.    . .    .     .
 
 
 

 a. Rate of Growth of consumption
 b. Exponential Growth
 c. Doubling Time
 d. Energy, federal budget, salaries

 a. Need for conservation
 b. Fossil Fuels- coal, petroleum

         We have already gained an insight into the nature of matter by looking at the atom and the nucleus. We add another aspect of that search for understanding the nature of the world by examining the relationships of matter and energy. Even though we have attempted to separate the two ideas, it is too simplistic to really attempt to describe one without the other. We will see, before the end of our discussions, that perhaps the real entity to describe is matter-energy as the very essence of the universe.

        Newton insisted that mass was a fundamental characteristic of matter and a constant at that. This became a fundamental assumption on which we based our interpreations of various phenomena. But in fact we are aware of many exceptions to that rule. For example, if we shine a flashlight the mass of the flashlight decreases. If sunlight shines on a plant, it gains mass. Well, we could explain this in terms of the photon theory of light, but we are always brought back to that idea of mass and energy being related.

       1905 was Einstein's greatest year. He published papers on the Special Theory of Relativity, Brownian Movement, and the Photoelectric Effect. He also published a lesser known paper "Does the Inertia of a Body Depend upon Its Energy Content?" This really addressed the relationship of matter and energy.

        In a future chapter we will explore the Special Theory of Relativity at a later time. We recognize for now that one usually dwells on the mind-boggling concepts of time-dilation and length-foreshortening. But the result that Einstein thought was most significant was the relationship between mass and energy. Indeed it was, for it explains and predicts concepts that permeate all branches of science, medicine, and industry. The large scale release of energy by fission and fusion, whether in reactors or through weapon systems, typically focuses our attention on related social, political and economic issues. Here we will explore the development of nuclear fission and fusion, including modern nuclear power plants, Breeder Reactor Power Plants and the search for Fusion as a hopefully ideal source of power for mankind. As a sideline we will also examine the elementary nature of nuclear weapons from the same viewpoint. We are not so concerned with the specific technologies themselves as with the basic processes of fission and fusion from which these technologies are derived. Understanding the basic physics, apart from being interesting aspects themselves, can help us in assessing some of the local, national and global issues related to these topics.

        Perhaps we have some insight into the fact that matter and energy are related on a qualitative scale. When light which is frequently recognized as a kind of energy, can have the dual wave-particle nature, it is not inconceivable that matter might also be viewed as an energy form with its dual particle-wave nature. Einstein quantitified this for us when he showed that the total energy of a system depends on the observer, or that the total energy is the sum of the energy when at rest plus the energy of motion. He showed that this could be written:
 
 

where m is the rest mass of the object and 1/2 mv² is immediately recognized as the kinetic energy or the energy of motion. Note if you will, that me has the units of energy (Joules) just as the kinetic energy does. If we wish to get a perpective on this, the rest mass of a proton is 1.6 X 10^-27 kg. This would calculate to be 931 MeV (mega or million electron volts) of energy. This would be a far simpler unit of energy than our Joules, ergs or BTUs in use today. But, alas, this aspect of nature was not known when energy units were developed.

        We see that matter and energy are equivalent. Mass itself, by its very nature, contains energy. Consider the following: two identical pots of soup are weighed and found to have identical masses. Let one be heated to a higher temperature and the masses again compared. It will be found that the hotter soup, by the virtue of having a higher energy content, also now has a greater mass!

        When a proton and a neutron are brought in close proximity so that they combine to make a deuteron (isotope of hydrogen with one proton and one neutron in the nucleus) we note that the mass of the deuteron is less than the mass of the proton plus the mass of the neutronl This is an observed fact. The description of the reaction shows that as the proton and neutron are combined a gamma particle accompanies the formation of the deuteron. It has an energy of about 3.5 X 10^-13 Joules. It is convincingly consistent that the very difference in the mass of the resultantant nucleus is less in me by the amount of that gamma photons This difference is called BINDING ENERGY. To split the deuteron into the proton and neutron again would require the addition of exactly that same amount of energy that binds the nucleus together (3.5 X 10^-13 Joules ).

Nuclear masses can change due to reactions because this "lost" mass is converted into energy. For example, combining a proton (p) and a neutron (n) will produce a deuteron (d). If we add up the masses of the proton and the neutron, we get

 The mass of the deuteron is m_d = 2.01355 u

 Therefore the change in mass =

          An atomic mass unit (u) is equal to one-twelfth of the mass of a C-12 atom which is about
          1.66 X 10^-27 kg. So, using E=mc² gives us energy/u = (1.66 X 10^-27 kg)(3.00 X 10⁸ m/s)²(1eV/1.6 X 10^-19 J) which is about 931 MeV/u. So, our final energy is

          Thus we say that the quantity 2.24 MeV is the binding energy of the deuteron. It is the mass deficiency between the masses of the constituent parts and the total combined.

          We cannot join two protons as readily as the latter process joined the neutron and proton to form the deuteron. We experience a strong coulomb repulsion that tends to keep them apart. It is possible quantum mechanically for them to join at high temperatures. This is a small, but finite probability. we discuss  it when we explore fusion as a process. There is evidence that two protons can be joined to make a diproton, but this is so short lived, so unstable, that it worth mentioning for interest only. In general, the single proton is more of an exception than the rule. Other elements are typically  stable if the number of neutrons equals the number of protons, up to about Atomic Number of 20.  Remember (refer to  the Periodic Table attached) that what makes hydrogen hydrogen is the fact that it has one proton. What makes helium helium is that it has two protons.

        Some forms of helium have one or two neutrons, but what makes  it helium is that pair of protons. Similarly, all
isotopes of Lithiuim have three protons, all isotopes of Berylium have four, Boron has five, carbon has six and so on.
The  stable isotopes of  these  all have the same number of protons and neutrons.  The electromagnetic force on the protons tends to repel the protons. In hydrogen there is no problem. But as we build  up more complex nuclei, the resultant forces are additive. For example,  if there are five protons, each one repels the other five. Thus the repulsive effect on any one proton is much greater than it was with two protons and with only  their mutual repulsion. Consequently, the strong nuclear force, which is  short in range, is less effective. But the strong nuclear force also binds the neutrons as well as the protons. So, with  their addition into the nucleus, we have a more strongly binding system. The neutrons help to mediate the strong nuclear force. We need them there on the gross nuclear level to "smear" out the nuclear glue.

        The Table below shows some  various isotopes with their respective numbers of neutrons and protons.
As we see nuclei with more than about twenty protons, the number of neutrons needs to be increased even more to bind the nucleus together. The states of these nuclei can be explained again from the wave mechanics. It is not our intent here to get into the quantum mechanics, but it does identify certain stable isotopes. Above about Atomic Number 83, we find unstable or radioactive elements. It was the investigation of these elements that led to the understanding of nuclear disintegration and transmutation.

        We are interested in that Binding Energy quantity. Nore so, we can tell how strongly the nucleus is bound if we divide the total binding energy by the number of nucleons. This gives us the binding energy per nucleon. See the Figure below.

We should note the Binding Energy per nucleon plotted on the y-axis and the total number of nucleons (protons and neutrons) on the x-axis. This is called atomic weight. Near the top of the graph we can identify a relatively stable area, near Fe (iron). To the left of this point we need to add energy to break the nuclei apart into its components. But, we get energy out if we combine components to make larger nucleil We call this FUSION. To the right of Fe we need to add energy to combine nucleons to make something heavier. But if we break it up, we get energy out of it! This is called Fission.

         Historically, we can look back to Enrico Fermi as one of the major contributors to quantum theory and our knowledge of  nuclear processes. In 1927 he was a Professor of Theoretical Physics at the University of Rome. He had been dubbed the name "pope" because he espoused the new faith - quantum theory. One of his  interests was to create new isotopes through the bombardment of materials. The neutron did  not have to overcome any coulomb (electromagnetic) barrier to enter the nucleus. This was a critical key to getting into the nucleus and making things happen. He worked on everything available, including uranium.

        It seems that sometimes major discoveries happen by chance, such as the discovery of pennicillin by Fleming. But usually such findings are made because the researcher is prepared for it. This happened here too. During an experiment Fermi noticed that the level of resultant radioactivity depended upon the surroundings. So a lead shield was placed around the-target uranium sample to alter the environment. Of course the neutron "bullets" were slowed down considerably. But the radioactivity increased a hundred fold! He hypothesized that this would happen if the sample were immersed in water. Now in Rome there seems to an availability of fountains and the story tells us that Fermi actually did the experiment in the backyard fountain with his predicted results. The conclusion was that the uranium nucleus could swallow slow neutrons easier than fast ones and in the process emitted an electron. We call this Beta decay. But it was observed that the resulting nucleus now had one more proton than before. i.e.; instead of 92 protons which was uranium, it had 93 protons. It wasn't uranium any more. It was now what we have come to know as Neptunium. (Recall from Chapter 6, how a neutron can become a proton with resultant beta decay to preserve charge.)

        Fermi announced this result, but neither he or anyone else was able to identify the process that really took place. The product was in fact still radioactive and thought basically to be still be uranium. What happened is that within the nucleus, the neutron transformed into a proton. To conserve charge, a beta particle, (electron) was also ejected. Along with this, unknown in nature, was the neutrino. Fermi recognized that momentum was not conserved in the process and hypothesized that "a little neutral one", or the neutrino (in Italian) was also emitted.

        It is also possible for the reverse process to occur. The proton may change into a neutron and emit a + charged Beta particle, or a positron. Accompanying this decay is another neutrino. Actually, for the former decay, neutron to proton with electron emmission, an anti-neutrino is given off and the actual electron neutrino is given off in the latter process. Note that charge and total mass number are conserved.

         You may recall that the weak nuclear force is responsible for the Beta decay and similar processes. For now, let us revisit the uranium targeted by the. neutrons. It was at Christmas time in 1938 that Hahn Meitner and Frederic Stassmann demonstrated that when uranium was bombarded with slow neutrons, one of the decay products was an isotope of Barium. Some processes that might take place are:

        Uranium actually has three stable (???) isotopes, U-234, U-235, and U-238. Only a trace is U-234 and less than a percent is U-235. Most of it, about 99% is U-238. It was found that it takes extremely energetic neutrons to make U-238 split. U-235 is the isotope that undergoes fission with slow neutrons. The U-235 captures the slow neutron, transforms into radioactive U-236 which is highly unstable and almost immediately ruptures into Barium-138 and Krypton-95. Note that two additional neutrons are produced. This provides an avalanche of neutrons if they react with other nuclei. In a small fraction of a second, 76 generations can be processed. If we raise two to the 76th power, we get about 10²³ nuclei that have been shattered! At only 3 X 10^-13 Joules per event, we have produced enough energy equivalent to about 20 thousand tons of TNT:

        There are other kinds of fission processes that can result from the bombardment of Uranium with slow neutrons.
Which process occurs depends on the energy of the neutron "bullet". It should be noted that these processes also gives off two or three neutrons (as well as the initial slow neutrons). These neutrons are not necessarily slow. In fact they have an energy of about 2 MeV!They would need to be slowed down to be effective. If the two neutrons as well as the original neutron that caused the fragmentation to occur can be used for successive reactions, we have a chain-reaction.

        Enrico Fermi led the team that built the first nuclear reactor, a controlled chain reaction machine. This reactor was built during the early days of World War II. The need to beat the Germans in constructing a nuclear weapon system was a priority project. Called the Manhattan Project, the successfull reactor was built under the stands of the football field at the University of Chicago. This writer remembers well the plaque that remained there commemorating the event. It was successfully run, under Fermi's direction, on December 2, 1942. It was a simple device with the uranium inserted into bored-out bricks in a pile. (The term pile is stilled used) To keep the reaction from "running" away out of control, cadmium rods were inserted to absorb the neutrons. If too many were produced, the cadmium would absorb them by inserting the rods. If too few were produced, pulling the rods out a bit would increase the reaction rate.

        Fermi still pursued his idea of adding neutrons (no electromagnetic repulsion to overcome) to the nuclei. When he added it to U-238 (remember that U=235 is used for the above fission reaction) U-239 is produced. This is highly unstable. It decays spontaneously into Neptunium and an electron (Beta decay described above) which spontaneously decays into Plutonium and another electron. This is another fissionable material, like U-235. It should be recognized that most of the Uranium is U-238 which does not readily fragment in the fission process. U-235 does. But it can be readily converted into Plutonium. In fact, in 1943 and 1944 three water cooled reactors were built just to produce Plutonium. This requires the U-235 ,.a small fraction of the total uranium available in the sample to produce fast neutrons. These fast neutrons then react with the U-238. More Plutonium is produced than U-235 consumed: This becomes the basic process that makes Breeder Reactors work.

        Breeder Reactors are not a reality in the United States today. Most of US nuclear engineers have gone to France, taking the United States' technology with them. France has embarked on an energy program dependent upon Breeder Reactors. One needs to consider the fact that the U-238 is unusable in the kinds of power plants in operation in the Unbited States. There is "...in the United States today, . . , 200,000 tons of depleted uranium. If used as a fuel for breeder reactors, that uranium is equivalent to the entire known coal reserves of the United States." (Technology & Society, Fall 1981) It sounds simple, just build breeder reactors and use the fuel we have already stored, ready to use. We would never have to tear up another shovel of Wyoming's land. to get coals This is an important consideration to ponder before one takes an adamant position against breader reactors. The environmental considerations are not simple. Weighing cost (not necessarily in dollars) vs. benefit is difficult. One must not approach it with blinders on.

         There are problems, with both coal and breeder reactors. With coal, a 1000 Mega-watt power plant must use 3 million tons of fuel per year, about 100 railroad cars per day! That releases into the atmosphere about 8 million tons of carbon dioxide and 50,000 tons each of nitrogen based oxides and oxides of sulfur which both combine with available water vapor to make acid compounds. In the past 10 years, NSP (now called Excel) has spent (paid by consumers, who else) about $300 million in Minnesota to improve the emissions to this "low" level. The problems with nuclear plant cannot be overlooked. The waste problem is the least understood and most misunderstood apsect of nuclear power. The radiation problem is reasonably well understood, but not by the public. We address both of these issues in the next unit, Nuclear Waste Management. Here we still are interested in the nuclear processes used in power plants and weapon systems.

        The standard nuclear power plant in use today in the United States produce electric power in the same way the coal fired plant does. Perhaps the process is antiquated, but it works and is cost effective. The fuel, whether it be coal or nuclear, makes heat. The heat is used to make steam. The steam turns a turbine, which produces electricity, just like the automobile engine turns a generator or alternator to make electricity for your battery. Look at the picture below:

        The reactor can be started, controlled and stopped by the control rods that are used to absorb neutrons. To start it up, merely remove the rods. To stop it, replace them. The reactor is typically surrounded by two containment vessels which considerably decreases any chance of problems from meltdown. Meltdown is the situation that would happen if a reactor went out of control, developed such high temperatures ,that it melted completely through the reactor vessel and containment structures and far enough into the ground to be carried away by ground water. This has never happened. It probably wont because of safety devices installed in the plants. There is evidence (worst case scenario) that an actual nuclear reaction took place naturally about 1.5 billion years ago in West Africa. It is comforting to note that the evidence suggests that the radiation did not spread as some person feared that it.might from a meltdown. The problem of meltdown is being studied actively today so it can be better understood.

        Note that the water that is drawn in to the plant and sent back to either the atmosphere or the river from which it came does not ever come in contact with radioactive contaminants. It is, however, hotter than when it entered the plant. It is curious to note that, for example, some of the best fishing in Minnesota is that area below the nuclear power plant near Red Wing. The environmental effects do not appear to really be hazardous, and in fact may even be beneficial. The DNR's main concern is for the number of fish being caught rather than their quality.

        There are two major types of reactors used in the United States:

Boiling Water Reactor - The BWR reactor typically allows bulk boiling of the water in the reactor. The operating temperature of the reactor is approximately 570F producing steam at a pressure of about 1000 pounds per square inch.

In the figure above, water is circulated through the Reactor Core picking up heat as the water moves past the fuel assemblies. The water eventually is converted to steam. The steam then passes through the Main Steam Lines to the Turbine-Generators.  In the sketch above there are 3 low pressure turbines, as is common for 1000 MWe plant, a typical sized plant. The turbines are connected together. The Generator produces the electricity, typically at about 20,000 volts AC. This electrical power is then distributed to a Generator Transformer, which steps up the voltage to either 230,000 or 345,000 volts. Then the power is distributed to a switchyard or substation where the power is then sent to the consumer. The steam, after passing through the turbines, then condenses in the Condenser, which is at a vacuum and is cooled by  river water. The BWR is unique in that the Control Rods, used to shutdown the reactor and maintain an uniform power distribution across the reactor, are inserted from the bottom by a high pressure hydraulically operated system. The BWR also has  a Suppression Pool which is used to remove heat released if an event occurs in which large quantities of steam are released from the reactor. The plant in Monticello, MN uses this design.

Pressurized Water Reactor:

These reactors were originally designed by Westinghouse for military  applications. The first commercial PWR plant in the United States was Shippingport, which was located near Pittsburgh, Pennsylvania.
 Refuelings must be done with the plant shutdown.

The Pressurized Water Reactor (PWR) has 3 separate cooling systems. Only 1 is expected to have radioactivity - the Reactor Coolant System. The Reactor Coolant System, shown inside the Containment, consists of 2, 3, or 4 Cooling "Loops" connected to the Reactor, each containing a Reactor Coolant Pump, and Steam Generator. The Reactor heats the water that passes
upward past the fuel assemblies from a temperature of about 530F to a temperature of about 590F. Boiling.  Pressure is maintained at approximately 2250 pounds per square inch through a heater and spray system in the pressurizer. The water from the Reactor is pumped to the steam generator and passes through tubes. The Reactor Cooling System is expected to be the only one with radioactive materials in it. Typically PWRs have 2, 3, or 4 reactor cooling system loops inside the containment. Cooling of the steam is provided by Condenser Cooling Water pumped through the condenser by Circulating Water Pumps, which take a suction from water supplied from the river, or Cooling Tower.

    Under appropriate operating conditions, the neutrons given off by fission reactions can "breed" more fuel from otherwise non-fissionable isotopes. The most common breeding reaction is that of plutonium-239 from non-fissionable uranium-238. The term "fast breeder" refers to the types of configurations which can actually produce more fissionable fuel than they use, such as the LMFBR. This scenario is possible because the non-fissionable uranium-238 is 140 times more abundant than the fissionable U-235 and can be efficiently converted into Pu-239 by the neutrons from a fission chain reaction.

    In the breeding of plutonium fuel in breeder reactors, an important concept is the breeding ratio, the amount of fissile plutonium-239 produced compared to the amount of fissionable fuel (like U-235) used to produced it. In the liquid-metal, fast-breeder reactor (LMFBR), the target breeding ratio is 1.4 but the results achieved have been about 1.2 . This is based on 2.4 neutrons produced per U-235 fission, with one neutron used to sustain the reaction.

    The time required for a breeder reactor to produce enough material to fuel a second reactor is called its doubling time, and present design plans target about ten years as a doubling time. A reactor could use the heat of the reaction to produce energy for 10 years, and at the end of that time have enough fuel to fuel another reactor for 10 years.

Liquid Metal Fast Breeder Reactor

    The plutonium-239 breeder reactor is commonly called a fast breeder reactor, and the cooling and heat transfer is done by a liquid metal. The metals which can accomplish this are sodium and lithium, with sodium being the most abundant and most commonly used. The construction of the fast breeder requires a higher enrichment of U-235 than a light-water reactor, typically 15 to 30%. The reactor fuel is surrounded by a "blanket" of non-fissionable U-238. No moderator is used in the breeder reactor since fast neutrons are more efficient in transmuting U-238 to Pu-239. At this concentration of U-235, the cross-section for fission with fast neutrons is sufficient to sustain the chain-reaction. Using water as coolant would slow down the neutrons, but the use of liquid sodium avoids that moderation and provides a very efficient heat transfer medium.

    France has made the largest implementation of breeder reactors with its large Super-Phenix reactor and an intermediate scale reactor (BN-600) on the Caspian Sea for electric power and desalinization.

       Often, when we hear nuclear we immediately think of "bomb" and it is not without good reason that we do so. While controlling a self-sustaining chain reaction has some prospects useful to mankind, any rapid release of energy has always had the application as a weapon system. Realizing that even though conventional weapons kill as "dead" as nuclear weapon systems, we still find nuclear weapons more objectionable. Again, it is not our purpose to elaborate on the ethics, economics, or strategic military advantages of such systems, but rather to understand the science behind their operation.

        The research, and in particular the Manhattan Project was designed to allow the development of more powerful weapon systems. World war II was awesome as far as wars go. It is mind boggling to consider the "waste" of energy sources in gasoline, the waste of materials as airplanes, ships and jeeps were destroyed in vast numbers, and the dramatic loss of life and limb. Yet fear and determination led scientists on to develop the biggest bombs yet.
 

The first nuclear bomb, called the A-bomb or atom bomb was called the "Thin Man". It, in size, was about 28 inches in diameter and 10 feet long. It weighed about 9,000 pounds, so in size it was reasonably conventional. But in the way it worked was very different. It used U-235 in large enough quantity to yield a massive amount of energy. We realize that slow neutrons can readily cause the fragmentation or fission of U-235. One problem arises when the number of slow neutrons that escape exceeds the number produced in the reaction. The reaction would die out unless a CRITICAL MASS is there, enough uranium so that the neutrons react with surrounding uranium before they escape. In the Thin Man, the critical mass is achieved by a three foot long cannon firing (conventionally) one part of the uranium into the other forming the critical mass. This bomb was dropped on Hiroshima, August 6, 1945. About 100,000 people died from the result of this explosion, either directly from the impact, or indirectly from the radiation. It is interesting to note that a study described in the McGraw Science Encyclopedia indicates that outside of a 2 kilometre radius of the impact that the numbers of leukemia (cancerous) incidents approached that of the normal population. One should note too, that more people than this were killed in the Tokyo fire raids led by Curt LeMay. What was so awesome was that this was only one bomb and it was directed at a population center.
 

"A bright light filled the plane," wrote Lt. Col. Paul Tibbets, the pilot of the Enola Gay, the B-29 that dropped the first atomic bomb. "We turned back to look at Hiroshima. The city was hidden by that awful cloud...boiling up, mushrooming." For a moment, no one spoke. Then everyone was talking. "Look at that! Look at that! Look at that!" exclaimed the co-pilot, Robert Lewis, pounding on Tibbets's shoulder. Lewis said he could taste atomic fission; it tasted like lead. Then he turned away to write in his journal. "My God," he asked himself, "what have we done?" (special report, "Hiroshima: August 6, 1945")

For interested individuals, it would be advisable to contact some of the following:

Committee on International Security and Arms Control, National Academy of Sciences

Hearings on The Changing Strategic Landscape of Nuclear Policy

GLOBAL ACTION TO PREVENT WAR: A COALITION-BUILDING EFFORT TO STOP WAR, GENOCIDE, & INTERNAL ARMED CONFLICT

        Their literature describes the deterrent policy of the United States, historical perspectives and the latest initiatives.  Anti-nuclear sources will play down or ignore the benefits of nuclear technology while amplifiying its drawbacks and risks. (Many make no distinction between nuclear weapons and nuclear energy). Pro-nuclear sources will concentrate on the benefits.

        We noted that through nuclear fission the fragmentation of a heavy nucleus yielded energy. In the case of fusion, however, it is the joining together of two lightweight nuclei that yields the energy. If one refers to the Binding Energy per Nucleon curve (earlier) we can see how strongly a nucleus is bound. Note that by fusion we can form nuclei with atomic numbers up to about Fe (iron). Beyond that, it takes significant amounts of energy to nucleosynthesize heavier elements. In nature, which prefers events which liberate energy rather than requiring energy (eg. a ball rolls downhill rather than uphill) the nucleosynthesis of the elements heavier than iron take place in a supernova event. For that brief moment when a star heralds its glory, it shines as bright as an entire galaxy. Note that the amount of heavy materials is relatively less than for the lighter materials that are made (albeit in stellar interiors) in normal events. A simple fusion operation results from the combination of two deuterium nuclei:

    This is not a very likely (probability is somewhat low that it will take place) reaction. One that is more favorable is one that produces other products and in a series of steps may produce the Helium. In the center of our Sun, the PP (Proton-Proton) Cycle takes place:

        This is only the PPI  cycle. Similar cycles (PPII and PPIII) can also take place. Any of them use four protons  to produce a Helium-4 nucleus. Both the fission and fusion processes release energy. But there still is a significant difference - the fission process actually can use the repulsion of the positive charged nucleons to help the reaction whereas the fusion process is somewhat hindered by the mutual repulsion of the nuclei to be joined. This means that they have to be sent together at relatively high speeds. The coulomb repulsion of two protons, the simplest situation, is of the order of 1000 KeV of energy. Even at 10 million Kelvins, the thermal energy of the particles is only about 1 KeV. That's a thousand times less than would be needed to overcome the barrier. Still, quantum mechanically, it has a chance to penetrate the barrier resulting from the mutual electromagnetic repulsion.

        It turns out that the probability is actually better for small charged particles than for those with higher charges. In any case, it makes it possible to happen. We think that nuclear fusion goes on in the sun, we can make it happen in an uncontrolled burst such as a hydrogen bomb, and we are trying to control that combination to produce a clean, essentially unlimited source of energy.

        It should be noted that basic research in this area is continuing. Our congress spends very little for research into fusion energy and alternative enrgy generation. It will take a major effort if we expect not only to be international leaders, but to become energy independent. It would seem that if we were capable of mounting enormous assault on space culminating in the lunar missions in less than a decade, that this too could be a reality if the priorities were clear.

        During World War II the atomic bomb was developed and used.. A concurrent development was the Hydrogen Bomb or simpy H-bomb. It was based on hydrogen fusion. This development was lead by Dr. Edward Teller, the father of the H-bomb. It was never built, even though it would release much more energy than would the A-bombs. There didn't seem to be a need until in August of 1949 the Soviets detonated their first atomic bomb, uranium based. Even though it was crude, their possession of a comparable weapon system even if the delivery of the weapon could not be accomplished, frightened us. We are very concerned about national security. This led the United States to further develop the hydrogen bomb. It was detonated at Eniwetoh Atoll in the Pacific on November 1, 1952. The Soviets detonated their first one about a year later. The arms race is still on.

        The H-bomb utilizes the principles of hydrogen fusion. It essentially combines hydrogen nuclei to make helium. In the process, energy is released. Vast amounts of energy are released. Look at the Binding Energy per nucleon curve. See how steep it is at the far left where the smaller particles are located. For each nucleon involved the rate of energy production is phenomenol. The basic processes involved are:

        The clever stroke of genius that made it possible was to carry a source of tritiumin a stable manner and then to raise the system to a high temperature, about 10 million degrees. Teller discovered that the cheap and stable Lithium could in fact yield the tritium for use in the fusion process. To get the temperature needed, a nuclear A-bomb was used. It was not a particularly powerful one, but enough to raise the temperature to the required level. Thus the name thereto-nuclear bomb was coined. Today the amount of energy available in nuclear weapons exceeds that required to destroy all life on the earth. Whether they can be delivered to a target is another completely different story.

        There are two process that are being developed to use nuclear fusion for commercial electric power generation. These two processes are still in the developmental stages. They are called laser fusion and magnetic confinement.

       Laser fusion is essentially a simple process. This is also called Inertial Confinement Fusion. One gathers small sphere of hydrogen and forces the fusion by bombarding the pellets with a burst of laser energy. This requires twenty laser pulses that deliver about 200 kilojoules of energy in a nano second. A nano-second is one billionth of a second. That means the rate of delivering the power is  greater than the entire United States electrical power generation capability! This process is being examined at Lawrence Livermore Labs in Berkely, California. It has promise, but has not yet been successful. We need a way to get the temperature needed to get the fusion started. Getting this to happen is not like burning fuel in a furnace. We need to be able to hold and confine the fuel and ignite it so it will produce energy.

        The Tokamak (a Russian word) seems to offer the most promise. It is somewhat of a problem to contain a "soup" at 10 million degrees temperature. You cant use a simple beaker or even the strongest furnace. The Tokamak utilizes a donut shaped torus where the magnetic field actually keeps the plasma confined. We don't have atoms at this temperature. We have a plasma or soup of protons and electrons. It is kept at a high density to be effective. The energy goes into the magnetic field which in turns develops the proton currents. The one at Princeton has been successful in generating 7.5 X 10 Kelvins for 100 ms. It has reached a break even point where it actually produced more energy than it consumed. Perhaps in twenty or thirty years we will see one of these on line in the United States. Operate your own (virtual) Tokamak.

        Fusion electrical power generation offers the best hope for mankind's energy needs. Electrical power is clean and if produced by fusion can be extraordinarily economical. Water could be the source of protons (sea water from the oceans) and the resultant products are not carcinogenic or radioactive. Helium is inert. It doesn't react with anything. We could use it at Fermi lab for the cooling of the superconducting magnets in the main accelerator ring. They already use about half of the world's supply.

      "Twinkle, Twinkle, Little Star. How I wonder what you are?" (sound version) That's a good question. We are thoroughly convinced that nature produces energy in the stars through nuclear fusion. We have learned much of today's store of knowledge on nuclear physics from the sun, a typical star.

        There are several processes that are possible in the stars, depending on whether the star is a main sequence star (normal), a red giant, or what. In general, the stars are the source of all the elements in the universe. our solar system, our planet, and indeed ourselves are merely made of materials that came from stars that have already died and contributed their matter to us.

        The normal stars, and about 90% of the stars are probably in this category, fuse hydrogen to make helium. The core of our sun is largely hydrogen which is being converted to helium through the P-P cycle. All main sequence stars
convert protons or hydrogen nuclei to helium. It takes four protons to make one helium nucleus. In the process, energy
is liberated and radiated from the sun's surface in the form of electromagnetic energy. The sun acts like a black body
giving off energy in the total black body spectrum. It acts like a 5800 Kelvin black body with its maximum intensity at
about the color of yellow. Perhaps that is why our eyes are most sensitiove to yellow.

        It is also possible for main sequence stars to produce helium from four hydrogen nuclei (protons) by using carbon as a catalyst. A catalyst is a chemical that acts in the reaction and ends up there after the conversion has taken place. In other words, it is used, but replenished in the process. The very bright stars, like Sirius A, the dog star, is one of these. It has some carbon in it for this carbon cycle which like the P-P cycles stil converts four protons into helium. But it reacts at hotter temperatures than sun-like stars.

        Red giant stars are cooler. In about five billion years (don't worry about it) our sun will complete its hydrogen conversion to helium and will expand to about Mars orbit. Yeah, it will consume the earth. Since the sun is a gas, the earth will probably continue to revolve about the center of the sun until it becomes a crisp. Anyway, its core will eventually gravitationally collapse and reach a temperature of about 100 million kelvins and start the conversion of helium into carbon. It will require three helium-4 nuclei to make a carbon nucleus. Usually after this stage of evolution the sun-like star will become a white dwarf which neat in itself. others, far more massive will become novas or supernovas and share their matter with the rest of the galaxy.

        The world of energy and matter is interesting. It is exciting and once we understand it, we no longer have to fear it. Properly controlled, it can help mankind; abused and it may lead to our destruction.
 
 

Chernobyl:

     Nuclear accidents have typically been avoided by wise planning in design and operation of nuclear plants. Nearly 90% of the electric capacity of France is produced from nuclear sources. In the United States it makes up a small part of the total electricity produced from Coal fired plants, natural gas, hydroelectric, etc. But the record has been marred by some accidents. The worst accident on record is the Chernobyl Event.

See The nuclear reactor accident at Chernobyl, USSR, byt Bernard L. Cohen, December 1987 American Journal of Physics. In it Professor Cohen explains the differences between US and Soviet built nuclear power plants, why the explosion ocurred, and why it is unlikely that such an event would take place in the United States. This will be placed on e-Reserves in the library for your usage.
 

Incomplete..  See:   Chernobyl: The Accident and Progress Since 1986

Managing Nuclear Waste Materials:

        What is considered to be "Nuclear waste"? Basically, dependent upon how intense the radiation source and the time for it to become essentially harmless to human beings, are the criteria to be used for classifying radioactive materials as low or high level waste.

       High level waste (HLW) is the type of waste generated by nuclear power plants. It  contains uranium byproducts, is very harmful to humans and other life forms, and has a half-life of about 10,000 years. It is considered to include the fuel assemblies, rods and waste separated from the spent fuel after removal from the reactor. In the 1960's when nuclear power offered a "clean" alternative to coal and a promise of cheap unlimited energy, many utilities purchased plants when they thought that they would be shipping the spent fuel for reprocessing after the fuel had been stored in the plant storage pool for 6 to 18 months. However, no reactors in the United States have been purchased since 1974.  This has largely been a political football. No president, Republican or Democrat, and no congress, has been willing to take the needed leadership to develop a national repository. (Yucca Mountain in Nevada is being considered. See below) Currently the spent fuel is stored at the nuclear power plant sites in storage pools or in large metal casks. In some cases, plants have had to re-design and modify the storage pools up to 2 times in order to keep running the plant. In Minnesota this has become a legislative focus and led to development of some wind power plants as a compromise to allow on site storage. The real question is how dangerous is it to store the materials on site?

        All nuclear plants have storage pools for spent fuel. These pools are typically 40 or more feet deep. In the bottom 14 feet are storage racks designed to hold fuel assemblies removed from the reactor. It should be noted that only 8 feet of water is needed to lower the radiation levels, the extra depth is a safety cushion. In many countries, the fuel assemblies, after being in the reactor for 3 to 6 years, are stored underwater for 10 to 20 years. The water serves 2 purposes:

   1.It serves as a shield to reduce the radiation levels that people working above may be exposed to.
   2.It cools the fuel assemblies that continue to produce heat (called decay heat) for some time after removal.

        Dry casks are used for storage at some locations in addition to the pools. Again, these are intended to be temporary until a federal repository is built.  In Minnesota, because the pools at the Prairie Island Plant (near Treasure Island Casino) are full, excess storage is needed. Under current legislation, Northern States Power Company may continue to store its spent  fuel at the Prairie Island power plant. The 1994 legislation allows up to 17 storage casks at  the site. Northern States Power Company (now called Excel) estimates that it will use up this capacity by 2002. Another crisis looms on the horizon.

Low Level Wastes (LLW) is the type of waste produced by medical uses, such as X-rays, or some manufacturing processes. Compared to high-level radioactive waste, it has much lower radiation levels and a much shorter half-life — 90 percent of the atoms become  harmless in 100 years.  It comes from from hospitals, ion exchange resin from reactor coolant treatment, etc.

Options for Disposal:

         For disposal of HLW there are some options. They are technical ooptions, all feasible to some degree. Deep geologic disposal allows the materials to be stored out of sight for a long time. It is costly, perhaps the most expensive alternative, but the preferred option at this point. One could merely store the material in large casks above ground and put a fence around it. The casks would be too large to be moved or taken by terrorists. Radioactive fuel sources were that way. They were brought together by human mining. They could merely be dispersed again as the cheapest way to dispose of it, especially into the ocean. But this prevents retrieval if needed later and there is always the concern in the back of one's mind that a fish might eat some of this and... Yet this is still statistically not an unreasonable method of disposal. It is not popularly accepted. Another alternative would be to launch it into outer space. That has the greatest risk if an accident were to take place on launch and it certainly would not be retrievable.

        The methods of choice include for. LLW - shallow land burial in regional compacts (agreements between states in a region). Each state will share in the costs and risks and each state agreed to take its turn. For  HLW - deep geologic storage.

        At a  US Nuclear Regulatory Commission Meeting in 1998, commissioners considered establishing a federal repository. Without regard to promoting or demoting the value nuclear power, the fact remains simply that we do have HLW to deal with.  It is consensus that a federal repository rather than individual states dealing with HLW makes more sense.

        Other sites include geologically stable areas. Statistically, if a place has been geologically stable, i.e., no recent (past 50,000 years) volcanic or tectonic movements, it probably will be stable for another 20,000 years. A flat topography will minimize groundwater gradients.If there are layered, or sedimentary geologic strata, chemical movements between layers are retarded. If old (very old) groundwater is found in the area, then it is suggestive that it doesn't move very much and probably won't do so in the future. The area needs to be in an arid region, not susceptible to glaciation. All these features minimize the probability of radioactive materials getting into groundwater, then transported to populated areas and finally consummed by humans. Salt mines in Louisiana, even the granite structures of northern Minnesota have been considered. But every place seems to typify the NIMBY (Not In My Back Yard) syndrone.

        An additional barrier to problems comes from dissolving the HLW into ceramic spherical pellets (about the size of a marble, and placing these in stainless steel storage containers about 24 inches in diameter and ten feet long. The federal repository will store about 13,000 of these containers. The stainless steel containers are to be placed in concrete vaults. The multiple level of protection minimizes risk to human population. Statistically, no system can reduce the probablity of risk to zero. But understanding risk makes it feasible to decide a plan of action. These containers are retrievable in the event that new technologies can make the use of the radioactive materials attractive in the future.

        Technical problems for disposal of HLW are few if any. The political, societal and philosophical problems are many. Uninformed people make decisions based on fears. Not only with nuclear waste, but in many other facets of life, people express NIMBY. LLW is recognized as a state, not a federal responsibility. regional compacts are already in place.

        Other nations have their own methods of handling both HLW and LLW. There is no international agreement of standards or methods of disposal. Sometimes, the final decisions becomes economic rather than environmental. Members of the IAEA have established some guidelines. It needs to be noted that while a small portion of the power in the United States is produced from nuclear sources (5 %) as much as 1/5th of the world depends on nuclear power for its electricity. In areas where coal or hydroelectric sources are not readily available it might be the the only reasonable alternative.

Decommissioning of Nuclear Plants:

        All good things must come to an end. No matter what safety record or what cost savings have been achieved, nuclear power plants eventually must be shut down. To date, 18 have been decommissioned in the United States. In general, the fuel products are still stored on site.

1. Nuclear Waste Management, NSF Chautauqua Course, Argonne Nations Laboratories.
 

2. NSP Pamphlet - Nuclear Power,
 

3. Keenan, Thomas, Radioactive Waste Management, Michigan State University, 1917.
 

4. Bartlett, Albert A, "Forgotten Fundamentals of the Energy Crisis", American Journal of Physics, 1978.

5. Cohen, Bernard L., "The nuclear reactor accident at Chernobyl, USSR", American Journal of Physics, Dec 1987.