Pile chimney barrel demolition mock-up, Sellafield, Cumbria

The Project

The scheme involved the site preparation and construction of a 7.5 m high full-scale mock-up of the iconic Sellafield Pile Chimney barrel, which is due for demolition. The mock-up was used to test the demolition rig and demonstrate the demolition methodology for the decommissioning of the 120m radioactively contaminated chimney. Our scope of work was to construct the full-scale chimney mock-up at an off-site test facility in West Cumbria to allow our client to install and test the decommissioning rig. This involved:

• Excavation of foundations and removal and disposal of 200Te of waste.
• Backfill the foundation with stone and concrete blinding.
• Install foundation and wall starter rebar.
• Pour the concrete foundation pad.
• Install 7.5m high curved trapeze RMD Kwikform formwork in 2m lifts in two semi-circular halves.
• Construct personnel access aperture.
• Install shuttering and rebar between the formwork shells.
• Pour the wall concrete in 2 off 14-hour pours.

The complex structure was constructed to high dimensional tolerances during adverse winter weather.

Key Quantities:

Excavated Material
0
Te
Rebar
0
Te
Concrete
0
m3

Challenges and Successes

The project was constructed during exceptionally cold winter weather which included long periods of rain, snow, and frost down to -7 Deg C. This made it difficult to bend and adjust the rebar to the required tolerances and limited our concrete pour windows. To overcome this, we installed digital thermocouples to monitor the ambient and rebar temperature to allow us to start the concrete pour. This also allowed us to monitor the temperature of the concrete as it cured. We worked weekends to pour the concrete during suitable weather conditions.

The trapeze formwork curvature demanded installation tolerances of 5-7mm which proved to be difficult to achieve in conjunction with the shuttering and rebar. By working with the designers and RMD Kwikform during the Early Contractor Involvement stage we were able to develop the construction sequence to achieve the required dimensional tolerances. Final iterative adjustments of the formwork were made to ensure all sections in both halves of the structure were within the dimensional tolerances.