Sellafield's plans to replace ageing nuclear waste facilities posing "significant risks" to the population face "considerable" uncertainty, a public spending watchdog has warned.
Owners of the Cumbrian nuclear power station do not know how long it will take to build storage and treatment centres for the hazardous material or how much the final bill is likely to be, according to the National Audit Office (NAO).
For more than 50 years operators failed to plan how to dispose of the radioactive waste and some of the older facilities have "deteriorated so much that their contents pose significant risks to people and the environment", said the report.
Progress in 12 of the 14 major buildings and equipment projects considered "critical" for reducing risk, which range in cost from £21 million to £1.3 billion, failed to achieve what they were supposed to and had not provided good value for money, the NAO said. Its report found there "is still considerable uncertainty in the schedules and costs" of the projects.
A long-term plan to clean up the Nuclear Decommissioning Authority-owned site, which is managed by Sellafield Limited, was agreed last year after an earlier one stalled because it was "unrealistic".
In a statement on its website, Sellafield Ltd said: "We welcome the report and are pleased that the NAO recognise the globally unique challenge we are facing in cleaning up and decommissioning the site. In their report the NAO also highlight a number of areas for improvement, mainly focused around the project management scope of work which equates to around a quarter of our annual budget.
"This is a problem we have recognised and we have already taken steps to strengthen our approach - both in terms of how we manage projects as a whole and how we develop better, more beneficial relationships with the supply chain."
Cumbria County Council's cabinet member responsible for nuclear issues said he was "deeply concerned" by the NAO report. Councillor Tim Knowles said: "I welcome the work that has been done by the National Audit Office and welcome the fact that a national body for external scrutiny has highlighted some issues about which I am deeply concerned.
"Local authorities in Cumbria work closely alongside the nuclear industry and recently we have had much improved links with the Nuclear Decommissioning Authority under their new leadership. Councils will need to be closely involved in the Nuclear Decommissioning Authority's improvement plan to improve the security and safety of interim storage as this is an issue which affects local people. This will require a major rethink of the current storage arrangements and major investment into the site.
"The report is a clarion call for immediate change and is completely separate from the quest for a deep geological repository to store high-level radioactive waste, which is likely to take decades. Any prospect of decades of concern and uncertainty about whether Sellafield's waste is safe is simply unacceptable. This report highlights what needs to be done now."