In this article the authors describe the use of robots to rectify a fault inside Sweden’s Ringhals 1 reactor. Ringhals 1 is an 830MW ABB-Atom Boiling Water Reactor located on the west coast of Sweden, south of Gothenburg.

In Ringhals one of the systems of primary importance is the series of 157 control red drive mechanism (CRDM) pipes that are welded to the bottom of the reactor vessel. These pipes hold the control rods which are driven up and down to maintain a stable nuclear reaction. Each of these 157 CRDM pipes has an associated smaller diameter pipe, called a SCRAM' pipe. In a reactor trip, high pressure water is pumped through these smaller pipes forcing the control rods up into the reactor vessels and shutting down the nuclear reaction.

One of these pipes was found to be leaking and it was necessary to carry out a repair as the correct operation of these pipes and the control rods is critical to the safe operation of the reactor. The technical challenge facing Ringhals was two fold. Firstly such a pipe repair had not been done before and required the leaking section of pipe to be removed and replaced with a new piece of pipe using a new 'parent metal' welding technique. The second challenge was perhaps more profound.

The leak was located close to the CRDM pipe in a section called the SCRAM nozzle. This meant that the repair had to be made in an extremely confined space with very limited access hence the application of specialised robots to execute what turned out to be a very successful operation.