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ATOMIC ENERGY IN INDUSTRY' I. PERLMAN Department of Chemistry and Radiation Laboratory, University of California, Berkeley, California
IN TAB past half-dozen
years, those whose research had carried them into the study of the atomic nucleus were witnesses to an interesting phenomenon-the birth of a new industry-the Atomic Energy Industry. To be sure other industries have been developed in years gone by and still others will appear in the future as a result of scientific research carried on with no other aim a t the moment than the exploration of the unknown. Today, tomorrow, or next year, in some laboratory will be sown the seeds of future industries which, to a greater or lesser extent, will change the manner of living of people for generations to come. What then is unique about atomic energy that its development merits particular attention? In the first place atomic energy shows promise of developing into a basic part of our economy as a source of power. It is not at all inconceivable that atomic energy will change our existence to the same extent or more so than the development of such other sources of power as the steam engine and the electric generator. Atomic energy has captured the imagination of all who have come in contact with it. To the scientist the machines of atomic energy unlock the door to limitless new observations, to the ultimate structure of matter, to new chemical elements, to the radioactive tracers that will allow new or better insight into the reactions of both inanimate matter and the life processes. To the engineer atomic energy presents the challenge of developing a new technology entirely foreign to previous engineering practice and the prospect of installing these power plants in remote sections not blessed with the natural sources of power-coal, water power, and petroleum. Since power is basic to the development of an industrial economy, the engineer may also look forward to industrial development in the many regions of the earth which are otherwise equipped with the necessary raw materials but which have no available power. The atomic power plant will be a curious installation. It will have very few of the characteristics of power plants as we know them now. The materials of construction will be as strange as the fuel. It is the nature of this new industry, the problems that beset it, and the prospects which i t offers for the future that will be dealt with in this discussion. Before beginning, i t is worth pointing out that the development of the atomic energy industry cannot a t present follow the normal development of a new in&ustry. This stems from the fact that atomic energy first emerged as a militarv weauon, bv far the most dev'Presented before the University of California Extension Division, November 8. 1946.
astating weapon ever devised. Its development, under present circumstances, will be carried out to a considerable extent under secrecy. Progress will certainly not be as rapid as it would be with free interchange of ideas and without the necessity of expending effort upon military aspects. From this it is seen that the threat of atomic warfare is a problem in the development of this industry every bit as knotty as the technical problems. For the present we will discuss the atomic energy industry within the framework of a control system, assuming that such a system will come into existence. A further consideration is worth noting beiore discussing the problems and prospects of an atomic energy industry. This is to place the present stage of development in proper perspective on a time scale. Atomic energy is too new a concept to be thoroughly digested a t this stage. It will be remembered that Faraday discovered the principles of electromagnetic induction about 1825, yet i t was literally generations before sizable industrial installations embodying these principles became a reality. In the case of atomic energy we have the unique experience of seeing the germ of an idea transmitted into a large industry in a period of time in which even one with a poor memory can recall the salient details of the development. It was in 1939 that two German workers, Hahn and Strassmann, were driven to the conclusion that uranium atoms actually split in two under the stimulus of a small particle, the neutron. LiteraUy within a matter of days, the significance of this discovery with respect to energy release was realized and experimentally confirmed. The obsewations were made on but a few atoms by means of sensitive instruments that could measure the energy of the reaction indirectly. However, a means of multiplying this reaction, first observed with a few atoms, to a scale where staggering amounts of energy could be liberated, was soon envisioned. This method depends upon what is called a "nuclear chain reaction," and I shall spend some time presently describing the "chain reactors" which constitute the only known means of releasing large scale atomic energy. By the end of 1942 the first nuclear chain reaction had been demonstrated in Chicago, and within a very few months construction had actually started on the huge.Hanford Engineer Works in Washington. I t is little wonder that in this short period of time we have not been able to establish a clear perspective on the over-all problem, especially since the thought and experimentation so far expended were largely placed on these specialized plants designed with an urgent military objective in view. Perhaps i t is
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too much to expect a t this early stage to be able t o state categorically what the cost of building an atomic power plant would be, what its operating characteristics might be, and whether or not it could compete favorably with other forms of power. However, some intelligent surveys have been made and I shall relay the results presently. Despite the gaps in our present knowledge one indisputable fact bears remembering. We do actually today have an atomic energy industry. It is highly specialized, just as the fighter aircraft differs from the commercial transport plane. Nevertheless, the nuclear chain reaction has been demonstrated, it can be controlled, and volumes and volumes of information pertinent to peaceful atomic energy development do exist. The Nuclear Chain Reaction. It has already been inferred that several different types of power plants are possible depending upon the use to which they are to be put. There are certain basic principles and processes common to any of these plants and these center around the nuclear chain reaction. It is worth pausing here to explain the nature of the nuclear chain reaction, the ingredients that go into it, and the energy that can be derived from it. We now know of three substances that have the necessary fission properties to sustain a chain reaction. These are the uranium isotope of mass 235, the plutonium isotope of mass 239, and the recently announced uranium isotope of mass 233. We shall call these simply uraniumlas, plutonium23Q, and uranium233. Of these, only U236 is found in nature while the other two are artificially produced. Since the nature of the chain reaction is common to all these substances, let us focus attention on the primary substance uranium. There are only two discoveries which must be recalled in visualizing the possibility of a nuclear chain reaction. The fist is the discovery of the fission process itself. If a neutron collides with a U2a6nucleus, it actually enters or amalgamates with this nucleus. This so disturbs the nucleus that in a very small fraction of a billionth of a second it explodes with great violence into two large fragments with the release of much energy. From this splitting comes the term nuclear fission to describe the process. The second discovery is that in addition to the two principal fission fragments several neutrons are liberated in the process. Since a neutron colliding with a UZ3$nucleus is what promotes the fission in the first place, one of these product neutrons can cause another UZ3$nucleus to undergo fission. Thus we see that the process results in a self-sustaining chain of events in which uranium atoms are split by neutrons, more neutrons are formed during the splitting, and these react with more uranium atoms and so on. Now if we multiply these single events by a very large number, such as one followed by 20 or more zeros, we get some idea of what is going on inside one of the large chain-reacting structures, or piles as they are called. However, the problem is not quite this simple.
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Neutrons are the life blood of the chain reaction and cannot be wasted, otherwise the reaction would stop. Unfortunately, all atoms have some ability to capture neutrons. When they do so, they do not split in two as does U225 but they just grab hold of these neutrons and settle down to a relatively calm existence once more. I t is for these reasons that materials of construction and all other materials that go into a pile must be carefully selected on the basis of their nuclear properties; in particular, they must have as low affinity for capturing neutrons as possible. Some impurities must be excluded even to the extent of one part per million because of their very high capacity for consuming neutrons. I shall not he able to go into the many factors that must be introduced into pile design. One item that should be mentioned is the presence of what is called the moderator. In the Hanford piles carbon in the form of graphite is used as a moderator. Many of you have probably heard that heavy water is important for atomic energy and that during the war commando raids and bombing missions were carried out in Norway in order to wreck the heavy water plants that were known to exist there. The value of this difficultly prepared substance is that it is an excellent moderator. A small experimental pile near Chicago is built with a heavy water rrioderator. Let us examine what the function of a moderator is. It so happens that the neutrons that come from a. uranium atom which is undergoing fission are of high energy. They are called fast neutrons. If all of the neutrons in a pile set up to operate with natural uranium were fast, there would be no chain reaction. This is because a fast or intermediate energy neutron does not cause fission with U235 nearly as efficiently as does a slow neutron. It will be remembered that ordinary uranium is less than one per cent UzS6; the remainder consists of U188 which does not undergo fission as does U235. Since Uza6 does not effectively use the fast neutron, it prefers to go with the more abundant Us" and the chain reaction would cease. However, if the neutrons can be slowed down without a t the same time disappearing, the balance is once more restored and sufficient neutrons go into UZ3$ to allow the chain reaction to proceed. Certain of the light elements, such as heavy hytlrogen, beryllium, and carbon, have this highly desirable property of slowing down neutrons without capturing them. A fast neutron enten one of these materials and bounces around like a billiard ball, losing some energy a t each collision. If you can now visualize many lumps or rods of uranium interspersed in a lattice arrangement with graphite, you have the basic picture of a nuclear chain reactor or pile a t Hanford. If we look a t the life history of a neutron it will be something like this: It is liberated as a fast neutron within a lump of uranium. In general, it will leave the uranium without change and enter the graphite. Here i t will undergo many collisions with carbon atoms, perhaps 100, during which its velocity will be reduced and it will finally
MARCH, 1947 Jind its way back into another uranium lump. Here it will either cause another fission or be captured by the more abundant U4", but a sufficient number go into fission of U235 to maintain the chain reaction. Besides the uranium itself and the moderator a reactor must also contain a cooling system for taking off the heat that is generated. I shall mention the problems of cooling somewhat later when the technology of the Hanford-type reactor and power-producing reactors are discussed. Another component of a reactor or pile is the control system, the mechanism which allows the machine to be turned on or off and which keeps it a t the desired operating level without either dying or running away. The principle of reactor control is rather simple. If rods made up of material with high capacity for absorbing neutrons are inserted into a reactor sufficiently far, they are able to drain off a sufficient number of neutrons to stop the chain reaction. If these rods are withdrawn, the chain reaction can proceed. By maintaining the rods a t just the right position, the reactor will operate a t a selected power level. The whole structure so far mentioned is enclosed in a massive shield to confine the radiation. This shield is designed to stop both neutrons and gamma rays, the high energy X-rays given off by many radioactive materials. Energy Release and Plutonium Production. The previous description is then, in essence, that of the nuclear chain reactor. I t is a power plant. For every pound of U235that undergoes fission about 10,000,000 kilowatt hours of energy are released as heat. If one pound of uranium or plutonium were to be burned in one day, it could supply the needs in power and light for a city of about one-half million people. The heat is generated within the uranium lumps and, by flowing a cooling agent over them, this heat could be brought outside of the pile and converted into useful energy. In the Hanford piles water is used as a cooling agent and the piles are run a t low temperatures since power output is not the objective. So far I have discussed only the mechanism of obtaining a chain reaction in uranium without saying anything of why a successful chain reaction was sought. In some piles of the futcre power generation itself will be the goal. That is not the objective for which the Hanford piles were constructed. The Hanford piles were designed for the production of the new isotope, Experimentation by Seaborg, McMillan, Segre, Kennedy, and Wahl using the Berkeley cyclotron had resulted in the discovery and preparation of plutoniumz39and in finding that it shared with U235the property of undergoing fission with neutrons. It was therefore a substance that had the possibility of use as a nuclear explosive if it could be produced in quantity. In producing plutonium23Y the pile simply acts as a neutron factory. Since more than one neutron is given up in each fission of (the number is between two and three) and only one is needed to promote the chain reaction, many of the
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excess neutrons can be used for any purpose desired. In natural uranium most of these are captured by the UZS8, the very reaction that must be curtailed through the use of the graphite moderator if the chain reaction is to go a t all. When U238captures a neutron, it will be remembered that i t does not undergo fission. Instead, through two successive spontaneous changes it ends up as plutonium23Q. Thus, the chain reaction with neutrons and UZ3=furnishes more neutrons, and these through capture by the UZS8convert it into plutonium23B. The job of obtaining plutonium is only about half over a t this point. The next step is to separate the plutonium from the uranium and, what is much more difficult, from the fission products. When a certain quantity of U235undergoes fission, i t produces roughly an equal weight of fission products. These are an assortment of some 15 different elements and are intensely radioactive. You are probably'familiar with the fact that an amount of radium as small as onethousandth of one pound is extremely dangerous to handle. One could obtain very serious damage from this quantity of radioactivity. For comparison the radioactivity of the fission products associated with the production of a moderate amount of plutonium can be equivalent to hundreds of pounds or even tons of -radium. Obviously, the chemical processes for separating the plutonium from the uranium and fission products must be done entirely by remote control behind many feet of concrete. The uranium that has been discharged from a pile a t Hanford is fed into huge chemical plants. The operators see nothing except an imposing array of gages and controls. The materials proceed through the plant through thousands of feet of piping connecting many processing vessels. The plutonium finally emerges completely separated from uranium and the fission products. Those of you who are familiar with chemical processes will realize the difficulties often encountered in separating any element down to the poini where only about one part per million remains. Yet in this particular problem some dozen different elements, each with its own chemical properties, must be separated to this extent. It might seem a t first sight that this is an extremely roundabout way of getting a fissionable material, compared with the direct isotope separation of UZ35from U238. In complexity of operations and number of steps this is so. However, separation of isotopes of uranium is an extremely difficult matter since isotopes of the same element have almost identical chemical properties. With the manufacture of plutonium a new element is formed and therefore chemical methods of separation are possible. Even though the separation of plutonium from uranium and the fission products is by no means simple, it requires far less effort than does the separation of isotopes. The separated plutonium during the war was fashioned into bombs where it could be made to undergo an explosive chain reaction. Yet the same sequence of steps outlined here is a prototype of an atomic energy
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industry in which power is produced in making plntonium; the plutonium is separated and it in turn can produce an equal amount of power by allowing it to react in a controlled fashion in smaller secondary power plants. I shall go into this relation between primary and secondary reactors somewhat later in considering the structure of a balanced atomic energy industry. Technological Problems. The technology in the atomic energy industry presents some entirely new problems to the engineer. The engineer in the atomic energy industries will be called upon to absorb an entirely new body of knowledge, that of the nuclear properties of substances. As in any building job, materials of construction are of primary consideration in designing a pile. I n a normal power plant the structural elements must have the necessary strength, must be able to withstand the elevated temperatures, and must not be subject to excessive chemical corrosion. All of these properties that must he satisfied may be considered as chemical and mechanical properties. I n designing a pile the consideration of these properties is no longer sufficient. As already mentioned, one must consider in addition the nuclear properties of every material that goes into the pile's construction. Any material that has a high ability to capture neutrons is automatically eliminated no matter how ideal might be its other properties. An excellent structural material like steel cannot be used in quantity in a pile because i t would use up too many neutrons. It is probable that sizable industries will grow for the production of materials with low ability to capture neutrons and which had no commercial outlet previously. Some of these materials will be entirely new to industry, others will be old commodities with new purity requirements. For example, one may take the case of graphite which was selected as the moderating medium for the Hanford piles. Graphite had been used chiefly as electrodes in the electrochemical industries and contained among other minor impurities very minute amounts of boron. Now this amount of boron is utterly innocuous if the graphite is to be used as an electrode, but because of the extremely high neutron a5nity possessed by boron even these minute amounts could not be tolerated in the piles. After considerable experimentation graphite was produced to meet these entirely new specifications. I n new piles of the future, no matter what shape they may take, the same concern for particular purity of all components will be evidenced. One of the knottiest problems in pile constmctiou is that of cooling. Let us again draw on the Hanford piles for illustrations of the problems encountered and then project these same ideas into the consideration of other piles. With the decision to employ water as a coolant for the plutonium production plants the question of a n adequate water supply became a paramount issue. I n the pile areas at Hanford a large fraction of the installations are concerned solely with the pumping and
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treatment of the water that is sent through the piles and eventually back to the river. The amount of water pumped Would take care of the needs of a large city. I n view'of the necessity of providing emergency stand-by equipment and elaborate safety controls, the entire water system is extremely complex. I n considering water as a coolant, it was n'ecessary to examine its neutron absorption just as any other material that goes into the pile. I n addition, since warm water would react with uranium metal, the uranium lump had to he covered; again the neutron absorption properties of the possible covering materials severely limited the choice. The corrosion properties of the covering jackets had to be thoroughly studied since the failure of even a single jacket could have been diastrous. Film formation on the slugs from minute impurities in the water was another serious problem that was overcome. A staggering amount of research and development went into the solution of these problems, and large water-treating plants were installed accordingly. A problem that is entirely unique to the atomic energy field is that of the radioactivity indncedin any material exposed to neutrons. The huge volumes ~f water precluded the possibility of lengthy storage, so that it was important that the exit water be sufficiently low in activity to permit its disposal into the river. Fortunately, pure water itself presents no insuperable problem because neutron reactions with hydrogen and oxygen produce either stable isotopes or unstable ones of very short half-life. However, small quantities of impurities in water could present a serious problem. Amounts as low as a few parts per million of certain elements could be activated during their brief passage through a pile to an extent where the water would be dangerous t o animal life, Tests were made on all water-treating processes to see that dangerous elements were removed and that others were not introduced. What has been said about water as a cooling medium applies to any other coolant in future piles. If a pile is to operate efficiently as a power plant, the temperature of operation must be raised far beyond that used i n the Hanford-type piles. Obviously, a different coolant than water must be adopted. Such cooling agents as permanent gases or even molten metals come to mind. One will again be facedwith the determination of the nuclear properties of the possible coolants. I n addition an entirely new uranium jacketing procedure must be worked out, taking into consideration the elevated operating temperatures and the chemical action of the cooling agent. I have said little in this discussion about future problems in the chemical separations plants. I n the plutonium production plants the uranium will have to be reprocessed a t intervals in order to extract the plutonium. Even in pure power plants operating, for example, on plutonium it may be necessary from time to time to shut down and to clean out the "clinkers" by reprocessing the plutonium. For each different
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type of pile or mode of operation a modification of the chemical extraction process would be required. Atomic Energy Industry of the Future. We have reviewed the problems of the atomic energy industry. It is fitting that the discussion close with a forecast of the future prospects. An excellent report has recently been drawn up by the Research Committee of the Northern California Association of Scientists, and I shall draw upon this for much of the following data. In the first place what are the possible foreseeable industrial applications of atomic energy other than power? There is the manufacture of special materials-the radioactive tracers which can be made in hitherto unknown quantities and which give such promise in furthering all branches of scientific research. In attempting to assess the commercial value of these radioactive substances which can be made in a pile, one is forced to the conclusion that a t the present time their manufacture would not in itself pay for the construction of a pile and processing plant. That is not to say that industries may not use these substances in actual manufacturing process control as well as for research but only that a t the present time one could probably not construct an atomic energy plant and write off the cost to this alone. It is my opinion, however, that these tracers will be produced in quantity as valuable by-products of the power plants and that a far as their true value to humanity is concerned the discoveries made through their use may far outweigh the good to he done by any new source of power. For example the radioactive form of carbon, CL4,can he produced in quantity in a pile. As many of you know, carbon is the element most characteristic of living matter. With carhon that virtually has a tag on it, the chemist, bio'chemist, and medical research men have one of the most important tools ever devised for studying the life processes, with all the implications that may have with respect to control of disease and food supply. The Power Industry. The manufacture of power by atomic energy does show promise of expanding the world's sources of energy. One should consider the possibility of atomic power's supplanting present means of power production or supplementing them in allowing power to be produced in hitherto inaccessible regions or for new purposes. I n contrast to the use of coal, once an atomic power plant has been constructed the amount of fuel which must be brought in for replenishment presents no transportation problem a t all. In the atomic power industry there will probably be two broad types of plants with respect to function. These are the primary plants' and secondary plants. The primary plants are best visualized as very large power units, up to one million kilowatts output, and which operate on uranium. These large plants would not only turn out power hut would also produce PuZ3# or UZa3. These plants would include chemical plants for separating$he PuZS*or UPSS. In the secondary Dower ~ l a n t sthe se~aratedPu23gor U233from the ~ r i mary plants would be consumed for power production.
I t so happens that for every kilowatt-hour of power produced in primary plants about one could be realized from the P u is~ the~ secondary ~ plants. One of the reasons for the distinction between primary and secondary plants is that the division fits into a possible plan for atomic energy control. The primary plants are termed unsafe because it is in these that large amounts of plutonium suitable for bomb production can be made. However, by suitable control of these primary plants, plutonium could he produced and dispensed in a denatured form, in which form it is rather unsuitable for bombs hut can he used in power plants. The secondary plants might be of smaller size than the primary units, and because they do not constitute a military threat, their operation could he relatively free of restrictions. Both secondary and primary piles would probably operate a t high temperatures; the coolant would heat some gas which in turn would operate a gas turb'me generating electricity. The electricity could then be transmitted as it is from any power plant. Estimates have been made of the cost of producing atomic power. They range from costs that will only compete with coal in those areas where it is expensive, say ten dollars per ton, to estimates that would have atomic power compete favorably with the cheapest present-day power. Both primary and secondary plants are power producers. Let us suppose that the primary plant is a one million-kw. plant which produces plutonium. This plant would he set up near some very large industrial area where the power would be sold a t or helow the prevailing cost in that vicinity. Then in the adjoining chemical plants the plutonium could be separated and sold to the smaller secondary plants. The secondary plant might be a 10,000-kw. unit, which is the power plant for a copper mine in Nevada or near the Arctic Circle or it might he the engine for a large ship. The question arises as to what price plutonium would have to be sold in order t o allow the primary plant to break even. If the primary plant is a large plant, it has been calculated that it could sell power a t four cents per kilowatt-hour, which would compete favorably with cheap coal and still sell plutonium a t a price that is not out of line with medium-price coal. When it is considered that there are many otherwise productive areas of the world where coal power may be considered very high priced, it is difficult to see how atomic energy can fail to be an important source of power. A word of explanation is in order for the statement that the economic production of power depends upon large power units. The relative economy in operating a large plant lies in the fact that the cost of the fixed installations may not increase much in going from a smaller to a larger plant. Also the inventory of fissionable material, such as plutonium, tied up in a pile is largely independent of power output and therefore is more economicallv used in a hiah-power ~ i l e . When a number of considerations of this sort are included in
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the calculations, one can arnve a t the low-cost figures energy as we know it now is definitely not a possibility. mentioned above. Perhaps the estimates are too op- However, ocean-going vessels could easily contain an timistic but at least they do show that the cost of atomic power engine. Perhaps in the more distant atomic power is not out of line with the cost of coal- future aircraft with virtually unlimited range will be produced power. powered by atomic energy engines since gasoliueFinally, a few words about the probability of mobile powered planes are even now being considered that power units. Since an atomic power plant must be would be so large and carry such huge fuel loads that equipped with a thick radiation shield, a light unit is the weight of an atomic power plant is being apnot possible. Thus an automobile powered by atomic proached.
