Reports from New Caledonia say an investigation has been opened after an incident at the Vale nickel plant.
The local newspaper says a device measuring the density of ore pulp was damaged in what the miner says amounted to a technical incident.
There was concern that a radioactive substance could have affected staff and the environment but an internal assessment found no risk.
It is not known what caused the glitch.
The Vale plant has seen a number of spills in recent years that prompted operations to be interrupted.
There has been intermittent tension over the plant, with demonstrators earlier this year causing more than 30 million US dollars worth of damage to the plant.