A nuclear plant is a Powerplant, using the Nuclear fission matter Fissile S to produce Chaleur of which a part is transformed into electricity. It is currently the principal implementation civil of the nuclear energy.
A nuclear plant consists of one or more nuclear reactors (up to 7), whose electric output varies from 40 MW to more than 1450 MW. According to the promoters of the future engine EPR, it should develop a power of 1600 MW. In 2006,442 engines function in 31 different countries in the world, that is to say a total of 370 GW producing approximately 17% of world electricity (see the Liste of the nuclear reactors). The number of built engine tends to decrease with the profit of a lengthening of the working life of the power stations (In 2006, the engines majority had from 15 to 36 years, seven having from 37 to 40 years, for 2006).
The June 27th 1954, the first nuclear plant civil was connected to the electrical communication with Obninsk in Soviet Union, with a power of electrical production of 5 Megawatts. The following nuclear plants were Marcoule in Provence on January 7th, 1956, Sellafield with the the United Kingdom, connected to the network in 1956, and the Nuclear reactor of Shippingport to the the United States, connected in 1957. This same year, the building work of the first engine of civil use in France (EDF1) started with the Nuclear plant of Chinon.
The world nuclear power increased quickly, rising of more than 1 gigawatt (GW) in 1960 until 100 GW at the end of the years 1970, and 300 GW at the end of the years 1980. Since, the world capacity increased much more slowly, reaching 366 GW in 2005, because of the Chinese nuclear program. Between 1970 and 1990 more 5  were built; GW per annum (with a peak of 33 GW in 1984). More of two thirds of the nuclear plants ordered after January 1970 were cancelled.
Increasing economic costs, due to the increasingly long durations of construction, and the low costs of fossile fuels, made the nuclear power less competitive in the years 1980 and 1990. In addition, in certain countries, the public opinion, anxious of the risks of nuclear accidents and of the problem of the radioactive waste, resulted in giving up nuclear energy.
A nuclear plant gathers the whole of the installations allowing the electrical production on a given site. It frequently includes/understands several sections, identical or not; each section corresponds to a group of installations designed to provide a given electric output (for example 900 MWe, 1300 MWe or 1450 MWe). In France, a section generally includes/understands:
- the building engine, enclosure seals which contains mainly the Nuclear reactor, the steam generator (three or four according to the generation), a pressurisor, part of the secondary water circuit and the primary water circuit , whose main role is to ensure the heat transfer between the heart of the engine and the steam generators;
- the building engine room, which contains mainly:
- a line of trees including/understanding the various stages of the Steam turbine and the Alternator,
- the Condenser,
of the additional buildings which contain in particular installation various of auxiliary circuits necessary for the operation of the nuclear reactor and the Maintenance, electric control panels feeding all the generating auxiliaries and diesel of help;
- a atmospheric air cooler (the most visible part of a nuclear plant), or simply a pumping station for the sections whose cooling uses the Sea water or of river.
The other installations of the powerplant include/understand:
- one or more electric stations allowing connection to the Electrical communication via one or several lines high voltage, as well as an interconnection limited between sections;
- an administrative building….
See also: Nuclear reactor
In a nuclear section, the Nuclear reactor is upstream of a thermal installation which produces vapor transformed into mechanical energy by means of a steam turbine; the alternator uses then this mechanical energy to produce electricity.
The essential difference between a nuclear plant and a traditional thermo plant is materialized by the replacement of a consuming whole of boilers of fossile fuels by a nuclear reactor.
To recover mechanical energy starting from heat, it is necessary to have of an hot source and a cold source.
- for an engine of the type REFERENCE MARK (Pressurized water reactor), the hot source is provided by the water of the primary education circuit, with the average temperature of 306 °C (286 °C in entry and 323 °C at exit, temperature of exit varying according to the power of the section);
- the cold source is provided by the water of a river or sea, or of the ambient air by evaporation in turns aéroréfrigérantes.
Thus, a nuclear section of REFERENCE MARK type comprises three independent important water circuits:
- the primary education circuit which is located in a pregnant containment.
the secondary circuit of water is a closed circuit, which breaks up into two parts:
- between the condenser and the steam generators, water remains in liquid form: it is the power supply of the steam generators; pumps make it possible to raise the pressure of this water, and of the exchangers of heat raise the temperature (60 of it bar and 220°C).
- this water vaporizes in 3 or 4 steam generators (according to the type of section; 900 or 1300/1450 MW) and vapor pipings feed successively the stages of the turbine laid out on the same line of trees. The vapor acquires an high speed at the time of its relaxation thus making it possible to involve the wheels with bladings of the turbine.
La left the last stage of the turbine gives directly on the condenser, an exchanger of heat whose pressure is maintained around 50 absolute mbar (Vide) by vacuum pumps. The condensate in this apparatus is re-used for réalimenter steam generators.
the coolant circuit ensures the cooling of the condenser . Water is cooled by a draft in a tower aéroréfrigérante from where a small portion (1,5%) of water escapes out of vapor in form from white plume. The cooling water can also be exchanged directly with a river or the sea.
The mechanical energy produced by the turbine is used to actuate the alternator which converts it into electrical energy, this one being evacuated by the Electrical communication.
When the nuclear section outputs electric output on the network, it is said that it is " couplée" with the network. The inopportune disconnection of the alternator to the network (what is called a " déclenchement"), requires an immediate reduction of the vapor supply of the turbine by Vanne S of adjustment laid out on vapor pipings, or else, its number of revolutions would increase until its destruction, because of the Centrifugal force excessive being exerted then on the bladings. Nevertheless, in this case, the section remains in service with low power: the turbine is in rotation and remains ready with the immediate recouplage on the network (the section is then " ilotée" : it feeds it even its auxiliaries).
Various types of power stations
- central with ebullient water reactor, moderated with the graphite of Soviet design (RBMK)
- central with pressurized water reactor of Soviet design (WWER)
- central with reactor natural-uranium-fueled, moderated by graphite, cooled by carbon dioxide (die natural Uranium graphite gas); of which the first engine of civil use in France (EDF1). This die was abandoned for the die REFERENCE MARK for economic reasons. These types of power stations are currently all with the stop;
- central with engine using of the natural uranium moderated by heavy water (Canadian die CANDU);
- central with Pressurized water reactor (REFERENCE MARK) (English PWR); this type of engine uses uranium oxide enriched like fuel, and moderate and is cooled by ordinary water under pressure. The REFERENCE MARKS constitute the essence of the current park: 60% in the world and 80% in Europe. France chose this type of engine, then under Westinghouse license, in 1969;
- central with pressurized heavy-water reactor (PHWR)
- central with advanced engine with the gas (AGR)
- central with ebullient Water reactor (REB) (English BWR); this type of engine is rather similar to a pressurized water reactor, with the important difference that primary water vaporizes in the heart of the engine, this under normal functioning;
- central with Nuclear reactor with fast neutrons and coolant sodium, like Super-Phenix.
Nuclear reactors and power stations in projectTendencies : In spite of the announced end of the Oil cheap, the number of nuclear reactors and power stations built and in project in the world is in strong reduction. Whereas for the only year 1970 the construction of 37 new engines had been started in the world (year), and that 6 were brought into operational service, in 2005, only three new engines were at the beginning of construction in the world, while only four completed engines were connected to the network. This decline started in 1986 (date of the Catastrophe of Tchernobyl and was stabilized towards 1994, date from which construction stagnated ata rate from 2 to 3 engines at the beginning of construction per annum).
Sauf with the Japan where the breeder '' Super Monju '' still functioned in 2006, stagnating to 246 MWe of production, the die breeding was abandoned (including for the Super-Phenix French) because of its risks and the lack of profitability (phoenix still functioned however in 2006 for a power of 233 MWe (source IAEA, 2006).
- the industry of the electric nuclear power now seeks to test an engine of new generation: EDF must, in France, to establish a nuclear plant of the type EPR (European Pressurized Reactor toilets) on the site of Flamanville, in the Manche, of a power envisaged of 1600 MW.
- On its side, the Russian company Sevmash announced to have started the June 14th 2006 the construction of the 1st Floating Nuclear plant in world (PASTES/ПАТЭС) by using the technologies developed for the military nuclear submarines. according to its manufacturing, this floating engine could provide electricity to big cities isolated from the Far North, at a cost less than by fossil energies.
Political debate on nuclear energy
See also: Debate on nuclear energy
Nuclear energy is a subject of political debate. 17% of electricity in the world are produced by the nuclear die, the proportion largely varying from one country to another.
Production of waste
See also: Radioactive waste
The radioactive waste come from various stages of the Cycle of nuclear fuel. 10% of this waste approximately are elements of strong radiological activity or long half-life.
See also: nuclear Dismantling
After the final adoption of the exploitation, a nuclear plant is entirely dismantled, including the nuclear reactors.
The materials and equipment of the nuclear reactors are dimensioned for a certain lifespan. Whereas some are replaced during the periodic stoppings of the engine (ex: steam generator), others remain in the engine. During dismantling, all the equipment is dismounted and sent if necessary in centers of storage of radioactive waste.
The dismantling of an engine is done in 3 stages:
- the stage of shut down final (MAD): unloading of fuel of the heart of the engine and its storage during 2 years in swimming pool of " décroissance" combustible building.
- the stage of partial dismantling : déconstruction of all the buildings outside the building sheltering the engine.
- the total dismantling : dismantling of the building engine.
Currently, the duration of the dismantling of a nuclear plant is estimated at 30 years between the reactor shut down and the handing-over of the site in an initial state.
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