Nuvia retires Category A risk at Sellafield

On Tuesday 12th June, Nuvia, working within an integrated team, successfully achieved a significant project milestone in the demolition of the First Generation Reprocessing Plant Stack at the Sellafield site by reducing the stack height from 61m to below 47m 67 days ahead of schedule.

This high-profile project milestone has been achieved through the integrated team of Sellafield Ltd, Nuvia and Supply Chain partners – Delta and Alimak being co-located and all working collaboratively using unique engineering solutions and work patterns.

Not only was this key milestone achieved ahead of schedule, but in doing so it has also become the first project in a generation to retire a Category A risk on the Sellafield site.

First Generation Reprocessing Plant Stack consists of a reinforced concrete windshield surrounding a stainless-steel flue. The stack initially stood approximately 61m high, on top of the reprocessing plant and extended some 122m above ground level however did not meet modern seismic structural standards so represented a risk to the surrounding facilities.

It could not be removed using more conventional access and demolition techniques due to its location on the congested Sellafield site, near to other important facilities.

As the main contractor, Nuvia amended the initial Delta International design to fit with the complex requirements of this project and then together with our supply chain partners built and commissioned a Self-Climbing Platform (SCP). This platform, using friction pads, then climbed the 61m stack over a period of 9 months. After reaching the summit on 23rd August 2017 a weather canopy was attached before the platform began a series of descents removing the stack and liner on each descent.

The SCP, a steel and aluminium frame construction, is clamped to the stack windshield using a set of circumferential bands which pass around the windshield. These are pre-tensioned to induce a contact bearing pressure on the stack windshield, effectively holding the SCP by friction. SCP provides a safe working platform to carry out demolition of the concrete wind shield and the steel flue liner.

Since the start of the project the team have embraced some innovative demolition techniques, such as switching from a slower dry core drilling system to a water recycling wet coring system, which is at least twice as fast. To date more than 92 TONNES of concrete and rebar windshield has been removed manually and 4.5 TONNES of stainless steel flue liner has been hand cut using plasma cutting tools.

The project is due to complete demolition of the stack in early 2020. Its ultimate demolition aids the environmental clean-up of the Sellafield site. A job which is set to continue for a century.