There are many uncertainties about the renaissance of nuclear power in the UK, particularly surrounding the level of public subsidy, but one thing remains constant: the industry's waste problem hasn't gone away.

The clean-up of nuclear legacy waste at the Sellafield nuclear reprocessing plant – a site historically plagued with mismanagement and technical difficulties – is running behind schedule, according to the 2009-10 annual report from the Nuclear Decommissioning Authority (NDA), which was quietly released in December.

The safe removal and treatment of legacy waste has failed to hit the targetsdue to "factors including deteriorating building structures, uncertain material inventories and difficult working conditions," the report says. The consolidation of "legacy sludges" in a storage pond are running behind, and the report gives no explanation for the delay.

An NDA statement says:

"Dealing with these facilities is the most challenging and complex task within the current decommissioning mission. The facilities date back to the early days of the civil nuclear industry and the nature of the materials they house and the facilities themselves all present major challenges in planning a detailed work programme."

On the specific clean-up delays, the statement said assessing the state of the facilities and undertaking repair and reinforcement work were part of the explanation.

Experts in the field say the ongoing problems at Sellafield are worrying, especially in light of the possibility of waste that will be created from new-build nuclear.

"Sellafield is a national disgrace. Sellafield is where we house the toxic legacy of our failed nuclear industry," said Paul Dorfman from the University of Warwick, who has worked extensively on radiation and nuclear waste issues with the government and industry.

"The history of waste storage in Sellafield is vast and complex and it's only recently that the NDA had to ask for further billions from the Department for Energy and Climate Change to make safe elements of our waste storage. We're not talking about bells and whistles here, we're talking about things that really need to be done."

Prof Andrew Blowers from the Open University became involved in the nuclear waste debate as a councillor in 1983, when a nuclear waste dump was proposed in Bedfordshire.

"The trouble with Sellafield is that it is a great big hybrid facility. Even just as a lay-person you can see it is just in a dreadful state ... I believe it to be the most dangerous spot in the world because of the pure concentration of stuff on the site. You have highly active liquid waste in tanks stored at Sellafield bubbling away. You have a platform above it and you have a load of pipework above it. I mean the risks at Sellafield are massive."

Blowers was a member of the first independent Committee on Radioactive Waste Management in 2003 and heavily involved in developing policies for dealing with nuclear waste. He is critical of the way those policies have been adopted by the government and the nuclear industry.

"Waste is clearly now one of their major difficulties. You have to have a scientifically robust and publicly acceptable solution," he says.

The setbacks in dealing with the legacy waste come as the government's commitment to new-build nuclear appears to be intensifying, with revelations recently that funds from the green investment bank could used.

The eight new nuclear power stations being proposed have no place in the UK, in Blowers's view, unless the real scale and impact of the waste and how it is to be dealt with is made clear to the public, and progress is made on dealing with legacy waste.

The approaches being considered by the government to manage new waste include geological disposal, which involves burying waste in underground rock formations, longer term storage on nuclear sites themselves, and disposing of low-level waste in landfill sites – a plan that has encountered fierce opposition from locals at the first proposed site in King's Cliffe, Northamptonshire.

He said proposals for storing waste longer term on site should be more explicitly discussed before new reactors are developed on sites.

"I don't think the process will be fair. I think the problem is that waste has been almost covertly dealt with because new build implies something completely different. Waste will be stored on the sites, which hasn't really been done before and the public is completely unaware."

Prof Gordon Mackerron, the director of the science and technology policy research unit at the University of Sussex and who chaired the original Committee on Radioactive Waste Management, agrees that the consequences of creating more nuclear waste have not been properly addressed and debated.

"The government has proposed a requirement that they store nuclear waste on site for a very long period, and why that's politically important is that spent fuel has been moved off to Sellafield as soon as it was feasible to do so in the past."

The consultation process on how to deal with nuclear waste and new nuclear plants across the country has been clearly lacking, according to both Blowers and Mackerron.

"What they're actually saying implicitly is that we don't care about the far future. Essentially they make it up as they go along. We have been calling very vigorously for another proper consultation. The consultation that they've been going through [which started in September 2010] has been pretty farcical," said Blowers.