Britain has amassed a stockpile of more than 100 tonnes of plutonium - enough for 17,000 bombs of the size that flattened Japan's Nagasaki in 1945, a report from the country's top science institution said on Thursday.
The toxic stockpile, which has doubled in the last decade, comes mainly from reprocessing of spent uranium fuel from the country's nuclear power plants, so to stop it growing the practice must end, the Royal Society said.
"There should be no more separation of plutonium once current contracts have been fulfilled," said the report "Strategy options for the UK's separated plutonium". Plutonium, one of the most radiotoxic materials known, is produced when spent uranium fuel from power stations is reprocessed to retrieve reusable uranium.
It can be processed into mixed oxide (MOX) fuel but it can also be used in nuclear weapons and so poses a security threat. "Just over six kilogrammes of plutonium was used in the bomb that devastated Nagasaki," said Geoffrey Boulton, the report's lead author. "We must take measures to ensure that this very dangerous material does not fall into the wrong hands."
Paradoxically, the Royal Society said the safest option was to leave spent fuel as it was when it came out of the reactor because it was so radioactive that it was far harder to handle. The second best was to produce and burn MOX pellets and then leave them unreprocessed. "Spent fuel is more radioactive and therefore harder to handle than plutonium - and more difficult to use in nuclear weapons because it would need to be reprocessed first," the report said.