Key milestone reached at Hinkley Point C

14 December 2020

UK-based contractor Balfour Beatty has holed through on the first of three off-shore tunnels which form part of the cooling-water system at the Hinkley Point C power station. The firm hailed the accomplishment as a key milestone in the construction of the power plant which is located in North Somerset, England.

Tunnel boring machine (TBM) ‘Mary’, one of three TBMs required for the project, completed the 3.5km-long Intake Tunnel 1 on 9 December 2020, having mined at depths of 33m under the Bristol Channel. It installed more than 2,300 segmental concrete rings as it advanced, each comprising six segments. After each ring was placed, the crew filled the annular gap, using around 12,000m3 of grout in total over the full tunnel length.

The ‘nuclear-standard’ precast segments were produced at Balfour Beatty’s purpose-built manufacturing plant in Avonmouth and transported to site. Some 38,000 segments will be needed to complete the three tunnels.

The TBM excavated around 340,000t of spoil which was taken out of the tunnel on various conveyors, including belt- and bucket-type variants. It was then loaded onto trucks and taken for on-site landscaping. Parts of the TBM will now be stripped and installed on another machine, but the remainder will be left in-situ under the Channel.

The two remaining cooling-water tunnels will be bored by the other two TBMs: ‘Emmeline’, the largest of the machines, has just started mining the 1.8km outfall tunnel; and ‘Beatrice’, which is using parts from TBM Mary, is set to launch early next year to excavate Intake Tunnel 2.

Speaking of the completion of Intake Tunnel No1, Balfour Beatty Project Director Roger Frost said: “This is a significant achievement – one that marks another step towards the successful delivery of the UK’s landmark nuclear power station, Hinkley Point C. The unrivalled expertise of our people, combined with our state-of-the-art offsite manufacturing facility in Avonmouth, has made it possible for us to break through the first of three off-shore tunnels.”