Hinkley Point C: Enhancing the Durability of Precast Concrete Tunnel Segments
Hinkley Point C is one of the UK’s most significant nuclear infrastructure projects, with its cooling water system relying on 5.3km of large-diameter seawater intake and outfall tunnels. With a 60-year design life required, enhanced protection of the precast concrete tunnel segments was essential.
Located on the coast near Bridgwater in north Somerset, Hinkley Point C is Britain’s first new nuclear power station to be built in a generation. At its heart are two huge reactors designed to power six million homes and provide about 7% of the UK’s electricity needs. Key items of equipment, including the second reactor, were successfully lowered into place using “Big Carl”, the world’s largest crane.
Nuclear power generation requires a constant source of cooling water to regulate temperature in the reactors. To keep itself cool, Hinkley Point C must have the capacity to draw in and flush out enough water to fill 4,200 Olympic swimming pools – every day.
Seawater will be extracted from the Bristol Channel through two 6 metre diameter intake tunnels which are each 3.5km in length. Once circulated around the reactors, the seawater is returned via a single 7 metre diameter outfall tunnel which is 1.8km long. The tunnels comprise 38,000 concrete segments.
To achieve the intended 60 year design life within a system which has the capacity to transfer 10.4 million cubic metres of water each day, it was determined that the concrete cover to the embedded steel reinforcement in certain of the segments should be enhanced to give the necessary durability. This resulted in an extensive study of different coating technologies to establish the best method of achieving this objective.
Cover enhancement for precast tunnel segments
Following successful site trials, Cemprotec E942 was approved for this demanding application. This is an epoxy and polymer modified cementitious coating which is applied to a thickness of 2mm, providing waterproofing properties equal to more than 2 metres of concrete.
Substrate preparation was by high pressure water jetting techniques operating at 340 bar. This is an ideal method of preparation as a fully saturated substrate is required prior to application. Owing to the particularly dense nature of the concrete, Cemprotec EF Primer was additionally used.
Application of Cemprotec E942 was undertaken by airless spray equipment, the second 1mm layer being applied when the first is stable but not fully set. This method optimises productivity, allowing completion of each segment during a single shift without risk of any intercoat contamination.
Cemprotec E942 is UKCA and CE Marked in full compliance with EN 1504-2 and is supported with an impressive range of test data.
Client
Contractor
Design Consultant
Hinkley Point C