Nuclear Power Plant

Nuclear Powerplant plant

•is a thermal power station in which the heat source is a nuclear reactor. As is typical in all conventional thermalpower stations the heat is used to generate steam which drives a steam turbine connected to a generator which produces electricity. As of 16 January 2013, the IAEA report there are 439 nuclear power reactors in operation operating in 31 countries.

•Nuclear power plants are usually considered to be base load stations, since fuel is a small part of the cost of production.

The Process

• In a nuclear-fueled power plant – much like a fossil-fueled power plant – water is turned into steam, which in turn drives turbine generators to produce electricity. The difference is the source of heat. At nuclear power plants, the heat to make the steam is created when uranium atoms split – called fission. There is no combustion in a nuclear reactor. Here’s how the process works.

Pressurized Water ReactorPressurized Water Reactors (also known as PWRs) keep water under pressure so that it heats, but does not boil. This heated

water is circulated through tubes in steam generators, allowing the water in the steam generators to turn to steam,

which then turns the turbine generator. Water from the reactor and the water that is turned into steam are in separate

systems and do not mix.

Boiling Water ReactorIn Boiling Water Reactors (also known as BWRs), the water heated by fission actually boils and turns into steam to turn the turbine generator. In both PWRs and BWRs, the steam is turned back into water and can be used again in the process.

Energy source

• Nuclear power stations work in pretty much the same way as fossil fuel-burning stations, except that a "chain reaction" inside a nuclear reactor makes the heat instead.

• The reactor uses Uranium rods as fuel, and the heat is generated by nuclear fission: neutrons smash into the nucleus of the uranium atoms, which split roughly in half and release energy in the form of heat.

• Carbon dioxide gas or water is pumped through the reactor to take the heat away, this then heats water to make steam.

• The steam drives turbines which drive generators.

• Modern nuclear power stations use the same type of turbines and generators as conventional power stations.• In Britain, nuclear power stations are often built on the coast, and use sea water for cooling the steam ready to

be pumped round again. This means that they don't have the huge "cooling towers" seen at other power stations.

• The reactor is controlled with "control rods", made of boron, which absorb neutrons. When the rods are lowered into the reactor, they absorb more neutrons and the fission process slows down. To generate more power, the rods are raised and more neutrons can crash into uranium atoms.

Efficiency

• One measure the efficiency of power plants that convert a fuel into heat and into electricity is the heat rate, which is the amount of energy used by an electrical generator or powerplant to generate one kilowatt-hour (kwh) of electricity. EIA expresses heat rates in British thermal units (Btu) per net kwh generated. Net generation is the amount of electricity a power plant (or generator) supplies to the power transmission line connected to the power plant. It accounts for all the electricity that the plant itself consumes to operate the generator and other equipment, such as fuel, feeding systems, boiler water pumps, cooling equipment, pollution control device and others.

• To express the efficiency of a generator or powerplant as a percentage, divide the equivalent Btu content of a kwh of electricity (which is 3,412 Btu) by the heat rate.

Emergency power supply

• The emergency power supplies of a nuclear power plant are built up by several layers of redundancy, such as diesel generators, gas turbine generators and battery buffers.

Feedwater pump

• The water level in the steam generator and nuclear reactor is controlled using the feedwater system. The feedwater pump has the task of taking the water from the condensate system, increasing the pressure and forcing it into either the Steam Generators (Pressurized Water Reactor) or directly into the reactor vessel (Boiling Water Reactor).

Safety valves• In the event of an emergency, two independent safety valves can be used to prevent pipes from bursting or the

reactor from exploding. The valves are 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 on a heat exchanger are connected to the intermediate cooling circuit.

Cooling system• A cooling system removes heat from the reactor core and transports it to another area of the plant, where the

thermal energy can be harnessed to produce electricity or to do other useful work. Typically the hot coolant is used as a heat source for a boiler, and the pressurized steam from that boiler powers one or more steam turbine driven electrical generators.[10]

Nuclear reactors

• 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

Steam turbine

• The purpose of the steam turbine is to convert the heat contained in steam into mechanical energy.

Generator

• The generator converts kinetic energy supplied by the turbine into electrical energy.

Waste streams

• Nuclear power has at least four waste streams that may harm the environment:• spent nuclear fuel at the reactor site (including fission products and plutonium

 waste)• tailings and waste rock at uranium mines and mills• releases of small amounts of radioactive isotopes during reactor operation• releases of large quantities of dangerous radioactive materials during 

accidents• The nuclear fuel cycle involves some of the most dangerous elements and

isotopes known to humankind, including more than 100 dangerous radionuclides and carcinogens such as strontium-90,iodine 131 and cesium -137, which are the same toxins found in the fall out of nuclear weapons".

Radioactive Waste

• The most long-lived radioactive wastes, including spent nuclear fuel, must be contained and isolated from humans and the environment for a very long time. Disposal of these wastes in engineered facilities, or repositories, located deep underground in suitable geologic formations is seen as the reference solution

• Common elements of repositories include the radioactive waste, the containers enclosing the waste, other engineered barriers or seals around the containers, the tunnels housing the containers, and the geologic makeup of the surrounding area.

Greenhouse gas emissions

• Nuclear power plant operation emits no or negligible amounts of carbon dioxide. However, all other stages of the nuclear fuel chain — mining, milling, transport, fuel fabrication, enrichment, reactor construction, decommissioning and waste management — use fossil fuels and hence emit carbon dioxide.There was a debate on the quantity of greenhouse gas emissions from the complete nuclear fuel chain.

• Many commentators have argued that an expansion of nuclear power would help combat climate change. Others have pointed out that it is one way to reduce emissions, but it comes with its own problems, such as risks related to severe nuclear accidents the challenges of more radioactive waste disposal. Other commentators have argued that there are better ways of dealing with climate change than investing in nuclear power, including the improved energy efficiency and greater reliance on decentralized and renewable energy sources.