Mammoet was tasked by contractor Höfer & Bechtel to lift the RPV at the Unterweser nuclear power plant in one piece and proposed a customised solution using an SBL 1100 – a moveable four-point hydraulic lifting gantry with a capacity of 1,100t that could be adapted to confined spaces.
Before the lifting system was installed on the operating floor, steel load distributors were installed. These were followed by tracks, four hydraulic lifting stamp jacks and two strand jacks to increase the lifting height of the system.
The strand jacks were installed on a hydraulic skidding track on the beams of the lifting system. This allowed the RPV to be lifted and lowered vertically and also moved laterally.
The RPV was lifted from the reactor pool and moved to a temporary parking position. Using the reactor building’s crane, the contractor then placed a dismantling rack at the now vacant spot. The RPV was moved back and lowered onto the dismantling rack, enabling the contractor to cut off the calotte (the spherical bottom of the RPV), which is part of the dismantling process. Next, the RPV was moved to the final dismantling position, which involved it being lifted over a wall, and lowered.
All the equipment was brought into the control area piece by piece and ‘foiled’ – or shielded against radiation – so that it could be decontaminated and removed after completion if required.
This was the first of five pressurised water reactor plants to be decommissioned for the operator PreussenElektra, and Höfer & Bechtel has been asked to use the expertise gleaned from the project again.
Philipp Boettcher, manager engineering at Mammoet in Germany, said the removal of the RPV was very demanding.
“Through the intensive cooperation, all parties involved have grown together and become a team. We are delighted that we were able to contribute to a safe project with our custom lifting solution and pave the way for another decommissioning project within the power plant fleet,” he said.
Mammoet lifting solution provides template for nuclear decommissioning project
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