Army bomb squad specialists have been called to the nuclear reprocessing plant at Sellafield to deal with hazardous chemicals found in a lab.
The chemicals, contained within a number of canisters, were discovered during a routine audit at a laboratory at the site in Cumbria.
They are industrial solvents, such as Tetrahydrofuran, which are potentially flammable in liquid states and can crystallise and become unstable when exposed to air.
None of the chemicals are nuclear or radiological materials, a spokesman for Sellafield said.
After the discovery of the chemicals, which had been stored in the lab since 1992, protocols for handling hazardous chemicals meant the Army Explosive Ordnance Disposal Team were called around 8pm last night to assess the situation.
An area of the site is cordoned off as a precaution - but the rest of the site is operational and the majority of weekend staff are working normally.
The Bomb Squad has returned this morning to help dispose of the chemicals safely.
A spokesman for Sellafield said the Army team will dig a trench, bury the canisters using sandbags, and detonate them in a controlled manner.
This will create a noise that will be audible off-site, but the Army said there is no cause for alarm.