For proponents of nuclear power, the Sellafield plant was the proud vanguard of Britain's post-war nuclear energy boom. To its detractors, this vast facility on the Irish Sea coast of Cumbria was - and remains - a monstrous waste of public money, not to mention a very real threat to health and safety, as evidenced by two high-profile radioactive leaks in 1957 and 2005.
Now, more than half a century after its inception, the facility which also houses the world's first nuclear power station is back at the top of the political agenda thanks to a damning report by the Public Accounts Committee (PAC).
Published in February, 'Progress at Sellafield' is highly critical of the decommissioning operation at the site, and will not be a comfortable read for Nuclear Management Partners (NMP), the consortium tasked with coordinating the clean-up, nor the Nuclear Decommissioning Authority (NDA), which recently extended NMP's contract for a further five years.
"Cleaning up the nuclear waste on this hazardous site is estimated to cost more than £70bn in cash terms. What's worse is that the cost is likely to continue to rise," said PAC chair Margaret Hodge MP. "The Nuclear Decommissioning Authority, which owns Sellafield and which appointed NMP, said itself that it did not expect NMP to meet its savings target for the first five years - despite NMP being on course to earn £230m for the job. Timescales have slipped and reprocessing targets have been missed. NMP has failed to provide the clear leadership, strong management and improved capabilities for the job."
Britain's nuclear legacy: the challenge of decommissioning
In its defence, NMP - a consortium comprising Areva, US-based URS and British firm Amec - points to the unprecedented scale and complexity of the clean-up operation.
Construction of the site, which was renamed Windscale in 1947, required a peak of 5,000 workers and was fast-tracked in order to transform what was a small munitions facility into one capable of producing materials, principally plutonium, in support of Britain's fledgling nuclear weapons programme.
The main decommissioning challenges relate to materials left over from this period and reprocessing operations that separated uranium, plutonium and fission products from spent nuclear fuel. The site's two air-cooled, open-circuit, graphite-moderated reactors, Windscale Piles 1 and 2, were built in the space of just two years with only minimal provision made for eventual decommissioning.
Radioactive waste is categorised by its radioactivity level into high (heat-generating), intermediate and low. High-level waste (HLW), the liquid by-product of reprocessing highly-radioactive spent nuclear fuel, is converted into glass blocks within steel containers and stored for at least 50 years.
Sellafield contains various categories of waste in ageing ponds and silos. Two buildings, B30 and B38, housed materials from obsolete Magnox nuclear reactors - the first of which became operational in 1956 - and building B41 contained aluminium cladding for the uranium fuel rods of Piles 1 and 2.
Another facility, the Shear Cave, was modified in the late 1960s to reprocess fuel from second-generation advanced gas-cooled reactors. This highly radioactive spent fuel had to be drained out into a settling facility, where the wash water can be safely recycled.
The task faced by Sellafield Ltd, the NMP subsidiary in charge of decommissioning, is made more difficult by the scale of the operation. The site in north-west England is home to an estimated 1,300 buildings containing many interdependent nuclear facilities and operations, including reprocessing programmes that continue to provide commercial income.
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"The site itself is one of the most congested industrial facilities in the world," said Chris Hallewell of Sellafield Ltd, the NMP subsidiary in charge of the clean-up. "With possibly 10,000 people working here on a daily basis, it's like a small town, so it's a huge challenge in a very, very tight space."
Counting the cost: Sellafield's £70bn clean-up bill
In light of these challenges, are the spiralling costs and delays outlined in PAC's 2014 report the fault of NMP and is the NDA guilty of underestimating the scale and complexity of decommissioning?
The figures make a compelling case for both claims. In 2013, PAC reported that NMP earned £54m in fees the previous year, despite only two out of 14 major projects being on track.
The latest report reveals that the estimated cost of the 'Magnox swarf storage silos retrievals' project increased from £387m in March 2012 to £729m in September 2013. In the 18 months since PAC last considered progress, the estimated delivery date of the 'pile fuel cladding silo' programme had been pushed back by six years from August 2017 to January 2023. PAC also takes issue with the NDA's strategy for dealing with plutonium stored at Sellafield.
"We have made good progress towards implementing the recommendations laid down by the PAC and will now focus on achieving the aims of the recommendations set out in this latest report," NDA chief executive John Clarke said. "Both NMP and the NDA now have a much better understanding of the issues and complexities that exist at the site and the challenges that lie ahead.
"Whilst progress has been made on a number of fronts, we will require significant improvements during the next contract period. We have had extensive discussions with NMP and made clear where these improvements must be made."
Back to the future: Sellafield site earmarked for new power station
The annual cost to the UK taxpayer of the mammoth clean-up operation at Sellafield has risen from £900m in 2005 to its current mark of $1.6bn. Sellafield Ltd is expected to start retrieving hazardous waste held in legacy facilities in 2015 and the project is scheduled to be completed in 2025.
But the Sellafield story doesn't end there. Having played a pivotal role in Britain's nuclear past, the area has been earmarked as one of eight sites to house a new nuclear power station.
The UK currently has 16 reactors generating about 18% of its electricity and all but one of these will be retired by 2023. The first of 19GW of new-generation plants are expected to be online by 2023 and the government aims to have 16 GW of new nuclear capacity operating by 2030 to maintain electricity supplies when coal-based power stations are closed.
Over the past five years, NMP claims to have generated in the region of £650m in efficiency savings, achieved the site's best-ever industrial safety performance and made the first retrieval in 50 years of spent fuel from a legacy storage pond.
The impetus is now on NMP to complete the clean-up on time and on budget in order to ensure that its rolling five-year contract with the NDA is renewed in 2018 and that there is an orderly transition of power to the owners of a new electricity generating station at the site in 2025.
"The first term of our contract has been characterised by many successes but also a number of disappointments and areas for improvement," said NMP chairman Tom Zarges recently. "Our job now is to build on our experience of the last five years to safely and reliably deliver our customer's mission, while further accelerating the pace of change and providing value for money to the NDA, government and the UK taxpayer".