Nuclear Power 2 Essay, Research Paper
Nuclear Power is a very complex subject and deals with a lot of social, scientific and political issues. The scientific side to Nuclear Power is probably the most complex of the three. Nuclear Power can turn you into ash in nanoseconds, render you retarded, or simply power your home. The process of nuclear fission, safety, destruction, will be discussed in the following pages along with history, present and future of this technology.
In the process of fission, two major parts are required on the atomic level, an element usually uranium 235 which has 235 protons and neutrons in its nucleus and a neutron. In a nuclear reactor the uranium used is always enriched which has an increased amount of fissionable nuclei. In the process of nuclear fission a uranium 235 molecule is split in two similar sized pieces after being hit by a neutron, after a neutron. The nucleus becomes suddenly so unstable that it splits into two major fragments and releases, on the average, two or three neutrons. Of these neutrons, at least one must succeed in producing another fission if the chain reaction is to persist. Billions of fissions will occur in a fraction of a second, thus a controlled chain reaction. I will discuss an uncontrolled chain reaction later. A large amount of energy is released after this process. This process is highly contained and controlled, insuring that the enormous amount of energy released is utilized. A small portion of the energy released is in the form of radiation but most of the energy occurs in the form of kinetic energy or heat. All of the movement during the fission process creates heat and this heat can be used to raise the temperature of water into high-pressure steam. The steam is used to turn a turbine and its mechanical energy is converted into electricity by a generator. The typical fission reaction involving Uranium 235 is,
92 U235 + 1 neutron = 38 Sr96 + 54 XE138 + 2 neutrons+energy
where the energy release is about 200 million electron volts (meV), a factor of 25 million greater than the combustion reaction of methane. Nuclear power plants harness the enormous energy releases from nuclear reactions for large-scale energy production. In a modern coal plant the combustion of one pound of coal produces about 1 kilowatt-hour (kWh) of electric energy. The fissioning of one pound of uranium in a modern nuclear power plant produces about 3 million kWh of electric energy. It is the incredible energy density (energy per unit mass) that makes nuclear energy sources of such interest. There are around 316 nuclear power plants in the world that create 213,000 megawatts of electricity.
The small amount Radioactive, or nuclear, waste is the by-product the nuclear fission process. Radiation and radioactive material are attributed to tissue damage in the molecules of cellular matter. Cells can be temporally damaged or destroyed for good. The severity of the injury depends on the type of radiation, the absorbed dose, the rate at which the dose was absorbed, and the radio-sensitivity of the tissues involved. The effects of radiation are the same, whether from a radiation source outside the body or from material within. The effects of a quick influx of radiation will cause cell death, and they become apparent within less than a few weeks. Slower and evenly increasing exposure is better tolerated because some of the damage is repaired while the exposure continues, even if the total dose is relatively high. If the dose is enough to cause effects, however, repair is less likely and may be slow even if it does occur. Exposure to doses of radiation too low to destroy cells can induce cellular changes that may be detectable clinically only after some years. The most common radiation poisoning is usually localized to a small area and may cause some tissue death, damage and gangrene. Radiation that can be found internally can cause delayed deterioration, destruction of cells and can even initiate cancer growth. Radiation doses are measured in grays or rads, 1 gray being equal to the dose absorbed when one kilogram of matter absorbs one joule of ionizing radiation, and 100 rads being equal to 1 gray. A dose of 40 grays will kill within 48 hours, 10-40 grays will cause death in 10 days. 1.5-10 g
Uranium, which contains about 0.7 percent uranium-235, is obtained from either surface or underground mines. The ore is concentrated by milling and then shipped to a conversion plant, where its form is changed to uranium hexafluoride gas (UF6). At an isotope enrichment plant, the gas is forced against a porous barrier that allows the lighter uranium-235 to penetrate more readily than uranium-238. This process enriches uranium to about 3 percent uranium-235. The depleted uranium-the tailings-contain about 0.3 percent uranium-235. The enriched product is sent to a fuel fabrication plant, where the UF6 gas is converted to uranium oxide powder, then into ceramic pellets that are loaded into corrosion-resistant fuel rods. These are assembled into fuel elements and are shipped to the reactor power plant. The world’s supply of enriched uranium fuel for powering commercial nuclear power plants is produced by five consortiums located in the United States, Western Europe, Russia, and Japan. The United States consortium-the federally owned United States Enrichment Corporation-produces 40 percent of this enriched uranium.
Nuclear power has other uses than just powering our homes. It propels military submarines, aircraft carriers, destroyers and who knows what else. Other uses for nuclear reactors is the production of radioactive isotopes that are created by bombarding non-radioactive substances with the neutrons released during fission and are used in scientific research, medical therapy and industry.
Substances such as ordinary water (light water), deuterium oxide (heavy water), and graphite have been found to be effective in slowing down neutrons during the fission process without reducing their number by absorption. The Uranium 235 rods are kept in rods in order to be able to insert them into the reactor where they are turned into energy. If the fissions begin to proceed at too great a rate, the result would be the release of an excessive amount of thermal energy and radiation and possibly cause meltdown of the core. Hence the term Nuclear Meltdown.
As a chain reaction continues, fission products accumulate in the reactor core. Most of these fragments are extremely radioactive and emit harmful gamma rays and neutrons. Consequently, thick, heavy concrete shielding to protect operators and other people in the vicinity against radiation must surround the reactor.
The disposal of radioactive fission products and spent-fuel assemblies poses a more difficult problem than does the containment of radiation in the reactor core. Some of these nuclear wastes remain dangerously radioactive for thousands of years and thus must be eliminated or stored permanently. We currently have no practical method of permanent disposal of nuclear waste.
The world’s first nuclear reactor was built at the University of Chicago under the direction of the Italian-born physicist Enrico Fermi. The reactor produced a chain reaction on Dec. 2, 1942. Following World War II, scientists and engineers in various other countries undertook efforts to develop reactors for large-scale power production. In 1956 the first full-scale commercial nuclear power plant was opened in Calder Hall, England. The following year the first American power station went online in 1957. Since then there were a lot of new power plants built until the late 1970s when there was a significant slowdown in the construction of new plants. The slow down can be attributed to the not in my back yard attitude, the rising cost of nuclear power plant construction and a drop in the projected rate of increase in electric-power demand. Major accidents at the Three Mile Island power station, near Harrisburg, Pa., in the United States, and the Chernobyl installation in the Soviet Union have left many afraid of nuclear power. France, Japan, South Korea, and Taiwan, which have few alternative-energy resources, however, have continued to increase their use of nuclear power.