A senior manager has been disciplined and another is facing action after a leak at the Sellafield nuclear plant.
The Thorp managers were suspended in April
The pair were suspended in April at the time of the leak at the plant's Thorp reprocessing complex, but details have only just emerged.
The action was taken after acid containing uranium and plutonium leaked from a pipe.
One of the managers has now returned to work, while the other remains suspended pending a disciplinary hearing.
A statement issued by Sellafield operator British Nuclear Group, said: "Two senior managers in Thorp were suspended in relation to the discovery of dissolver liquor in the plant's feed clarification cell.
"One has been through disciplinary process and has now returned to work.
"The outcome of the process is between the company and the individual and it is not considered appropriate to comment further.
"The second individual remains suspended pending the disciplinary hearing."
In June an investigation into the leak by the Nuclear Installations Inspectorate (NII) found "significant deficiencies".
It ordered improvements, which must be introduced by October.
Work at the Thorp complex was halted when the leak, which could have occurred as long ago as August 2004, was discovered in April.