British Nuclear Fuels has been fined £12,000 after pleading guilty to breaches of health and safety regulations. The operator of the Sellafield reprocessing works in Cumbria was also ordered to pay £10,000 costs.

 Whitehaven magistrates' court heard how the company failed to register radioactive sources used to test alarm systems. Some of the sources contained plutonium and, in one case, a radioactive source was found in the office drawer of a former employee.

 The prosecution came after an investigation by the Environment Agency. Nick Webb, representing the agency, told the court: "Clearly any loss of control of such substances does have a potential for significant impact on human health and the environment."

 The prosecution was brought after BNFL admitted failing to register mobile radioactive sources at Sellafield and the Drigg low-level radioactive waste disposal site between January 1997 and last December. The company also failed to register the storage and use of radioactive material at Ramsden Dock in Barrow-in-Furness.

 The court was told that this was BNFL's 10th conviction in 10 years for environmental offences. Andrew Carr, representing BNFL, said: "It is a bitter blow to be back in court."

 He added that the company acknowledged it had failed to meet its own high standards.

 The company was at the centre of a scandal 18 months ago after The Independent revealed that workers at Sellafield had falsified safety records on shipments of mixed oxide fuel (Mox) bound for Japan.

 The scandal cost BNFL's chief executive John Taylor his job and forced the Government to cancel the privatisation of the company. Last week, BNFL suffered a fresh setback after the Government ordered a fourth public consultation into plans to open the £460m Mox facility at Sellafield for commercial operations.