There are two reactor cores at Hartlepool Power Station.
Hartlepool Nuclear Power station generates 3% of Britain's energy, but decommisioning is scheduled for 2014.
The government has named Hartlepool on a list of eight sites in England and Wales where new nuclear power stations could be built.
The list, announced in October 2010, replaced a tally of 11 locations given initial approval by the previous Labour government.
The proposed new power stations are still subject to planning approval.
The present power station has two reactors, each generating 600MW of electricity. If a new reactor were to be built, it would be one of a new generation of facilities, with just one reactor generating 1800MW.
The other major difference would be what happens to the waste. At the moment it is taken to Sellafield by train, the new generation plants are expected to store the waste on site.
Plant tour: Radiation screening
All staff leaving the reactor core have to be screened for radiation.
Everyone who needs access to the reactor building is logged on a computer and given a PIN. Once they enter the building, that PIN is used to issue them with a personal dosimeter that must be worn at all times inside the reactor building.
On leaving the reactor head, all visitors and staff must wash their hands, before being screened with a hand held radiation detector, much the way security guards check passengers at an airport.
This is followed by a stage two screening, in which the individual places their hands inside a stronger detector and stand on detector pads to check their boots.
They then move on into a second room, where there is a full body detector. Only once they have passed through this can they leave, and the exit is on the other side.
Plant tour: Reactor core
Hartlepool Power Station has two reactor cores.
Enriched uranium from Preston is arranged into long rods, then submerged in water inside a pressure vessel.
Within the Uranium, neutrons collide with the nuclei of the atoms, splitting them in two and releasing more neutrons in the process. These neutrons then collide with other nuclei, perpetuating the process, which releases vast amounts of heat energy.
At this stage, left to their own devices, the rods would eventually overheat and melt.
To prevent this, control rods made from a material that absorbs neutrons are inserted between the uranium fuel rods.
These control rods can be moved up and down within the reactor to control the number of neutrons that are removed from the process. This allows operators to vary the speed of the reaction and the energy released.
The heat is used to take water from 300C, at a pressure of 1,450 pounds per square inch and raise it up to 600C and a pressure of 2,320 pounds per square inch. Once the superheated steam is at this temperature and pressure, it is ready to generate power for the National Grid in the Turbine Room.
Plant tour: turbine room
The turbine room at Hartlepool Power Station.
When it comes out of the reactor, the steam is superheated to 600C and at a pressure of 160 Bar.
It is used to drive five turbines. As it passes through each turbine, the steam loses energy, so each is designed to generate the maximum amount of energy at consecutively lower pressures. The turbine room contains one high pressure turbine, one intermediate pressure turbine and three low pressure turbines.
The turbines turn a 600MW generator. The water then has to be cooled, courtesy of the River Tees.
Plant tour: Water intake
One of the screening drums at Hartlepool Power Station.
Once the steam has generated as much electricity as it can (Hartlepool Nuclear Power Station is about 40% efficient), it's still too hot to go back into use.
To get the water down to the 300C they need to feed the reactor, the steam passes through a condenser, where it is cooled by water collected from the River Tees.
The water is collected, filtered and then pumped through a unit full of cooling pipes, through which the steam passes as it is slowly cooled by the river water.
Once the water has been used, it has to be left to cool itself, before being pumped out to the North Sea meaning, effectively, part of the River Tees flows through the power plant.