Balfour Beatty and EDF Energy have celebrated a major milestone at the new Hinkley Point C nuclear power station in Somerset.

The Balfour Beatty team has successfully completed the breakthrough of the longest and final onshore cooling-water tunnel, at the landmark project.

The team excavated through 600 metres of ground to create a total of five tunnels, and worked safely and swiftly to spray the ground with 9000m3 of concrete to stabilise the recently formed underground structures. In total, the process required over 1.6 million hours across the tunnels, with the programme of works completed to schedule.

The five onshore tunnels will now undergo secondary lining works to further stabilise the sprayed concrete.

The tunnels will play an essential role in the critical cooling water system for the nuclear power station, responsible for transferring over 120,000 litres of water per second to Hinkley Point C from the Bristol Channel.

The same team has prepared three portals to facilitate the launch of the Tunnel Boring Machines (TBM), which will excavate the tunnels for the main cooling water system. The first TBM has already set off on its journey, having travelled over 2.5 kilometres, 33 metres under the Bristol Channel.

Alistair Geddes, Balfour Beatty project director for Hinkley Point C's tunneling and marine project, said: "This is a significant step forward in the successful delivery of the first new nuclear power station in the UK for over 20 years."

On completion, Hinkley Point C will supply safe, secure, low carbon electricity to around six million homes.