Three exothermic processes release nuclear energy: - 1) Radioactive decay, where a proton or neutron in the radioactive nucleus decays spontaneously by emitting a particle 2) Fusion, two atomic nuclei fuse together to form a heavier nucleus 3) Fission, the breaking of heavy nucleus into two nuclei Radioactive decay It is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide. For example: a carbon-14 atom (the "parent") emits radiation and transforms to a nitrogen-14 atom (the "daughter"). This is a random process on the atomic level, in that it is impossible to predict when a particular atom will decay, but given a large number of similar atoms, the decay rate, on average, is predictable. The trefoil symbol is used to indicate radioactive material. The danger classification sign of radioactive materials The SI unit of radioactive decay (the phenomenon of natural and artificial radioactivity) is the becquerel (Bq). One Bq is defined as one transformation (or decay) per second. Since any reasonably sized sample of radioactive material contains many atoms, a Bq is a tiny measure of activity; amounts on the order of TBq (terabecquerel) or GBq (gigabecquerel) are commonly used. Another unit of (radio) activity is the curie, Ci, which was originally defined as the activity of one gram of pure radium, isotope Ra-226. At present it is equal (by definition) to the activity of any radionuclide decaying with a disintegration rate of 3.7 × 1010 Bq. The use of Ci is presently discouraged by SI. Nuclear Fission An atom's nucleus can be split apart. When this is done, a tremendous amount of energy is released. The energy is both heat and light energy. Einstein said that a very small amount of matter contains a very LARGE amount of energy. This energy, when let out slowly, can be harnessed to generate electricity. When it is let out all at once, it can make a tremendous explosion in an atomic bomb. The word fission means to split apart. Inside the reactor of an atomic power plant, uranium atoms are split apart in a controlled chain reaction. In a chain reaction, particles released by the splitting of the atom go off and strike other uranium atoms splitting those. Those particles given off split still other atoms in a chain reaction. In nuclear power plants, control rods are used to keep the splitting regulated so it doesn't go too fast. If the reaction is not controlled, you could have an atomic bomb. But in atomic bombs, almost pure pieces of the element Uranium-235 or Plutonium, of a precise mass and shape, must be brought together and held together, with great force. These conditions are not present in a nuclear reactor. The reaction also creates radioactive material. This material could hurt people if released, so it is kept in a solid form. The very strong concrete dome is designed to keep this material inside if an accident happens. This chain reaction gives off heat energy. This heat energy is used to boil water in the core of the reactor. So, instead of burning a fuel, nuclear power plants use the chain reaction of atoms splitting to change the energy of atoms into heat energy. The water from around the nuclear core is sent to another section of the power plant. In the heat exchanger, it heats another set of pipes filled with water to make steam. The steam in this second set of pipes turns a turbine to generate electricity. Nuclear Fusion Another form of nuclear energy is called fusion. Fusion means joining smaller nuclei (the plural of nucleus) to make a larger nucleus. In the process, some of the mass of the hydrogen is converted into energy. The sun uses nuclear fusion of hydrogen atoms into helium atoms. The easiest fusion reaction to make happen is combining deuterium (or “heavy hydrogen) with tritium (or “heavy-heavy hydrogen”) to make helium and a neutron. Deuterium is plentifully available in ordinary water. Combining the fusion neutron with the abundant light metal lithium can produce tritium. Thus fusion has the potential to be an inexhaustible source of energy. To make fusion happen, the atoms of hydrogen must be heated to very high temperatures (100 million degrees) so they are ionized (forming a plasma) and have sufficient energy to fuse, and then be held together i.e. confined, long enough for fusion to occur. The sun and stars do this by gravity. More practical approaches on earth are magnetic confinement, where a strong magnetic field holds the ionized atoms together while they are heated by microwaves or other energy sources, and inertial confinement, where a tiny pellet of frozen hydrogen is compressed and heated by an intense energy beam, such as a laser, so quickly that fusion occurs before the atoms can fly apart. Here is a more detailed analysis on the conditions that are needed for fusion: Temperature In order to release energy at a level of practical use for production of electricity, the gaseous deuterium-tritium fuel must be heated to about 100 million degrees Celsius. This temperature is more than six times hotter than the interior of the sun, which is estimated to be 15 million degrees Celsius. Confinement The required temperatures have been attained. The problem is how to confine the deuterium and tritium under such extreme conditions. A part of the solution to this problem lies in the fact that, at the high temperatures required, all the electrons of light atoms become separated from the nuclei. This process of separation is called ionization, and the positively charged nuclei are referred to as ions. The hot gas containing negatively charged free electrons and positively charged ions is known as plasma. Plasma Confinement Because of the electric charges carried by electrons and ions, a plasma can be confined by a magnetic field. In the absence of a magnetic field, the charged particles in plasma move in straight lines and random directions. Since nothing restricts their motion the charged particles can strike the walls of a containing vessel, thereby cooling the plasma and inhibiting fusion reactions. But in a magnetic field, the particles are forced to follow spiral paths about the field lines. Consequently, the charged particles in the high-temperature plasma are confined by the magnetic field and prevented from striking the vessel walls. Plasma Heating In an operating fusion reactor, part of the energy generated will serve to maintain the plasma temperature as fresh deuterium and tritium are introduced. However, in the startup of a reactor, either initially or after a temporary shutdown, the plasma will have to be heated to 100 million degrees Celsius. Ohmic Heating Since the plasma is an electrical conductor, it is possible to heat the plasma by passing a current through it; in fact, the current that generates the poloidal field also heats the plasma. This is called ohmic (or resistive) heating; it is the same kind of heating that occurs in an electric light bulb or in an electric heater. The heat generated depends on the resistance of the plasma and the current. But as the temperature of heated plasma rises, the resistance decreases and the ohmic heating becomes less effective. It appears that the maximum plasma temperature attainable by ohmic heating in a tokamak is 20-30 million degrees Celsius. To obtain still higher temperatures, additional heating methods must be used. Neutral-Beam Injection Neutral-beam injection involves the introduction of high-energy (neutral) atoms into the ohmically -- heated, magnetically -- confined plasma. The atoms are immediately ionized and are trapped by the magnetic field. The high-energy ions then transfer part of their energy to the plasma particles in repeated collisions, thus increasing the plasma temperature. Radio-frequency Heating In radio frequency heating, oscillators outside the torus generate high-frequency waves. If the waves have a particular frequency (or wavelength), their energy can be transferred to the charged particles in the plasma, which in turn collide with other plasma particles, thus increasing the temperature of the bulk plasma Scientists have been working on controlling nuclear fusion for a long time, trying to make a fusion reactor to produce electricity. But they have been having trouble learning how to control the reaction in a contained space. If we are successful, we will have an energy source that is inexhaustible. One out of every 6500 atoms of hydrogen in ordinary water is deuterium, giving a gallon of water the energy content of 300 gallons of gasoline. What's better about nuclear fusion is that it creates less radioactive material than fission, and its supply of fuel can last longer than the sun. Fusion would be environmentally friendly, producing no combustion products or greenhouse gases. While fusion is a nuclear process, the products of the fusion reaction (helium and a neutron) are not radioactive, and with proper design a fusion power plant would be passively safe, and would produce no long-lived radioactive waste. Design studies show that electricity from fusion should be about the same cost as present day sources. A lot of science and engineering had to be learned to get fusion to where we are today. Both magnetic and inertial fusion programs expect to build their next experiments that will reach ignition and produce more energy than they consume. If all goes well, commercial application should be possible by about 2020, providing humankind a safe, clean, inexhaustible energy source for the future. Accidents with Nuclear Energy Although Three Mile Island was a success story, the accident at Chernobyl, 20 years ago this month was not. But Chernobyl was an accident waiting to happen. This early model of Soviet reactor had no containment vessel, was an inherently bad design and its operators literally blew it up. The multi-agency U.N. Chernobyl Forum reported last year that 56 deaths could be directly attributed to the accident, most of those from radiation or burns suffered while fighting the fire. Tragic as those deaths were, they pale in comparison to the more than 5,000 coal-mining deaths that occur worldwide every year. No one has died of a radiation-related accident in the history of the U.S. civilian nuclear reactor program. (And although hundreds of uranium mine workers did die from radiation exposure underground in the early years of that industry, that problem was long ago corrected.) Arguments against nuclear energy There are many arguments, some related specifically to nuclear energy and others stemming from more general ideas about society. One of the more discussed arguments is with waste disposal. The problem of disposal of nuclear wastes hasn't been solved. There are several good technical solutions, but the political problem hasn't been solved in the U.S. Another topic would be the cost-benefit issue. The energy required building nuclear plants, operating them, and mine and process the uranium may be so large as to cause a net energy deficit. The basic fact about nuclear energy is that the input energy is 4.8 percent of output energy if gaseous diffusion is used to enrich uranium and 1.7 percent if the newer centrifuge technology is used. Another way of looking at the same facts is that if gaseous diffusion is used for enrichment, the energy invested in building the plant is paid back in 5 months, whereas if centrifuges are used the payback time is 4 months. Operational safety as well as safeguards in materials control are also huge issues for consideration as Radiation from operating nuclear reactors and other activities involved in nuclear energy is dangerous. Further, nuclear reactors produce plutonium, and plutonium is terrible because it can be used to make bombs. Safeguards are indeed needed. The Drawbacks to using Nuclear Energy Despite the fact that nuclear energy offers great benefits as an alternative source of electric power, nuclear energy as a whole, is still a controversial issue in many countries. The reasons for this center round the issues of safety, waste And nuclear weapons. Current state of nuclear energy Operating nuclear plants generate 20 percent of U.S. electricity, but no new plants have been ordered in a long time. The Electric Power Research Institute (EPRI) asked utility executives what would make them start ordering nuclear plants again. The 1994 December article reopening the Nuclear Option by John Douglas in the EPRI Journal gives their answers. It looks difficult but not impossible. "The plants must be simpler and have higher design margins and enhanced safety features; they must be economically competitive with other forms of generation; they must be standardized; and they must be prelicensed by the NRC." All this presumes that fossil fuels will continue to be available and not restricted too much by worries about global warming. If this changes, the requirements for new nuclear power plants in the U.S. will be greater. Remember that the U.S. is a special case politically and in the availability of natural gas and that other countries are still building nuclear plants. Future of Nuclear Energy In the last forty years we have seen nuclear energy take its place as a major source of electricity worldwide, on both economic and resource strategy grounds. Today the question of global warming focuses attention on the extent to which nuclear energy offsets it, and may increasingly do so in the future. At present nuclear power displaces nearly two and a half billion tonnes per year of carbon dioxide emissions worldwide relative to coal, that is to say if the 2400 TWh of nuclear electricity in 1999 were produced by coal, 2.4 billion tonnes would be the extra CO2 arising. Every 22 tonnes of uranium used for electricity saves the emission of about one million tonnes of carbon dioxide, relative to coal. Nuclear energy now provides over 16 percent of the world's total electricity. It has the potential to contribute much more, especially if greenhouse concerns lead to a change in the relative economic advantage of nuclear electricity, or its ethical desirability. In Australia, governments are reluctant to face up to the question of utilizing nuclear energy, because the issue is remote geographically, and certainly the coal industry would argue, with some justification, that it is far from urgent here. We are virtually the only developed country where, when you switch on the light, you are not getting some nuclear electricity to help lighten your way. Of course there is enormous appeal in the proposition that we should develop "renewable" technologies to harness more of the sun and the wind. I fully support such developments, and hope that we can do rather better than the official 2% target. However, we need also to recognize that such sources are intrinsically unsuited to providing base-load electricity, which requires reliable and continuous supply on a gigawatt-day (million kilowatt day), rather than kilowatt-hour, scale. Much electricity demand is for reliable, continuous supply, which simply cannot be met on any significant scale from intermittent and occasional sources such as wind and solar photovoltaic. For instance, Victoria requires more than 4 million kilowatts (GWe) of continuous base-load supply, and the further 3 GWe of fluctuating demand does not coincide with daylight hours or strong winds. In providing base-load electricity, uranium competes mainly with coal. I suggest that the large-scale use of natural gas for this purpose raises some major ethical issues in squandering such a valuable energy resource and hydrocarbon feedstock in that way. As you will be aware, in most countries electricity demand is increasing much faster than overall energy demand. This is partly because in many applications other than heating, using electricity increases efficiency and so means using less energy overall. Public debate about the virtues and threats of nuclear energy is about options for producing electricity. None of the options is without some risk or side effects. The obvious fact that nuclear power doesn't produce carbon dioxide is increasingly relevant to its role in the world's energy mix. In fact of course there is likely to be some carbon dioxide produced at various stages in the front end and the back end of the nuclear fuel cycle, the amount depending on what assumptions you make about the energy intensiveness of enrichment and the efficiency and source of that energy input. The amount is trivial. For several overseas countries, meeting their national greenhouse gas emission targets would be impossible without their substantial use of nuclear power for electricity generation. Since 1980 France's carbon dioxide emissions have been reduced to one third, as the nuclear portion of its electricity rose to 75%. The previous German Government acknowledged that its emission reduction targets would be totally unrealistic without nuclear power, and only the rhetoric has changed. The European Commission is quite clear that the EU cannot make any useful impact on carbon dioxide emissions without heavy dependence on nuclear energy. Nuclear waste is frequently trotted out as the major bogey of nuclear energy. While the nuclear fuel cycle does generate various nasty wastes, all of the hazardous ones are contained and managed, rather than being discharged to the environment. The main focus of attention is high-level waste containing the fission products and transuranic elements generated in the reactor core. High-level waste is highly radioactive and hot. The distinctive feature of high-level nuclear wastes is that their radioactivity decays dramatically. After 40 years, the heat and radioactivity has dropped to less than one thousandth of its level at the time the spent fuel is removed from the reactor, providing a technical incentive to delay disposal until radioactivity has decayed to such a level. Meanwhile they are easily and safely stored. To ensure that no significant environmental releases occur over periods of tens of thousands of years, a 'multiple barrier' disposal concept is used to immobilize the radioactive elements in high-level and some intermediate-level wastes and isolate them from the biosphere. It involves stabilizing, containment and finally, remote disposal. The cost of waste disposal is generally paid for by a levy on the electricity as it is produced, and is thus funded in advance by consumers. After three decades of concern regarding the possibility of uranium intended for commercial nuclear power finding its way into weapons, we now have substantial quantities of military uranium going the other way and being used for commercial nuclear power generation. It needs to be diluted about 25:1 with depleted uranium left over from enrichment plants. This is now a significant source of the world's uranium for electricity. But it is not so big that it threatens mine production. Rather, you have the usual situation for any mineral product where low cost mines displace high cost ones, and that is why in real terms the prices of practically all-mineral commodities have been trending downward for more than a hundred years. There is no reason to believe that uranium will be any exception. Weapons proliferation is a problem, which was identified and tackled early in the development of nuclear energy. The international safeguards regime is perhaps the main success story of UN Agencies; though having achieved its initial purpose (once thought to be ambitious) it is now being extended to tackle the problem on a broader front. The main concerns regarding proliferation have been where governments such as India, Pakistan and Israel have placed themselves substantially outside of these and therefore outside of most world trade in uranium and related materials. For at least the next decade, and when the present construction programs are completed, only the Asian region is likely to see significant growth in nuclear reactor construction. The main present growth in capacity is coming from plant upgrades. The sustained uranium demand now expected in the next 25 years, much beyond earlier predictions, arises from plant life extensions. For instance, despite being an obsolete technology, the oldest plants in UK have been approved to continue operating for 50 years, and the first license renewals for US nuclear plants have extended operating lives from 40 to 60 years, while further utilities are applying for the same. Nuclear power is and will remain an important energy resource, especially as world energy use climbs inexorably and the proportion of electricity in this increases. Half a century's experience in harnessing the power of the atom has provided a good basis for going forward with newer technologies for nuclear power generation and for managing the associated wastes. No energy conversion technology producing electricity is without risks or environmental effect. All the implications of all the available options need to be examined carefully. Nuclear power is the only energy-producing industry, which takes full responsibility for all its wastes and fully costs this into the product. As we enter the 21st century, nuclear power offers the world a felicitous coincidence of environmental virtue and necessity in the provision of large-scale, base-load electricity. However, public acceptance remains the key factor influencing its future, and perhaps intelligent citizens who already have knowledge and experience of nuclear medicine will be able to give a lead in changing that positively. Conclusion: - Overall, nuclear energy has proven to be most beneficial to our society. As a result of this technology, the United States has decreased its dependency on foreign-imported oil. In fact, the United States saves about 12 billion dollars each year through the lack of oil it imports from other nations. Nuclear energy has also proven to be a protector of the environment because of the lack of CO2, greenhouse gasses, and other gases it emits into the atmosphere. There are, however, some major drawbacks to using nuclear energy. These drawbacks include the actual safety of using nuclear energy, the waste it produces, and the atomic weapons that nuclear energy promotes. Overall, however, we believe that the use of nuclear energy greatly outweighs any other source of energy. |
