Union representatives at the Sellafield nuclear reprocessing plant have urged the 10,000 workforce to co-operate with an investigation into an act of sabotage, even if this means implicating a colleague.
A probe has been launched into deliberate damage of equipment at the plant in Cumbria.
British Nuclear Fuels (BNFL) confirmed it had asked the UK Atomic Energy Authority Police to investigate the cutting of cables on a robotic arm on a maintenance tool which handles nuclear waste.
The incident last month comes amid fears over safety standards at Sellafied which has seen some countries suspend their dealings with the plant.
A spokeswoman for Sellafield refused to speculate on claims there was a saboteur among the 10,000 workforce.
But union representatives at the site have sent a joint letter to staff appealing for them to assist the investigation, even if it means providing information which may implicate fellow workers.
Six master slave manipulators were put out of use after wire cables, which allow machines to be operated from a remote location, were cut.
A spokeswoman for BNFL said the matters was taken "very seriously".
She said: "The company will initiate appropriate proceedings if any individual or individuals are proven to have caused this damage deliberately."
Jack Dromey, national spokesman for the BNFL unions, confirmed today that a letter had been sent out to staff by the unions.
He said: "No-one is more at risk from a Sellafield saboteur than the work force.
"The local unions have denounced this dangerous act and are working with the police to find the culprit."
This is the latest safety scare to rock Sellafield.
Last month the Nuclear Installations Inspectorate, Britain's nuclear watchdog, issued a series of damaging reports about Sellafield alleging a lack of a safety culture.
This week Switzerland joined a growing number of countries voicing their concern about the plant.
Germany has suspended dealings with the plant and Japan has insisted a consignment of fuel be returned.
Switzerland is halting all fuel shipments to Sellafield after the Swiss nuclear safety inspectorate called for safety improvements.Reuse content