Nuclear power reactors produce different kinds of nuclear waste, but the most important is spent fuel.
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When uranium fuel has been burned-up and removed from a reactor it is extremely radioactive and is stored in underwater cooling ponds nearby which physically resemble a deep swimming pool. The pond water must be cooled because the spent fuel temperature remains hot for several years.
Water in the cooling ponds provides a very effective radiation shield until fission product radiation in the spent fuel has decayed appreciably. After five years cooling the spent fuel is removed from the cooling pond and either recycled in a reprocessing plant or placed in a dry spent fuel store. Nuclear reactors produce a remarkably small volume of radioactive waste compared with their electricity output.
The government's CoRWM committee estimated that the construction of a new fleet of ten PWR reactors to replace the UK's retiring 11GWe nuclear power fleet would produce only 32,000 cubic metres (14,000 tonnes) of spent fuel over their future 40 year working lifetime.
This is about the same volume as eight four-bedroom family houses. But CoRWM also estimated that this would increase the total radioactivity of Britain's stored nuclear waste by a factor of nearly three times greater than today.
The most important kind of nuclear waste is spent reactor fuel. Spent fuel remains dangerously radioactive for many decades.
Fifty years after removal of spent fuel from the reactor, the radiation dose to a person standing nearby an unshielded spent fuel assembly would still give a potentially fatal radiation dose of 5 Sieverts within four hours of exposure (radiation level 1,150 mSv/hr @ 30cm distance from a 50-year aged CANDU fuel bundle). The spent fuel would be reasonably safe to touch for short periods of time after 200 years (radiation level 37 mSv/hr @ 30cm distance). However the radiotoxic hazard from one tonne of spent fuel drops to the same toxicity level as the original fresh uranium fuel only after about 100,000 years. For these reasons the UK government intends that spent fuel waste will eventually be disposed about 1km deep below ground in a permanent Geological Disposal Facility (GDF), providing engineered containment for one million years.
In 2008 the government invited communities in England and Wales to volunteer to host the proposed national nuclear waste repository in their local community. Three local authorities near Sellafield in Cumbria have expressed an interest so far.
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