[Return]

Nature's nuclear reactor inspires scientific curiosity

 The Los Alamos Monitor July 14. 2002

By Roger Snodgrass

lamonitor@lamonitor.com

Monitor Assistant Editor

Posted with permission of the Los Alamos Monitor

This is the first of two articles.

Almost 30 years ago, French scientists realized that one of the world's richest uranium mines located in the Gabon Republic in Africa held a natural wonder, the fossil remains of a nuclear reactor billions of years old.

 Lately, the Oklo reactor, one of the world's most remarkable phenomena, continues to inspire new scientific hypotheses and underpin important cosmological evidence:

A cover story in Discover magazine about to reach the newsstands lays out an ambitious theory that an Oklo-like natural reactor lies at the center of the earth and is responsible for earth's magnetic field.

A Los Alamos National Laboratory theoretical physicist, working with an international team of scholars, co-authored a paper in May that uses data from Oklo to test the consistency of a universal constant.

The Oklo deposits held the first and only spontaneous nuclear reactor ever discovered. As its amazing story came to light, six separate zones in the heap of uranium were found to have undergone a natural nuclear fission reaction nearly 2 billion years ago. For hundreds of thousands of years, they produced a relatively small amount of heat before exhausting the radioactive mixture they needed to generate energy.

The amount of energy, as calculated by the French Atomic Energy Commission, was about 15,000 megawatt-years, the energy that might be released from six tons of uranium-235.

 "That is approximately the energy produced by the reactor in a large nuclear power plant in four years," wrote George Cowan shortly after the discovery.

Among many scientists throughout the world who were fascinated by the discovery, Cowan headed the nuclear chemistry division at LANL at the time. One of the founders of Los Alamos National Bank, he was also deeply involved later in the formation of the Santa Fe Institute, among many other achievements.

            "I thought it was a phony," he said about his impression of early reports on Oklo, but after several visits to Gabon and further analysis, he began to understand what had happened.

As he explained in an article in Scientific American in September 1976, in an encyclopedia essay, and in lectures he gave around the country for a couple of years, there were convincing reasons to believe that nature had been the inventor of nuclear fission.

The uranium at Oklo in the southeastern corner of the former colony of French Equatorial Africa contained its own inescapable evidence.

Throughout the solar system natural uranium consists uniformly of 99.27 percent of uranium-238, the element's most common isotope, and .72 percent of a more fissionable isotope, uranium-235. A discrepancy of one part per thousand is considered within the bounds of normal, but ore from Oklo was found to be missing 30 parts per thousand of the U-235.

It was unheard of. Ultimately, the mystery was unraveled, when it was discovered that in the pockets of depleted uranium ore a characteristic spectrum of byproducts of nuclear fission were also present and in the distinctive ratio that might be anticipated if a natural fission reactor had produced them.

The U-235 from Oklo had been depleted partly because it had become the fuel of the reactor. It had also dwindled through time, simply by its own radioactive decay.

            By calculating how long ago the U-235 had been sufficiently concentrated to fuel a chain reaction, the scientists were able to date the time it was operating to 2 billion years ago, about the age of rocks in which the uranium ore was found.

"The earth is a restless place," said Cowan, noting that for him the real questions were how the Oklo natural reactor had formed and why it had survived.

In answering the geological puzzle, he discovered that the uranium deposit that provided the radioactive matrix had precipitated on the edge of a tectonic plate and spread over a rift. The continent that broke away, containing a part of the deposit, became South America, and Cowan said what had been the adjacent piece was now in Brazil and had probably sunk through geological processes 18 to 20 kilometers below the surface of the earth.

Other natural reactors may have fired up there, he speculated, although we may never know. 

At that time Cowan was involved in the question of how to store radioactive wastes from weapons production and nuclear power plants for thousands of years. His trips to Africa were paid for because of the growing national interest in solving the storage problem.

Coincidentally, that matter was provisionally decided by a vote in the U.S. Senate last week, affirming the Bush administration's decision to create a geological nuclear waste repository at Yucca Mountain in Nevada.

For Cowan, the lesson of Oklo did not point to a geological solution to waste storage, but rather to the chemical and mineralogical processes by which nature aggregates and keeps intact whole storehouses of its treasures over billions of years.

There are coal deposits 2 billion years old, he said. And once placer deposits of gold are laid down, they are permanent from the point of view of a chemical reaction.

Cowan said he was asked to provide congressional testimony on the nuclear waste repository and said contrarily, "You can't prove the integrity of five cubic miles of rock."

With no passion to revive an old argument, he suggested that nature had demonstrated better solutions for holding fissionable material harmless over long periods of time, like black sand beaches made up of a radioactive mineral known as monozite.

Having gone to school on the world's oldest known nuclear reactor, which nature and not man invented, Cowan's perspective was influenced by the earth's own safekeeping history.

"If you had fission products in that kind of material, you wouldn't have to worry," he said.

Next: New uses for an ancient reactor

Ancient nuclear reactor still going

 The Los Alamos Monitor July 16. 2002

By Roger Snodgrass

lamonitor@lamonitor.com

Monitor Assistant Editor

Posted with permission of the Los Alamos Monitor

 This is the second of a two-part series

             Since discovery in September 1972, the Oklo natural reactor of Gabon in central Africa has fired the imagination and aroused the curiosity of scientists interested in drawing out the implications of such a rare and ancient phenomenon.

Compared to the energetic efforts of Enrico Fermi and his team at the University of Chicago in the early 1940s, the imperceptible pace of the work of nature eons ago seems almost lackadaisical.

Yet both man and nature, as Oklo attests, succeeded in creating a nuclear reaction, but nature did it 2 billion years earlier.

"An extraordinary sequence of seemingly improbable events," George Cowan called it in a Scientific American article in July 1976, that introduced many people to the Oklo phenomena.

"It is chastening to find that ... an unassertive community of modest bacteria built a set of nuclear reactors that ran for millions of years," wrote James Lovelock, in "The Ages of Gaia," which proposed in 1988 the controversial idea of a planet that is literally alive.

Oklo, because of its 2.5 billion year history, because of the unique properties of its nuclear materials, because of its very implausibility, apparently still has a number of stories to tell.

One of them appeared in May as a formal paper in the e-print arXive, a major electronic forum for scientific discussion. "Nuclear data in Oklo and Time-Variability of Fundamental Coupling Constants," in the arcane arena of phenomenological energy physics.

The paper seeks to address a question that that has troubled physicists since the 1930s when doubts arose about whether the fundamental laws of nature have been constant since the beginning of the universe.

The consistency of the constants of the universe like the speed of light, the electron charge, the force of gravity have been questioned in order to solve contradictions in various theories of how the cosmos was formed. Some scholars have contended, for example, that the gravitational constant has actually varied over time.

John Webb, a researcher at the University of New South Wales in Australia, and his colleagues used a highly precise spectograph at the Keck telescope in Hawaii trained on quasars, at the core of galaxies on the edge of the known universe, to test a constant known as the fine-structure constant, a number that determines the strength of interactions between charged particles and electromagnetic fields.

Webb's conclusion a few years ago was that the fine structure constant was changing, with the star-shaking implication that if one constant changed others might have changed as well.

If so, all bets would be off in some of the most fundamental cosmological equations of our time.        

A Los Alamos physicist who collaborated on the paper that studied data from the Oklo reactor, Peter Möller said the unique features of the Oklo reactor made it possible to test the fine structure from another angle.

"You can check over a very long time; and see if it changes a little bit over a short time," he said.

In this case the researchers focused on an observation by a Russian physicist in 1976 that the measurement of samarium-149, an isotope of a rare earth element, could be used to determine how much nuclear reactions might have changed from the time of the Oklo reactor to today.

"We can compare what actually happened in the Oklo," said Möller. "If the force was different the outcome would have been different."

"One result," he said, "was consistent with no change in the constant. But we can say that with a higher accuracy than before."

At the same time, the paper concludes that there may still be some room to declare a variation in the fine-constant, and that the question merits further attention.

A somewhat more controversial issue that is about to receive much more public attention is a theory that J. Marvin Herndon, a geoscientist and geological consultant in San Diego, has been developing for about 10 years. He has recently teamed with Daniel F. Hollenback, a nuclear engineer at Oak Ridge National Laboratory in Tennessee, to present a more elaborate version of the hypothesis in a paper submitted last year to Proceedings of the National Academy of Science.

The idea is that a huge Oklo-like reactor, formed from a ball of uranium at the very center of the earth, is still functioning and is responsible for such puzzling phenomenon as the planet's fluctuating magnetic field and thermal energy.

Herndon's hypothesis about to go public in the realm of popular science as the subject of an article by Brad Lemley in the current (August 2002) issue of Discover magazine.

In an interview late last week, Herndon said he had first learned of the Oklo reactor in1972, as a graduate student, and the concept formed the basis for his later description of what he describes as a geo-reactor, a fast-neutron fuel breeder operating over the entire period of geologic time at or near the center of the earth.

Herndon's theories stem from analogies with heat radiated from Jupiter, Saturn and Neptune for which he proposed Oklo-like planetary-scale reactors as early as 1992.

Later, he found corroboration in the composition of a class of meteorites known as enstatite chondrites.

"In those meteorites, as much as half of the uranium occurs in the portion corresponding to the Earth's core," he argued in a 1998 paper presented to the American Geophysical Union. "Uranium ... would be expected to precipitate from the Earth's core at relatively high temperatures and, at the pressures involved, would be the densest substance and would tend to collect at the center of the Earth."

Herndon garnered additional support from Hollenbach, who used codes from a nuclear reactor fuel-depletion studies to model the deep-Earth reactor theory.

Hollenbach's calculations under a specific set of assumptions demonstrated that a ball of uranium of a certain size at the center of the earth would indeed stay critical for over 6 billion years.

The production and ejection of lighter by-products from the chain reaction, causing periods when the fission fluctuates or ceases, was proposed as an explanation for the fact that the earth's magnetic field shuts itself off approximately every 200,000 years while reversing polarity.

Hollenbach's calculations also added another checkpoint: that one of the expected consequences of a deep-Earth nuclear reactor was a ratio of isotopes of helium-3 to helium-4 that corresponds to observed ratios from deep-earth wells

This particular Oklo-derived concept may have a tough time finding acceptance in some parts of the scientific community.

"The nuclear community doesn't have much of a problem with it," said Hollenbach. "Geophysicists love it or hate it. Most really hate it right now, but some are coming over to the idea that it's a possibility."

A LANL geophysicist confirmed that impression. He estimated that the probability that the theory was correct was "essentially zero." Since his statements about the work of the authors were so unkind, he asked not to be quoted by name.

Herndon seemed to be well-aware of the likelihood of criticism.

"I'm hugely swimming upstream," he said. "The establishment doesn't challenge what I'm doing. They just ignore it."

In the far-flung sphere of interest generated by the Oklo reactor, a lively new debate may be a more probable outcome.

After all, if a 2 billion-year-old mystery can be solved and new lessons learned all along the way, why not the question of the deep-earth reactor?

Science may grumble at the extra work, but will probably sharpen its pencil and find a way to approve it or reject it, like it has so many other profound and wooly ideas.

Comment received by the Los Alamos Monitor

 "Scientists don't like to admit they have been backing the wrong idea! Remember the plate-tectonics theory for a similar set of geologists? The more an idea would have a major negative (in the sense of different thinking) impact on a segment of science, the less likely it will ever see print, for all the freedom of expression that is perceived in the sciences. Even many novel ideas that address areas that have no explanation, but do not fit the tenets, do not see print. A scientist who would hide behind anonymity in his opinion about a subject is of the same ilk as those who would make sure it got panned in peer review; also anonymously! Posted with permission of the Los Alamos Monitor and Joel M Williams. 

Scholarium

 By J. Marvin Herndon

Galileo described precisely the often negative nature of human response to new ideas. The two articles by Roger Snodgrass each contain the description of such a response; but the two responses differ considerably, however, in their manifestation. In the first article, Dr. George Cowan, of Los Alamos National Laboratory, thought that the Oklo reactor “was a phony”, but then investigated and ultimately became an authority on the subject. In the second article, a Los Alamos National Laboratory geophysicist made on record and anonymously “unkind remarks” and an unqualified and unjustified estimate that the probability of the theory being correct is "essentially zero”, thus putting the Director of LANL,  in the embarrassing situation of being expected to explain the analysis and the directive involved.

[Return]