The mammoth has lifted the ton-heavy reactor plug for DD

Success: the massive metal plug that closed Denmark's biggest research reactor DR3 has been pulled open and replaced with a lid. Due to heavy radiation down from the reactor tank, the historic operation has been planned in detail over the past years. DD praises the cooperation with Mammoet and Bladt Industries.

P The stopper - known in the jargon as a top shield plug or TSP - has closed the radioactive tank as close as the stopper in a thermos bottle. It weighs 22 tons and it is highly radioactive on the underside after more than 40 years of reactor operation. It was therefore necessary to lift the stopper up and shield it in one continuous movement. The moment the stopper was lifted, a moving lid was rolled over the tank as a new shield, so that the powerful radiation was constantly enclosed.

Limited space
Part of the challenge was the limited space. The reactor tank is cast into a square concrete tower that is 6 x 6 metres wide and 10.5 metres high. The tower stands in a tall, cylindrical hall with only a few metres of working space facing the walls. Cranes and lifting equipment therefore had to be driven in in assembly kits and erected on site. The Dutch heavy lifting company Mammoet carried out the historic task for Danish Decommissioning. Mammoet has lifted and removed entire reactor tanks from nuclear power plants around Europe on several occasions. The company is also responsible for laying the new roof of the concrete sarcophagus enclosing the Chernobyl plant. They have also carried out specialised tasks such as lifting the nuclear submarine Kursk from the bottom of the Arctic Ocean.

Special equipment
Bladt Industries in Aalborg has custom-made the movable lid and the shielding containers in which the reactor plug has been put down. The shielding consists, as a precaution, of two containers – one cylindrical in one square – each of which would have been adequately shielded.

"We have had an incredible working relationship with Bladt Industries, who have delivered exactly what we needed, and with Mammoet, who work very professionally, quickly and thoroughly. There have been many safety details in this lift and I am really pleased with our own staff and with Mammoet's efforts," says Project Manager Per Holtzmann Søndergaard from Danish Decommissioning.

Robot cutting
Now that the reactor plug has been removed and securely shielded, Danish Decommissioning will start cutting the reactor vessel itself from the inside. This will be done with a robotic arm through hatches in the new lid.