核电英语300句.doc
UNIT 1 HIESTORY OF NUCLEAR POWER</O>
1,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 world’s 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 word’s 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 POWER
1,During the present century,the world’s 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 sun’s 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 RADIOACITIVITY<O
1,An atom consists of a positively charged nucleus surrounded by negatively charged electrons,so that the atom as a whole is electrically neutral.<O></O>
2,Atomic nuclei are composed of two kinds of fundamental particles,namely,protons and neutrons.<O></O>
3,The proton carries a single unit positive charge equal in magnitude to the electronic charge.<O></O>
4,The neutron is very slightly heavier than the proton and is an electrically neutral particle.<O></O>
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.<O></O>
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.<O></O>
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.<O></O>
8,The unstable substances undergo spontaneous change,i.e.,radioactive decay,at definite rates.<O></O>
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.<O></O>
10,In many instances of gamma rays,which are penetrating electromagnetic radiation of high energy,accompany the particle emission.<O></O>
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.<O></O>
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 CONTROL<O
1,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.<O></O>
2,If the potentially unsafe conditions should arise,a protection system would automatically shut down the reactor.<O></O>
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.<O></O>
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.<O></O>
5,The control material commonly used in pressurized water reactor is alloy of 80(weight) percent silver,15 percent indium and 5percent cadmium.<O></O>
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.<O></O>
7,When a reactor core is being assembled,the neutron absorbing control robs are fully inserted,so the reactor is sub critical.<O></O>
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.<O></O>
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.<O></O>
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.<O></O>
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.<O></O>
12.A control system consists of three control poops,i.e.,“operator (manual) loop”,“automatic loop” and,load loop”.
UNIT 4 NUCLEAR FISSION<O
1,The neutron-nuclei reactors fall into three general categories,namely,scattering,capture and fission.>>
2,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 REACTORS<O
1,A device in which nuclear fission energy is released in a controlled manner is called nuclear reactor.>>
2,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 INSTRUMENTATION<O
1,In addition to conventional instrumentation,such as that required fir measuring temperatures,pressures,coolant flow rates,etc.,devices (sensors) for determining the neutron flux play an important role in reactor control and safety.>>
2,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 REMOVAL
1,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 MATERIALS
1,A unique aspect of reactor environment is the presence of intense nuclear radiations of various types.<O></O>
2,Mechanical properties,such as tensile strength,ductility,impart strength and creep,must be adequate for the operation conditions.<O></O>
3,The material must be able of being fabricated or joined,e.g.,by welding,into the required shape.<O></O>
4,An important requirement for structural and cladding materials is that they have a small adsorption cross section for neutrons.<O></O>
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.<O></O>
6,Ordinary water is attractive as a moderator because of its low cost,its excellent slowing-down power.<O></O>
7,Water of high degree of purity,especially free from chloride ions,is necessary to minimize corrosion.<O></O>
8,The fuel material should be resistant to radiation damage that can lead to dimensional changes,e.g.,by swelling,cracking,or creep.<O></O>
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.<O></O>
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.<O></O>
11,The pellets are ground to specified dimensions and are loaded into thin zircaloy tubes which serve as cladding.<O></O>
12,The small annular gap between the fuel pellets and cladding contains helium gas to improve the heat transfer characteristic
UNIT 10 REACTOR SAFETY<O></O>
1,In general,the goals of reactor safety are to reduce the probability of an accident and to limit the extent of the radiological hazard.<O></O>
2,Nuclear reactor systems are designed with a number of barriers to the release of radioactivity,namely,fuel pellets,fuel-rod cladding,primary coolant boundary and containment.<O></O>
3,The basic philosophy of the design of nuclear power plants has been described as defense in depth,expressed in terms of five levels of safety.<O></O>
4,The first level of safety is to design of reactor and other components of the system so that they will operate with a high degree of reliability and the chances of a malfunction are very small.<O></O>
5,The purpose of safety is to design the reactor and other components of the system so that they will operate with a high degree of reliability and the chances of a malfunction are very small.<O></O>
6,The third level of safety is to provide engineered safety features,such as emergency core cooling system,containment spray system,and emergency eclectic power.<O></O>
7,Plants are now being required to develop accident management programs,which should reduce the likelihood of uncontrolled radioactivity releases during accident.<O></O>
8,Finally,emergency planes are developed that include provisions for sheltering and evacuation to further reduce potential doses to the public.<O></O>
9,Suitable redundancy shall be provided to assure that the safety system function can be accomplished assuming a single failure.<O></O>
10,One way to minimize common-mode failure is by diversity,that is by the use of two or more independent and different methods for achieving the same result,e.g.,reactor shutdown in an emergency.<O></O>
11,The evaluation of the safety of a nuclear power plant should include analyses of the response of the plant to postulated disturbance in process variables and to postulated malfunctions of equipment.<O></O>
12,An electric utility desiring to operate a nuclear power must first apply to the NNNA for a construction permit and then for an operating license.<O></O>
UNIT 11 QYALITY ASSURANCES<O1,Quality Assurance (QA) is referred to as planned and systematic actions necessary to provide adequate confidence that an item or facility will perform satisfactorily in service.<O></O>
2,Quality Control (QC) includes such as actions that provide a means to control and measure the characteristics of an item,process or facility in accordance with established requirements.<O></O>
3,Reliability is the probability that a device,system or facility will perform its intended function satisfactorily for a specified time under stated operating conditions.<O></O>
4,An overall quality assurance program shall be established to provide for control of the constitute activities associated with a nuclear power plant,such as design,construction,manufacturing,commissioning and operation.<O></O>
5,All programs shall provide that the activities affecting quality are accomplished in accordance with written procedures,instructions or drawings.<O></O>
6,Activity affecting quality includes designing,purchasing,fabricating,manufacturing,handling,shipping,storing,cleaning,erecting,installing,testing,commissioning,operating,inspecting,maintaining,repairing,refueling,modifying and decommissioning.<O></O>
7,A documented organization structure,with clearly defined functional responsibilities,level of authority and lines of internal and external communication for management,direction and execution of the quality assurance program shall be established.<O></O>
8,The preparation,review,approval and issue of documents essential to the performance and verification of the work shall be subject to control.<O></O>
9,Design control measures shall be applied to items such as the following,radiation protection; physics and stress analysis,thermal,hydraulic,seismic and accident analysis; compatibility of materials; accessibility of in-service inspection,maintenance and repair and delineation of acceptance criteria for inspection and tests.<O></O>
10,Hold-points beyond which work shall not proceed without the approval of a designated organization,if such inspection or witnessing of the inspection is required,shall be indicated in appropriate documents.<O></O>
11,Measures shall be established to control items which do not conform to requirements,in order to prevent their inadvertent use or installation.<O></O>
12,Quality assurance records shall represent objective evidence of quality and should include the results of review,inspections,tests,audits,monitoring of work performance,material analysis and power plant operation logs,as well as closely related data,such as qualification of personnel,procedures and equipment,repairs,required and other appropriate documents.
UNIT 12 INTRODUCTION TO PWR NPP<O></O>
1,A pressurized water reactor (PWR) generating system is a dual cycle plant consisting of a closed,pressurized,reactor coolant system (primary) and a separate power conversion system (secondary) for the generation electricity.<O></O>
2,The use of a dual cycle design minimizes the quantities of fission products released to the power conversion system components and subsequent release of fission products to the atmosphere.<O></O>
3,The primary system consists of a pressure vessel containing the nuclear fuel and reactor coolant loops connected in parallel to the reactor vessel.<O></O>
4,Each reactor coolant loop contains a reactor coolant pump,a steam generator,loop piping and instrumentation.<O></O>
5,The reactor coolant system also contains a pressurizer connected to one of the loops for system pressure control.<O></O>
6,During operation,the reactor coolant system transfers the heat produced in the reactor to the steam generator where steam is produced to supply the turbine generator to produce electricity.<O></O>
7,The entire reactor coolant system is located in containment (reactor building) which isolates the radioactive reactor coolant system from the environment in the event of a leak.<O></O>
8,The turbine building contains all the power conversion system,including turbines,moisture-separator/reheaters,feedwater heaters,condenser etc.<O></O>
9,The control building contains the central control room with its console and control panels,as well as the relay room.<O></O>
10,A fuel storage area is provided for handling and storage of new and spent fuel.<O></O>
11,Auxiliary building contains safety related and potentially radioactive auxiliary system,such as residual heat removal system,the safety injection system,the component cooling system etc.<O></O>
12,The safety injection system is an emergency system that provides for the injection of borated water from the refueling water storage tank into reactor coolant sytem in the event of LOCA.<O></O>
UNIT 13 REACTOR VESSSEL AND INTERNALS<O></O>
1,The reactor vessel and internals support and align the reactor core and its associated components.<O></O>
2,Additionally,the vessel and internals provide a flowpath to ensure adequate heat removal capability from the fuel assemblies.<O></O>
3,The reactor vessel is a cylindrical,with a welded hemispherical bottom heat and a removable,flanged and gasketed,hemispherical upper head.<O></O>
4,The head flange is sealed to the vessel flange by two metallic,o” rings which fit into grooves machined in both flanges.<O></O>
5,The reactor vessel and heat are constructed of a manganese molybdenum alloy steel with all surfaces in contact with the reactor coolant clad with weld deposited stainless steel for corrosion resistance.<O></O>
6,Sample of reactor vessel and weld materials are provided to evaluate the effect of radiation on the fracture toughness of the reactor vessel.<O></O>
7,Reactor vessel closure head penetrations include,control rod drive mechanism adapters and reactor vessel head vent.<O></O>
8,The bottom head of the vessel contains penetrations for connection and entry of the in-core nuclear instrumentation.<O></O>
9,The reactor internals consist of the lower support structure,the upper support structure and the in-core instrumentation support structure.<O></O>
10,Lower core support structure consists of the core barrel,the core buffer,the lower core plate and support columns,the thermal shield,the intermediate diffuser plate and the core support.<O></O>
11,A thermal shield attached to the core barrel is provided to reduce radiation damage to the reactor vessel during operation.<O></O>
12.The upper core support structure consists of the upper support assembly and the upper core plate,between which are contained support columns and control rod guide tubes.
__________________
UNIT 14 REACTOR CORE<O></O>
1,The reactor components consist of the fuel assemblies and all components which can be inserted into a fuel assembly to reactor power,power distribution or flow distribution.<O></O>
2,Fuel assemblies are square arrays (17×17 or 15×15) of long thin zircaloy tubes containing slightly enriched UO2 in the form pellets.<O></O>
3,Fuel assemblies are aligned by pins in the upper and lower core plates which mate with holes in the top and bottom nozzles.<O></O>
4,All control rod guide thimbles are filled with control rods,burnable poison assemblies,source assemblies or thimble plugging assemblies.<O></O>
5,A rod cluster control assembly consists of a group of individual neutron absorber rods fastened at top end to a common spider assembly.<O></O>
6,The absorber material used in the control rods is usually silver-indium-cadmium alloy sealed in stainless steel tubes.<O></O>
7,Control rods are designed to respond to fast reactivity changes while show changes such as fuel burnup are compensated by boron concentration changes.<O></O>
8,The burnable poison assemblies are designed to provide a fixed discrete poison during the initial core load.<O></O>
9,To insure adequate indication for the operator during long-term reactor shutdown and during reactor startup,neutron source assemblies are installed in the core.<O></O>
10,In order to limit core bypass though the control rod guide thimbles in fuel assemblies not containing control rods,sources assemblies,or burnable poison rods,the fuel assemblies at these locations are fitted with thimble plugging assemblies.<O></O>
11,Control rod drive mechanisms are magnetic jack assemblies which move control rods in discrete steps and tripping is accomplished by de-energizing the mechanisms and allowing the control rods to fall by gravity into the core.<O></O>
12,Reactor coolant enters the reactor vessel through the inlet nozzles,flows downward between the vessel wall and core barrel,then reverses direction and flows up through the core to remove the heat generated in the fuel assemblies,enters the upper plenum,and exits through the outlet nozzle.<O></O>
UNIT 15 PRESSURIZER<O></O>
1,A single reactor has only one pressurizer regardless of the number of loops.<O></O>
2,The pressurizer is a vertical,cylindrical,cylindrical vessel with hemispherical top and bottom heads.<O></O>
3,At nominal full power conditions,approximately sixty percent of the pressurizer volume is saturated water with the remaining saturated steam.<O></O>
4,Electrical heaters are installed through the bottom head while the spray nozzle,relief valve and safety valve connections are located in the top head of the vessel.<O></O>
5,The pressurizer has four basic functions,pressurization during startup; maintaining normal RCS pressure during operation; limiting RCS pressure changes during transients and preventing overpressure.<O></O>
6,During system pressurization,the electric heaters are energizing to raise the temperature of pressurizer and produce more steam.<O></O>
7,During steady-state operation,a small number of heaters are energized to make up heat losses to ambient.<O></O>
8,If pressure increases by a predetermined amount,the pressure control system modulates the spray valves to admit relatively cool water to the steam space to condense some steam,which reduces its density and limits the pressure increase.<O></O>
9,If pressure decreases by a predetermined amount,the pressure control system will energized electrical heaters to boil more water and return pressure to normal.<O></O>
10,If pressure increases toward design limits,power operated relief and self-actuating code safety valves will dump inventory from the steam to limit pressure.<O></O>
11,The purpose of power operated relief valve is to prevent reactor pressure from activating the high pressure reactor trip or from reaching the set point of the safety valves.<O></O>
The pressurizer relief tank collects,condenses and cools the discharge from the pressurizer safety and power operated relief valves.
UNIT 16 STEAM GENETATOR<O></O>
1,The steam generators are vertical,shell and U-tube heat exchangers where energy from the hot pressurized reactor coolant is transferred to the secondary coolant to produce dry,saturated steam.<O></O>
2,The dry saturated steam produced is used to operate the main turbine and auxiliaries in the production of electricity.<O></O>
3,The steam generator design requirements are to produce saturated steam with less than 0.5percent moisture by weight.<O></O>
4,The tubesheet and the heat transfer tubes form the boundary between the radioactive primary system and the non-radioactive secondary system.<O></O>
5,Reactor coolant enters the steam generator consists of the inlet nozzle,Flows through the inlet chamber,U tubes,outlet chamber and levels it from outlet nozzle.<O></O>
6,The secondary side of the steam generator consists of the feed and steam nozzles,the tube bundle and supports,the tube bundle wrapper,primary and secondary moisture separators and appropriate instrumentation and blowdown penetration.<O></O>
7,The lower shell is the evaporator containing the tube bundle and the upper shell s the steam drum containing the steam separating and drying equipment.<O></O>
8,The steam generator operates as a natural circulation boiler.<O></O>
9,In order to support and align the steam generator tubes and prevent flow induced movement,tube support plates are provided.<O></O>
10,The blowdown line is provided to remove corrosion products which would concentrate at the tubesheet.<O></O>
11,Nuclear power plants are equipped with N-16 detector on the steam line for indicating U-tube leakage.<O></O>
12.There are two types of steam generator level indication,wide range and narrow range.
UNIT 17 REACTOR COOLANT PUMP<O></O>
1,The reactor coolant pump provides sufficient forced circulation flow to ensure adequate heat transfer.<O></O>
2,The reactor coolant pump is vertical,single stage,centrifugal pump to pump large volumes of reactor coolant at high temperature and pressure.<O></O>
3,The pump consists of three sections from bottom to top,the hydraulic section,the shaft seal section and the motor section.<O></O>
4,The hydraulic section consists of the inlet and outlet nozzles,casing,flange,impeller,diffuser,pump shaft,pump bearing,thermal barrier and thermal barrier heat exchanger.<O></O>
5,The shaft seal section consists of the number one,controlled leakage seal and the number two and three rubbing face seals,These seals are located within the main flange and seal housing.<O></O>
6,The motor section consists of a vertical,squirrel cage; induction motor with an oil lubricated double Kingsbury thrust bearing,two oil lubricated radial bearings,a flywheel and help establish natural circulation.<O></O>
7,A flywheel extends flow coastdown after a loss of power to maintain flow through the core and appropriate support equipment.<O></O>
8,An anti-reverse rotation device prevents the pump from turning backwards which would increase core bypass flow and pump starting current.<O></O>
9,Shaft sealing is accomplished by a film riding controlled leakage seal with a backup rubbing face seal.<O></O>
10,The operation of the seal package assures near zero leakage from reactor coolant system at the reactor coolant pump shaft.<O></O>
11,Seal water injection through the thermal barrier heat exchanger cools and lubricates the seal and pump bearing.<O></O>
12.Cooling for the motor bearing and barrier heat exchanger is from the component cooling water system.
UNIT 1 HIESTORY OF NUCLEAR POWER</O>
1,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 world’s 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 word’s 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 POWER
1,During the present century,the world’s 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 sun’s 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 RADIOACITIVITY<O
1,An atom consists of a positively charged nucleus surrounded by negatively charged electrons,so that the atom as a whole is electrically neutral.<O></O>
2,Atomic nuclei are composed of two kinds of fundamental particles,namely,protons and neutrons.<O></O>
3,The proton carries a single unit positive charge equal in magnitude to the electronic charge.<O></O>
4,The neutron is very slightly heavier than the proton and is an electrically neutral particle.<O></O>
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.<O></O>
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.<O></O>
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.<O></O>
8,The unstable substances undergo spontaneous change,i.e.,radioactive decay,at definite rates.<O></O>
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.<O></O>
10,In many instances of gamma rays,which are penetrating electromagnetic radiation of high energy,accompany the particle emission.<O></O>
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.<O></O>
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 CONTROL<O
1,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.<O></O>
2,If the potentially unsafe conditions should arise,a protection system would automatically shut down the reactor.<O></O>
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.<O></O>
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.<O></O>
5,The control material commonly used in pressurized water reactor is alloy of 80(weight) percent silver,15 percent indium and 5percent cadmium.<O></O>
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.<O></O>
7,When a reactor core is being assembled,the neutron absorbing control robs are fully inserted,so the reactor is sub critical.<O></O>
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.<O></O>
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.<O></O>
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.<O></O>
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.<O></O>
12.A control system consists of three control poops,i.e.,“operator (manual) loop”,“automatic loop” and,load loop”.
UNIT 4 NUCLEAR FISSION<O
1,The neutron-nuclei reactors fall into three general categories,namely,scattering,capture and fission.>>
2,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 REACTORS<O
1,A device in which nuclear fission energy is released in a controlled manner is called nuclear reactor.>>
2,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 INSTRUMENTATION<O
1,In addition to conventional instrumentation,such as that required fir measuring temperatures,pressures,coolant flow rates,etc.,devices (sensors) for determining the neutron flux play an important role in reactor control and safety.>>
2,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 REMOVAL
1,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 MATERIALS
1,A unique aspect of reactor environment is the presence of intense nuclear radiations of various types.<O></O>
2,Mechanical properties,such as tensile strength,ductility,impart strength and creep,must be adequate for the operation conditions.<O></O>
3,The material must be able of being fabricated or joined,e.g.,by welding,into the required shape.<O></O>
4,An important requirement for structural and cladding materials is that they have a small adsorption cross section for neutrons.<O></O>
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.<O></O>
6,Ordinary water is attractive as a moderator because of its low cost,its excellent slowing-down power.<O></O>
7,Water of high degree of purity,especially free from chloride ions,is necessary to minimize corrosion.<O></O>
8,The fuel material should be resistant to radiation damage that can lead to dimensional changes,e.g.,by swelling,cracking,or creep.<O></O>
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.<O></O>
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.<O></O>
11,The pellets are ground to specified dimensions and are loaded into thin zircaloy tubes which serve as cladding.<O></O>
12,The small annular gap between the fuel pellets and cladding contains helium gas to improve the heat transfer characteristic
UNIT 10 REACTOR SAFETY<O></O>
1,In general,the goals of reactor safety are to reduce the probability of an accident and to limit the extent of the radiological hazard.<O></O>
2,Nuclear reactor systems are designed with a number of barriers to the release of radioactivity,namely,fuel pellets,fuel-rod cladding,primary coolant boundary and containment.<O></O>
3,The basic philosophy of the design of nuclear power plants has been described as defense in depth,expressed in terms of five levels of safety.<O></O>
4,The first level of safety is to design of reactor and other components of the system so that they will operate with a high degree of reliability and the chances of a malfunction are very small.<O></O>
5,The purpose of safety is to design the reactor and other components of the system so that they will operate with a high degree of reliability and the chances of a malfunction are very small.<O></O>
6,The third level of safety is to provide engineered safety features,such as emergency core cooling system,containment spray system,and emergency eclectic power.<O></O>
7,Plants are now being required to develop accident management programs,which should reduce the likelihood of uncontrolled radioactivity releases during accident.<O></O>
8,Finally,emergency planes are developed that include provisions for sheltering and evacuation to further reduce potential doses to the public.<O></O>
9,Suitable redundancy shall be provided to assure that the safety system function can be accomplished assuming a single failure.<O></O>
10,One way to minimize common-mode failure is by diversity,that is by the use of two or more independent and different methods for achieving the same result,e.g.,reactor shutdown in an emergency.<O></O>
11,The evaluation of the safety of a nuclear power plant should include analyses of the response of the plant to postulated disturbance in process variables and to postulated malfunctions of equipment.<O></O>
12,An electric utility desiring to operate a nuclear power must first apply to the NNNA for a construction permit and then for an operating license.<O></O>
UNIT 11 QYALITY ASSURANCES<O1,Quality Assurance (QA) is referred to as planned and systematic actions necessary to provide adequate confidence that an item or facility will perform satisfactorily in service.<O></O>
2,Quality Control (QC) includes such as actions that provide a means to control and measure the characteristics of an item,process or facility in accordance with established requirements.<O></O>
3,Reliability is the probability that a device,system or facility will perform its intended function satisfactorily for a specified time under stated operating conditions.<O></O>
4,An overall quality assurance program shall be established to provide for control of the constitute activities associated with a nuclear power plant,such as design,construction,manufacturing,commissioning and operation.<O></O>
5,All programs shall provide that the activities affecting quality are accomplished in accordance with written procedures,instructions or drawings.<O></O>
6,Activity affecting quality includes designing,purchasing,fabricating,manufacturing,handling,shipping,storing,cleaning,erecting,installing,testing,commissioning,operating,inspecting,maintaining,repairing,refueling,modifying and decommissioning.<O></O>
7,A documented organization structure,with clearly defined functional responsibilities,level of authority and lines of internal and external communication for management,direction and execution of the quality assurance program shall be established.<O></O>
8,The preparation,review,approval and issue of documents essential to the performance and verification of the work shall be subject to control.<O></O>
9,Design control measures shall be applied to items such as the following,radiation protection; physics and stress analysis,thermal,hydraulic,seismic and accident analysis; compatibility of materials; accessibility of in-service inspection,maintenance and repair and delineation of acceptance criteria for inspection and tests.<O></O>
10,Hold-points beyond which work shall not proceed without the approval of a designated organization,if such inspection or witnessing of the inspection is required,shall be indicated in appropriate documents.<O></O>
11,Measures shall be established to control items which do not conform to requirements,in order to prevent their inadvertent use or installation.<O></O>
12,Quality assurance records shall represent objective evidence of quality and should include the results of review,inspections,tests,audits,monitoring of work performance,material analysis and power plant operation logs,as well as closely related data,such as qualification of personnel,procedures and equipment,repairs,required and other appropriate documents.
UNIT 12 INTRODUCTION TO PWR NPP<O></O>
1,A pressurized water reactor (PWR) generating system is a dual cycle plant consisting of a closed,pressurized,reactor coolant system (primary) and a separate power conversion system (secondary) for the generation electricity.<O></O>
2,The use of a dual cycle design minimizes the quantities of fission products released to the power conversion system components and subsequent release of fission products to the atmosphere.<O></O>
3,The primary system consists of a pressure vessel containing the nuclear fuel and reactor coolant loops connected in parallel to the reactor vessel.<O></O>
4,Each reactor coolant loop contains a reactor coolant pump,a steam generator,loop piping and instrumentation.<O></O>
5,The reactor coolant system also contains a pressurizer connected to one of the loops for system pressure control.<O></O>
6,During operation,the reactor coolant system transfers the heat produced in the reactor to the steam generator where steam is produced to supply the turbine generator to produce electricity.<O></O>
7,The entire reactor coolant system is located in containment (reactor building) which isolates the radioactive reactor coolant system from the environment in the event of a leak.<O></O>
8,The turbine building contains all the power conversion system,including turbines,moisture-separator/reheaters,feedwater heaters,condenser etc.<O></O>
9,The control building contains the central control room with its console and control panels,as well as the relay room.<O></O>
10,A fuel storage area is provided for handling and storage of new and spent fuel.<O></O>
11,Auxiliary building contains safety related and potentially radioactive auxiliary system,such as residual heat removal system,the safety injection system,the component cooling system etc.<O></O>
12,The safety injection system is an emergency system that provides for the injection of borated water from the refueling water storage tank into reactor coolant sytem in the event of LOCA.<O></O>
UNIT 13 REACTOR VESSSEL AND INTERNALS<O></O>
1,The reactor vessel and internals support and align the reactor core and its associated components.<O></O>
2,Additionally,the vessel and internals provide a flowpath to ensure adequate heat removal capability from the fuel assemblies.<O></O>
3,The reactor vessel is a cylindrical,with a welded hemispherical bottom heat and a removable,flanged and gasketed,hemispherical upper head.<O></O>
4,The head flange is sealed to the vessel flange by two metallic,o” rings which fit into grooves machined in both flanges.<O></O>
5,The reactor vessel and heat are constructed of a manganese molybdenum alloy steel with all surfaces in contact with the reactor coolant clad with weld deposited stainless steel for corrosion resistance.<O></O>
6,Sample of reactor vessel and weld materials are provided to evaluate the effect of radiation on the fracture toughness of the reactor vessel.<O></O>
7,Reactor vessel closure head penetrations include,control rod drive mechanism adapters and reactor vessel head vent.<O></O>
8,The bottom head of the vessel contains penetrations for connection and entry of the in-core nuclear instrumentation.<O></O>
9,The reactor internals consist of the lower support structure,the upper support structure and the in-core instrumentation support structure.<O></O>
10,Lower core support structure consists of the core barrel,the core buffer,the lower core plate and support columns,the thermal shield,the intermediate diffuser plate and the core support.<O></O>
11,A thermal shield attached to the core barrel is provided to reduce radiation damage to the reactor vessel during operation.<O></O>
12.The upper core support structure consists of the upper support assembly and the upper core plate,between which are contained support columns and control rod guide tubes.
__________________
UNIT 14 REACTOR CORE<O></O>
1,The reactor components consist of the fuel assemblies and all components which can be inserted into a fuel assembly to reactor power,power distribution or flow distribution.<O></O>
2,Fuel assemblies are square arrays (17×17 or 15×15) of long thin zircaloy tubes containing slightly enriched UO2 in the form pellets.<O></O>
3,Fuel assemblies are aligned by pins in the upper and lower core plates which mate with holes in the top and bottom nozzles.<O></O>
4,All control rod guide thimbles are filled with control rods,burnable poison assemblies,source assemblies or thimble plugging assemblies.<O></O>
5,A rod cluster control assembly consists of a group of individual neutron absorber rods fastened at top end to a common spider assembly.<O></O>
6,The absorber material used in the control rods is usually silver-indium-cadmium alloy sealed in stainless steel tubes.<O></O>
7,Control rods are designed to respond to fast reactivity changes while show changes such as fuel burnup are compensated by boron concentration changes.<O></O>
8,The burnable poison assemblies are designed to provide a fixed discrete poison during the initial core load.<O></O>
9,To insure adequate indication for the operator during long-term reactor shutdown and during reactor startup,neutron source assemblies are installed in the core.<O></O>
10,In order to limit core bypass though the control rod guide thimbles in fuel assemblies not containing control rods,sources assemblies,or burnable poison rods,the fuel assemblies at these locations are fitted with thimble plugging assemblies.<O></O>
11,Control rod drive mechanisms are magnetic jack assemblies which move control rods in discrete steps and tripping is accomplished by de-energizing the mechanisms and allowing the control rods to fall by gravity into the core.<O></O>
12,Reactor coolant enters the reactor vessel through the inlet nozzles,flows downward between the vessel wall and core barrel,then reverses direction and flows up through the core to remove the heat generated in the fuel assemblies,enters the upper plenum,and exits through the outlet nozzle.<O></O>
UNIT 15 PRESSURIZER<O></O>
1,A single reactor has only one pressurizer regardless of the number of loops.<O></O>
2,The pressurizer is a vertical,cylindrical,cylindrical vessel with hemispherical top and bottom heads.<O></O>
3,At nominal full power conditions,approximately sixty percent of the pressurizer volume is saturated water with the remaining saturated steam.<O></O>
4,Electrical heaters are installed through the bottom head while the spray nozzle,relief valve and safety valve connections are located in the top head of the vessel.<O></O>
5,The pressurizer has four basic functions,pressurization during startup; maintaining normal RCS pressure during operation; limiting RCS pressure changes during transients and preventing overpressure.<O></O>
6,During system pressurization,the electric heaters are energizing to raise the temperature of pressurizer and produce more steam.<O></O>
7,During steady-state operation,a small number of heaters are energized to make up heat losses to ambient.<O></O>
8,If pressure increases by a predetermined amount,the pressure control system modulates the spray valves to admit relatively cool water to the steam space to condense some steam,which reduces its density and limits the pressure increase.<O></O>
9,If pressure decreases by a predetermined amount,the pressure control system will energized electrical heaters to boil more water and return pressure to normal.<O></O>
10,If pressure increases toward design limits,power operated relief and self-actuating code safety valves will dump inventory from the steam to limit pressure.<O></O>
11,The purpose of power operated relief valve is to prevent reactor pressure from activating the high pressure reactor trip or from reaching the set point of the safety valves.<O></O>
The pressurizer relief tank collects,condenses and cools the discharge from the pressurizer safety and power operated relief valves.
UNIT 16 STEAM GENETATOR<O></O>
1,The steam generators are vertical,shell and U-tube heat exchangers where energy from the hot pressurized reactor coolant is transferred to the secondary coolant to produce dry,saturated steam.<O></O>
2,The dry saturated steam produced is used to operate the main turbine and auxiliaries in the production of electricity.<O></O>
3,The steam generator design requirements are to produce saturated steam with less than 0.5percent moisture by weight.<O></O>
4,The tubesheet and the heat transfer tubes form the boundary between the radioactive primary system and the non-radioactive secondary system.<O></O>
5,Reactor coolant enters the steam generator consists of the inlet nozzle,Flows through the inlet chamber,U tubes,outlet chamber and levels it from outlet nozzle.<O></O>
6,The secondary side of the steam generator consists of the feed and steam nozzles,the tube bundle and supports,the tube bundle wrapper,primary and secondary moisture separators and appropriate instrumentation and blowdown penetration.<O></O>
7,The lower shell is the evaporator containing the tube bundle and the upper shell s the steam drum containing the steam separating and drying equipment.<O></O>
8,The steam generator operates as a natural circulation boiler.<O></O>
9,In order to support and align the steam generator tubes and prevent flow induced movement,tube support plates are provided.<O></O>
10,The blowdown line is provided to remove corrosion products which would concentrate at the tubesheet.<O></O>
11,Nuclear power plants are equipped with N-16 detector on the steam line for indicating U-tube leakage.<O></O>
12.There are two types of steam generator level indication,wide range and narrow range.
UNIT 17 REACTOR COOLANT PUMP<O></O>
1,The reactor coolant pump provides sufficient forced circulation flow to ensure adequate heat transfer.<O></O>
2,The reactor coolant pump is vertical,single stage,centrifugal pump to pump large volumes of reactor coolant at high temperature and pressure.<O></O>
3,The pump consists of three sections from bottom to top,the hydraulic section,the shaft seal section and the motor section.<O></O>
4,The hydraulic section consists of the inlet and outlet nozzles,casing,flange,impeller,diffuser,pump shaft,pump bearing,thermal barrier and thermal barrier heat exchanger.<O></O>
5,The shaft seal section consists of the number one,controlled leakage seal and the number two and three rubbing face seals,These seals are located within the main flange and seal housing.<O></O>
6,The motor section consists of a vertical,squirrel cage; induction motor with an oil lubricated double Kingsbury thrust bearing,two oil lubricated radial bearings,a flywheel and help establish natural circulation.<O></O>
7,A flywheel extends flow coastdown after a loss of power to maintain flow through the core and appropriate support equipment.<O></O>
8,An anti-reverse rotation device prevents the pump from turning backwards which would increase core bypass flow and pump starting current.<O></O>
9,Shaft sealing is accomplished by a film riding controlled leakage seal with a backup rubbing face seal.<O></O>
10,The operation of the seal package assures near zero leakage from reactor coolant system at the reactor coolant pump shaft.<O></O>
11,Seal water injection through the thermal barrier heat exchanger cools and lubricates the seal and pump bearing.<O></O>
12.Cooling for the motor bearing and barrier heat exchanger is from the component cooling water system.
