NUCLEAR INDUSTRIES UMPAR, Abdulbashiet Mangayao UNTE, Khadija Masorong NUCLEAR POWER • • • • • Wilhelm Ostwald, a famed chemist advanced the hypothesis that energy not mass, is the fundamental basis of matter. Becquerel discovered radioactivity in 1898, and the existence of isotopes was shown around 1900 which led to findings that pointed the way to nuclear processes. Nuclear energy is the energy in the nucleus, or core, of an atom. Nuclear energy can be used to create electricity, but it must first be released from the atom. Nuclear energy supplies about 10 percent of the world's electricity and approximately 20 percent of the energy in the United States. A total of 30 countries worldwide are operating 440 nuclear reactors for electricity generation. Nuclear power is encountering such resistance now, and undoubtedly fusion will also be resisted when it develops. Major difficulties have also risen because of the delays in construction combined with high interest rate and the dangers of nuclear power use, as seen by some persons, arise to some extent from destruction observed from the use of atomic bomb. NUCLEAR REACTIONS • • The first spontaneously decaying substances discovered were radium and polonium by the Curies is a marvelous scientific achievement. Nuclear reactor-produced isotopes now replaced these substances for industrial and medicinal uses and are far cheaper and safer. A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. URANIUM AND THORIUM FUSION • Neutrons react with uranium and thorium to produce new isotopes, some stable, others having extremely short half-lives. • Neutrons released by fission are at high energy levels (fast neutrons) and can react in fast reactors, but most reactors require that they be slowed down to thermal speed before they can be captured by Uranium 235. The common isotopes or uranium and thorium, do not split (fission) on absorbing a neutron, but do form other elements that undergo rapid, spontaneous decay to yield isotopes that are fissionable, so they are usable for power production. • URANIUM AS AN ENERGY SOURCE • • Uranium is the fuel most widely used by nuclear plants for nuclear fission. Uranium is considered a nonrenewable energy source, even though it is a common metal found in rocks worldwide. Nuclear power plants use a certain kind of uranium, referred to as U-235, for fuel because its atoms are easily split apart. Capital costs for electrical energy made in nuclear-fueled plants are greater than for traditional fuels, but uranium is the lowest cost fuel available at present and its price has risen at a lower rate than those fuels during the last 15 years. NUCLEAR FUELS • • • • • Sources and Reserves – Uranium is more abundant in the earth’s crust than mercury and is present in about the same amount as tin and molybdenum. Thorium, while less widely used than uranium, is a suitable nuclear fuel and is not very rare. Mining and Milling Ore – The purification utilizes an organic solvent extraction, a difficult isotope separation process, and finally a unique process-the synthesis of an element, plutonium. Refining and Purification Isotope Enrichment Gaseous diffusion process Gas centrifuge process Conversion – A high degree of protection against even minor contamination is essential if the necessary purity is to be obtained. CONVERSION NUCLEAR FUELS SELECTION • The three fissionable isotopes, U-233, U-235, AND Pu-239, have a higher probability of fission than capture when absorbing a neutron. These are the only common material which can sustain a nuclear fission reaction, and therefore they are the nuclear fuels. MECHANICAL FORMING AND ELEMENT FABRICATION • To form fabricated fuel elements, fuels are pressed, sintered; ground to the exact size, inserted in a sheath of stainless steel, zirconium, or one of the zircalloys; pressurized with helium; carefully welded shut; then assembled into convenient sized groups for handling. NUCLEAR REACTORS • • • Nuclear reactors are machines that contain and control nuclear chain reactions while releasing heat at a controlled rate. A nuclear power plant uses the heat that a nuclear reactor produces to turn water into steam, which then drives turbine generators that generate electricity. Nuclear power plants are among the safest and most secure facilities in the world. It is any of a class of devices that can initiate and control a self-sustaining series of nuclear fissions. Nuclear reactors are used as research tools, as systems for producing radioactive isotopes, and most prominently as energy sources for nuclear power plants. There are three major types of reactors now operating: Burners, Breeders and Converters. BURNERS • Burners commonly use uranium enriched in U235 and some type of moderator to produce heat and slow down the neutrons to maintain the chain reaction. BREEDERS • • Breeders are designed to produce more fuel than they consume. Breeders run without moderators, so the speed of their neutrons is nearly that at which they are expelled after fission. They are designed to extend the nuclear fuel supply for the generation of electricity, and have even been mistakenly called a potential renewable energy source. Breeder reactors require chemical processing of a great deal of radioactive material, an expensive process which, among other problems, makes their use to produce electrical power questionable economically. CONVERTERS • Converters use U-238 as a fertile material to produce Pu-239 and usually not designed to produce useful heat. ATOM BOMBS • Atom bomb are designed to produce enormous amounts of energy in a very brief time. FUSION REACTIONS • • In a fusion reaction, two light nuclei merge to form a single heavier nucleus. The process releases energy because the total mass of the resulting single nucleus is less than the mass of the two original nuclei. The leftover mass becomes energy. The conversion of hydrogen to helium converts matter into energy. FUSION • Fusion of atoms to form more complex ones can be accompanied by loss of mass with the consequent generation of energy. The most promising fuels are deuterium and tritium, sources far less limited than uranium, thorium, oil or coil. PROCESSING NUCLEAR MATERIALS • • • Procedures for separating uranium and plutonium from the radioactive fission products present in spent fuel elements were developed early. These processes involving solution of fuel elements as nitrates and separation using tributyl phosphate solvent (Purex process) or hexone. Nuclear materials came into existence in the 1950s and began to grow as an internationally recognized field of endeavor late in that decade. Nuclear material is a threat if used to make a nuclear bomb or if spread by a conventional bomb. Nuclear bombs can be made from plutonium or highly enriched uranium. Plutonium is produced in plants that reprocess waste from conventional reactors. Natural uranium contains approximately 0.7% of the fissile isotope U-235. Conventional reactors use uranium slightly enriched to approximately 5% U-235. Low-enriched (to 20%) U-235 is used in research reactors. Highly enriched U-235 is a category higher than 20%, and weapons-grade U-235 is enriched to 90%. ISOTOPES AND ISOTOPE SEPARATION • • The existence of stable isotopes was known before nuclear technology developed, but the nuclear industry has given great impetus to isotope separation and use. Production of isotopes by planned transmutation is possible, but economical processes for large quantities more frequently involve the separation of naturally occurring elemental mixtures or their extraction as by-products. Separation of isotopes is more difficult than ordinary chemical processes, but several techniques are well established. Separation of isotopes may be done by distillation, chemical exchange, electrolysis, gaseous diffusion, gravitational processes, thermal diffusion and aerodynamic (nozzle) processes. Deterium - isotope of hydrogen with a nucleus consisting of one proton and one neutron, which is double the mass of the nucleus of ordinary hydrogen (one proton). Tritium - is a hydrogen atom that has two neutrons in the nucleus and one proton. Tritium is produced naturally in the upper atmosphere when cosmic rays strike nitrogen molecules in the air. Tritium is also produced during nuclear weapons explosions, and as a byproduct in nuclear reactors. Miscellaneous Isotopes – Isotopes may be used as tracers for studying structural chemistry, in biological, chemical and physical research, and for geological studies. PROTECTION FROM RADIOACTIVITY • • • Radiation hazard is a subject often approached from a highly emotional point of view, probably because radiation cannot be detected by human senses. Protection against radiation is possible with insulation. Just as the heat from a fire reduces as you move further away, the dose of radiation decreases dramatically as you increase your distance from the source. Shielding: Barriers of lead, concrete, or water provide protection from penetrating gamma rays. Shielding must not the only problem but also containment must also be considered. WASTE DISPOSAL • • The disposal of nuclear waste presents problems, but most are now political rather than technological. Some radioactive materials must be stored for centuries until they decay to harmless materials, others rapidly become harmless By removing long-lived isotopes for separate handling, contractors can greatly reduce storage time for most nuclear waste and with proper management, it will become harmless within 100 years. REFERENCES • • • • • • SHREVE,_NORRIS_5th_ED.pdf https://www.sciencedirect.com/topics/engineering/nuclear-material https://www.energy.gov/science/doe-explainsnuclear-fusionreactions#:~:text=In%20a%20fusion%20reaction%2C%20two,The%20leftover%20mass%20becomes%20energy. https://www.eia.gov/energyexplained/nuclear/nuclear-power-plants-types-ofreactors.php#:~:text=Nuclear%20reactors%20are%20machines%20that,turbine%20generators%20that%20genera te%20electricity. https://www.nationalgeographic.org/encyclopedia/nuclear-energy/ https://www.energy.gov/ne/articles/advantages-and-challenges-nuclear-energy
