Jun 27 Lifting on rails
An ingenious, self-propelled lifting gantry has, over the past week, removed five partition walls from the so-called Hot Cells. This marked the commencement of the next phase in the complex project.
DDeep within an office building are six interconnected concrete cells, which were used from 1964 to 1989 for handling radioactive materials. Due to the high radiation levels, it is currently not possible to enter the cells, and among the six nuclear facilities to be decommissioned on the Risø peninsula, the Hot Cells represent the most complex challenge.
The Decommissioning of the Hot Cells commenced in 2008. Since 2012, after the removal of certain highly radioactive 'hotspots', time has been dedicated to planning and preparing the next major steps, not least the remote-controlled sandblasting of the cells. The team is now nearing readiness for the actual decontamination of the Hot Cell structure.
“As an initial step, we chose to remove the five shutters – a type of partition wall that can be raised and lowered between the cells – before sandblasting,” explains project manager Bjarne Rasmussen, elaborating: “Otherwise, the sand could damage the threads of the lifting/lowering mechanism, making it very difficult to retrieve the five shutters at a later stage.”
A Sideways Lift
The sub-project to remove these shutters has just been completed, proceeding smoothly and faster than anticipated. The team collaborated with foreign expertise to ensure its success.
In May, the Swedish company Extrem Borr & Sågteknik AB arrived and assisted in cutting through the shutter housings – large metal boxes that were attached above the Hot Cells. Prior to this, the five shutters had been hoisted into place within their respective housings.
Mammoet has now visited. The Dutch heavy lifting company has previously assisted Danish Decommissioning with challenging lifts and is well-known in the nuclear industry. The company has, among other things, been contracted to install a new roof on the concrete sarcophagus encapsulating the Chernobyl plant.
Although lifting five shutter housings may seem like a minor task compared to Chernobyl, it has been far from uncomplicated. The ceiling height in the room above the Hot Cells is low, making it necessary to lift the eight-ton shutter housings slightly and maneuver them sideways out. This required meticulous planning and excellent teamwork between the Mammoet personnel and Danish Decommissioning.
Practically, Mammoet executed the task by laying a long rail on each side of the row of shutter housings. A lifting gantry, capable of advancing with hydraulic assistance, was then positioned on these rails. The gantry was first placed over the outermost shutter housing, which was subsequently lifted with chains and relocated. A metal plate was then welded underneath the housing – both to provide radiation shielding and to ensure stability during transport. The gantry then traversed the rails with its load to a hydraulic platform, which was lowered, allowing a forklift to transport the shutter housing the final distance to the ground. This entire process was then repeated for each of the remaining shutter housings.
Get ahead of schedule
It took four working days for all five shutterhouses to be lifted away and taken to a storage facility, where they are now awaiting further treatment. The holes left by the houses over Hot Cells have been closed, first with a specially designed cover and then with a 'dummy butter'. In total, the work, including the installation and dismantling of equipment, has taken ten days.
“Of course, there were some unforeseen minor issues along the way, such as ceiling screws that we had to grind down because they were obstructing the lifting gantry. The dummy shutters we had fabricated also required slight shortening, as the original drawings from the 1960s did not accurately reflect the actual construction. Nevertheless, everything proceeded smoothly overall, and we actually finished several days ahead of schedule,” says Bjarne Rasmussen.