SWILLING around murky ponds in the oldest part of Sellafield, a nuclear research and reprocessing centre in Cumbria, is a soupy, radioactive sludge. For years boffins working on Britain’s first military and civil nuclear programmes abandoned spent fuel and other nastiness into the pools and tanks, which now grow decrepit. Though perhaps not the “slow-motion Chernobyl” which some environmental campaigners make out, the site is subject to one of the most complex nuclear clean-ups in the world.

Sellafield is the trickiest of several challenges facing the Nuclear Decommissioning Authority (NDA), a government body that manages the contractors who swab out Britain’s defunct facilities. Their projects swallow up about two-thirds of the budget of the Department of Energy and Climate Change; Sellafield alone costs £1.7 billion ($2.8 billion) a year, almost as much as the roughly £2 billion spent subsidising renewable energy in 2013. On March 31st NDA awarded a £7 billion contract to decommission 12 more of Britain’s oldest reactor sites over 14 years to a consortium including Babcock, a British engineering firm, and Fluor, an American one.

These big sums reflect problems peculiar to Britain. It ploughed into nuclear bomb-making in the 1940s, and nuclear power in the 1950s, with little plan for how contaminated structures would be dealt with. Its first reactors were each built to different specifications, and all contain more irradiated material than is found in more modern designs. The pioneers underestimated the costs of decommissioning, and the meagre sums put aside for this were further diluted during privatisation, says Malcolm Grimston of Chatham House, a think-tank.

Mismanagement has probably made a tough job more difficult. In 2009 bosses thought Sellafield would cost £46.6 billion to make safe; the latest estimate is £70 billion, and rising. In February MPs on the public accounts committee slammed the performance of Nuclear Management Partners, the private consortium currently contracted to detoxify it. They questioned NDA’s decision, in October, to award it a second five-year contract, and said taxpayers bore most of the risks.

The NDA has “learnt lessons” from Sellafield, says Bill Hamilton, a spokesman. No one expects the sites in its latest contract—which include shuttered power stations at Hinkley Point, Sizewell and Dungeness—to prove nearly as complicated. Its chosen contractor will remove some of the nastiest waste and demolish superfluous buildings, but will not have to dismantle the reactors themselves, which will stand idle, and toxic, for up to 70 years.

That will give some of the remaining radiation time to dissipate, making the final demolition a little easier. But this slow process is also a way of putting off the bill. Stephen Thomas of the University of Greenwich would prefer a speedier clean-up, which might reduce the likelihood of future leaks and also ensure the skills needed to safely dispose of the stations will not decay. He regrets that each year NDA has only enough money to do “the minimum needed to keep them out of court”.

Shaving decades off the decommissioning periods would indeed probably save money in the long run. Yet that depends on authorities swiftly finding a place to hold the radioactive rubble. At present shallow vaults in newer parts of Sellafield hold Britain’s most troublesome waste, but that is an expensive and temporary solution, and not a good way to secure the many thousands of tonnes of additional toxic debris that would be produced by taking apart Britain’s reactors.

Most people now agree that the best solution is to bury it. For years the government has sought councils willing to host such a site in return for jobs and money. Last January politicians in Cumbria vetoed applications from eager councillors in two of its districts. This summer the government will probably nudge them again, and with good reason. Sellafield’s neighbours know as well as anyone what happens when a generation passes the buck.