12 out of 14 major projects at Sellafield nuclear reprocessing plant have failed to deliver what was planned in 2012, according to the National Audit Office.

The spending watchdog's report accuses the managers of Britain's largest and most hazardous nuclear site of being behind schedule and unfit for purpose, with potentially disastrous implications.

The publicly-funded Nuclear Decommissioning Authority (NDA), managed by the Department of Energy and Climate Change (DECC), owns the Cumbrian site. The report says that the NDA inherited a legacy of poor planning lasting several decades when it took ownership of Sellafield in April 2005. However, its initial plan was inadequate.

It now faces an "intolerable risk" from hazardous waste stored in run-down buildings and cannot estimate how long it will take to build the facilities required. The site holds the equivalent of 27 Olympic-sized swimming pools of high-level radioactive waste.

Following the appointment in November 2008 of a consortium of private sector companies, Nuclear Management Partners Ltd, to make sure operators Sellafield Ltd deliver value for money, a new plan was approved in May 2011 for the cleanup of the site. The estimated date for completion of this is over a century away: 2120.

The new plan resulted in a £20bn increase in the cost of decommissioning to £67bn (undiscounted) in March 2012, over three years earlier.

Despite this, the NAO report says: “Significant uncertainties and scheduling risks remain, which the authority is working to understand and address.

"For example, there is considerable uncertainty over the time required and cost of completing facilities to treat and store highly radioactive material held in deteriorating legacy ponds and silos."

Margaret Hodge, chair of the Commons Public Accounts Committee, said: “Projects of this length and ambition are ripe for dithering and delay. I am dismayed to discover the clean-up of Sellafield is no different.

"The authority's revised plan sees critical milestones shunted back by up to seven years. Hazardous radioactive waste is housed in buildings which pose intolerable risks to people and the environment."

A spokesman for Sellafield Ltd, welcomed the report's findings and said it was "making improvements" in commercial operations, including the reprocessing of spent nuclear fuel. It expects to deliver at least 8% of its £1.4bn planned savings.

But most projects have not provided good value for money, despite the fact that Nuclear Management Partners made Sellafield Ltd take on new staff, at an additional cost to the NDA of £76m between November 2008 and March 2012.

These critical projects include the design and build of complex chemical engineering projects to extract, make safe and store hazardous nuclear waste from old plants.

Amyas Morse, head of the National Audit Office, said: "Securing future value for money will depend on the Authority’s ability to act as an intelligent client, to benchmark proposed levels of performance and to provide better contractual incentives for making faster progress towards risk and hazard reduction."

A spokesman for DECC, whose annual combined current and capital budget is equivalent to the £3bn a year cost of Sellafield’s operations, said:

"The UK has a difficult legacy of nuclear waste to manage, which for too long was not given due prominence.

"The government has made cleaning up and decommissioning the nuclear legacy a priority and is maintaining funding even at a time when it faces difficult spending decisions. This enables the NDA to continue to make progress on decommissioning, with the focus being on tackling the highest hazards at Sellafield.

"Substantial progress is being made in tackling the unique and complex challenges at Sellafield. Cost savings of over £425m have been generated and a further £1bn of previously planned investment avoided.

“Last year was the site’s best year for reprocessing operations in seven years and real progress is being seen in tackling a number of high hazard facilities.”

But the NAO counters that: "The Authority does not yet have adequate external benchmarks to assure whether the plan is sufficiently challenging."

Its projects have accrued "significant lifetime cost increases and delays of between 2 and 19 months during 2011-12".

It calls for better benchmarking, research to see how other organisations handle the kind of contract that it has with Sellafield Ltd, better risk management and individual responsibilities for project delivery, and more frequent reporting on its performance.

The UK still has no long-term plan for dealing with its existing nuclear waste, apart from storing it above ground.

Story: David Thorpe, News Editor