Hinkley Point C Nuclear Power Station – Marine and Tunnelling Contract

At Avonmouth, we have adapted to our new normal with COVID-19 quicker than most. Why? Because unlike other civil engineering projects, the supporting site to the Hinkley Point C construction site had to continue progress at pace due to its status as a National Critical Infrastructure Project.

Located in The Bristol Port in Avonmouth, Kilnbridge has kept their 200 strong team working safely and efficiently throughout these unprecedented times, and have ensured the continued construction of the six heavily reinforced concrete Class 1 nuclear safety structures - known as the Outfall and Intake Heads. These are complex concrete structures which will be transported and lowered to the seabed of the Bristol Channel and connected with the cooling water tunnels currently being constructed at the HPC Site.

The programme targets are being maintained in line to see these mighty structures transported to their final undersea destinations offshore from the new power station in 2021.

The entire team and their respective supply chain members have demonstrated an incredible example of collaborative working during these unprecedented times, which has fostered a new and efficient way of working towards the delivery of these c. 5000T seismic-resistant elements. The density and complexity of reinforcement have necessitated the extensive use of digital construction techniques and 3D modelling, with reinforcement densities of 900kg/m3 in places and positional tolerance of less than 5mm in several areas providing significant challenges for the project team.

The Kilnbridge team; lead by Graeme Stewart, Rick Kopec, David Sanchez, Jeremy Jubb, Kestutis Sileikis, Michael Tiffoney and many more, are determined to construct these extraordinarily complex nuclear structures to the exacting quality and safety standards required, and within the challenging programme for the successful outcome of this nationally important project.

One of the partially completed Intake Head structures. After the removal of all decking this structure is ready to be lifted to ensure that it does not exceed any weight limits. This photograph and the weighing operation took place at the end of March 2020.

One of the partially constructed intake structures, ready for its interim weighing in late March 2020. Once completed, it will be lifted and transported off the edge of the dock wall onto an awaiting barge for transportation to its final destination approximately 40 miles away.

Our most advanced structure, in Avonmouth Docks, Bristol. In early August 2020. The first reinforcing bar was placed in this structure in November 2018 and, as the lead structure, it has been the provider of huge amounts of invaluable learning for the three further identical Intake Heads which follow it.

These c. 35m x 17m x 7m tall structures weighing circa 5000t will be very impressive once complete, the first of their kind to be constructed in the UK. Densely reinforced and of a particular/unusual shape and size, the six No. heads will be required to serve the cooling system of the new Hinkley Point C Nuclear Power Station for the next 60+ years.

The second most progressed Intake Head structure taking shape in early August 2020. This Intake Head is being prepared for concrete to be placed.

Engineering control and accuracy is an essential requirement for this complex build. Here we see another one of the four Intake Heads taking shape.

The above extracts from the 3D model and 2D drawings show some of the highly-dense areas of reinforcement within the Intake and Outfall Heads. The installation sequence is critical for the efficient installation of the reinforcement, and the accurate cutting, bending and checking is also essential. By staggering the construction phase of each of the two different head types, invaluable learning has been gained to ensure that the trailing construction activities can be optimised for a safer, more efficient build. Numerous collaborative sessions have been held by the entire project team to ensure that any lessons learned are captured and applied for the future, identical work types.

With the fourth Intake Head concrete pour completed, attention is immediately focused towards getting it stripped of support decking and prepared for the interim weighing operation.

The leading Intake Head structure stands proudly in the Avonmouth Docks site. The next pour (roof slab) will be the uppermost pour which will signify substantial completion of the structure.

This Intake Head structure, being prepared for its fifth concrete pour in August 2020. This will be the final one of the four Intake Heads to be completed and transported from Avonmouth docks in 2021.

The dense reinforcement being safely and carefully covered in fresh nuclear grade concrete in June 2020. Another c. 180m3 towards a total of c. 2000m3 of concrete required per Intake Head.

Intricate and bespoke formwork solutions allow for exact shutter positioning to ensure that the nuclear safety and quality requirements are fully met. This is no ordinary reinforced concrete project.

Both Outfall Head structures under construction on the dockside in the sunshine of August 2020. These will be the first elements to be transported from Avonmouth Docks their final resting place on the seabed of the Bristol Channel some 40 miles away. Once commissioned and in use, they will ensure that the seawater used to cool the nuclear reactors is safely deposited back into the Bristol Channel.

Intricate, strong yet accurate shutters are required alongside the complex and dense reinforcement on both Outfall Head structures to form the very particular shapes required. Note the Super Duplex Stainless Steel lifting lug in position, which will be used by the huge floating cranes to lift the Heads from their transportation barges and lowered to the sea bed above the tunnels which are currently being constructed beneath.

Some areas of these complex class 1 nuclear structures have reinforcement to concrete densities of over 900kg/m3 which increases the challenges faced by the project team, not only in the installation of the reinforcement but also the placement and compaction of the concrete. Special, self-compacting concrete mixes have been developed specifically for use in some areas. This is one of the two Outfall Head in June 2020.

An Intake Head structure being prepared for the interim weighing operation via its red transport beams at the end of March 2020. Some may say, it's far too impressive to be placed on the sea bed!