Discharges of waste from Sellafield continue to be the main source of artificial radioactivity in the Irish Sea, according to a report by the Radiological Protection Institute of Ireland.
The year-long study found that consumption of fish and shellfish was the main way the Irish population was exposed to radiation as a result of the discharges.
The Minister for the Environment, Mr Cullen, said the results of the report were further evidence that the reprocessing at Sellafield was a "dirty business".
"We will not let up in our efforts to close the plant. The Government is and will continue to exhaust every diplomatic and political channel to see an end to activities at Sellafield," Mr Cullen said.
The Radiological Institute's principal scientific officer, Dr Tony Colgan, said that the level of radiation appeared to have reached a plateau, but he emphasised that it was still safe to eat seafood from the Irish Sea.
Dr Colgan said that the institute would continue to seek reductions in the level of radioactive discharges under a marine pollution treaty known as the OSPAR convention.
The Government, meanwhile, is awaiting the findings of its legal case under the United Nations OSPAR convention. Next month it will bring another legal case to the European Court of Arbitration under the Law of the Sea.
British Nuclear Fuels, however, insists that a report from a nuclear industry watchdog, the Nuclear Installations Inspectorate, confirms that it is operating safely and has successfully overhauled its management and control of operations.
Mr Brian Watson, director of the Sellafield site, said that the plant's safety performance was improving all the time and operating "consistently well".
Opposition parties, however, restated their demands that the plant be closed.
The Labour Party's spokesperson on nuclear safety, Mr Emmet Stagg, said that the Government was not pushing hard enough for the closure of the plant.
