Nuclear power station

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The production of electricity happens indirectly. The warmth, which develops during the nuclear fission, is transferred to a cooling agent, whereby this is warmed up. Under normal conditions the cooling agent consists of water; during the heating up water vapour is produced, which propels then a steam turbine. A nuclear power station in most cases consists of several blocks, which produce completely independently electric current for itself. Beginning of 2006 were world-wide 442 nuclear power stations at the net. Planned the building of 120 to 140 new nuclear power stations is world-wide in the next 10 years.

Also a future fusion reactor would be a nuclear power station. However the power production from nuclear fusion is in the technical yardstick so far only still far to article of research and development and of the industriellen use (conditions: 2006).

Introduction and word origin

Physical basis for the enterprise of a nuclear power station is the thermal energy, which develops for E = m C during splitting of atomic nuclei due to a mass defect after the relationship formulated by Einstein '' ''.

For the energy freed with nuclear reactions and radioactive transformations 1899 the term atomic energy was coined/shaped by Hans Geitel; at that time however the knowledge of the structure of atoms was missing. Due to these realizations, in particular the knowledge about the existence of the atomic nucleus, is the today's correct scientific technical term nuclear energy. Derived from it the synonymous terms nuclear power station (KKW) and atomic power plant (nuclear power plant) developed. The term atomic power plant was used 1960 for the experimental nuclear power station bald. 1966 were used (similarly for example to the English designation Nuclear power plans - NPP) for the power stations Rhine mountain and Gundremmingen A the designation nuclear power station.

Reactor types and function mode

In nuclear power stations different reactor types are used, which by the used nuclear fuels, cooling circuits and moderators to essentially differ. The most important are:

• Light-water reactor (LWR): As reactor coolant here light water is used, which is the water most frequently occurring in nature, in an educated manner with the light hydrogen isotope 1H. The light water serves at the same time as moderator. As fuel enriched uranium with a U-235 proportion between approximately 1.5 and 6 per cent is suitable. The LWR implemented as
  • Pressurized water reactor (DWR): The reactor coolant transports the nuclear fission warmth in a closed cycle, which primary cycle, from the reactor pressure vessel to several steam generators, with which in a secondary cycle steam is produced for the drive of the turbines. This secondary cycle is not any more part of the controlled area. The turbines remain free by radioactive pollution. To the type of the pressurized water reactors also the European Pressurized Water Reactor (EPR) belongs.
  • Boiling water reactor (SWR): The reactor coolant in the reactor pressure vessel one evaporates and directly to the turbines one supplies. The entire water vapour cycle is thereby part of the controlled area. Favourably opposite the DWR the something is unfavorable better efficiency and the simpler, more economical structure, the radioactive pollution in the steam system and the technical complication by the two-phase mixture from water and steam bubbles in the reactor.

• Heavy-water reactor (HWR): Heavy water (D2O) as reactor coolant becomes with heavy hydrogen, which deuterium, in an educated manner, absorbs that neutrons less strongly. Therefore nature uranium with a proportion at U-235 can be used of approximately 0.7 per cent as fuel.

• RBMK: The RBMK is a reactor of Soviet design, which graphite as moderator and water use as cooling agent, therefore can to the enterprise uranium with the natural isotopic distribution be used. The design makes the enterprise of these reactors very uncertain, therefore they are not no more built after the disaster by Tschernobyl. However still some reactors of this design with some technical improvements are further in enterprise in the area of the former Soviet Union.

• Liquid metal-cooled breeder reactor (fast breeder): The breeder reactor produces fissile plutonium from the otherwise not usable uranium isotope 238 during the enterprise. Liquid sodium, which does not brake neutrons ("“moderates"”), as reactor coolant begun and warms up a second, radioactivity-free sodium cycle over an intermediate heat exchanger. This produces steam for the turbine in the steam generator. The sense of the technically fastidious breeder reactor technology is those approx. 30 times better utilization of the uranium, which could be obtained in the group of breeder reactors, reprocessing and light-water reactors.

• High-temperature reactor (HTR): This type of reactor uses Heliumgas as cooling agent and graphite as moderator. The primary nuclear fuel is 235U, besides bred nuclear fuel contributes to the energy production. The fuel elements are enclosed in Graphitkugeln and form in the reactor core a globular cluster - therefore also the designation pebble-bed reactor. With a high-temperature reactor a relatively high use temperature from 300 to 950 "°C, therefore also its name develops. The thorium high-temperature reactor (THTR) served as prototype for this system.

The most important component of a nuclear power station is the nuclear reactor. In it the splitting processes take place. Many nuclear power stations are built with several nuclear reactors, which per their own steam generators, turbine and generator to float. In such a case one speaks of several reactor blocks.

Fuel

As nuclear fuel in most nuclear power stations operated today enriched uranium (U-235 portion approx. 3%-4%) is used. There are world-wide many power stations with a use license for MOX fuel elements, so also in Germany. Mixing oxide (MOX) is a mixture made of uranium oxide and plutonium oxide. Plutonium has a higher energy output as fuel, is thus more efficient than uranium. The use of higher plutonium portions (Pu-239) in the MOX is however both due to the capable of bearing armsness of the plutonium and disputed because of the higher safety requirements of a reactor operated with plutonium, e.g. breeder reactor.

Reactor regulation

(S. also criticality) depending upon type of reactor there are different procedures to adjust the thermal achievement. For this for example gradual bringing of the control rods in and the adjustment of the boron concentration in the primary cycle count. The reactor can be regulated, started and switched off over its neutron flux, by one neutron-absorbing materials as for instance cadmium, gadolinium or boron gives to the reactor core, and/or neutron-slowing down materials (so-called moderators) like graphite, water, or heavy water adds or removes. This takes place e.g. at short notice with the help of the control rods and with pressurized water reactors at longer term by means of addition and/or withdrawal of boric acid in the reactor cooling circuit. In practice the electrical achievement at the turbine governor, which can be produced from the generator to, is given and the thermal achievement of the reactor is adjusted automatically.