Thorium is the Earth’s greatest source of stored energy. Created billions of years ago in the final moments of a dying star, it holds enough energy in the structure of its nucleus to safely power human society for millions of years.

Thorium has been gently releasing its energy by slow decay for billions of years, providing most of the heating of the interior of the Earth and powering the magnetic field that shields us from the fierce solar wind, as well as powering plate tectonics, vulcanism, and carbon recycling. Our planet itself is already thorium-powered, and we are the living beneficiaries of that incredible energy.

In 1940, a chemist’s scientific curiosity led to a breakthrough that unlocked our understanding of how we could use thorium to generate energy and other wonderful and valuable materials. The chemist was young Glenn Seaborg, and using the scientific facilities at his disposal at the University of California, Berkeley, he first demonstrated how thorium could be coaxed into releasing its energy on demand for human benefit.

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The key was to strike thorium with a neutron, an uncharged particle found in the nucleus of atoms. Thorium absorbs the neutron and then undergoes a series of transformations that turn it into uranium-233. Further investigation showed that uranium-233 was fissile, which meant that it would potentially split into two smaller nuclides called fission products when it was struck by a low-speed neutron. It would also release two or three additional neutrons.

Seaborg’s discovery of uranium-233 was significant, but he pressed on further and used one of the first nuclear reactors in the world to examine its properties in greater detail. What he found was later described by him as a “50-quadrillion dollar discovery.”

Seaborg and his colleagues found that uranium-233 would undergo nuclear fission nine times out of ten it was struck by a neutron, and when uranium-233 fissioned, it released an average of 2.5 neutrons. These were magic numbers, they meant that uranium-233 produced 2.3 neutrons per neutron absorbed, and that was enough neutrons to allow thorium to be consumed as a nuclear fuel.

Uranium-233 is only produced from thorium. Its ability to sustainably utilize thorium is the central attribute that still draws our attention over 70 years later. Thorium (via uranium-233) can be consumed sustainably in reactors that have slowed-down neutrons. Natural uranium unfortunately cannot.

If a thorium reactor is started with uranium-233 and is not wasteful with its neutrons, it can use thorium as a fuel and release nearly all of the stored energy that it contains. Much like you expect to use all the gas you pump into the tank of your car, isn’t it reasonable to want to use all of the nuclear energy in a potential nuclear fuel? Coupled with efficient chemical processing, use of thorium as a nuclear fuel implies no wasted fuel and an elimination of the problem of long-lived nuclear waste.

Thorium’s potential efficiency as an energy source could cause us to rethink the energy resources of the world. Imagine a single cubic meter of material—average continental crust—taken from anywhere in the world. That cubic meter contains, on average, about two cubic centimeters of thorium and half a cubic centimeter of uranium, if each was in its metallic form. If that thorium were converted to energy in a liquid-fluoride reactor, it would be equivalent to the energy in thirty cubic meters of the finest crude oil in the world.

Truly this is a transformational technology that can turn average ores into a energy resource of this magnitude. It is not difficult to understand why Glenn Seaborg and Alvin Weinberg were so optimistic about the future of energy from thorium.

At these efficiencies, the amount of thorium that you would need to provide all the energy for your entire life would easily fit in the palm of your hand and would cost a few cents.

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