For the insertion of the components of the Proton Therapy installation by Mevion, a recess was left in the 3.4 m thick roof of the bunker. The recess is not definitively closed because it must be able to be opened later for maintenance purposes.
In the meantime, all parts have been inserted through the roof recess and the roof recess must be closed permanently as a “constructive” operation.
The “roof hatch” is made up of separate prefab concrete parts that are stacked on top of each other in brickwork. The roof is closed in half a day.
See the timelapse of 12 April 2018. The images are taken from the ZON PTC webcam.