Going underground

The scientific and nuclear industries are coming to accept that deep burial is the only way to treat nuclear waste. Andrew Lee reports.

The need for the UK to establish a national repository for its nuclear waste has become even more pressing since September 11. Fear of vulnerability to terrorist attack could be the factor that finally ends decades of indecision and prompts the government to order a deep underground dump similar to that planned by the US at Yucca Mountain in Nevada.

Advocates of burying radioactive waste deep below the earth believe there may never be a better chance to make a convincing case that this offers a safe, long-term solution for placing the material beyond the reach of even the most determined terrorist.

To make that case they will have to overcome public mistrust almost as toxic as the waste itself. But overcome it must be, according to many who believe that decision time is here.

In one of the ironies that abound in the nuclear world, the UK recently began giving technical and financial assistance to Russia as part of an international push to clean up that nation’s dire nuclear legacy. But while the UK helps the Russians, there remains the small matter of what to do with its own 20,000 tonnes of solid, long-life nuclear waste. Over the coming decades this will rise to 500,000 tonnes as the waste generated by decommissioned nuclear reactors is added to the stockpile.

Dealing with this amount of radioactive material is a massive challenge in its own right. But the heightened state of anxiety over terrorist activity has added greatly to concerns about having waste lying around on the surface of the UK, often stored under less than ideal conditions (see sidebar).

It needs to be put out of harm’s way. The best way to do that, many experts believe, is by ’geological disposal’: burying it deep below the earth’s surface where it will be inaccessible to terrorists now and harmless to future generations.

Dr. Kevin Langley, head of southern sites projects for the UK Atomic Energy Authority, confirmed that the wind was blowing in that direction.

’I think that since September 11 there is more political momentum to build a deep repository sooner rather than later,’ he said. International scientific opinion has certainly swung behind this solution. Last month the International Atomic Energy Agency published the results of a two-year investigation into the options for radioactive waste management. Its findings could hardly be more conclusive.

According to the IAEA, security concerns over terrorist activity ’lead strongly and unequivocally to disposal [as opposed to storage] being desirable at as early a date as is reasonable.’

The report said: ’After several decades of research on the disposal of nuclear wastes, geological disposal is the only approach that has gained widespread credibility in the scientific community.’ The IAEA declared it ’highly unlikely’ that an alternative process or technology for dealing with nuclear waste will emerge in the foreseeable future. ’The argument that action should be postponed until a scientifically better solution is developed is not convincing,’ it said.

Deep disposal therefore has gained the necessary scientific credibility, and the technology to make it happen is available now.

However, the agency is forced to admit that these are by no means the only factors in play. ’The issue is not one that is solely technical,’ its report said, with political, economic and social considerations equally relevant. According to the IAEA, public opposition to disposal ’results in de facto continued storage on the surface, since it is an exception to find a community that supports the development of a disposal facility in its midst’.

Politicians, the IAEA noted, place a great deal of weight on public opinion because it determines the way votes will be cast. ’Although there are good reasons to favour disposal, they do not provide a strong political driving force towards disposal.’

The UK government claims to have grasped the nettle with the publication last month of its draft Nuclear Sites and Radioactive Substances bill. This legislation will pave the way for creation of the Nuclear Decommissioning Authority, which will be charged with organising the clean-up of the UK’s nuclear legacy, at an estimated cost of £48bn. The government has also announced the formation of a Committee on Radioactive Waste Management (CoRWM), which will recommend how higher-activity radioactive wastes should be dealt with.

The US, meanwhile, seems to be following the IAEA and a large body of technical and scientific opinion in concluding that deep disposal is pretty much the only game in town. Amid much controversy the US government is pressing ahead with plans to build a nuclear waste repository at Yucca Mountain in Nevada.

And in what many believe could be a role model for the UK, Finland has achieved a broad consensus on the need for a deep storage facility – and to such an extent that two towns bid against each other to be the site for burial of waste (see sidebar).

In contrast, the last attempt by UK nuclear reprocessing body Nirex to establish a UK depository, at the Sellafield nuclear plant in Cumbria, ended in failure in 1997 when the government ruled that a sufficiently watertight scientific case had not been made for such a waste storage facility.

The battle in the UK will be to win over the hearts and minds of the public – to turn around decades of public mistrust and industry mismanagement in the nuclear field. The Royal Society highlighted the importance of this in a paper outlining its concerns over radioactive waste management policy. A scientific working group, chaired by Prof. Geoffrey Boulton of the department of geology and geophysics at Edinburgh University, warned: ’Current institutions and processes do not command public confidence.’

The Royal Society’s paper was published before the government outlined plans to establish the NDA and CoRWM. Boulton says that he is concerned that the necessary clarity of roles and responsibilities would still be lacking.

’We desperately want to avoid going around in the same wretched, weary circle we have been going around in for the past 25 years,’ he said. According to Boulton, what is needed is ’a body sitting in a direct line between the public and the government, setting out good science and engineering. ’The outcomes of research have got to be comprehensible and demonstrable in the public domain.’

The crucial questions are: can a suitable site for deep disposal be found? And can a case for it be made? Boulton believes both questions can be answered in the affirmative. ’In my view, it would be possible to find a disposal site that would satisfy the safety criteria,’ he said. Demonstrating its safety for storage of nuclear material is, he added, a greater challenge, but is possible nonetheless.

As a geologist, Boulton said he could point to a particular part of the earth and show that over tens of thousands of years it had behaved in a predictable manner. He stressed that, with the technology for placing the material available, deep disposal remains the only viable option for long-term storage of nuclear material: ’If there is an alternative, I haven’t come across it.’

Boulton’s fellow Edinburgh geologist Dr Stuart Haszeldine, who has carried out research on behalf of Nirex, said the east coast of England, for example, offered attractive sites because the natural flow of water was downwards further into the rock rather than upwards, which might eventually see it disrupt the geology of any storage site. ’There are a number of factors to be considered, but predictability is the key,’ said Haszeldine. ’Equally importantly we have to raise the level of technical debate.’

The nuclear industry – described by Boulton as ’often its own worst enemy’ – appears to share the increasingly widespread view that a public case for long-term disposal needs to be made, and urgently. Ann McCall, head of safety and strategy development at Nirex, admitted that the industry has a lot of lost ground to make up. ’On the face of it we have done absolutely nothing about nuclear waste since the industry started,’ she said at an Institute of Physics conference. ’We have to raise public awareness, get people to accept there is a problem and also accept that there is a solution.’

McCall said the technical aspects of building a repository were ’not a problem’ and pointed out that the disposal of waste needs to be divorced from the wider debate over future nuclear power programmes. The existing stockpile is not going to go away.

’Irrespective of the issues surrounding new nuclear development there will still be waste. It is the societal, not scientific aspects of the problem that will ultimately decide what happens,’ said McCall.

Nirex has made reassuring noises over consultation, debate and a transparent decision-making process before any decision on the location of a deep repository is made. But old habits die hard, and Nirex has been accused of secretly drawing up a list of possible sites for a future repository. In May there was uproar in Scotland when local environmentalists claimed the Moray Firth had been pinpointed by Nirex as a potential burial site and had commissioned geological research.

Nirex insists nothing has been decided and any work being carried out is purely for general research – an assertion backed up Edinburgh University’s Haszeldine. Nirex said that to make public any potential sites would cause needless anxiety in areas where nothing may happen.

When a plan for a deep repository is met with widespread applause and the recognition that, at last, one of the UK’s biggest environmental problems is being tackled, the nuclear industry will have won its biggest battle.

Harwell: cleaning up the 1960s nuclear mistakes

The need for a national repository for the UK’s radioactive waste will become ever more pressing as the country’s nuclear facilities are steadily decommissioned. The problem has been exacerbated by mistakes made in the 1950s and 1960s, when some waste was stored in unsuitable containers that are now beginning to degrade.

At Harwell, in rural south Oxfordshire, the UK Atomic Energy Authority has embarked on a multimillion-pound, 20-year programme to recover radioactive waste from three so-called tube stores.

The waste contained in the stores is the legacy of decades of nuclear research at the site, and also includes material from other research centres and hospitals. Most of it is classified as intermediate-level waste, sufficiently dangerous to require long-term safe storage away from all human contact.

The plan is to repackage the waste from the tube stores into 500-litre drums, which will be held in a new vault store at ground level on the site until the national repository is opened.

Harwell was the home of UK nuclear research for many years. The UKAEA is now in the process of decommissioning and delicensing parts of the site prior to its sale for development as a business park.

But the new vault store will remain a feature of this part of Oxfordshire until the government settles on its plan for a national underground dump.

Harwell has three tube stores containing a total of more than 1,700 tubes. The tubes are set vertically in a concrete floor and vary in depth from 2.5m to 4.5m. They are around 400mm in diameter and are sealed with a steel and concrete cap. Each tube contains up to three or four cans of radioactive waste; there are around 10,000 cans of different sizes in total. Many of these have been filled with waste that would have been dumped at sea, but that practice was ended in 1983.

The problem is that the vast majority of the cans used in the two oldest tube stores, which began receiving waste in 1959 and 1962 respectively, are made from mild steel. Unlike stainless steel, this material is susceptible to corrosion from both the inside and out. Since the active waste-retrieval programme began late last year engineers have found that many of the cans have rotted through completely and shed their contents into the bottom of the tubes.

Another problem is the incomplete records of what each can is supposed to contain. The main components of the waste are known to be metals and organic materials, smaller quantities of cement, graphite, radioactive sources, glass and ceramics. Some of the contents have reacted with damp in the tube and contributed to the corrosive process.

The UKAEA’s objective is to retrieve, treat and repackage all the waste by 2020. To achieve this it designed a unique set of waste-retrieval technologies capable of remotely cleaning the tubes, sorting and repackaging the waste.

This in turn required the building of a dedicated facility around the waste store capable of handling the material, cementing it into the 500-litre drums and depositing them, again remotely, in the new vault store. The running and infrastructure costs of the project come to £5m a year and the UKAEA expects to spend a further £80m-£100m on plant and equipment.

The first part of the retrieval process is assembling the MK1 retrieval machine over one of the tubes. At 100 tonnes, the machine is cumbersome and can take three or four days to move from one tube to the next, having to be dismantled each time it is moved.

In the early days, staff sometimes failed in the difficult task of aligning the retrieval machine correctly over the tube mouth, adding to the time it took to complete just one of the hundreds of tubes. The MK1 is also only able to operate in the smallest of Harwell’s stores. The UKAEA is tendering for the design and build of a second machine that will be able to operate in the larger of the two legacy waste stores. Here some of the tube heads are too close to the building’s wall for the MK1 machine to gain access.

Once the MK1 machine has removed the tube cap, a gripping tool is sent down to retrieve the first can. Sometimes the bottoms of the cans fall through as they are lifted and the waste drops back into the tube. To clear this, a series of tools capable of grappling with the different-sized pieces of waste are needed. Each time an unusual object is encountered a new tool must be designed to pick it up. This then has to be introduced into the retrieval machine, another time-consuming process.

Once the cans are successfully withdrawn from the tubes they are transported in a sealed flask to a series of shielded cells, where they are opened remotely, their contents tipped out and sorted.

Waste needing no further decontamination is loaded into a 500-litre stainless steel drum, the approved Nirex container for deep disposal. The first drum was deposited in the new vault store earlier this year. The vault store has 1.5m-thick concrete walls and roof to contain radiation and is served by a gantry crane.

The next phase of the project is to build a cementation plant that will fill each drum with grout to pacify and stabilise the contents, again to Nirex guidelines. The drums will be returned to the vault to await eventual transfer to the deep dump.

A total of 350m3 of waste are expected to come out of the tube stores alone, filling 2,000 of the 500-litre Nirex drums. This represents a fraction of what the UK will have to dispose of in a national repository.

On the same site, also in storage, are 2,000 sealed sea drums that were on their way for disposal when the sea dumping ban came into effect. The contents of these drums are held in a void surrounded by concrete. The UKAEA will have to establish yet another process to open these safely. It is expected that the tops of the drums will have to be sliced off, allowing the contents to be repackaged for deep disposal. – George Coupe.

Finland: deep disposal with public approval

In Finland the battle to secure broad public acceptance of nuclear power – and a deep depository to deal with the resulting waste – has already been won, thanks to some straight talking by the government.

The freezing Finnish climate, particularly in the north, means that energy consumption throughout the year is relatively high. However, the issue of nuclear power is particularly emotive for the Finns, as the region was badly affected by fallout from the Chernobyl disaster.

Much of the population and many Finnish parliament members were opposed to the expansion of their nuclear power programme. But a frank, open and inclusive discussion of the country’s energy options turned that around, leading to the conclusion that it was vital to build a national repository and new nuclear power plant. The public consultation process was so successful that two towns bid against each other to host the dump.

Under plans announced in 2001 and finalised this year, up to 6,500 tons of spent uranium will be sent to the island of Olkiluoto in western Finland and encapsulated in 25-ton disposal canisters made from nodular cast iron enclosed in a watertight 5cm-thick stainless copper shell. Experiments have shown that the material would take hundreds of thousands of years to corrode, even under oxidising conditions.

The waste canisters will be lowered into the ground in a lift and placed in holes 7m or 8m apart at the bottom of tunnels drilled between 500m to 700m below the surface in the bedrock. Each will be 25m from the next and will be connected by transport tunnels.

Once in place the canisters will be surrounded by bentonite clay, which expands when it absorbs water to prevent direct water flow to the canister and protects it against minor bedrock movements. The tunnels will be sealed with a concrete barrier. Even if water came into contact with the canisters, at such depths oxygen is scarce, minimising the chances of corrosion. Only the canister transfer shaft, a personnel shaft and a working shaft will connect the facility to the surface. Once the encapsulation plant is full and is decommissioned the tunnels will be filled with a mixture of bentonite and crushed stone, before the shafts are closed.

Though the buried material will not require monitoring, with some difficulty it could be retrieved by future generations if a better disposal or reprocessing method became available. Most of the filler material could be dug out and the bentonite clay could be treated with salty water to turn it to slurry before the canisters could be lifted out.

The facility, built by Posiva Oy, is expected to be ready in around 10 years, costing an estimated £500m, of which a quarter will be construction costs. The money will be collected by adding a percentage to the cost of nuclear generated power. – Julia Pierce.