Nuclear centrals:
Components of a nuclear centrals:
Nuclear reactor:
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Nuclear reactors are used at nuclear power plants for electricity generation and in propulsion of ships. Heat from nuclear fission is passed to a working fluid (water or gas), which runs through turbines. These either drive a ship's propellers or turn electrical generators. Nuclear generated steam in principle can be used for industrial process heat or for district heating. Some reactors are used to produce isotopes for medical and industrial use, or for production of plutonium for weapons. Some are run only for research.
Components of a nuclear reactor
There are several components common to most types of reactors:
Fuel. Uranium is the basic fuel. Usually pellets of uranium oxide (UO2) are arranged in tubes to form fuel rods. The rods are arranged into fuel assemblies in the reactor core.*
* In a new reactor with new fuel a neutron source is needed to get the reaction going. Usually this is beryllium mixed with polonium, radium or other alpha-emitter. Alpha particles from the decay cause a release of neutrons from the beryllium as it turns to carbon-12. Restarting a reactor with some used fuel may not require this, as there may be enough neutrons to achieve criticality when control rods are removed.
* In a new reactor with new fuel a neutron source is needed to get the reaction going. Usually this is beryllium mixed with polonium, radium or other alpha-emitter. Alpha particles from the decay cause a release of neutrons from the beryllium as it turns to carbon-12. Restarting a reactor with some used fuel may not require this, as there may be enough neutrons to achieve criticality when control rods are removed.
Moderator. Material in the core which slows down the
neutrons released from fission so that they cause more fission. It is
usually water, but may be heavy water or graphite.
Control rods. These are made with neutron-absorbing
material such as cadmium, hafnium or boron, and are inserted or
withdrawn from the core to control the rate of reaction, or to halt
it.* In some PWR reactors, special control rods are used to enable the
core to sustain a low level of power efficiently. (Secondary control
systems involve other neutron absorbers, usually boron in the coolant –
its concentration can be adjusted over time as the fuel burns up.)
* In fission, most of the neutrons are released promptly, but some are delayed. These are crucial in enabling a chain reacting system (or reactor) to be controllable and to be able to be held precisely critical.
* In fission, most of the neutrons are released promptly, but some are delayed. These are crucial in enabling a chain reacting system (or reactor) to be controllable and to be able to be held precisely critical.
Coolant. A fluid circulating through the core so as
to transfer the heat from it. In light water reactors the water
moderator functions also as primary coolant. Except in BWRs, there is
secondary coolant circuit where the water becomes steam. (See also later
section on primary coolant characteristics)
Pressure vessel or pressure tubes. Usually a robust
steel vessel containing the reactor core and moderator/coolant, but it
may be a series of tubes holding the fuel and conveying the coolant
through the surrounding moderator.
Steam generator.(not in BWR) Part of the cooling
system where the high-pressure primary coolant bringing heat from the
reactor is used to make steam for the turbine, in a secondary circuit.
Essentially a heat exchanger like a motor car radiator*. Reactors may
have up to four 'loops', each with a steam generator. Since 1980 some
110 PWR reactors have had their steam generators replaced after 20-30
years service.
* These are large heat exchangers for
transferring heat from one fluid to another – here from high-pressure
primary circuit in PWR to secondary circuit where water turns to steam.
Each structure weighs up to 800 tonnes and contains from 300 to 16,000
tubes about 2 cm diameter for the primary coolant, which is radioactive
due to nitrogen-16 (N-16, formed by neutron bombardment of oxygen, with
half-life of 7 seconds). The secondary water must flow through the
support structures for the tubes. The whole thing needs to be designed
so that the tubes don't vibrate and fret, operated so that deposits do
not build up to impede the flow, and maintained chemically to avoid
corrosion. Tubes which fail and leak are plugged, and surplus capacity
is designed to allow for this. Leaks can be detected by monitoring N-16
levels in the steam as it leaves the steam generator.
Containment. The structure around the reactor and
associated steam generators which is designed to protect it from outside
intrusion and to protect those outside from the effects of radiation in
case of any serious malfunction inside. It is typically a metre-thick
concrete and steel structure.
The terrestrial environment is contaminated by radionuclides in air, rain , irrigation , soil, etc. . leaks from nuclear facilities, waste storage or nuclear weapons explosions . Radionuclides can enter the cycle of matter , joining the primary producers of biomass - plants, fungi, algae , bacteria, And through them pass to animals and humans.
Another problem is the release of water in the sea despite being treated may affect the marine ecosystem.
Definetelly, nuclear power plants are a factory of plutonium -239 a (chemical and radioactively ) nonexistent extremely toxic element in the biosphere and uranium -238 or depleted . The latter is used in the lining of all types of ammunition , at the time of impact becomes a flammable aerosol when contacted with oxygen . These micron particles , transported by wind and rain over long distances, remain in the environment for thousands of years and becoming emitting radioactivity by decay into other elements of increased radioactive intensity.
The operation:
Nuclear power plants consist mainly of four parts:
- The nuclear reactor , where the nuclear reaction.
- The steam generator ( only in PWR plants ) .
- The turbine , which drives an electric generator to produce electricity from steam expansion .
- The condenser , a heat exchanger that cools the steam transforming back into liquid .
- The nuclear reactor is in charge of carrying the fission or fusion of the atoms of the nuclear fuel, such as uranium , plutonium generated as waste , releasing a large amount of heat energy per unit mass of fuel .
- The steam generator is a heat exchanger that transfers heat from the primary circuit , through which water is heated in the reactor circulates , the secondary circuit , changing the water into steam which is subsequently expanded in the turbine , producing movement of the fabric which in turn rotate the generator , producing electricity. Through a transformer to the electrical network voltage electricity transmission is increased.
- After expansion in the steam turbine is condensed in the condenser , where it transfers heat to the cold water coolant in PWR plants comes from cooling towers . A condensed time, returns to the nuclear reactor to begin the process again.
- Nuclear plants are always close to a cold water supply such as a river , lake or sea, to the cooling circuit using either cooling towers or not.
Types of nuclear centrals:
Nuclear centrals in Spain:
- Santa María de Garoña. Situada en Garoña (Burgos). Construida entre 1966 y 1970. Puesta en marcha en 1970. Tipo BWR. Potencia 466 MWe. Su refrigeración es abierta al río Ebro. Cierre programado para julio de 2013.11
- Almaraz I. Situada en Almaraz (Cáceres). Puesta en marcha en 1980. Tipo PWR. Potencia 980 MWe. Su refrigeración es abierta al embalse artificial (creado para ese fin) de Arrocampo.
- Almaraz II. Situada en Almaraz (Cáceres). Puesta en marcha en 1983. Tipo PWR. Potencia 984 MWe. Su refrigeración es abierta al embalse artificial (creado para ese fin) de Arrocampo.
- Vandellós II. Situada en Vandellós (Tarragona). Puesta en marcha en 1987. Tipo PWR. Potencia 1.087,1 MWe.
- Trillo. Situada en Trillo (Guadalajara). Puesta en marcha en 1987. Tipo PWR. Potencia 1.066 MWe.
Proyectos paralizados en la moratoria nuclear:
- Lemóniz I y II (Vizcaya).
- Valdecaballeros I y II (Badajoz).
- Trillo II (Guadalajara).
- Escatrón I y II (Zaragoza).
- Santillán (Cantabria).
- Regodela (Lugo).
- Sayago (Zamora).
The afectation in nature:
The activity related to nuclear energy, even in the absence of accidents, resulting in a high concentration of radioactive materials , which has serious consequences for human health and other living beings. The main damage to health are realized by the ability of radioactive substances , especially when we eat , to alter the DNA in our cells , making them prone to cancer.The terrestrial environment is contaminated by radionuclides in air, rain , irrigation , soil, etc. . leaks from nuclear facilities, waste storage or nuclear weapons explosions . Radionuclides can enter the cycle of matter , joining the primary producers of biomass - plants, fungi, algae , bacteria, And through them pass to animals and humans.
Another problem is the release of water in the sea despite being treated may affect the marine ecosystem.
Definetelly, nuclear power plants are a factory of plutonium -239 a (chemical and radioactively ) nonexistent extremely toxic element in the biosphere and uranium -238 or depleted . The latter is used in the lining of all types of ammunition , at the time of impact becomes a flammable aerosol when contacted with oxygen . These micron particles , transported by wind and rain over long distances, remain in the environment for thousands of years and becoming emitting radioactivity by decay into other elements of increased radioactive intensity.
The transformation of energy:
History of nuclear centrals:
- 1st Period: The first nuclear power plant was to be built in the former USSR in 1954, the only country with a center of this kind, until in 1957 built two central UK. Already in this first period there were accidents like those at Mayac (Russia), which killed over 200 people, and Windscale (UK), which pollute an area of 500 km2, which do not come to light until years later, favoring the proliferation of these plants.
- 2nd Period: a second time, when the oil crisis caused many industrialized countries to bet on this technology within its energy development plans, governments saw nuclear energy system to produce electricity at a lower cost opens , and in principle, it was less aggressive to the environment than other systems. This explains that since 1960, where the total was 16 plants worldwide, you switched to 416 in 1988.
- 3rd Period: Acts as Chernobyl, made him the confidence that had hitherto never recovered. In Chernobyl (Ukraine) April 26, 1986, radioactive and toxic materials are expelled 500 times that were released by the atomic bomb dropped on Hiroshima in 1945. There is talk of more than 200,000 cancer deaths related to the accident, and an area where the radioactivity will not disappear until after 300,000 years.
Today there are 443 nuclear power plants in the world accounting for 17% of global electricity production. The EEUU is the country with most nuclear centrals, they have 104, France have 58 almost 15 times less surface than EEUU, in Japan there are 54 but are not in operation, and in Spain there are 8 nuclear reactors.
No hay comentarios:
Publicar un comentario