Mar 04 Icy solution to environmental problem

When project engineer Morten Dalby opens his eyes at 5am, he immediately grabs his mobile to remotely start the Danish De commissioning's very own ice machine. A few hours later, a large box of dry ice is ready on the Risø Peninsula to clean environmentally hazardous paint.

D When Risø Nuclear Station was built in the late 1950s, the best paints of the time were used for both equipment and the interior building parts. The paint was flexible, colour-resistant and durable – and filled with the now banned ingredients PCBs, lead and mercury.

This presented the project team responsible for dismantling the DR 3 reactor and associated facilities with something of a headache. What is the best way to clean up environmentally hazardous and radioactive paint, taking into account both work environment the future storage of the waste?

After a series of experiments, the choice has fallen on a slightly unconventional method: ice blasting. Three millimeters thick sticks of CO2 ice (dry ice) are fired against the paint. The sudden cooling makes the paint stiff and crisp, so it is easier to release when the flow of -79 degrees cold ice rods continuously hammers onto the surface.

The cooling is also beneficial for work environment employees' work environment, as the paint is too cold to emit toxic gases.

And then the ice blasting has a clear advantage in terms of waste: it leaves nothing but the purified radioactive paint for future landfill. In a traditional cleaning process, such as sand blasting, a large amount of secondary waste would be generated and would also have to be deposited.

When dry ice is heated, it changes phase directly from ice to gas. During ice blowing, the CO2 gas is sucked out through the ventilation system, which is equipped with filters and radiological monitoring, while the paint is vacuumed up in a dense, shielded packaging.

To give employees some flexibility in the cleaning work, Danish Decommissioning has chosen to invest in an ice machine rather than buying in dry ice. Morten Dalby got the idea for his own ice machine during a run in Risø's beautiful countryside:
"Quite by chance I came across a CO2 tank that DTU uses for some experiments with crops. It turned out afterwards that DTU only uses the tank during the growing season from April to August, so now we have installed an ice machine at the tank and use it during the other months."

The CO2 used in the ice cream machine is purchased through a supplier from Sweden – where it is, incidentally, a by-product of vodka production.