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Nuclear power engineering in the world

Increasingly more countries - both developed and developing — nowadays arrive to the necessity of commencement of developing the peaceful atom. Nowadays there a tendency in the world – so called «nuclear renaissance». The most  reserved forecasts say that in the perspective of  2030 up to 500 power units will be exploited on the planet  (for comparison, nowadays there are 435 power units).

Annually nuclear power plants in Europe enable to avoid 700 million tones of СО2 as emissions and in Japan — 270 million tones of СО2. Acting nuclear power stations in Russia annually prevent emission of 210 million tones of the carbonic acid gas to the atmosphere. By the given value our country is on the fourth place in the world only. 

The most nuclear power plants (63 nuclear power plant, 104 power units) are exploited in the United States. France is on the second place (58 power units), Japan is on the third place (50 power units). For comparison: in Russia 10 nuclear power plants (33 power units) are exploited.

The given list also includes 6 reactors in the Taiwan (China).

According to IAEA as of 26/06/2012.

The largest nuclear power plant in the word is Kashiwazaki Kariva (Japan) with the capacity of 8200 MW (7 BWR-type reactors with the installed capacity of 110—1356 Mw). The largest nuclear power plant in Europe is Zaporozhskaya nuclear power plant (Ukraine) with the capacity of 6000 MW (6 VVER-1000 reactors). In Russia Balakovskaya, Lenigradskaya, Kalininskaya and Kurskaya nuclear power plants have the largest capacity (4 reactors with the capacity of 1000 MW each).

Global warming is a hazardous process of a gradual rise of annual average temperature of the Earth atmosphere and World Ocean. One of the causes of this phenomenon is the so-called “greenhouse effect”: growing atmospheric content of carbonic acid (СО2), methane (CH4), nitrous oxide (N2O), perfluorocarbons (PFC), hydrofluorocarbons (HFC) and sulfur hexafluoride (SF6), with the ensuing rise of average air temperature near the Earth surface. Because of this effect, average Earth temperature became 0.74°C higher over the period from 1906 to 2005.

Climatic change effects already shown up, in particular, as more frequent and strong hazardous weather phenomena, sprawl of infectious diseases. Other possible effects include changes in precipitation rate and frequency, glacier thawing and sea level rise, growing threats to ecosystems and biodiversity. All this entails significant economic damage, puts in jeopardy ecosystem stability, as well as the human health and life. 

The conclusions made by scientists suggest that persisting climatic changes may have even more grave consequences in future if the mankind fails to take proactive preventive measures. Thus, scientists have proved that the thawing of permafrost soil may cause tens of times more intense production and emission of nitrous oxide N2O which has a greenhouse effect.

To control the climate changes, 159 countries signed in December of 1997 in Kyoto the so-called Kyoto agreement on reducing greenhouse gas emissions. A new agreement was to be signed in Copenhagen on December 7-18, 2009, but the potential signees failed to reach a consensus.

Broader use of non-carboric and renewable sources was recognized as a global warming control measure.

Three mutual transformations of the energy occur at the nuclear power plant: nuclear energy comes into the heat energy, the heat energy comes into the mechanical energy and mechanical energy comes into the electric energy.

In practice it looks as follows. The basis of the plant is a reactor, which is a structurally allocated volume, into which the nuclear fuel is loaded and where the controlled chain reaction takes place. Uranium-235 is divided by slow (heat) neutrons, as a result of which a huge amount of heat is released. The given heat is taken away from the active zone by a heat carrier – liquid or gaseous substance coming through the volume thereof. Mostly used heat carrier is water and in fast neutron reactors – metal melt (for example, sodium in the BN-600 reactor). Thus the most complex transformation – nuclear energy into the heat energy – is exercised. 

The heat taken away by the heat carrier in the active zone of the reactor is used for acquisition of a water vapor rotating the turbine of the electric generator. Mechanical energy of the vapor created in the vapor generator is directed to the turbogenerator, where it is transformed into the electric energy and further by wires comes to consumers. This is the way, in which the second and the third transformations occur. Then the vapor is refrigerated and the water condensate returns to the reactor once again for the repeated use.

What types of reactors exist and what is difference between them?

In Russia two types of reactors is exploited. For the single-loop nuclear power plant (RBMK (literally - large-capacity channel reactor) reactors) the heat carrier – vapor mix is created in the very reactor, is divided in to water, which returns to the loop by forced circulation, and the vapor, which is sent to the turbine. That’s why there is nor distinct division into the first and second loops for a single-loop nuclear power plant, and all equipment of the power plant is radioactive, although to a different degree. If the loop of the heat carrier (water) and the working medium (vapor) are divided, then such nuclear power plants are called two-loop nuclear power plants. Example is – VVER (literally – water moderated water-cooled energy reactor) reactor, which number at Russian nuclear power plants is the greatest. 

All reactors have their own fuel and other features. At plants with RBMK reactors the reactor itself represents a graphite stack (graphite performs the function of the neutron moderator), in which technological channels with the nuclear fuel are located. The water coming through the given technological channels is heated up to boiling. In the drum separator the vapor is separated from the water and then comes to the turbine, i.e. the vapor created upon water boiling in the active zone of the reactor comes to the turbine. After cooling in the condenser the vapor is condensed and the water with the help of pumps is returned to the reactor. Cooling of the condenser is exercised by the water from the cooling pond with the help of the pump. 

At two-loop nuclear power plants with VVER-type reactors the heat carrier loop works in radiation conditions and is called as the first loop контур. Heat carrier (pressurized water without boiling) by the main circulation pump is fed to the reactor, where it is heated and further comes to the vapor generator, where is give the heat to the vapor. Mechanical energy of the vapor creating in vapor generator is sent to the turbogenerator, where it is transformed into the electric one and comes to consumers. Water of the first loop coming through the active zone of the reactor where the nuclear fuel is located becomes radioactive. That’s way all equipment of the first loop has a protective casing. Vapor loop is not radioactive and is called as the second loop. The vapor created in the vapor generator is sent to the turbogenerator. After the turbogenerator the vapor comes to the condenser, where it is condensed and by the pump the vapor is fed to the vapor generator. Then the condensate is cooled in the recirculation cooling system. The given systems may be of the following three types – with cooling towers, cooling ponds and sprinkling basins.

What a nuclear power plant represents?

Nuclear power plant in any country represents a set of buildings, in which the relevant technological equipment is located. The main building, in which a reactor room is located, is the basic one. The very reactor, the basin for maturing of the nuclear fuel and fuel-handling machine (for fuel loading) are located therein, and all this equipment is under supervision by operators of the block control board.

The main element of the reactor is the active zone. It is located in the concrete shaft. Compulsory elements of any reactor are the control and protection system enabling to exercise the selected mode of the controlled chain fission reaction, and the emergency protection system for rapid termination of the reaction upon occurrence of any emergency situation. All this is mounted in the main building.

There is also the second building, in which the turbine room is located: vapor generators and the turbine itself. Further by the processing chain are condensers and high-voltage power lines coming outside the boarder of the plant site. There are also building for handling and storage of the depleted nuclear fuel in special basins and administrative buildings on the territory. Besides, plants are equipped, as a rule, by some elements of the recirculation cooling system – cooling towers (concrete tower contracting upwards), cooling pond (whether natural or artificially created) or sprinkling basins (big basins with sprinkling devices).

Scheme of the nuclear power plant