Building a shield of concrete for the ITER machine

The scientists working for ITER will use many different technologies to develop and analyse the biggest plasma to date. Powerful magnet systems, extreme hot and cold temperatures, sophisticated robotics, new materials and thousands of high-tech subsystems will be deployed inside the machine. This state of the art fusion device will be protected by a 3.5 metre thick wall, known as the “bioshield”, which will ultimately act as a safety layer between the machine and the building hosting it.

This shield made of concrete will be more than 30 meters high to protect the ITER cryostat, responsible for generating the freezing temperatures surrounding the machine. “The concrete that will be used for the Tokamak bioshield is a type of concrete that doesn’t need to be vibrated” explains Luis Aspilcueta, working for Energhia. “The density of the metallic framework, the thousands embedded plates weighing several tonnes and the concrete for the bioshield make this shield one of the most complex elements of the ITER buildings”. To understand how this protective shield will have to be constructed, a mock up representing 1/18th of the Tokamak bioshield was built. It is currently located at the entrance of the worksite and it represents the first stage of the bioshield’s construction.

In May 2015 the reinforcement works of the bioshield’s first level started and are expected to be completed in November 2015. Once the reinforcement works of the south façade were completed, the formwork was placed all around the structure to pour the concrete. On October 21, 620 m3 of concrete were poured from 4:00 to 17:00 with the help of a concrete pump installed on the edge of the Assembly Hall building and one mast inside the seismic isolation pit. More than 15 people working in two shifts were involved in the operation. During at least 13 hours, concrete was poured to cover 3/5th of the basement two level of the Tokamak bioshield.

Standing from up above, one can notice a 3.5 metres wide ring emerging at the centre of the Tokamak building. On Tuesday 27 October, the formwork has been removed and the civil engineers have started to check if the result complies with the confinement requirements. 28 days will be necessary for the concrete to reach its final strength. The protective layer of the Tokamak machine is in progress, as the whole worksite is evolving.