Sizewell C early works to commence with site creation and ground trials

In mid-January, the Sizewell C project triggered its development consent order (DCO), which the government approved in July 2022. This gave the project the formal green light for construction to begin.

The final go-ahead came after all necessary obligations set out in a document signed with East Suffolk Council and Suffolk County Council had been satisfied. These included activities ranging from key road surveys to the establishment of governance groups. None of the discharged obligations, however, related to ground engineering activities.

This week, plant is being delivered to Sizewell C’s temporary construction area.

A Sizewell C spokesperson told NCE sister title Ground Engineering that the early works will include:

• putting in place the local infrastructure that is needed to build the project, including a two-village bypass and other improvements to the A12, the park and rides and freight management facility, and rail lines
• building the roads on the site itself to provide direct access for construction vehicles, putting up perimeter fencing to ensure safe and secure site boundaries, and starting construction and fit-out of our welfare units and site offices for the team
• continuing ecological and archaeological works on the main site and across the associated development sites, as well as conducting ground trials for civil engineering works and commencing drainage and earthworks.

AtkinsRéalis was chosen to provide civil engineering design services across the project.

At the British Geotechnical Association’s annual conference in 2022, Atkins Réalis chief engineer Mark Scorer said that determining the most cost-effective construction techniques and finding innovative design solutions “is predicated on replication from Hinkley Point C” by learning “key lessons”.

As part of this, more extensive ground investigation campaigns were carried out for Sizewell C. These included approximately 1,500 locations, with numerous boreholes, trials pits and in situ mechanical tests undertaken through progressive investigations.

Unlike Hinkley Point C, Sizewell C is being built on soft marshy ground.

“The geology that we’ve got there, we’re looking at a reasonable amount of made ground from the neighbouring Sizewell B construction. We’ve got our recent deposits consisting of some alluvial clays and peats – some beach deposits which can be quite soft – and then we’ve got the bedrock crag deposits, below which you find the Thames Group, the Lambeth Group, and down to the Chalk eventually," Scorer explained.

A cut off wall will be constructed near the perimeter of the nuclear licenced site boundary in reinforced concrete to create a watertight box around the main construction area. It will also perform an earth retaining function. It includes a 2km long diaphragm wall embedded to 50m depth into the Harwich Formation, part of the Thames Group.

Once the cut off wall has been installed, the “big dig” can begin – roughly 4M.m³ needs to be excavated from the main construction area. This will be done without blasting and by controlling the excavation so that there is no impact on the Sizewell B facility.

A key change to the project is the aspect of “decoupling” the tunnelling works from the main excavation activities. In contrast, the tunnelling launch for Hinkley Point C was carried out from within the project's main heatsink structures.

Project funding

Sizewell C is being developed by French energy company EDF with support from the UK Government. Its cost has been estimated to be at least £20bn.

The government took a 50% stake in the scheme in late 2022, after buying out China General Nuclear due to concerns about Chinese involvement in UK infrastructure.

On the heels of the DCO being triggered, the UK government made an additional £1.3bn available to support the construction of Sizewell C. The funding package will allow the early construction works to continue ahead of a final investment decision later this year.

The additional investment consolidates the government’s position as the majority shareholder in the project, reached in December 2023. It follows a £700M funding pledge in November 2022 and a further £511M last summer.

The Independent recently reported that energy company Centrica was eyeing Sizewell C as a “possible future investment”.

Once completed, the 3.2GW nuclear power station is expected to supply enough energy to power 6M UK households.

Based on the government’s Civil Nuclear Roadmap, the UK is aiming to quadruple nuclear power generation to up to 24GW by 2050. It has committed to exploring another power plant similar in scale to Sizewell C, simplifying regulation and building a fleet of small modular reactors.

In related news, last month, EDF announced that Hinkley Point C’s completion would be delayed to 2031 and the project could cost up to £35bn.

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