No car has ever run on thorium, and none is close to it. The idea of a "100-year" or "million-mile" thorium engine began with a 2011 concept from a small US company. That company never showed a working prototype, and nuclear engineers have explained why the design could not deliver the energy it promised. Thorium is a real and interesting nuclear fuel, but its energy is only released inside a reactor, not by heating a lump of metal with a laser.
Below we look at what was actually proposed, what thorium is, why the numbers in the viral story do not add up, and where thorium power genuinely stands today.
What Laser Power Systems proposed
The story traces back to Laser Power Systems, a Connecticut firm led by Dr. Charles Stevens. Around 2011 the company described an engine in which a laser would heat a small piece of thorium. The heat would boil water, the steam would spin a turbine, and the turbine would make electricity to drive the car.
Press coverage repeated striking figures: a few grams of thorium powering a car for a million miles, or for a century without a fill-up. A prototype was promised within about two years. It never appeared, and the company did not publish peer-reviewed results or independent test data.
By late 2013 Stevens himself was playing down the automotive angle. Speaking to Mashable, he said: "Cars are not our primary interest." He argued that car makers were invested in petrol engines and that thorium would first have to prove itself in other industries. His stated goal was a turbine about the size of a household air-conditioning unit that could supply power to buildings or remote villages. Nothing of that kind reached the market either.
What thorium actually is
Thorium is element 90, a slightly radioactive, silvery metal named after the Norse god Thor. It is fairly common: estimates put it at roughly three times as abundant as uranium in the Earth's crust. India, Brazil, Australia and the United States hold some of the largest known deposits, much of it in monazite sand.
Its main isotope, thorium-232, has a half-life of about 14 billion years, close to the age of the universe. That long half-life is the reason it decays so slowly, and also the reason a lump of thorium gives off very little heat by itself.
The crucial detail is that thorium-232 is fertile, not fissile. It cannot sustain a chain reaction on its own. In a reactor it absorbs a neutron and, after two short decays, becomes uranium-233, which does split and release energy. Thorium also needs a "starter" such as uranium-235 or plutonium to provide those first neutrons.
Why a laser-heated thorium engine cannot work
Heating something with a laser does not make it release nuclear energy. As Kirk Sorensen, a nuclear engineer and long-time thorium advocate, pointed out in a 2014 critique, the laser design treats thorium as a hot block that stores heat. Any dense material, even an ordinary rock, could play that role. The system would be subcritical, meaning no nuclear reaction takes place at all.
That breaks the whole chain of numbers in the viral story:
- The energy comparison is borrowed from fission. Thorium's enormous theoretical energy per gram applies only if it is bred into uranium-233 and split inside a reactor. Fission releases about 80 terajoules per kilogram of fuel, while good coal gives about 24 megajoules, a ratio of a few million. The often-repeated "20 million times coal" figure overstates even the best case, and a laser heater would capture none of it.
- The laser needs power. Whatever electricity drives the laser has to come from somewhere, and a heat-to-steam-to-electricity loop loses a large share of energy at every step.
- A real nuclear version would not fit in a car. A genuine thorium reactor needs a moderator or fast-neutron design, a starter fuel, heavy shielding, cooling and a licence. Those requirements, plus crash safety and waste handling, rule out a vehicle-sized unit with today's technology.
Thorium is dense (about 11.7 grams per cubic centimetre, heavier than lead), and that may be where the "one of the densest materials" line came from. Density, however, says nothing about how much usable energy a material holds.
The radiation claim, checked
In the same interview Stevens said the radiation from his device could be blocked by a single sheet of aluminium foil. There is a grain of truth here. Thorium-232 decays mainly by emitting alpha particles, which are stopped by paper, foil or even the outer layer of skin.
The fuller picture is less tidy. Over time thorium's decay products build up, and some of them emit penetrating gamma rays that foil does not stop. Thorium dust is also hazardous if inhaled, because alpha emitters do their damage inside the body. Any machine using kilograms of thorium in fission would produce intensely radioactive fission products and would need serious shielding. Thorium is manageable with proper handling, but "no worse than a dental X-ray" is not a fair summary of a nuclear power system.
Where thorium power is real
Thorium's genuine story is in power stations, not cars. Some highlights:
- Early US reactors. Indian Point Unit 1 in New York used a thorium-uranium fuel mix after starting up in 1962. The Molten-Salt Reactor Experiment at Oak Ridge ran from 1965 to 1969 on uranium-233, the fuel thorium breeds. The Shippingport reactor in Pennsylvania operated as a thorium breeder from 1977 to 1982.
- India. With huge thorium reserves and little uranium, India has built its long-term nuclear plan around thorium and has projected that it could supply a large share of its electricity by mid-century.
- China. China's small experimental molten-salt reactor, TMSR-LF1, received an operating licence in 2023, and larger units are planned.
Supporters point to thorium's abundance, lower plutonium output and shorter-lived waste. Critics point to the cost of fuel fabrication, gamma-emitting uranium-232 in spent fuel, and the decades of engineering and licensing still needed. Both sides agree on one thing: thorium is a reactor fuel, and its future lies in large, shielded plants.
Common myths about thorium cars
- "A few grams will last 100 years." Only in a reactor that breeds and fissions it, which no car can carry.
- "Car companies are hiding it." The concept never produced a working prototype or published data. There was nothing to hide.
- "It is completely harmless." Thorium is only mildly radioactive as a metal, but its decay chain and any fission products need proper handling.
- "Cadillac built one." The Cadillac World Thorium Fuel concept, reportedly shown in 2009, was a design study by an independent designer, not a running nuclear vehicle.
How to judge "free energy" car stories
The thorium car shows a pattern worth recognising. A real scientific fact (thorium holds huge energy when fissioned) gets attached to a device that does something quite different (heats a block with a laser). Big, round numbers spread quickly, while the missing prototype is forgotten.
A few simple questions help. Has the device been shown working in public? Are there test results from independent engineers or peer-reviewed papers? Does the story explain where the energy comes from at each step, including the energy needed to run the system itself? If the answers are no, it is best to treat the claim as an idea, not an invention.
For cleaner transport, the progress that has actually happened is less dramatic but very real: better batteries, more efficient electric motors, hydrogen fuel cells in some fleets, and cleaner electricity grids to charge them.
Sources: Energy From Thorium: The mythology of the thorium car (Kirk Sorensen, 2014); Wikipedia: Thorium; Wikipedia: Thorium-based nuclear power; Laser Power Systems.
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