Nuclear fuel cycle reimagined: Powering the next frontiers from nuclear waste

The successful completion of such a novel project through its full life cycle portends a broader shift in nuclear waste policy. For decades, the back end of the nuclear fuel cycle has been characterized by political deadlock and growing inventories of spent fuel in temporary storage. Despite significant reactor innovations in recent years, both the DOE and the private sector are only now paying attention to fuel cycle innovation.

Today, major tailwinds are driving renewed interest in deploying RPSs, small nuclear batteries that can provide dozens to hundreds of thermal to electrical watts. New technologies and falling costs are opening austere locations to new applications. Private ventures are looking to mine new resources, from critical minerals on the seabed to exotic helium-3 on the lunar surface. Planetary geologists and deep sea biologists alike are seeking long-duration and persistent access to remote locations. And amidst a renewed great power competition, the United States and its allies seek security of contested environments.

This new demand offers a potential course correction for fuel cycle policy. Compared with other types of radioisotope applications, such as medical and industrial, RPSs require relatively high amounts of nuclear material, often in the tens of thousands of curies. Remarkably the most promising RPS fuels, such as Sr-90, cesium-137, and americium-241, pose most of the thermal and radiation challenges of spent reactor fuel. Thus, RPS demand could provide a broader catalyst for recycling and reuse technologies as a pathway to reduce waste liabilities.

Concurrently, existing radioisotope demand, particularly for medical applications, is projected to rise rapidly around the world. Conventional medical production facilities are old and approaching retirement, creating potential supply gaps.

Innovation is now spreading across the fuel cycle, led by markets and increasingly by policy. Ultimately, this shift could transform nuclear “waste” from a liability into a strategic asset.

The RPS renaissance

Unlike traditional power sources that depend on solar or hydrocarbons, RPS devices convert heat from naturally decaying radioisotopes into reliable electricity for years without refueling. Plutonium-238 is the most widely known radioisotope for its applications for NASA’s planetary science goals. However, more than 1,000 Sr-90 systems were used for terrestrial applications in the late 20th century, with over 100 deployed by the United States alone.

Today, RPSs are experiencing a remarkable renaissance driven by expanding applications in frontier environments.

Developments in the space sector are perhaps the most high-profile. SpaceX and other launch vehicle innovators are widely employing reusable rocketry to increase launch cadence. Between SpaceX’s Starship, Blue Origin’s New Glenn, and NASA’s Space Launch System, the United States now has three different super heavy launch vehicles capable of sending previously unfathomable amounts of mass to deep space. Meanwhile, multiple companies are developing medium launch vehicles to compete with Falcon 9, diversifying transportation options to the lunar surface.

In parallel with launch vehicle advancements, the costs of getting to the lunar surface are falling rapidly. In the last 18 months, U.S. commercial companies Intuitive Machines and Firefly have delivered three landers to the lunar surface. For the first time, deep space exploration of the moon and Mars is going commercial.

In addition to exploration and robotic science on the lunar surface, there is rapidly growing interest in space mining. Multiple start-ups are now under contract to supply lunar He-3 for national security applications and are eyeing future markets to supply fusion reactors and quantum computers.

The lunar south pole contains substantial water ice deposits that can be used for refueling in space, igniting a space economy that is projected to reach hundreds of billions of dollars by 2040.

Technology for harsh conditions

Firefly’s Blue Ghost lander successfully reached the lunar surface in early March. (Photo: Firefly Aerospace)

The lunar surface is unforgiving. In equatorial regions, a full lunar day lasts one Earth month, meaning spacecraft need to survive a frigid two-week-long lunar night. The areas with water ice, some of which are subject to permanent shadow, are even more challenging. Solar and batteries struggle to power spacecraft through the long lunar night and cannot operate in such shadowed regions. This is where RPSs shine.

It is not an overstatement to say that RPSs could be the foundation of a lunar economy—or a Martian economy, where weak solar rays and persistent dust storms make RPSs the technology of choice for long-duration missions.

Many companies and countries are exploring a wide range of advanced RPS technologies for space applications. The U.S., United Kingdom, South Korea, Japan, India, China, and Australia are all expanding Pu-238 capabilities or exploring new isotopes such as Sr-90 or Am-241. As with other space innovations, many countries are turning to public-private partnerships.

Terrestrially, modern applications of RPS technologies are no less transformative. Remote regions, extreme environments, and strategic infrastructure increasingly demand robust, reliable power solutions.

On land, RPSs provide energy solutions that traditional batteries or renewable sources cannot reliably deliver. They can power remote scientific observation posts in the Arctic and Antarctic. Underground applications, such as deep mines or seismometers, can benefit from resilient power. In the longer term, ubiquitous RPSs can support high-priority, off-grid applications like emergency response systems.

In maritime environments, RPSs offer seabed power thousands of meters under the surface. In just the last several months, national concerns about critical mineral supply have reignited long-standing interest in deep-sea mining. This emergent industry can readily supply nickel, cobalt, and copper, but its operation takes place almost three miles beneath the surface. The long duration of RPS technology and its robustness means it can power environmental monitoring equipment for this new industry, ensuring such mining is done responsibly. More broadly, seabed RPSs can support many types of deep-sea infrastructure, from offshore energy to oceanography and from critical infrastructure protection to maritime domain awareness.

What makes the RPS renaissance particularly significant is its timing. It coincides with growing recognition that traditional approaches to SNF management have reached an impasse, creating an opportunity to reimagine the entire back end of the fuel cycle.

From liability to asset

The conventional view of SNF and low-level waste is that of a liability.

The DOE’s Nuclear Waste Fund, meant to cover the agency’s liability for disposing of 60-plus years of commercial used nuclear fuel, now exceeds $50 billion. Cleanup of defense-­related waste continues across the country, with an eventual bill similarly measured in the many billions.

The mission patch for the BUP-500 partnership. (Image: Zeno Power)

Schematic of the BUP-500. (Image: U.S. DOE)

This problem is not new. In the 1970s, the DOE initiated the Byproducts Utilization Program (BUP) to identify beneficial applications of byproduct material in SNF. By developing technologies to utilize them and encourage their commercial adoption, BUP represented a potential approach to reduce the challenges of SNF management.

Ultimately, Sr-90 efforts within the program culminated in the design and fabrication of the BUP-500, the largest RPS ever built. It provided 500 watts-electric at the beginning of its life, sourcing over 1 million curies of Sr-90 from defense waste. Built at Oak Ridge National Laboratory in 1986, BUP-500 included the last domestic Sr-90 heat source built until Zeno’s Z1. The end of the Cold War led to falling demand for RPSs for terrestrial use.

For the last three and a half decades, BUP-500 has languished at ORNL in storage outside of the building in which it was built. Representing the largest single source of byproduct material at the lab, the unlucky RPS posed a significant disposal liability. While on-site storage was not expected for another three decades, the facility it was at was scheduled over the next couple of years for demolition as part of revitalization efforts at the Oak Ridge site.

Enter Zeno Power. In 2023, the small start-up announced awards with both the U.S. Space Force and U.S. Navy to develop Sr-90 RPS technology for space and seabed applications. Reemergent great power competition rekindled Department of Defense interest in Sr-90 power for austere environments, and Zeno began eyeing commercial and scientific applications on the new frontiers. But the company needed a large initial feedstock for its first demonstration systems.

On learning about the BUP-500, Zeno reached out to the DOE Office of Environmental Management about the possibility of beneficially reusing the old RPS to provide fuel for new ones. DOE-EM, its prime cleanup contractor United Cleanup Oak Ridge, and Zeno developed a public-private partnership to enable the reuse.

This effort was not without its challenges. Many regulatory barriers had to be addressed, not least of which was transferring DOE-owned material to the commercial regulatory framework. A transportation exemption from the U.S. Department of Transportation was needed, which was ultimately granted due to the BUP-500’s robust design. ORNL readily completed a National Environmental Policy Act review, finding the plan warranted a categorical exclusion.

In early 2024, DOE-EM and UCOR transported the BUP-500 to a commercial radiological facility owned by Westinghouse Electric Company. Zeno is actively working to disassemble the old RPS and use its feedstock to produce approximately ten new RPS units, commercial pathfinders toward an RPS renaissance.

The motto of the partnership was “Reduce, Recycle, and Revitalize,” capturing the win-win-win nature of the overall efforts. DOE-EM and UCOR were able to reduce their liability, securing a pathway to transfer a large byproduct material source off-site. Zeno can recycle nuclear material for beneficial reuse to meet its contracts with the space force and navy while also broadly supporting national security and scientific missions and starting its mission to revitalize Sr-90 RPS technology for 21st-century applications. Meanwhile, ORNL makes progress in the revitalization of its site.

An emergent nuclear recycling ecosystem

The BUP-500 partnership is not an isolated success. Rather, it signals a broader shift in how the United States can manage and capitalize on the back end of the nuclear fuel cycle. The emergence of commercial radioisotope power markets, burgeoning medical isotope demand, and advances in isotopic separation technologies are creating a new paradigm. Materials once destined for disposal can now reenter the nuclear economy.

RPS technologies are uniquely suited to recycling efforts because of their relatively high activity levels and scaling demand. Fueling a generator to produce enough heat for remote operations requires tens of thousands of curies of Sr-90. Many applications, such as lunar infrastructure or seabed science observatories, require dozens of such systems.

Further, the best radioisotope power fuels are those with relatively high thermal density and long half-lives, precisely the characteristics that pose challenges for SNF management. Sr-90 and Cs-137 comprise a large portion of fission yield and have half-lives of about 30 years, producing a substantial portion of the thermal and radiation load of SNF. The decay of plutonium-241 in spent fuel produces Am-241, which similarly becomes a large thermal and radiological management challenge.

Accordingly, removing RPS fuels from spent fuel creates a virtuous cycle:

Separating heat-generating isotopes reduces the thermal load on disposal facilities, simplifying storage design and operation.

Without these isotopes and their multidecade or multicentury half-lives, material can be ready for permanent storage faster.

Separation processes create opportunities to extract other radioisotopes of interest, which can further improve the overall venture.

Reduced liability from removing radioisotopes and potential sales for beneficial reuse alter the economics of recycling. Recycling SNF and reusing the remaining uranium-235 has long been a technical dream but an economic nightmare. Uranium ore is too cheap to justify the high expenses of fuel recycling for uranium alone, even considering conversion and enrichment costs for raw uranium—particularly because long-term disposal of the remaining fission products and actinides is still needed.

RPS demand upends this paradigm. Taking Sr-90, Cs-137, and Am-241 out of SNF reduces the liability of disposing of remaining material. This greatly improves the economics of the whole process by reducing the cost of final disposal, even before accounting for multiple potential revenue streams from RPS feedstock sales. Other demand sources could further stack revenue sources.

The challenges in supplying medical radioisotopes are well-known at this point. Retiring production facilities and growing global demand created supply chain disruptions. An aging global population, especially in Asia, is driving a growing need for cancer diagnostics and other medical radioisotope treatments. More hopefully, new technologies like theranostics use radioisotopes to both diagnose and treat cancers, promising precision oncology.

In the last decade, multiple innovators have arisen to address medical supply challenges:

Among other candidate radioisotopes, SHINE Technologies is establishing molybdenum-99 and lutetium-177 production, the most in-demand medical isotopes.

In 2024, TerraPower Isotopes started producing actinium-225 at commercial scales, derived from DOE uranium-233 stockpiles.

Atomic Alchemy is working to produce a wide variety of radioisotopes for space, industrial, medical, and other applications.

RPS demand is already poised to accelerate these efforts. In June 2024, SHINE Technologies and Zeno announced a partnership to recycle nuclear waste into RPS fuel, particularly for Sr-90 RPSs. In November 2024, Atomic Alchemy and Zeno signed a memorandum of understanding to develop RPS fuel supplies. Atomic Alchemy was subsequently acquired by Oklo, which harbors fuel recycling ambitions of its own.

Opportunities for a revitalized fuel cycle

The convergence of commercial demand, national security imperatives, and technological readiness presents a chance to reimagine America’s nuclear fuel cycle. Where traditional fuel cycle strategies have focused narrowly on deep geological disposal, a more nimble and economically grounded approach is emerging. Private-sector innovation can unlock multiple strategic opportunities for the nation.

Over the last decade, Congress and the private sector bet heavily on advanced reactor innovation to restore the nation’s commercial nuclear power competitiveness. Advanced reactors offer significant advantages but need concurrent spent fuel solutions to reach their full potential. Without clear SNF pathways, siting concerns may prove limiting for many potential applications.

Similarly, export markets may be limited due to the lack of fuel takeback and disposal. For countries considering American advanced reactors, the prospect of developing their own disposal capabilities is often a primary barrier. Worryingly, Russian and Chinese trade deals often include fuel takeback, a significant advantage over American competitors.

With a robust recycling ecosystem, the U.S. could provide similar offerings, opening many new markets for American exporters. Private-sector dynamism could thus compete on a level playing field with state-backed programs.

The rise of large-scale RPS use also creates opportunities for policy and regulatory reform. Industrial-scale manufacturing of RPS units will entail process waste volumes that require improved approaches and solutions. In particular, challenges related to Greater-than-Class-C waste can create solutions and momentum to guide future spent fuel management policy.

Building out a fuel cycle innovation ecosystem can also revitalize the nuclear industrial base. It can spark high-tech manufacturing and create skilled jobs, particularly at DOE legacy sites that have significant advantages for such innovation. For many communities, fuel cycle innovations can make beneficial reuse efforts a reality. Indeed, they already have for ORNL with BUP-500. Recycling isotopes from domestic sources also reduces U.S. dependence on foreign sources, underscoring their nature as a strategic resource in the modern era.

From waste to watts

The convergence of RPS development and nuclear waste management represents a rare opportunity to expand nuclear innovation. The strategic implications extend beyond energy to America’s competitiveness in critical technologies and domains. RPSs enable persistent operations in frontier environments where alternative power sources are impractical—environments that are now vital for both national security and scientific leadership.

The commercial and DOE partnerships forming around isotope recovery and utilization serve as building blocks for future action. Beneficial reuse has commercial value and technical feasibility. It can revitalize national lab communities. This approach can break the decades-long impasse in nuclear waste policy.

Yesterday’s “waste” is really tomorrow’s power source for humanity’s boldest endeavors, from exploring the depths of the ocean to establishing a permanent presence on the lunar surface. That transformation represents not just technical innovation, but a fundamental reimagining of what is possible when we view SNF as a resource rather than a liability.

Alex Gilbert is vice president of regulation at Zeno Power. Harsh S. Desai is Zeno Power’s chief commercialization officer. Patrick Snouffer is a senior program manager, fuel supply chain, also at Zeno Power.