In France, where the nuclear power industry currently delivers 87.5% of the electricity, the handling and processing of uranium fuel is efficient, serious, and business-like. Most uranium is imported from the highly productive pitchblende mines in Central Africa. At COMURHEX Malvési in the Narbonne region of south-west France, it is milled, refined, and converted to uranium-tetrafluoride. It is a fine, yellow powder, and in the United States we call it “yellow-cake” because it so closely resembles a certain pastry mix from Betty Crocker. In France they just call it “uranium-tetrafluoride.”

From Malvési the powdered uranium compound is shipped to COMURHEX Pierrelatte on the Tricastin nuclear site, in the Rhône valley between Drôme and Vaucluse. Here the powder is further fluorinated into uranium-hexafluoride, or “hex,” feeding into the enormous gaseous diffusion plant on site owned by Eurodif, a European multinational subsidiary of COGEMA. A third of all the hex in the world, some 14,000 metric tons, goes through this plant every year. It is the second largest commercial uranium-diffusion operation in the World, after Russia’s Minatom.

The purpose of the diffusion process is to take naturally mined uranium, which is 0.7202% uranium-235, or U-235, and make it into 20.0% U-235 for energy production.⁶ U-235 is the special variety of uranium that produces power in a nuclear reactor, and the rest, almost entirely U-238 with a touch of U-234, is just inert filler. The highly corrosive hexafluoride gas with enhanced U-235 content is then de-fluorinated and converted to uranium oxide, a chemically stable, hard, black solid, for use as fuel in nuclear plants.

Ever vigilant against the diversion of U-235 for clandestine use, the French monitor each gram of their 14,000 metric-tons-per-year hex for its isotope content, using mass spectroscopy. One day in May 1972, the alarms went off in the Pierrelatte facility. The U-235 concentration in a batch of hex was only 0.7171%, showing a significant deficit of 0.0031%. Such a discrepancy required explanation, so an investigation was launched immediately by the Commissariat á l’Énergie Atomique, or CEA. The uranium ore from a particular shaft at the Oklo Mine in Gabon, Africa, seemed short of U-235. Further probing found samples with deficits as high as 0.440%. French physicist Francis Perrin was charged with finding what had happened to the missing U-235. Theft for weapons production was feared.

All the uranium in the earth has been locked in geologic structures since the formation of the planet, with no external uranium introduced, so it is all the same age. Uranium is the heaviest of the 92 natural elements, and it was the last material created, almost as an afterthought, by the super-nova destruction of a distressed star several billion years ago. Uranium is naturally unstable, and it deteriorates into lesser elements. The gradual transformation of uranium begins with a decay into the element thorium and ends, after 17 stumbles into transient atoms, with the formation of non-radioactive lead. It takes tens of millions of years. Of the two important types of uranium, U-235 and U-238, U-235 decays faster. With each passing year, there is less uranium in the earth and more lead, and the concentration of U-235 in the mix drops down, slowly. After over 4 billion years on earth, most of the uranium has turned into lead, but of what is left, the percentage of U-235 in 1972 should have been precisely 0.7202 in every uranium mine on the planet.

The U-235 had not been extracted surreptitiously in any step of the transportation or processing. The uranium deficit must have originated in the ore in the mine. How was this possible?

There was only one explanation for the missing U-235. It had fissioned away, and for that to have happened it must have been in a working, power-producing nuclear reactor. Further sampling of minerals at the site and some calculations confirmed it. The now stable remains of fission products were trapped in the rock formations with the uranium ore. At three locations in the Oklo mines in Gabon, Central Africa, there were 16 naturally occurring nuclear reactors, formed in the veins of high-quality uranium ore. On September 25, 1972, the CEA announced that self-sustaining nuclear chain reactions had occurred in the Oklo mines about 1.5 billion years ago.⁷

At the time the reactions started, the U-235 content in the natural uranium was 3%, which is the concentration used today in some power reactors, achieved artificially by gaseous diffusion. The uranium had been sitting there for billions of years when something changed and groundwater started leaking into the underground deposit. The water acted as a moderator, slowing neutrons down to fission-producing energies, and the reactors fired up. The reactors operated in pulse mode, with the water being heated to a few hundred degrees Celsius, boiling away, and temporarily shutting down for cool-off. The operating interval was about 2 hours and 30 minutes. The power production continued for a few hundred thousand years, which, needless to say, is an admirable and unprecedented working life for a nuclear machine. They produced power at a rate of 100 kilowatts in the form of heat, made 11,907 pounds of radioactive waste, and 3,307 pounds of plutonium.

The water-logged, sandstone/shale structure of the Oklo mines is hardly an ideal geologic depository for nuclear waste. We would never consider using such a place for long-term storage of radioactive fission by-products. Yet, in 1.5 billion years the toxic remnants of the Oklo reactor operations had barely migrated a few centimeters. Nothing poisonous had made its way into the ground-water, there was no evidence of biological harm, and the highly radioactive fission products had remained in place until they decayed into stable end-products. Mother Nature had effectively built a power-reactor cluster, pulled the controls, and ran the thing for a long time without causing any harm. For a technical community with plans to run the earth on nuclear power, this ancient reactor site provided three findings: It was a good idea to put radioactive waste in clay to stabilize it, designing a reactor was not as difficult as nuclear engineers would have you believe, and the first working chain-reaction was not in Chicago in 1942, but was in Africa beneath the surface of the Earth.

The Oklo reactors were a fascinating occurrence, but although they were very early examples of nuclear power, they were not the first. In fact, all of the energy we have ever used on Earth originated in nuclear reactions, mostly from the big fusion reactor, the Sun. It takes small atoms, such as hydrogen, and fuses them into larger atoms, all the way up to carbon. The small atoms individually weigh more than the combination of two, and the weight difference expresses itself as radiant energy. It is a direct mass-to-energy conversion, spraying the universe with radiant energy. The Earth is close enough to benefit from it, without being close enough to be over-exposed.

Engineered solar power is, of course, from the Sun, but so is wind power, as it is the Sun’s heat that causes cold air to try to get under warm air, causing air currents. Hydro power is solar, as water is lifted into the clouds by evaporation, and it rains down into reservoirs. Petroleum and coal are solar power in long-term underground storage, as they were once biological material that grew and stored energy at least indirectly because of sunlight. The energy of a great tree shaking the ground as it topples over traces back to the Sun, building cellulose structures using photosynthesis, as is the warmth of a wood fire or any newly developed bio-fuel.

In a technical sense, even fission power from U-235 is ultimately solar in nature, but it was not our Sun that produced it. Fission power is another stored-energy mode from geologic deposits, such as petroleum, only it was not created on Earth. The energy locked up in uranium is millions of times more intense than the energy stored in coal or oil, and it was put there when a monstrously large star reached the end of its useful life and exploded. In the extreme energy environment of a super-nova, heavy elements are assembled on a different scale than the daily fusion events in the Sun. When the heavy elements experience inverse-fusion, coming apart and reverting to smaller atoms, they radiate power. The weights of the smaller fragments do not add up to the weight of the original element, and the deficit becomes radiant energy. With the Oklo mine discovery in 1972, we learned that without our help the Earth has experienced energy production, storage, and conversion on both ends of the nuclear binding-energy spectrum, from fusion to fission. Until the late 19th century, energy production in this manner was not understood. It was not even up to fantasy levels at this early point.