A gas-cooled nuclear reactor consists of the reactor itself and a heat exchanger. The reactor contains uranium fuel elements which are surrounded by graphite moderators and topped by charge tubes for loading fuel elements, and boron control rods. The whole reactor is contained in a pressure vessel surrounded by a concrete shield.

From the reactor the hot gas flows through a duct into the heat exchanger which is outside the concrete radiation shielding. In the heat exchanger, steam is generated in a secondary loop. There a pipe brings in water which is heated to steam, and this then flows out to the turbo-alternator. Meanwhile the hot gas sinks to the bottom of the heat exchanger and passes through a gas blower which pushes it into a cool gas duct and back to the reactor.

As can be seen, this is a continuous cycle that keeps the reactor from overheating, while carrying away the heat and steam, which will power the turbines.

(161 words)

The two diagrams show how electricity can be generated from the rise and fall of water caused by sea waves.

The process involves a structure which is mounted on the side of a cliff or sea wall. This structure consists of a large chamber. One end is open to the sea, and the other leads into a vertical column, which is open to the atmosphere. A turbine is installed inside this column and this is used to generate the electricity in two phases.

The first diagram indicates that when a wave approaches the device, water is forced into the chamber, applying pressure on the air within the column. This air escapes to atmosphere through the turbine, thereby producing electricity.

The second diagram illustrates the next part of the process when wave retreats. As the water level falls, the air from outside the column is sucked back in through the turbine. As a result, electricity continues to be generated. The turbine rotates only in one direction, regardless of the direction of the air flow.

In conclusion, we can see that this structure is useful as electricity is generated in both phases: entering and retreating of water.

(195 words)

Ocean thermal energy conversion (OTEC) is a system that converts heat energy into the electric power using the temperature difference between surface seawater, which can be up to 29 degrees Celsius, and deep seawater, which is only 5 degrees Celsius.

The main components of the system are an evacuated evaporation chamber, a turbine and a condensing chamber. The solar energy of the sun heats up the surface water and this warm water is introduced into the evacuated evaporation chamber, where it boils. As it boils, salt is deposited and water vapour is generated. This vapour then drives a turbine to generate electricity. After it powers the turbine, the water vapour enters the condensing chamber, which is cooled by the water from the depths of the ocean. The water vapour is condensed in this chamber, producing drinking water. Meanwhile, waste salt water is discharged into the ocean and the process can be repeated.

(152 words)

The diagram illustrates how aluminium cans are recycled. First, the cans need to be taken to special collection centres instead of being thrown away with the normal refuse. The cans are collected from here and taken to a factory where they are first sorted and then cleaned. Next, the cans are shredded and crushed in a special machine.

The metal is then heated to a high enough temperature to allow the aluminium to melt. It is then rolled out flat to a thickness of between 2.5mm and 6 mm, depending on what it is going to be used for. The aluminium is now ready to be recycled into new packaging, such as drink containers. Finally, the new cans are delivered to a soft drinks factory where they are filled. The cans can now be sold to the public and reused. In the UK, 74 per cent of all aluminium cans that are sold are recycled.

(155 words)

This diagram shows that there are a number of processes involved in the commercial production of frozen fish pies. The main ingredients consist of fresh salmon, peas and sauce, with sliced potatoes, and they are prepared separately. The potatoes, which may have been delivered up to a month in advance, are cleaned, peeled and cut into slices. The slices are boiled and then chilled before being stored until needed. The preparation of the fish is more labour intensive than the preparation of the potatoes. Within twelve hours of being delivered to the factory, the fresh fish is cooked by being steamed with lemon juice and salt. Then the skin and bones are removed by hand and disposed of, before a visual inspection takes place.

After this, the pies are assembled in microwaveable containers Peas and sauce, which have also been prepared, are added to the fish and then the pie is covered with a layer of cooked potato slices. The pies are then wrapped and frozen. At this point, they are ready for dispatch, or they may be stored at the factory before being dispatched.

(185 words)

The diagram shows a process for producing electricity for home use. The equipment consists of a large tank, boxes and pipes that would be able to fit into a garage-sized room.

Electricity is produced using methane gas, generated from a mix of compost and water in a large steel tank. The tank is about the same height as a person and about twice as wide. Methane rises to the top of the tank and is collected and stored in a gas storage system. The stored gas is the fuel source used in the energy conversions that happen next.

Once compressed in a gas compressor, the methane fuels a combustion engine, which in turn produces mechanical energy. Having been transferred to a generator, the mechanical energy is then transformed into electrical energy, which is then stored in a battery. At this stage the electricity is ready for home use.

(150 words)