Army bomb disposal experts were called to the Sellafield nuclear reprocessing plant last night after a 'chemical incident'.
A number of buildings at the Cumbrian site were evacuated as part of the operation and a 100m exclusion zone was set up around the affected lab.
The chemicals, contained within a number of canisters, were discovered during a routine audit at a laboratory.
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 official statement from Sellafield said:
"In line with best practice and established procedures, we alerted the relevant partner agencies and sought advice on managing this material in accordance with the Control of Substances Hazardous to Health regulations.
"The army’s Explosive Ordnance Disposal Team deal with hundreds of these issues every year, recovering chemicals from science laboratories in places like schools and universities.
"Because this is happening on the Sellafield site we exercise extreme caution and leave nothing to chance."
The Bomb Squad returned this morning to help dispose of the chemicals safely.
The canisters will be buried in a trench using sandbags before they are detonated 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.
Sellafield reprocesses and stores nearly all of Britain's nuclear waste.