Mitsubishi Heavy Industries Ltd replaced the internal structure of a reactor vessel at the No. 1 reactor at Shikoku Electric Power Co’s Ikata power station in Ehime Prefecture, Japan, in one single piece.

The 100 tonne stainless steel structure that was replaced consists of a lower part housing the fuel assemblies and an upper part supporting them and is 8m in length with an internal diameter of 2.8m. The gap between the structure and the vessel measures 0.4mm at the narrowest part. A specially developed remote-control system was used for precision positioning.

The work would have taken about 200 days if dividing or cutting the structure had been involved. MHI completed the task in 70 days by extracting the whole structure from the vessel and placing it in a container.