Nuclear power plant

(States Twitter)-Nuclear power plant (NPP) is a thermal power station in which the heat source is one or more nuclear reactors.

Nuclear power plants are base load stations, which work best when the power output is constant (although boiling water reactors can come down to half power at night).

The conversion to electrical energy takes place indirectly, as in conventional thermal power plants: The heat is produced by fission in a nuclear reactor (in a coal power plant it would correspond to the boiler) and given to a heat transfer fluid - usually water (for a standard type light water reactor). Directly or indirectly water vapor-steam is produced. The pressurized steam is then usually fed to a multi-stage steam turbine. Steam turbines in Western nuclear power plants are among the largest steam turbines ever. After the steam turbine has expanded and partially condensed the steam, the remaining vapor is condensed in a condenser. The condenser is a heat exchanger which is connected to secondary side such as a river or a cooling tower. The water then pumped back into the nuclear reactor and the cycle begins again. The water-steam cycle corresponds to the Rankine cycle.

Nuclear reactors

See also: Nuclear reactor

A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. The most common use of nuclear reactors is for the generation of electric energy and for the propulsion of ships.

The nuclear reactor is the heart of the plant. In its central part, the reactor core's heat is generated by controlled nuclear fission. With this heat, a coolant is heated as it is pumped through the reactor and thereby removes the energy from the reactor. Heat from nuclear fission is used to raise steam, which runs through turbines, which in turn powers either ship's propellers or electrical generators.

Since nuclear fission is creates radioactivity, the reactor core is surrounded by a protective shield. This containment absorbed radiation and prevent radioactive material released into the environment. In addition, many reactors are equipped with a dome of concrete to protect the reactor against external impacts.

In nuclear power plants, different types of reactor, different nuclear fuels, differing cooling circuits and moderators are sometimes used.

Steam turbine

The object of the steam turbine is to convert the heat contained in steam into rotational energy. To the turbine shaft, the shaft of the generator is coupled. In nuclear power plants are mostly Saturated steam turbine Application. The turbine has a high-pressure part, and usually two or three low pressure stages. Due to the high moisture vapor after the high pressure part of the steam is dried before entering the low pressure part of means of steam heating and high-speed deposition. At the end of the last blade row of the low pressure part of the steam has a moisture content of about 15%. The expansion into the wet steam region leads to a high working efficiency, but with the disadvantages associated with wet steam.

If the generator to hand over by a disturbance generated electrical energy can, he takes little analogy to mechanical energy. In response to this Load drop would be the Speed the turbine to increase the allowable operating limit by the threat of self-destruction too high Centrifugal. To avoid this process, are close to the turbine inlet valves in the steam pipe installed. If this quick-closing valves activated, they direct the steam bypassing the turbine directly into the Capacitor. In parallel, the reactor is shut down because of the full reactor power capacitor can absorb only a limited time.

The engine house with the steam turbine is usually structurally separated from the main reactor building. It is oriented to fly from the destruction of a turbine in operation as no debris in the direction of the reactor.

In the case of a pressurized water reactor, the steam turbine hermetically separated from the nuclear system. To detect a leak in the steam generator and thus the passage of radioactive water at an early stage is the outlet steam of the steam generator mounted an activity meter. In contrast, boiling water reactors and the steam turbine with radioactive water applied and therefore part of the control area of ​​the nuclear power plant.

Generator

The generator converts kinetic energy supplied by the turbine into electrical energy. Low-pole AC synchronous generators of high rated power are used. The Olkiluoto nuclear power plant was the largest synchronous generator (as of 2010) made. It has a rated power 1992 MW.

Main coolant pump (PWR) and forced circulation pump (BWR)

The reactor coolant pump in the case of the DWR has the task to circulate the coolant between the reactor and steam generators. In western nuclear power plants, the nuclear reactor is fed with four redundant pumps (loops), each separated by Redundancy structurally accommodated in the reactor building. The design of the pump corresponds to a Centrifugal with a one-piece forged body. The throughput is up to 10,000 l / s at a pressure of 175 bar and a maximum allowable temperature of 350 ° C. The increase in pressure through the main coolant pump when DWR indicates pressure loss in the reactor, steam generators and piping system. Even after the failure of the main coolant pumps (RESA is the result of) the circulation and thus the heat dissipation is by so-called Natural circulation guaranteed.

In the case of boiling water reactor are the reactor pressure vessel forced circulation pumps to avoid core wings attached to their interpretation is approximately equal to those in a PWR. You are responsible for the safety of the plant is not absolutely necessary.

Besides these main coolant pump of a nuclear power plant has usually still have several emergency supplies at different pressure levels, the case of disturbances (see Design basis accident) Maintain the cooling of the reactor core.

Safety valves

The pressure in the reactor pressure vessel at an incident, to limit upward, two independent safety valves are available. The pressure relief prevents bursting of pipes or reactor. The valves are in their capacity designed so that they can derive all of the supplied flow rates with little increase in pressure. In the case of the BWR, the steam is directed into the condensate chamber and condenses there. The chambers are on heat exchanger connected to the intermediate cooling circuit.

Should not close the safety valves, are very close again safety shut any, should, if necessary, prevent coolant accident. The non-closing of a safety valve led to a serious accident at Three Mile Island.

History

Electricity was generated for the first time by a nuclear reactor on December 20, 1951 at the EBR-I experimental station near Arco, Idaho in the United States. On June 27, 1954, the world's first nuclear power plant to generate electricity for a power grid started operations at Obninsk, USSR . The world's first commercial scale power station, Calder Hall in England opened in October 17, 1956.

For more history, see nuclear reactor and nuclear power.

For information on the Chernobyl accident which only had a partial containment structure, see that subject and RBMK and nuclear power.