How Balfour Beatty connected Hinkley Point C’s cooling system tunnels and shafts

Balfour Beatty completed major engineering works to deliver the tunnels and shafts for Hinkley Point C’s cooling system, but connecting them has been a significant challenge in itself.

As principal contractor for the offshore elements of new nuclear power station Hinkley Point C, Balfour Beatty has already undertaken several feats of engineering. The package of works encompasses the cooling system for the power station that will provide 120,000 litres/s of water to ensure its safe operation.

This system features three tunnels under the Bristol channel – two 3.5km intake tunnels and one 1.8km outfall tunnel – each connected to the seabed via two 20m deep vertical shafts.

Creation of the shafts first saw the six large intake heads, the largest weighing 5,000t, lowered onto the seabed using heavy lift barges. Balfour Beatty engineers then drilled the 5.5m diameter shafts through the bottoms of the intake heads and around 25m into the seabed.

Vertical shaft liners, each weighing 270t, were then lowered in. These feature world-first pre-installed isolation caps that stop the seawater flowing into the shafts until the time is right. This allowed work to continue in the tunnels below.

Boring the tunnels and creating the shafts with outfall heads on the seabed have been the largest and most eye-catching parts of Balfour Beatty’s work on Hinkley Point C so far. However, the decision was made to use an “offline” approach, meaning these two major pieces of infrastructure do not directly connect.