Filaments in bulbs are made of thin tungsten wire. When a current flows through tungsten wire it becomes white hot at about 2500deg C. The dissipation of heat through the glass bulb however, avoids the temperature reaching the melting point of tungsten which is 3380deg C.

Using Nuclear Power

A nuclear reactor produces it's useful energy mainly in the form of hot steam, which issues from the heat exchanger connected to the reactor core. The generation of electricity is the main task that we have given to this energy. As in oil fired and coal fired power stations, the steam drives turbines which in turn power large generators. The electricity then produced is fed into the national grid - the national network of electricity supply lines. My sketch below shows a simplified diagram of a water cooled reactor.

How a Reactor Works

The designers of nuclear reactors face many problems. They have to get the heat produced by fission out of the reactor, but they have keep the radiation and neutrons emitted whenfission occurs inside the reactor. The chain reaction must proceed at just the right pace - too slow and it will stop, too fast and the reactor will overheat. Another problem concerns the neutrons circulating in the reactor. These must not be allowed to take up too much energy because nuclear fuel undergoes fission most readily when struck by slow neutrons. fast moving neutrons tend to bounce off the fissile atoms instead of entering them and producing fission.

The centre of the reactor is called the core. Here the nuclear fuel is housed inside Fuel rods. Around it is placed a moderator - a substance that acts to slow neutrons, such as graphite or water. Control rods made of neutron absorbing materials such as cadmium or boron are also inserted into the core. If the chain reaction needs to be slowed or stopped, the control rods are pushed into the core to remove some of the neutrons causing fission. To remove the heat produced in the fuel rods, a liqued or gaseous coolant is pumped through the core. When it leaves the core, it goes to a Heat exchanger, where it gives up it's heat before returning to the core. The whole core is surrounded by a thick shield of concrete or immersed in a deep tank of water to prevent neutrons and gamma rays escaping. The control rods are operated and new fuel rods are fed into the reactor by machines outside the core.

Electricity is measured in units of power called watts. It was named in honour of James Watt, the inventor of the steam engine. One watt is a very small amount of power. It would require nearly 750 watts to equal one horsepower. A kilowatt represents 1,000 watts. A kilowatt-hour (kWh) is equal to the energy of 1,000 watts working for one hour. The amount of electricity a power plant generates or a customer uses over a period of time is measured in kilowatthours (kWh). Kilowatthours are determined by multiplying the number of kW's required by the number of hours of use. For example, if you use a 40-watt light bulb 5 hours a day, you have used 200 watts of power, or .2 kilowatthours of electrical energy.