New Plug Seals Dounreay Reactor Clean-up

23rd June 2023

Upgrade work was required to the primary cold trap loop (PCTL) vessel before it could be used on the next stage of decommissioning.

Dounreay's prototype fast reactor decommissioning team is in the process of connecting up the reactor vessel and pipework to water vapour nitrogen (WVN) treatment skids, which will destroy the residual sodium in the system, and enable it to be dismantled safely.

The PCTL removed impurities from the sodium primary reactor sodium by cooling it to a point where impurities solidified and could be filtered out by doughnut-shaped mesh ‘sieves', before the cleaned sodium was returned to the reactor.

It became obvious during camera and radiation probe inspections that the original gasket on the vessel sealing the plug in place was in very poor condition, which meant it would be unlikely to achieve the seal required to carry out the WVN treatment.

The project to install a new plug to the PCTL vessel was important as the plug acts as a radiological shield from the contents of the vessel and will enable it to be re-used as part of the WVN clean up.

Local company, Envision, designed the plug using 3D laser scanning; another local company, JGC Engineering, designed and manufactured a bespoke tool to clean and collect debris from the PCTL vessel.

The plug was bolted on, tested and filled with lead shot to provide shielding.

The project will now move onto the design work for the WVN treatment equipment to convert the vessel into a cleaning system for the filter baskets used in the PCTL system.

Chris Gregory, Assistant Project Manager said: > I would like to thank Envision and JGC Engineering who worked with our own team to scan, design, and manufacture the tools required. The passing of the seal test at the end brought about a successful and well-deserved conclusion to the project.

Graeme Dunnett, Head of Reactors said: > The completion of this work is a significant step forward in our decommissioning plans to reuse the PCTL vessel for the WVN process. My thanks go out to our in-house team and to the members of the supply chain involved in this project.