What is a nuclear powerplant?

A 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.

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

Main article: 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 creates radioactivity, the reactor core is surrounded by a protective shield. This containment absorbs radiation and prevents radioactive material from being 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 reactors, nuclear fuels, and cooling circuits and moderators are sometimes used.

Steam turbine

Main article: Steam turbine

The object of the steam turbine is to convert the heat contained in steam into rotational energy. The engine house with the steam turbine is usually structurally separated from the main reactor building. It is aligned to prevent debris from the destruction of a turbine in operation from flying towards the reactor.^{[citation needed]}

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

Main article: Electric generator

The generator converts kinetic energy supplied by the turbine into electrical energy. Low-pole AC synchronous generators of high rated power are used.

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.[13] 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.

 Feedwater pump

The Feedwater pump have the task of the water from the feedwater tank to the vapor pressure in the reactor and the steam generator to bring and promote a water with approximately 2200 kg / s. The power required amounts here to about 20 MW per pump. About the feed water system, the water level in the steam generator and nuclear reactor is controlled. Emergency power supply [Edit]

The Emergency power supply a nuclear power plant is several times redundant built up by diesel generators and battery buffers. The battery backup provides uninterrupted coupling of the diesel units in the network secure. If necessary, the emergency power supply allows the safe descent down the nuclear reactor. Less important auxiliary systems such as, for example, heat tracing of pipelines are not receiving it. The majority of the required power is used to supply the feed pumps and Notspeisepumpen order to shut down the nuclear reactor, the Decay heat even with a Failure of the power system, A Blackout permanently dissipate.