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Windscale Pile Chimney: Removing an icon

The Windscale Pile Chimney is one of the most visible reminders of the country’s atomic mission.

Standing 125m tall, the iconic chimney is unmissable when Sellafield is in sight.

Now, 60 years after the Windscale fire which ended its useful life, the chimney is set to be demolished – disappearing from view for the very last time. Read on to find out about this remarkable part of the country’s nuclear story, and how it will disappear.

The Windscale Pile Chimney towers over Sellafield in every sense of the word. It’s the largest stack on the site, and dominates the skyline as Sellafield comes into view. For many people, it is the building they picture when Sellafield comes to mind.This is in no small part due to its significance to the country’s nuclear mission, and its infamous history that followed.

In the aftermath of the Second World War people feared a third. Atomic weapons were seen as the best deterrent. Countries around the world raced to develop their own nuclear capability. Following early collaboration with American scientists on the Manhattan Project, Britain was forced to develop its own capability following the US Congress signing of the McMahon Act, which prohibited the sharing of atomic secrets with other countries.

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Sellafield was chosen as the location to produce the plutonium needed for the bomb, and a munitions factory became a nuclear site. The British government authorised the construction of the two Windscale pile reactors in 1947, in 1950 the first reactor went critical and by 1952 the first billet of metallic plutonium was produced. The two 125m tall ventilation chimneys were built during this period, and their iconic appearance was cemented by nuclear pioneer, and Windscale chief engineer, John Cockcroft, who insisted that filters be added to the chimneys. As construction was well under way at this point, they were installed to the top of the structures, giving the chimneys their unique shape.

Despite being known locally as ‘Cockcroft’s follies’, they proved their value with the fire in Windscale reactor 1 in 1957. It was the filter at the top of the Windscale Chimney 1 that prevented this disaster from becoming a catastrophe, by limiting the amount of radiation released into the environment. Following the fire, both reactors were closed, and the chimneys were no longer needed. The second chimney was demolished in 2001, however the contamination from the fire made the challenge of removing chimney 1 much more significant.

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The implications of the Windscale fire

The 1957 fire was a wake-up call for the nuclear industry. It led to vast operational and technological improvements in nuclear reactor design, technology, licensing and regulation, which have stood the test of time. The Office for Nuclear Regulation is the country’s nuclear regulator and its predecessor organisations were founded in the aftermath of the fire – recognising that regulation needed to be more robust. In the early days, the pace of developments outstripped that of regulation. Over the years since the fire, the nuclear industry’s relationship with its regulators has developed, and is now represented by the G6. Formed in spring 2014, it is made up of representatives from Sellafield Ltd, ONR, the Environment Agency, the Nuclear Decommissioning Authority, the Department of Energy and Climate Change and UK Government Investments. The aim of the group is to work together to safely and securely accelerate hazard and risk reduction at Sellafield. This pragmatic approach has helped the pile chimney project progress.

How do you solve a problem like Pile Chimney 1?

Once one of a pair, Windscale Pile Chimney 1 now exists as a reminder of Sellafield’s history. It’s a 125m tall, 14m in diameter concrete structure, which stands solidly in the heart of the Sellafield site.

Given we’re this year remembering the sixtieth anniversary of the fire that closed the reactor it supported, the chimney’s useful life has long since departed. The condition of the stack – which no longer meets modern structural standards – means that its demolition is now a priority. The passage of time, along with more advanced assessment and decommissioning techniques, enables this.

The first decommissioning work started in the 1980s with the removal of some of the brick and ancillary facilities. Decommissioning work recommenced in 2014 with the opening up of the structure. This was followed by the removal of the now-legendary filter galleries from the top of the stack. Since that point, work has been focused on progressing procurement and preparing the stack for the demolition of the diffuser, which is located below the former filter galleries. The team were keen for the project to proceed in the most cost-effective, fit for purpose, way. Learning from the demolition of the first chimney coupled with a ‘think differently’ philosophy, looking outside the nuclear industry, led to the development of a straightforward, three step approach.

1. Cut the structure into large blocks

2. Use the tower crane to lift and move the large block sections

3. Use available licensed landfill facilities to avoid the need for unnecessary decontamination

In progressing this option, the project had to overcome resistance – namely that we don’t use tower cranes at Sellafield, we hadn’t demolished a facility in this way before, and would need a different type of safety case. Contracts were signed for this work in late 2016. The next stage will be preparing for the arrival and installation of the tower crane in autumn 2017. Demolition of the diffuser will start in November, and should take a little under two years to complete.

Following this, the plan is to complete the remainder of the demolition to the pile cap, 35m line by April 2021. Chris Wilson, the senior project manager, explains: “We have been working tirelessly for three years with AECOM of the Design Services Alliance and industrial demolition experts on this project in order to develop a robust design and methodology for demolition that can now be put into practice. During this time we’ve been working closely with our regulators and stakeholders, to ensure they’re confident in the approach we are taking.

“We’ve been able to take learning from the project to demolish chimney 2 in 2001, and where possible, will be applying this to chimney 1. Our approach has been to adopt and apply proven demolition techniques and processes used outside of the nuclear industry, avoiding the need for bespoke design and creating a fit for purpose approach to this significant demolition project.”

A collaborative approach

Like many of our major projects, the Windscale Pile Chimney decommissioning project is a joint effort, involving a number of partners.

  • A core team of around 25 Sellafield Ltd employees have been working on the project.
  • Another thirty employees are provided through the Decommissioning Delivery Partnership (DDP) consortium ADAPT, which is made up of Areva, Doosan and Atkins. ADAPT are bringing specialist skills and experience from across a wide range of sectors. The team will be integrated with the Sellafield team to ensure progress.
  • Kaefer are providing specialist engineering services and demolition access.
  • The Design Services Alliance is providing engineering inspection and validation services. The alliance has been integral to getting the project to the stage it’s now at.
  • The project is supported by specialist teams from across our organisation. They provide specialist skills, undertake the intelligent customer role, and provide an appropriate level of scrutiny to the project, to ensure it is delivered safely.

ADAPT is delighted to be undertaking this work. It means that our joint venture companies, AREVA, Doosan Babcock and Atkins can pool our significant global expertise to work with Sellafield Ltd on this iconic project, which will deliver both a decommissioning priority and a visible legacy of skyline change.

Decommissioning the chimney is an important piece of work and one where we’re committed to thinking differently to deliver a cost-effective, fit for purpose solution that uses the most appropriate demolition techniques making use of local SMEs wherever possible.

Paul Terry
ADAPT Framework Manager

Smarter waste management

Demolishing a chimney the size of the Windscale Pile Chimney will create a large amount of waste – 5,000 tonnes in fact, and with varying degrees of radiological contamination. Sensible, cost-effective waste management is an important part of the future of Sellafield, as we clean up the site – removing facilities that have completed their mission.

This means knowing what waste we’ll create, what the classification of this is, and how we will dispose of it. By doing that we can identify the most suitable waste disposal routes, get a better understanding of the cost and negotiate the appropriate disposal contracts. This project has identified and understood its waste disposal needs prior to demolition, and the best routes have been identified, minimising unnecessary cost.