The second one of the three underground marine tunnels at up to 33 metres below the seabed of the Bristol Channel has been completed. These tunnels are part of the nuclear power station being built.

Once complete, the tunnels will form a critical part of Hinkley Point C’s cooling system and will have the capacity to transfer 120,000 litres of water per second.

https://www.geplus.co.uk/news/hinkley-point-c-second-offshore-tunnel-completed-14-10-2021/