DFR clean-up’s a dirty job

DFR clean-up’s a dirty job

The decommissioning teams taking apart Dounreay’s famous dome are reducing the hazard every minute of every day.

A new plant has been designed and built to remove five tonnes of radioactive ‘sludge’ that remains after draining 1000m3 of water from the two deep chambers used historically to store spent fuel from the Dounreay Fast Reactor.

The pond chambers are concrete vaults similar to a swimming pool and the water provided shielding for workers from the radiation emitted by spent fuel placed in racks on the bottom.

DFR’s own pond project team invented a facility capable of immobilising the pond debris in 200 litre drums by mixing with cement. A large pump was used to transfer the brown gunk from the pond floors into one tonne filter bags to remove excess water.

Various technical trials have been carried out over several months to ensure the consistency was right for the equipment being used to remove, solidify and store the hazardous substance.

The process works by sucking up the debris using a peristaltic pump which transfers it to a tank to measure the volume. Cement is then mixed separately before the cement and sludge are transferred by gravity into a 200 litre drum at the mixing station below. A paddle mixes the drum contents for one hour before the drum is moved to a temporary storage area to solidify. The drum is then taken for storage as waste.

The sludge solidification plant was fabricated and installed into DFR by Gows of Lybster.

Commissioning is now complete and eight drums of immobilised sludge have been removed. This phase of the project is expected to treat up to five tonnes of the debris for storage in thirty cemented drums.

DSRL’s project manager George Groat explained: “Sludge retrieval and packaging is a very challenging part of this project. Removing the final remnants following years of storage is a tricky process and the design, manufacture and commissioning of a new plant is a large undertaking. We are delighted with how efficiently this is working which takes us another step closer to decommissioning DFR as part of the site shutdown plan.”