Three tunnel boring machines, each weighing roughly 1,500 tonnes, have been built for the project. They will be used to dig two 3.5km cooling water intake tunnels and a 1.8km outfall tunnel in the Bristol Channel.
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 from the Bristol Channel.
At peak, the three tunnel boring machines (TBMs) will excavate more than 11 tonnes of rock per minute.
A total of 38,000 concrete segments will be installed to support the three underground marine tunnels at up to 33 metres below the estuary seabed. The pre-fabricated nuclear-grade concrete segments are being manufactured by Balfour Beatty.
The first TBM been named Mary by local school children in honour of Mary Anning, a palaeontologist and fossil finder who lived in Lyme Regis.
TBM Mary will be run by 12 operators including a pilot, with supporting teams at the surface. She will be able to reach a maximum speed of 120mm per minute, or 0.7km/h.
Hinkley Point C construction director Rob Jordan said: “The start of tunnelling at Hinkley Point C represents a hidden but vitally important milestone in the construction of the UK's first new nuclear power station in a generation. Delivered to schedule, this achievement underlines the continued progress being made to ensure that Hinkley Point C will be ready to supply the UK with the reliable low carbon electricity that it needs to combat climate change.”
Balfour Beatty project director Alistair Geddes added: “This is a significant milestone, critical to the successful delivery of the first new nuclear power station in the UK for over 20 years. Having installed the first permanent segment ahead of schedule, this milestone is testament to Balfour Beatty’s expertise and to the collaborative approach required to deliver a project of this scale and complexity.”
Balfour Beatty is contracted to three major packages of works at Hinkley Point C. It was first appointed to deliver the electrical works package in a joint venture with NG Bailey in 2015, the tunnelling and marine package in 2017 and most recently the 400kV overhead line project on behalf of National Grid in 2019.