Radioactive waste is one of the biggest problems the nuclear industry faces.
The greatest concern is the small proportion of nuclear waste that is "high-level waste" - waste so radioactive that it generates heat and corrodes all containers, and would cause death within a few days to anyone directly exposed to it.
In the UK this accounts for less than 0.3% of the total volume of nuclear waste but accounts for about half the total radioactivity.
No man-made container could survive the tens of thousands of years it will take for high-level waste to decay to safe levels.
No country has yet implemented a long-term solution to this problem, although Finland and the US have plans to build repositories deep underground in areas identified for their geological stability. This solution is one of those under consideration in the UK.
Spent nuclear fuel is highly radioactive, but can be reprocessed to extract the remaining usable uranium and plutonium, a process which reduces the need to mine fresh uranium and cuts the volume of waste.
In countries where reprocessing takes place, high-level radioactive waste is the waste left behind after the uranium and plutonium have been extracted. In the UK, this is treated as shown in the graphic above.
In these countries, spent fuel, uranium and plutonium are not currently categorised as wastes (because they can be used), although they must be stored like radioactive wastes - and there is the added security concern that plutonium can be used to make nuclear bombs.
If reprocessing is not part of the cycle, the spent fuel itself is high-level waste.
Intermediate level wastes are mixed with concrete and stored in tanks, drums and vaults at the sites where they are created.
If the UK's reactors all operate to their current shutdown dates and no more are built, there will be an estimated 36,590 cubic metres - enough to fill 14 Olympic-sized swimming pools - of intermediate and high level waste in the UK.
Most of the country's low-level waste is stored in sealed concrete vaults at a purpose-built store in Drigg, Cumbria, although some is considered safe enough to go into hazardous waste landfill sites.
The Drigg store currently contains 960,000 cubic metres - equivalent to 384 Olympic swimming pools - of waste.