Molten Salt Reactors Could Turn Nuclear Waste Into Power—And We Had One Running in 1962.Then we abandoned it

A transformational nuclear energy concept emerged in the early 1960s: a reactor that didn’t merely generate electricity and leave behind hazardous byproducts, but one that consumed its own spent fuel. Developed at Argonne National Laboratory, the molten-salt reactor prototype demonstrated a closed fuel cycle capable of dissolving used uranium in salt, chemically extracting valuable isotopes, and fabricating fresh fuel—all while dramatically reducing the volume and longevity of high-level waste. Yet political concerns over plutonium separation led to the U.S. abandoning recycling research in 1977, consigning America’s spent fuel to decades of “once-through” storage. Now, amid climate urgency and energy security worries, companies and national labs are revisiting this proven technology. If successfully commercialized, waste-burning reactors could slash storage needs from hundreds of millennia to mere centuries, unlock centuries’ worth of domestic fuel, and accelerate the transition away from fossil power. But technical, regulatory, and economic hurdles remain—and the clock is ticking if we hope to reclaim the breakthrough we first demonstrated over sixty years ago.

The Reactor That Ran on Waste

Origins at Argonne

In 1962, Argonne National Laboratory rolled out its Molten Salt Reactor Experiment (MSRE), the first reactor designed to operate on liquid fuel rather than solid fuel assemblies. Fuel salts—uranium tetrafluoride dissolved in a mixture of lithium and beryllium fluorides—circulated through the core, transferring heat to a secondary salt loop and then to a steam turbine, all while remaining at ambient pressure.

A True Closed Fuel Cycle

Unlike conventional light-water reactors, which extract less than 1% of a uranium pellet’s energy before the fuel is declared “spent,” the MSRE design could continuously strip out newly bred plutonium and residual uranium. Chemists dissolved irradiated salt in special cells, used electrochemical separation to isolate usable isotopes, and reformulated the remaining fluid into fresh fuel. This process left behind only fission products—highly radioactive but far fewer in mass—and cut the time those byproducts remained hazardous from hundreds of thousands of years to mere centuries.

Why Recycling Was Abandoned

Proliferation Fears and Policy Shifts

In 1977, President Jimmy Carter, concerned that separated plutonium could be diverted into weapons programs, banned commercial reprocessing of spent fuel in the United States. Although President Reagan lifted the ban in 1981, the industry had already pivoted toward a once-through cycle, spurred by the lower immediate capital costs and a growing domestic uranium supply. Research into molten-salt and other advanced reactor systems waned, and the MSRE was decommissioned, its lessons largely shelved.

Economic and Technical Barriers

Reprocessing remains capital-intensive. Building the chemical plants, hot cells, and safeguards needed to handle highly radioactive fluids and separate plutonium safely poses long lead times and regulatory complexity. Utilities also faced competition from cheap natural gas in the 1980s and 1990s, which undercut the economics of expensive nuclear innovations.

The Modern Comeback

Renewed Interest in a Carbon-Constrained World

With climate change accelerating and electricity demand rising, the calculus around nuclear has shifted. Advanced reactor developers—from start-ups like Oklo and TerraPower to established national labs—now see molten-salt and fast-spectrum reactors as key to both low-carbon baseload power and tackling the spent-fuel inventory.

Partnerships and Pilots

Argonne has signed memoranda with companies exploring small modular reactors (SMRs) that leverage its salt-chemistry patents. Meanwhile, France and Japan continue to operate commercial recycling plants—albeit with conventional oxide fuel—maintaining a closed cycle that informs U.S. efforts. Demonstration projects are slated for the late 2020s, aiming to prove continuous salt cleanup and on-site fuel fabrication at utility scale.

Implications for Energy and Waste Management

Dramatically Reduced Footprint

By consuming transuranics (plutonium and minor actinides) alongside uranium, waste-burning reactors can shrink the volume of long-lived radioisotopes by over 90%. The remaining fission products require secure storage for a few hundred years, not tens of millennia.

Domestic Fuel Security

Rather than relying on mined uranium, a fleet of recycled-fuel reactors could draw entirely on spent fuel assemblies already on-site at U.S. power plants. This domestic resource would insulate against geopolitical supply shocks.

Accelerating Decarbonization

Integrating waste-burning reactors into a low-carbon grid could displace coal and gas plants more rapidly, tapping into plentiful fuel while easing concerns about nuclear waste repositories.

Challenges Ahead

• Regulatory Reform: Current U.S. Nuclear Regulatory Commission (NRC) frameworks are built around light-water reactors and once-through fuel; new rules for molten-salt chemistry and on-site reprocessing will be required.

• Cost Competitiveness: First-of-a-kind demonstrations carry high risk premiums. Public-private partnerships and loan guarantees may be needed to bridge the “valley of death.”

• Public Perception: Decades of “nuclear waste equals monsters in barrels” imagery have ingrained fear. Advocates must convincingly communicate that recycling technology neutralizes both waste volume and longevity.

A Second Chance for Innovation

The molten-salt reactor wasn’t a pipe dream—it was built, tested, and proven over half a century ago. What it lacked then were sustained policy support and an urgent climate imperative. Today, those conditions are changing. If public and private stakeholders can navigate the political, technical, and economic hurdles, we may yet reclaim the reactor that turns radioactive liability into a clean-energy advantage.

The question is no longer whether we can do it, but whether we will—with the climate clock ticking and the spent-fuel piles growing.