia, Namibia, Niger and China.

The most recent U.S. Energy Information Administration data reinforce the dependence behind that argument. U.S. reactor owners and operators received 93% of their uranium deliveries from foreign sources in 2025. Canada supplied 32%, Kazakhstan 28% and Australia 15%, while U.S.-origin material accounted for 7%. Operators paid a weighted average of $58.46 per pound, up 11% from 2024.

A mine built from fiber and buoys

Uranium occurs in seawater at extremely low concentrations, spread across an estimated 4 billion-plus metric tons globally. That enormous resource produces Fluxnium's eye-catching claim of roughly 50,000 years of potential nuclear fuel. The useful question is how much can be recovered at a price utilities will accept.

Fluxnium licensed uranium-adsorption chemistry developed at U.S. Department of Energy national laboratories. Fluxnium uses high-surface-area polymer fibers designed to selectively capture dissolved uranium as seawater passes over them. The fibers are braided into long lines and suspended from offshore buoys using infrastructure modeled on seaweed and mussel farms.

After an estimated 30 to 60 days in the ocean, operators retrieve the lines and chemically remove the captured uranium. Fluxnium plans to purify the material into yellowcake and return the fibers to the water for several additional cycles. The process avoids digging ore and producing the mine tailings associated with conventional extraction, though offshore operations introduce their own manufacturing, maintenance, permitting and logistics costs.

Green told TechCrunch that the underlying components have all been demonstrated separately. Fluxnium's work centers on raising the fibers' surface area, reducing manufacturing expense and arranging the system for repeatable marine deployment. That description captures the commercial challenge: Fluxnium is building an offshore production process around proven chemistry rather than presenting a new chemical discovery.

The $200-per-pound problem

Earlier national-lab work produced uranium at a reported cost above $200 per pound, more than twice the price Green cited for Western supply. Fluxnium says its higher-surface-area material captures more uranium and lowers that figure. Commercial economics remain unproven, and the next meaningful proof point is a measured cost per pound from a representative open-water system.

The cost calculation has several moving parts. Fluxnium must manufacture enough fiber, deploy and recover it at sea, separate the uranium, regenerate the adsorbent and refine the material into yellowcake. Fiber losses, biofouling, storms, vessel time and the number of viable reuse cycles can all alter the result. A laboratory improvement in uranium uptake solves only one part of that chain.

Other groups are chasing the same bottleneck. On July 24th, Austin-based SuperCritical Materials disclosed an exclusive Battelle license for uranium-adsorbent technology developed by Pacific Northwest National Laboratory and research partners. In 2018, PNNL and LCW Supercritical Technologies produced five grams of yellowcake using modified acrylic fibers exposed to seawater.

Those demonstrations establish that uranium can be recovered from the ocean. They also show why Fluxnium's defensible value will come from production engineering, offshore operations and cost discipline. Green has spent two decades building businesses around that handoff from science to industrial process.

Fluxnium is arriving as reactor developers and large electricity buyers push nuclear projects forward. A 2024 Department of Energy framework called for 200 gigawatts of additional U.S. nuclear capacity by 2050, including 35 gigawatts by 2035. More reactors would pull the fuel question forward, particularly if utilities continue to seek supply outside Russia and other geopolitically exposed markets.

The $7 million seed gives Green and McDermott room to move Fluxnium from materials development toward open-water evidence. The ocean already holds the uranium. Fluxnium now has to prove that its fibers can collect it cheaply enough to become a mine utilities will treat like any other supplier.