Mammoet loads four 300-tonne steam generators at Unterweser
30 Second Takeaway
Mammoet has completed the transport and load-out of four steam generators, each weighing 300 tonnes, from Germany’s decommissioned Unterweser Nuclear Power Plant. Two 12-axle-line self-propelled modular transporter units moved each generator overnight to a former ferry ramp at Kleinensiel, about five kilometres away. A temporary ramp kept the transporters level on the site’s 4.2-degree slope. Mammoet then used a floating sheerleg crane to transfer the generators to an overseas vessel during a two-hour tidal window.
Transport route shifted to former ferry ramp
The work was the second phase of a project that began in 2024, when Mammoet engineered the removal of the four generators from the reactor building in one piece. For the latest phase, Mammoet was contracted by Orano NCS to move them from the power plant to a vessel bound for Cyclife’s nuclear waste treatment facility in Sweden.
Each generator measures approximately 20 metres long and 4.5 metres in diameter. The original plan was to load them at the power plant quay, but strong tides there would have required dredging. The project team instead chose a former ferry ramp at Kleinensiel, around five kilometres from the plant.
SPMTs moved generators overnight
Each generator was transported overnight on two 12-axle-line self-propelled modular transporter (SPMT) units. Road permits restricted the movements to the hours between 22:00 and 06:00.
At Kleinensiel, the ramp’s 4.2-degree downward gradient posed a challenge. The SPMTs could not level themselves on the slope, even at full jack stroke. Mammoet built a temporary ramp over the existing structure so the transporters could remain horizontal. This helped prevent the generators’ centre of gravity from shifting during the subsequent lifting operation.
Load-out planned around two-hour tide window
The load-out depended on the River Weser’s tidal range, which can reach three metres. The water needed to be high enough for the floating sheerleg crane to approach the ramp, while the SPMTs also had to remain clear of the water.
Using forecast water-level data, Mammoet identified a two-hour lifting window from 09:00 to 11:00. During that period, the sheerleg crane lifted each generator from the SPMTs and transferred it to the overseas vessel for shipment to Sweden.
About Mammoet
Mammoet provides engineered heavy lifting and transport services for large and complex projects. Its work includes transporting, installing and decommissioning heavy structures and equipment across industries such as energy, infrastructure and heavy industry. The company uses specialised lifting and transport equipment to plan and carry out project-specific operations.
View website: https://www.mammoet.com/
About Orano NCS
Orano NCS provides nuclear logistics and transport services, including the planning and movement of nuclear materials and heavy components. Its services also include engineering and radiation protection support. For the Unterweser project, Orano NCS commissioned Mammoet to carry out the generators’ transport and load-out.
View website: https://orano-ncs.com/en/
About Cyclife
Cyclife provides radioactive waste treatment and nuclear decommissioning services. Its Swedish facility treats waste for Swedish and international customers, with a focus on reducing waste volume and recycling materials. The four steam generators are being shipped there for treatment.
Frequently Asked Questions
How heavy were the steam generators?
Each of the four steam generators weighed 300 tonnes.
How were the steam generators transported to the load-out site?
Each generator was moved overnight on two 12-axle-line SPMT units, with road permits limiting transport to between 22:00 and 06:00.
Why was a temporary ramp built?
The former ferry ramp at Kleinensiel had a 4.2-degree downward gradient. The temporary ramp allowed the SPMTs to remain level, helping prevent a shift in the generators’ centre of gravity during lifting.
Why was the load-out scheduled around the tide?
The floating sheerleg crane needed sufficient water depth to approach the ramp, while the SPMTs needed to stay clear of the water. The team identified a two-hour lifting window using water-level forecasts.
Where are the steam generators being sent?
They are being shipped to Cyclife’s nuclear waste treatment facility in Sweden.
