The big waste puzzle

A major part of the work to dismantle the old nuclear facilities is the packaging of radioactive waste in containers. The space in each container must be used to the best of its ability, and it takes both ingenuity and careful planning to get this puzzle to a click.

D It is a matter of avoiding cavities, explains Per Søndergaard, project manager for the decommissioning of the DR 3 reactor:
"Our goal is that the waste should fill as little as possible. And compactly packed containers also reduce the risk of water entering and pulling radioactivity to the surroundings."

In the fall of 2014, a 17-ton heavy and 21/2 meter wide shielding ring was lifted away from its place around the top of the DR 3 reactor tank. Since then, the ring has rested in a large container, and the DR 3 team is now taking advantage of the space in and around the ring.

"First we had custom made some triangle frames for the four corners. In this we have placed a number of tubes that were mounted on top of the fuel elements," says Per Søndergaard and continues: "Now we are in the process of making some moon-shaped containers to be inside the ring. They will be filled with pipes and other materials from trials. And at the center of it all comes a cylinder with bits of thin steel rods that have absorbed a lot of radiation."

When planning the puzzle, account must be taken of the shape, size and weight of the waste. In addition, the different types of material must play together so that the less active materials screen for the more active and the total radiation from the container does not exceed the permitted limits.

A sarcophagus in the container
The next major step in dismantling the DR 3 reactor is the cutting of the inner tank and the placement of the tank bits in containers. One container is ready to receive the most active element of the inner tank: a grid that stands on the bottom and has held the pipes with fuel elements in place.

The lattice must be laid to rest in a yellow iron sarcophagus, which is itself radioactive waste. It has previously been used for shielding in the heavy water compartment and can now be reused as shielding material. However, the DR 3 team has had to cut the sarcophagus's thick iron lid to make it fit in the container.

"We think a lot about recycling, both to save and to avoid creating additional radioactive waste. The saw we use to cut through thick iron, for example, we have received cheap, as it was already a little contaminated by cutting radioactive materials," says Per Søndergaard with satisfaction in the voice.

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