A leak of highly radioactive nuclear fuel dissolved in concentrated nitric acid, enough to half fill an Olympic-size swimming pool, has forced the closure of Sellafield's Thorp reprocessing plant. The highly dangerous mixture, containing about 20 tonnes of uranium and plutonium fuel, has leaked through a fractured pipe into a huge stainless steel chamber which is so radioactive that it is impossible to enter. Recovering the liquids and fixing the pipes will take months and may require special robots to be built and sophisticated engineering techniques devised to repair the £2.1bn plant.