Each reactor core is made up of around 6,000 blocks (3,000 of these are graphite bricks containing fuel channels) which are all connected together.
Uranium fuel is inserted into the graphite core through channels. Control rods, containing boron, are also inserted through other channels to control the reaction; they are also used to shut down the reactor. The graphite core also performs an important safety function by providing the structure which allows CO2 gas to flow through the reactor, removing heat from the nuclear fuel and providing heat to the boilers.
During the normal operation of the reactors the structure of the graphite bricks will change, including some cracking in some of the bricks as they age or through loss of weight. This is in line with our expectations and is included in the design and safe operation rules for the stations, and within the limits approved by our independent regulator, the Office for Nuclear Regulation (ONR).
EDF Energy has an extensive graphite research programme which benefits from the expertise of our own team of graphite specialists, along with expert academics at several universities across the U.K. This has allowed us to develop an extensive understanding of how our reactor cores age.
- You can find out more about how a nuclear reactor works here
- For more information on the International Atomic Energy Authority's (IAEA) graphite knowledge base, click here
- The Office for Nuclear Regulation has produced some helpful background information on graphite here
- You can find a useful film by Dr Jim Reed, graphite expert, here. This includes a 1/4 scale model of the graphite core on the shaker table for seismic behaviour.