Mammoet was assigned to remove the two steam converters, each weighing around 155t, from the control area of the power plant.
In the planning phase, Mammoet’s engineering team developed a precise and efficient holistic solution for the safe removal of large components.
During the execution phase, these would need to be moved vertically and then tilted to a horizontal orientation, before being lifted from the building to wait for transportation below. In all, Mammoet’s engineering team spent only a few weeks forming a combined lifting and transport solution with strand jacks, designed specifically for this working environment.
"Our extensive experience from decommissioning projects enabled us to involve swiftly in the ongoing decommissioning process and develop a safe solution in a relatively short time." Dr. Sören Müller, Team Leader Nuclear and Logistics at Mammoet Germany.
Due to the high radiation protection requirements on site, the entire tooling, equipment and 100t of fabricated steelwork had to pass special radiation checks before being brought into the control area. This considerable time factor had to be taken into account in the planning so that the overall deadline could be met.
Prior to execution, all core components including the support strap, temporary lifting device and the skidding beam for the transverse skidding operation were subjected to a thorough load test. After successful acceptance by the authorities, work could begin in the control area.
First, the support strap had to be installed onto the first steam converter. Due to its installation position in a narrow housing, the upright-positioned component was difficult to access and first had to be jacked up with hydraulic climbing jacks and moved laterally.
After the support strap was attached, the temporary lifting device took over the steam converter. It was pushed out of the housing centimeter by centimeter with a skidding device and finally placed precisely onto a skidding track. The now horizontal steam converter was then rotated by 90 degrees and lowered.
In this position, the large component could be removed from the control area to a gantry built several stories high against the building exterior. Due to interfering edges and the narrow diameter of the opening, only a few centimeters of clearance were available to perform the operation.
After removal, the steam converter was lifted from this portal gantry in a tandem operation, by a 1200-tonne and a 750-tonne mobile crane, and loaded for transport on the power plant site. The second steam converter followed the same procedure. Lastly, four subcoolers were moved, lifted and handed over to the customer for loading into special containers.
"We were very satisfied with the technical solution and the cooperation with Mammoet. The very well-planned and safe removal of the steam converters was an important step in the overall decommissioning process." Stefan Lindemann, Project Manager Dismantling Large Components at RWE Nuclear GmbH.
The well-coordinated team executed all work safely and on time, in compliance with all regulatory requirements in nuclear facilities.