核电英语300句.doc

核电英语300句.docUNIT 1 HIESTORY OF NUCLEAR POWER1. The discovery of nuclear fission in 1939 was an event of epochal significance because it opened up the prospect of entirely new source of power.2. The worlds first self-sustaining nuclear fission chain was realized in the united states at the University of Chicago, 2kWt CP-1, on December 2, 1942.3. A prototype of the submarine reactor (called STR Mark 1) started operation at Arco, Idaho, in March 1953and the first nuclear powered submarine commenced its sea trials in January 1955.4. The words first industry nuclear power plant (5MW) was commenced in the U.S.S.R on June 27, 1954.5. The ShippingPort PWR, the first central-station nuclear power plant in the United States, went to operation on December 2, 1957.6. A 20MW nuclear-power demonstration plant in Canada has put in operation since October 1963 and the first CANDU power reactor unit at Douglas Point (200MW) reached full power operation in 1968.7. The first nuclear reactor (HWRR) in China went critical on June 13, 1958 and started power operation on September 23, 1958.8. The first atomic bomb in China was successfully exploded on October 16 and the first hydrogen bomb in China on June 17, 1967.9. The first nuclear submarine in China commenced its sea trials on August 23, 1971.10. The 300 MWe QNPC, designed and constructed by China, was connected to the gird of electricity generation on December, 15, 1991.11. The Daya Bay Nuclear Power Station was connected to the gird on August 31, 1993 and started commercial operation on February 1, 1994.12. In addition to QNPC and Daya Bay Nuclear Power Station, other nuclear power plants are being constructed inChina. UNIT 2 DEMAND FOR ELECTRC POWER1. During the present century, the worlds consumption of energy has grown rapidly due to the per capita increase in the use of energy for industry, agriculture and transportation.2. It is of special interest, the larger and larger proportions of the energy used are in the form of electric power.3. The generation of electricity requires primary energy sources and the increasing demand for electric power can be satisfied only if such primary sources are rapidly available.4. The main energy sources for the generation of electricity have been the fossil fuels, i.e., coal, natural gas, oil and hydroelectric (water) power.5. The adverse environmental effects of strip mining and the burning of coal, as well as increasing costs, are making coal less attractive for the generation of electricity.6. Although new reserves of oil and natural gas are being discovered, it appears that the worldwide production of these fuels will start to decrease around the turn of the century.7. Coal and petroleum provide the essential raw materials for the production of chemicals, including medicinal products, dyes, fibers, rubber and plastics.8. In the long run, the fossil fuels may prove to be more valuable in the respect of chemicals production than as primary sources of energy.9. The idea of making use of the suns energy is very attractive, but considerable research and development will be required before electricity can be generated from solar energy on a commercial scale.10. Nuclear energy can be made available either by the fission of heavy atomic nuclei or the fusion of very light ones.11. The fusion process has been demonstrated, both in experiments and in the hydrogen bomb; but is doubtful-that fusion energy can make any significant contribution to the power requirements before the end of the century.12. Nuclear fission has been established as a primary source of energy at costs that are competitive with electricity from other sources.UNIT 3 RADIOACITIVITYO1. An atom consists of a positively charged nucleus surrounded by negatively charged electrons, so that the atom as a whole is electrically neutral.2. Atomic nuclei are composed of two kinds of fundamental particles, namely, protons and neutrons.3. The proton carries a single unit positive charge equal in magnitude to the electronic charge.4. The neutron is very slightly heavier than the proton and is an electrically neutral particle.5. For a given element, the number of protons present in the atomic nucleus is called the atomic number of the element and the total number of nucleons, i.e., of protons and neutrons is called the mass number.6. The term nuclide is commonly used describe an atomic species whose nuclei have a specified composition, that is to say, a nuclide in nature is a species having given atomic and mass numbers.7. Such nuclides, having the same atomic number but different mass number, are called isotope, e.g., three forms of uranium isotopes in nature with the atomic number 92 but mass number 234, 235 and 238, respectively.8. The unstable substances undergo spontaneous change, i.e., radioactive decay, at definite rates.9. The radioactive decay is associated with the emission from the atomic nucleus of an electrically charged particle, either a alpha particles, i.e., helium nucleus, or a beta particles, i.e., an electron.10. In many instances of gamma rays, which are penetrating electromagnetic radiation of high energy, accompany the particle emission.11. The most widely used method for representing the rate of radioactive decay is by means of the half life, which is defined as the time required for the number of radioactive nuclei to decay to half its initial value.12. Since the number of nuclei (or their activity) decays to half its initial value in a half-life period, the number (or activity) will fall to one-fourth by the end of two half-life periods, and to less than 1 percent of its initial value after seven half-life periods.UNIT 6 REACTOR CONTROLO1. In the normal operation of a reactor, the functions of the control system may be divided into three phases, i.e. startup, power operation and shutdown.2. If the potentially unsafe conditions should arise, a protection system would automatically shut down the reactor.3. An essential requirement of the control system is that it must be capable of introducing enough negative reactivity to compensate for the build-in (excess) reactivity at initial startup of the reactor.4. Four general methods are possible for changing the neutron flux in a reactor, they involve temporary addition or removal of (1) fuel, (2) moderator, (3) reflector, (4) a neutron absorber.5. The control material commonly used in pressurized water reactor is alloy of 80(weight) percent silver, 15 percent indium and 5percent cadmium.6. The procedure most commonly employed, especially in power reactor, is the insertion or withdrawal of a material, such as boron or cadmium, having a large cross section for the absorption of neutrons.7. When a reactor core is being assembled, the neutron absorbing control robs are fully inserted, so the reactor is sub critical.8. During startup, the control rods are withdraw slowly, thereby permitting a gradual increase in the reactivity until the reactor becomes critical and then slightly supercritical.9. The neutron flux is thus allowed to increase at a safe, controlled rate until its magnitude corresponds to the desired operating power level of the reactor.10. The rods are then inserted to the extent required to keep the system exactly critical, so that the neutron flux and power level remain steady.11. To shut the reactor son, the control rods would be reinserted in to the core, there by decreasing the reactivity neutron flux and the power output.12.A control system consists of three control poops, i.e., “operator (manual) loop”, “automatic loop” and “load loop”.UNIT 4 NUCLEAR FISSION2. After absorption of a neutron, a nucleus breaks into two lighter nuclei, called fission fragments, with the liberation of a considerable amount of energy and two or three neutrons; this phenomenon is called nuclear fission.3. It should be noted that it is only with the fission nuclides that a self-sustaining fission chain is possible.4. Uranium-233, Uranium-235, Uranium-239, which will undergo fission with neutron of any energy, are referred to as fission nuclides.5. Since fission of thorium-232 and uranium-238 is possible with sufficient fast neutron, they are knows as fissionable nuclides; moreover, since thorium-232 and uranium-238 can be converted into the fissile nuclides, uranium-233 and plutonium-239, respectively, they are also called fissile nuclides.6. The fission of a single uranium-235 (or similar) is accompanied by the release of over 200MeV of energy, with may be compared about 4eV released by the combustion of an atom of carbon-12.7. The neutrons can strike other uranium atoms and cause additional fission and the continuing process of fissioning is known as a chain reactor.8. Since two or three neutrons are liberated in each of fission whereas only one is required to maintain a fission chain, it would seem that once the fission reaction were initiated in a given mass of fissile material, it would readily sustain itself.9. However, such is not the case because not all the neutrons produced in fission are available to carry on the fission chain, that is, some neutrons are lost in nonfission reactions (mainly radioactive capture),whereas other neutrons escape from the system undergoing fission.10. The minimum quantity of such material that is capable of sustaining a fission chain is called the critical mass. UNIT 5 GENERAL FEATURES OF NECLEAR REACTORS2. In outline, a reactor consists of an active core in which the fission chain is sustained and in which most of the energy of fission is released as heat.3. The core contains the nuclear fuel, consisting of a fissile nuclide and usually a fertile material in addition.4. The function of the moderator is to slow down the high-energy neutrons liberated in the fission reactor.5. The purpose of reflector is to decrease the loss of neutrons from the core by scattering back many of those which have escaped.6. The heat generated in the reactor is removed by circulation of a suitable coolant, such as ordinary(light) water, heavy water, liquid sodium(or sodium-potassium alloy), air and helium etc.7. The higher the temperature of the steam, the greater the efficiency for conversion into useful power.8. If the energy released in the reactor is to be converted into electric power, the heat must be transferred from the coolant to a working fluid to produce steam.9. Reactor control, including startup, power operation and shutdown is generally by moving control rods.10. In most commercial thermal reactors the fuel is either uranium (0.7% uranium-235), with heavy water or graphite as the moderator, or uranium containing 2-4 percent of the fissile isotope, with ordinary water as the moderator.11. Based on the purpose, the reactor can fall into experimental (or research) reactor, production reactor, power reactor, dual purpose (power and production) reactor or nuclear heating reactor.12. According to the type of coolant and moderator, reactor can be called pressurized water reactor, boiling water reactor, heavy water reactor (e.g. CANDU), graphite reactor, or liquid metal cooled reactor.UNIT 7 INSTRUMENTATION2. Many instruments for the detection of nuclear radiation are dependent upon the behavior in an electrical field of the ion-pairs formed by the ionizing particles in their passage through a gas.3. Neutrons are unchanged particles and therefore cannot cause ionization directly, so they must interact with matter by means of a nuclear reactor which, in turn, will generate charged particles.4. The changed particles will cause ionization within a gas-filled detector and these ion pairs will produce a voltage pulse or some mean level current when collected at the electrodes of the detector.5. Since the neutron flux covers a wide range (12 decades), no single instrument can provide a satisfactory indication of the neutron flux and hence three ranges, i.e., source range, intermediate range and power range, of instrumentation are used to obtain accurate flux level measures.6. BF3 gas generated filled detectors (proportional counter) are used in source range, compensated ion chamber are in the intermediate range, and uncompensated ion chamber in the power range in some nuclear power plant.7. Since gamma radiation from fission and fission products in a reactor can be very intense, the compensated ionization chambers are required in the intermediate range.8. The fission chamber is coated with a uranium compound and pulse produced by the fission fragments resulting from the interaction of neutrons with the uranium-235 are so large that there is no difficulty in discriminating even against “pile-up” pluses from gamma rays.9. Pressure, defined as force per unit area, is one of the measured and controlled properties.10. Typically application of Borden tube pressure sensors is locally mounted pump suction and discharge pressure gages.11. Thermocouples are utilized as temperature sensors t core exits.12.The hot and gold leg temperature detectors of Reactors Coolant System are Resistance Temperature Detectors (RTDs).UNIT 8 ENERGY REMOVAL1. In practical, the maximum power level of a reactor is normally determined by the rate at which the energy (heat) can be removed.2. In nuclear reactor operating at high neutron flux, such as those intended for central station power or ship propulsion, the design of the core depends just as much on the heat removal aspects as on nuclear consideration.3. The term thermal-hydraulic design is commonly used to describe the effort involving the integration of heat transfer and fluid mechanics principles to accomplish the desired rate of heat removal from the reactor fuel.4. The temperature in a reactor could increase continuously until the reactor is destroyed if the rate of heat removal were less than the rate of heat generation.5. The rate of heat generation and heat removal must be proper balanced in a operating reactor.6. The maximum of permissible temperature must be definitely established to make sure that the cooling system is adequate under anticipated operating conditions.7. The temperature at any point in a reactor will be greater than that of the sink by amount equal to the sum of all the temperature drops along the heat-flow path.8. The goal of reactor thermal-hydraulic design is to provide for the “optimum” transport of heat from the fuel to its conversion into useful energy, normally in a turbine.9. By “optimum” is meant a proper balance between many opposing parameters, such as coolant flow rate, temperature distribution in the core, materials, etc.10. An important aspect of the thermal-hydraulic design is concerned with conditions that might arise from an accident.11. Provision must be made in the design to accommodate deviations from normal operating conditions, such as following partial or complete loss in the coolant flow.12.Three general mechanisms are distinguished whereby heat is transferred from one point to another, namely, conduction, convection and radiation.UNIT 9 REACTOR MATERIALS1. A unique aspect of reactor environment is the presence of intense nuclear radiations of various types.2. Mechanical properties, such as tensile strength, ductility, impart strength and creep, must be adequate for the operation conditions.3. The material must be able of being fabricated or joined, e.g., by welding, into the required shape.4. An important requirement for structural and cladding materials is that they have a small adsorption cross section for neutrons.5. The alloys in common use as cladding material are zircaloy-2 and zircaloy-4, both of which have good mechanical properties and corrosion resistance.6. Ordinary water is attractive as a moderator because of its low cost, its excellent slowing-down power.7. Water of high degree of purity, especially free from chloride ions, is necessary to minimize corrosion.8. The fuel material should be resistant to radiation damage that can lead to dimensional changes, e.g., by swelling, cracking, or creep.9. The fuel material should have a high melting point and there should be no phase transformations, which would be accompanied by density and other changes, below the melting point.10. Uranium dioxide, ceramic which is the most common fuel material in commercial power reactors, has the advantage of high-temperature stability and adequate resistance to radiation.11. The pellets are ground to specified dimensions and are loaded into thin zircaloy tubes which serve as cladding.12. The small annular gap between the fuel pellets and cladding contains helium gas to improve the heat transfer characteristicUNIT 10 REACTOR SAFETY1. In general, the goals of reactor safety are to reduce the probability of an accident and to limit the extent of the radiological hazard.2. Nuclear reactor systems are designed with a number of barriers to the release of radioactivity, namely, fuel pellets, fuel-rod cladding, prim