Hubbert’s Early Take On Nuclear Energy

By Jason Brenno of the Hubbert Tribute

This article is offered in celebration on the 53rd anniversary anniversary of M. King Hubbert’s Seminal speech on March 8th, 1956 that correctly predicted the 1970 peak of U.S. oil production.

The mission of the Hubbert Tribute is to decipher our energy past, present, and future. Hence, we are investigating how U.S. energy policy was architected over the past century. The article reviews how experts thought about energy and nuclear energy in particular in the 1950s and how this led accomplished scientists such as M King Hubbert to promote a nuclear powered future that may not be considered probable or even viable today.

Based on his classic paper Nuclear Energy and the Fossil Fuels – and in particular the graph below – Hubbert appears to have believed in 1956 that nuclear energy would become a long term source of energy at a magnitude far greater than that of fossil fuels. A key question to keep in mind is given that Hubbert had at least partially bought into this concept, what effect did it have on decision makers at the time?


Some clues to Hubbert’s reasoning appear in the M King Hubbert oral history. An interview with M King Hubbert speaking about his 1956 paper Nuclear Energy and the Fossil Fuels is quoted below:

Doel: I’d like to continue today on the topic of oil and natural gas resources in the United States, which we began in our last discussion. In 1956 you made a presentation to the API in San Antonio concerning predictions of oil and natural gas reserves. How did that presentation come about?

Hubbert: In the summer, I believe it was, spring and summer of 1955, I had began service and had a couple of preliminary meetings of the Advisory Committee of the National Resource Council to the Atomic Energy Commission on Waste Disposal. Land Nuclear Waste Disposal.

In the course of those hearings, I had obtained information which I had not had before, on the magnitude of the energy that could be obtained from fission. And the basic figure that came out of some of these reports was that the fission of one atom of U 235 released a specified amount of thermal energy, 200 million electron volts, as I remember the figure. From this, I did some calculation on the amount of uranium that it would take to generate say all the electric power of the United States for a specified length of time. What it was a general feeling that whereas previously I’d regarded nuclear energy as unpromising because of the scarcity of uranium and thorium

Doel: Were you familiar with the Survey’s mining of uranium at the time?

Hubbert: Not particularly. But I was unaware of the enormous magnitude of the energy contained in a small amount of uranium or thorium. So this awareness of the magnitude of the energy, as compared with the relative scarcity of uranium and thorium, changed the picture in my mind, as to the practicality of nuclear power. Well, this was in the earlier part of 1955, in the spring and summer, these meetings with this committee and the AEC people. So that in turn reflected on my previous analyses of energy based on the fossil fuels. Some time in the fall of 1955, about November, as I remember, I was on a trip to Denver, on company business. At breakfast in the hotel I encountered one of the Shell production engineers whom I knew from Houston, and we had breakfast together. During the breakfast conversation, he remarked that he was I think chairman of the program committee of the forthcoming meeting of the Southwest Division or the Production Division of the Southwest Section of the American Institute, American Petroleum Institute, which was to meet in San Antonio in March. And they were looking for someone who could give them a broad brush picture of the overall world energy situation.

According to Hubbert, this was the first time he had included nuclear energy in his discussions of the overall energy outlook. He had only recently obtained sufficient information in his work for the Atomic Energy Commission to give a presentation on the subject. While it appears at the time he was convinced that atomic energy was a viable source for future world energy needs, Hubbert did ultimately change his mind on the viability of atomic energy later in his life. As he explains below in the M King Hubbert Oral History:

Doel: Has your thinking about the problems of nuclear disposal changed since your first exposure to those issues back in the 1950’s?

Hubbert: Not significantly. The problem is here, and it appears more intractable now than it did then. And the thing that finally influenced my attitude there for 10 years or so was if this problem is manageable, with the technology existing, using low grade sources of uranium, we had not infinite supplies but very large supplies of energy. Further, if we could go to fusion, and could utilize deuterium from the ocean, which could be extracted at small energy cost, as compared with its energy content, why, then you’d be at an almost astronomical level of energy resources. Well, what’s subsequently happened, with regard to fission, and that is the irresponsibility of the AEC, of penny pinching financially, nuclear power without the backup of what would have to be done. That performance is still going on, essentially unaltered, and it drew me to the conclusion that that isn’t the answer to our energy problems, and the sooner we get rid of it the better off we’re going to be. I would never recommend shutting all the plants down tomorrow, but certainly phasing them out. See, we haven’t faced up to the big problem: what are we going to do with these radioactive plants when we have to dismantle them? We haven’t had that yet. So, that was when I took another look at solar energy, and I came to the conclusion it was a change of conclusion. Before, I thought that solar energy, although large, was so diffusive that it was impractical.

I changed my mind on that. With solar cells, existing solar cells but with improvements, and utilizing what I call the chemical route of collecting in solar cells where there’s good solar energy, storing it chemically, utilizing flat planes or tankers, liquids or gases, for delivery. That is entirely practical for producing all the industrial energy that we have any use for, with the very small fraction of available areas for collection.

Doel: I was curious that in the 1971 SCIENTIFIC AMERICAN article you mentioned a number of solar energy possibilities, and you mentioned an idea that had been proposed by Alan Meinel, the astronomer and his wife. How had you come into contact with people who were working in solar energy at that time?

Hubbert: I think I met him when I was out at the University of Arizona giving a lecture. A friend of mine invited me to his house and had Meinel to the same dinner. And he gave me a considerable lot of information on his work with regard to solar energy. He was using not the solar cells but thermal, collecting solar energy thermally. And he was very enthusiastic about it at the time. At least he convinced me for the first time that it was practical, which I hadn’t previously conceived it to be.

To have a frank conversation on this subject, one must consider what exactly is meant by the term nuclear energy. For example, when pundits say nuclear energy is necessary for reducing dependence on foreign oil and especially now lowering greenhouse gas emissions, what exactly is implied? An in depth look into this issue reveals that the present fleet of light-water reactors still have a serious problem even if one were to believe that these reactors are economical, safe, do not pose emission risks during normal operations, and the waste is disposed of properly (all of which are debatable). As with oil, the looming problem is resource depletion. The current fleet of reactors uses a form of uranium that is not common in nature (U-235) and whose production is likely to peak in several decades. While it is true that the light-water reactors can also burn plutonium from weapons disposal and reprocessing of spent fuel, the issue of proliferation of weapons-grade plutonium is real and would be greatly amplified if the United States and other countries were to begin reprocessing fuel as is done in France. Given that uranium 235 is finite and the importance of reducing the possibility of proliferation, it seems imprudent to promote expansion of nuclear technology as a solution, at least in its present form.

There are two distinctly different forms of nuclear reactors: those that use more fuel than they consume (the vast majority of the operating reactors) and those that produce more fuel than they consume – that is, breeder reactors or more commonly known these days as Generation IV reactors. This begs the question: if breeder reactors were the primary source of power would fuel depletion be an issue. The answer is for all practical purposes no. As mentioned above, however, the issue of proliferation remains a very real issue especially in the current geopolitical context. Plutonium would have to be reprocessed in much larger quantities than today for as long as a breeder reactor economy is in existence.

Discussion today about nuclear power should focus upon the viability of the breeder reactor. If we are to rely upon nuclear power as a primary energy source, the breeder reactor will be inevitable. Any proposals for continuing on the path of nuclear energy should at least recognize this.

In his paper Nuclear Energy and the Fossil Fuels, Hubbert explains atomic energy and its potential in a way that is still relevant today after more than half a century:

The fissionable elements, as indicated in Table 1, comprise two isotopes of uranium U-235 and U-233 and one of plutonium, Pu-239. Of these, only one U-235 occurs naturally and the other two are man-made, Pu 239 being derived by a radioactive transformation from U-238 and U-233 from thorium. The isotopes, U-235, U-233 and Pu-239 are known accordingly as fissionable or fuel materials; whereas U-238 and Th-232, while not themselves fissionable, can be converted into fissionable isotopes and so are known as fertile materials.

Naturally occurring uranium consists of the isotopes, U-238 and U-235, in the ratio of 140 to 1. Any given quantity of natural uranium contains 99.3 percent of U-238 and 0.7 percent of U-235. Natural Thorium consists of the single isotope TH-232.


The elementary nuclear power reaction is that indicated in Figure 25. Here U-235 in a critical amount is undergoing fissioning. When a U-235 atom is struck by a neutron, it breaks into fragments known as fission products which consist of other atoms near the middle of the table of atomic numbers, and also releases neutrons which strike other U-235 atoms, thereby maintaining a chain reaction. Each fission releases, on the average, 200 million electron volts of heat which like the heat of combustion of coal or oil can be used to drive a steam power plant.

The objections to the sole use of U-235 are its scarcity and the large amounts of energy required to separate it from U-238. Hence very great importance attaches to the possibility of converting the fertile materials by means of the breeder reaction. The breeder reaction for U-238 to Pu-239 which is then fissionable. By a similar reaction Th-232 can be converted to U-233 which is also fissionable. It has been experimentally demonstrated that both these reactions are possible and are capable of producing from the fertile materials more material than is consumed. Thus, in principal, by means of properly developed breeder reactors it is possible to consume whole uranium and thorium. In the subsequent discussion it will be assumed that complete breeding will have become standard practice within the comparatively near future.

Now for the energy that is released by the fissioning of a given amount of uranium (or thorium). As indicated in Table 2, the fissioning of 1 gram of U-235 releases 2.28 X 104 kw-hr of heat, which is equivalent to the heat of combustion of 3 tons of coal or 13 barrels of oil. One pound of U-235 is equivalent 1400 tons of coal or 6000 barrels of oil. Within narrow limits the same values are valid for U-238 and for thorium.

Using the foregoing data, the uranium equivalents of the fossil fuel reserves of the United States are shown in Table 3. The energy of 358,000 metric tons (1 metric ton is equal to 10 ^6 grams or 2205 pounds) of uranium is equal to that of all the fossil fuel reserves of the United States. In Table 4 it is shown that the uranium content of all the coal, oil and gas and water power to be consumed in the United States during 1956 amounts to only 553 metric tons.



Magnitude of the Uranium Reserves

With this review of the requirements we now ask: What is the magnitude of the supplies? The uranium contents and fuel equivalents of the principal sources of uranium in the United States are shown in Table 6. The ores which are currently being produced, the so called high-grade ores, are the type found principally in the Colorado Plateau. These are said to average about 0.35 percent uranium or 3500 grams per metric ton, equivalent to about 10,500 tons of coal or 45,000 barrels of oil per metric ton of ore.

The so called low-grade ores are the phosphate rocks and the black shales which have uranium contents in the range of 10 to 300 and 10 to 100 grams per metric ton, respectively. Even so, such rocks are equivalent to 90 to 900 tons of coal or 390 to 900 barrels of oil per metric ton for the phosphates, and to 30 to 300 tons of coal for or 130 to 1300 barrels of oil per metric ton of rock for the black shales. Even granite, as has been pointed out by Harrison Brown (1954) and by Brown and Silver (1955), contains about 13 grams of thorium and 4 grams of uranium per ton which is equivalent to about 50 tons of coal or 220 barrels of petroleum per metric ton of granite.

Hubbert continues to describe the massive quantities of low grade resources of uranium found in the United States and possibly in the rest of the world and concludes:

From these evidences it appears that there exist within minable depths in the United States rocks with uranium contents equivalent to 1000 barrels or more of oil per metric ton, whose total energy content is probably several hundred times that of all the fossil fuels combined. The same appears to be true of many other parts of the world. Consequently, the world appears to be on the threshold of an era which in terms of energy consumption will be at least an order of magnitude greater than that made possible by the fossil fuels.”

Further in the paper, Hubbert concludes:

We may at last have found an energy supply adequate for our needs for at least the next few centuries of the “foreseeable future”.

The sources that Hubbert references for some of this knowledge are:

The Challenge of Mans Future Harrison Brown 1954 Viking Press New York

The Possibilities of Securing Long Range Supplies of Uranium, Thorium and Other Substances from Igneous Rocks Harrison Brown and L.T. Silver 1955 United Nations International Conference on the Peaceful Uses of Atomic Energy, Geneva (preprint)

Although the book The Challenge of Mans Future is over 55 years old its knowledge and assumptions are still relevant today. It identifies many of the problems facing mankind then and still now, clearly articulating one of the largest problems which is the need for a plentiful, affordable long term source of energy. Harrison Brown concludes that a long term source of energy is essential to maintaining both the standard of living that industrial man has achieved and the population levels of this planet then and even more so today.

Another source of information listed in Nuclear Energy and the Fossil Fuels that may have also been a contributor to the idea of the viability of nuclear power (using the breeder reactor) is the book Energy In the Future by Palmer C. Putnam. This book also asserted the viability of the breeder reactor. On Page 249 Putnam stated this of nuclear energy’s potential:

Reserves of Uranium and Thorium. World reserves, economically recoverable, are estimated at some 25 million tons of uranium and 1 million tons of thorium. Breeding is assumed, with a net effective burn-up of about one third of the mined metal. Thus the reserves would yield over 575 Q – over 25 times the net economically recoverable reserve of coal, and over 100 times that of oil-gas. A good part of the nuclear reserve is in the United States.

Note that the unit of energy Putnam refers as a Q is equal to a billion billion British thermal units of heat.

The importance and influence of this book will be the subject of future articles. It should be noted that Harrison Brown also cites this book as a source for The Challenge of Mans Future. Brown may have built upon some of the work of Putnam in his ideas on atomic energy.

Although it appears from the oral history that Hubbert was not entirely sold on the idea of powering our world on granite, he was comfortable with the concept of using the large quantities of low grade uranium as a fuel source. This idea of using low grade uranium resources as our reserves of fossil fuel become scarcer is also found in The Challenge of Mans Future. Brown asserts that after low grade sources of uranium and thorium along with minerals are depleted, mankind will have to use granite as our primary source of energy and minerals. According to Brown, uranium and thorium can be obtained fairly easily from granite. The energy from the uranium and thorium can be used to provide the energy and to obtain the minerals necessary for industrial civilization and its burgeoning population.

Brown concluded that should it be possible to develop an economical breeder reactor (which at the time he thought was achievable), industrial civilization could in principal use much more energy. In such a future, developing countries could eventually have a standard of living similar to that of the future industrialized world. The requisite energy to achieve this would first be available in low grade uranium ores and eventually granite. Brown also suggests that should the breeder reactor concept be an economic failure, mankind will be forced to use fossil fuels at an ever increasing rate. This would then subject industrial civilization to the Hubbert curve, portending its ultimate decline. Brown by no means assumed that the process of using granite to power our society was an easy proposition, but instead viewed this proposal as a critical tool for mankind to continue to develop and maintain its growing industrial civilization.

It is the assumption that low grade sources of uranium, and in some cases the misinterpretation of this assumption that appears to have led to one of a series of great miscalculations related to energy in human history. While Hubbert’s optimism about the prospects of the breeder reactor in the 1950s might at first blush appear to be one scientist in the wilderness, this is not the case. Future articles will discuss the prevalency of this point of view in the ensuing decades, and how it influenced U.S. energy policy or the lack thereof.

The astute reader may also notice a few more interesting assumptions in Hubbert’s paper Nuclear Energy and the Fossil Fuels:

  • Much larger amounts of recoverable coal than are believed to be recoverable today

  • Oil shale as a probable future source of petroleum

  • Nuclear Energy could offset declines in petroleum production as shown in the Figure below.


The future articles will address these observations along with the influence of Harrison Brown and The Challenge of Mans Future, in addition to a few other publications that have added to this series of great miscalculations and their influence to this day.


The Challenge of Man’s Future, Harrison Brown 1954 Viking Press New York

Energy In the Future, Palmer C Putnam Van Nostrand New York

A portion of the content of this article, including quotations by M. King Hubbert, are from an oral history interview with Marion King Hubbert by Ronald E. Doel, January 4 to 6 February 1989, located at the Niels Bohr Library, Center for the History of Physics of the American Institute of Physics, College Park, MD

Nuclear Energy and the Fossil Fuels, M King Hubbert Chief Consultant (General Geology). Presented before the Spring Meeting of the Southern District Division of Production, American Petroleum Institute, Plaza Hotel, San Antonio, Texas March 7, 8, 9. 1956 Publication NO. 95, Shell Development Company Exploration and Production Research Division, Houston, Texas, June 1956. To be published in Drilling and Production Practice 1956 American Petroleum Institute.

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