Securing a nuclear waste disposal site for the future

The timescales involved mean it is necessary to keep a record of what waste you are dealing with and where it has come from and require the vision to anticipate what activities may affect it in the years to come.

At the Low Level Waste Repository, near Drigg, West Cumbria, the nature of nuclear waste has created a unique set of circumstances where the site is beginning the process of closing down with over 100 years’ work still left to do. 

The story of the repository began during World War Two when the 100 hectare site was originally requisitioned to be used as the site for the Drigg Ordnance Factory, with around 3,000 workers producing hundreds of tonnes of TNT every week. During this time five of these people gave their lives for the war effort when they were killed in accidents at the site.

However, with the advent of the nuclear age in the 1950s, the area was used to dispose of the increasing amount of low level contaminated waste produced at sites around the UK.

This included material contaminated during the Windscale Fire at the Sellafield site in 1957.

"The nuclear industry was really starting to get going in the late 1950s so the UK needed a secure place for disposing of lower activity waste," says Martin Walkingshaw, chief operating officer at Nuclear Waste Services (NWS), which operates the repository.

Alongside its work at the facility NWS is also delivering a Geological Disposal Facility (GDF) as a long-term solution for the most hazardous radioactive waste.

Between 1959 and the early 1990s the method for disposing of the waste - which typically arrives by rail from nuclear, military, medical and other sites around the UK - was to tip it into trenches from the back of trucks and then bury it in a similar way to conventional landfill.

Martin Walkingshaw, chief operating officer at Nuclear Waste Services (Image: Low Level Waste Repository)

A different approach was then adopted from the mid 1980s of placing the waste in steel containers for disposal in a concrete vault. This approach was fully implemented by 1995, and in 2008 Cumbria County Council granted permission to create a second engineered vault with capacity to dispose of 5,500 containers.

Containers of low-level radioactive waste are filled with grout, a mixture of Portland cement, pulverised fuel ash and plasticizer, to hold material in place and provide a firm foundation for the multi-layered ‘cap’ that will eventually cover the site.

The grouted containers are stacked in the engineered vaults on the northern area of the site, alongside the legacy landfill trenches - an area which covers around 40 hectares in total.

Anywhere between 150 and 200 people work at the repository each day overseeing the process and maintaining the site and its equipment.

Over the years huge amounts of material has come to the repository, with industry sometimes taking the view it was safer to send something for disposal even if there was only a chance of it being very lightly contaminated.

"The easiest solution, if you were at a site like Sellafield, or Calder Hall or up in Chapel Cross was that, unless you could be absolutely sure something was not contaminated, you would send it to the repository for disposal; the nuclear industry does not take chances,” says Martin.

"That conservative approach, alongside very low limits and definitions around what you can release as clean material, basically drove a lot of waste to the repository that with a bit of effort, you could clean up.

"The net effect of that was we started filling the repository up at an unsustainable rate, and there was a real possibility, around about 2004 that we could run out of space within a couple of decades.”

Since 2007 government policy decreed that the nuclear industry should follow the same process as for the disposal of conventional waste, with a focus on avoiding creating waste or reusing and recycling it where possible.

"So these days the bulk quantities of material that we talked about aren't coming anymore. They're being sent down different routes,” says Martin.

As part of its efforts to reduce waste, the repository works with companies like Cyclife UK, based in Workington, that treats contaminated steel, enabling it to be recycled.

The organisations and businesses which produce the waste have also been doing much more to cut the amount of material they send to West Cumbria, with 98 per cent now being treated, reused and recycled.

This has seen the number of containers that come to the site every year reduce from 700 to around 20 or 30.

(Image: Low Level Waste Repository)

"It's about waste-informed decommissioning," says Mike Pigott, site director for Nuclear Waste Services.
"You need to know which bin something is going in prior to ultimately starting the dismantling. Some of it might be combustible, you can potentially treat the metal with sandblasting or acid baths or dips or whatever it might be. Very low level waste rubble can be diverted to alternate hazard landfill sites to protect the physical capacity of the repository.

"The repository is a national asset. There is only one of them. It's the primary location for low level radioactive waste disposal in the UK. So we have to use it responsibly.”

The vast majority of the waste at the site will have a radioactive half life of just a few years or decades, with a very small amount having a half life of thousands of years.

How radioactive something is and, therefore, how potentially harmful it may be is measured in micro sieverts.

"We have to demonstrate, through our safety case, that the dose to people today and in the future as a result of exposure to the repository is less than 20 micro sieverts per year," says Martin.

"A micro sievert is a very, very small amount of radiation, a lot less than a dental X-ray or a transatlantic flight. We are incredibly conservative.”

With most of the focus of work at the site concentrated on its northern half, the southern part - perhaps counterintuitively for somewhere that handles nuclear waste - has become a valuable habitat for species such as adders, natterjack toads and blue butterflies.

The site employs a full-time ecologist to monitor and manage its wild spaces and to help offset its storage activities with biodiversity net gain.

Mike and Martin attend regular meetings of the West Cumbria Site Stakeholder Group, which is made up of representatives from organisations including local authorities, the emergency services, trade unions and regulators.

The group has a working group which meets throughout the year to discuss and scrutinise progress at the repository.

The Nuclear Decommissioning Authority also funds the Copeland Community Fund, which was set up with an initial endowment of £10m in 2010 to recognise the area’s role in hosting the site for the UK.

A further £1.6m is also paid into the fund each year and it has supported over 430 projects and invested £30m into the local community.

Additionally, the repository runs the Low Level Waste Repository Socio-economic Fund, which provides support to local initiatives and community groups, with a total of £85,000 of funding each year.

Work on installing the final engineered cap over parts of the site continues to progress, with the recent appointment of contractor Graham Construction.

The 10-metre thick engineered cap will consist of several layers, including a  layer of boulders designed to thwart anyone trying to drill through the cap in the future.

"We assume that at some point in the future knowledge of what has been disposed of in here is forgotten, and if they built a housing estate on the top of it and try to drill a borehole in there it stops them. We have to think in that mindset. Our legacy is ultimately generations ahead of us,” says Mike.

"When we ultimately step away from the repository at the end of our mission, it's really important for us that the final cap protects people and the environment from the hazard that exists for as long as it needs to.”

Over the coming hundred years the site will continue to dispose of waste which will then be covered over and capped as time moves on.

By 2130 it is expected that all of the waste identified for disposal at the site will be in place and completely covered over.

It will then enter a period of “institutional control” during which it will be secure with limited access allowed. It is likely legal covenants will then be put in place to stop certain types of development on the site.

The 2130 date ties in with the NDA’s timeline for decommissioning Sellafield and may change if that alters in the future.

"We take our legal responsibility incredibly seriously, but similarly, our moral obligations,” says Mike.

“We have to be able to look subsequent generations in the eye and be comfortable with the work that we're doing today, ultimately protecting them tomorrow.”