TECHNICAL | SHAFTS, CAVERNS
MARINE TUNNEL WORKS HINKLEY POINT C: The BTS evening meeting in April heard about the marine tunnels works on
Hinkley Point C project from Barry Gilsenan, Senior Tunnel Manager with Balfour Beatty, who also provided this report of the lecture; Joe Hardwick, Engineering Manager with Balfour Beatty; and, David Maddison, Associate Director with Jacobs.
A schematic showing the arrangement of tunnels at end of Hinkley Point C project’s Outfall Tunnel, located offshore in the Bristol Channel. The tunnel-to-shaft connections will convey spent cooling water to Outflow Heads for diffusion to sea.
Three speakers discussed Hinkley Point C (HPC) nuclear power project’s Marine Works package, giving focus to the offshore tunnels and the tunnel-to-shaft connections in their lecture to the BTS, at the ICE in London and streamed online, on 16 April. The project is located in Somerset, south- west England, with the offshore tunnels reaching out into the Bristol Channel as part of the cooling water system. First speaker was Joe Hardwick who has experience
in heavy civil construction and design across the UK and Australia. Joe has been on HPC for nearly six years and is Balfour Beatty’s Engineering Manager for central engineering on the marine and tunnels scope. David Maddison is Associate Director of Tunnelling
at Jacobs. David is a design and project manager with more than 10 years’ experience in the nuclear tunnelling industry, having primarily worked from site on HPC and is transitioning to work on Sizewell C. The third speaker was Barry Gilsenan, who has more
than 30 years’ experience in construction, including Crossrail’s eastern running tunnels and caverns, the Bond St station upgrade and Paddington step-free access tunnels. He is Balfour Beatty’s Senior Tunnel Manager on the HPC marine tunnels. Joe introduced the project and tunnel works, handed
over to David to discuss design, and then Barry focused on construction. They took questions afterward.
16 | September 2026
HINKLEY POINT C – TUNNELS CONTEXT HPC is the first new nuclear power station to be constructed in the UK for a few decades. The power plant has two reactor units and a total power capacity of 3.2GW. In comparison, Joe said, Sizewell B (completed in 1995) is about 1.2GW. EDF will be the final operator and owner, and it is the
majority funder of HPC. The project is also funded by China General Nuclear (CGN). They have set up a new company, New Nuclear Build (NNB). NNB and EDF are client, principal contractor and principal
designer for the overall project. Balfour Beatty is a Tier 1 subcontractor on the project, the works, including the onshore and offshore tunnels, being responsible for their design and construction under an NEC3 ECC contract. In the design, Balfour Beatty is supported by Jacobs, and by others in many other aspects of the major project. The main tunnel works relate to the power plant’s
cooling water system, which cools the condenser beneath the turbines. On the coast of the Bristol Channel, there are two long seawater Intake Tunnels to bring in cooling water, and a shorter joint Outfall Tunnel, located centrally between them, that returns the flows to the sea by diffusion. To achieve the inflows and diffusion outflows, each tunnel has two shafts and those are topped by head structures that sit on the seabed. Though, below the seabed, it was
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