The Minister for the Environment, Mr Cullen, summed up reaction to the news that the THORP nuclear plant at Sellafield is to cease reprocessing activity in 2010 as one of "cautious optimism".
However, the Minister said he had sought immediate clarification from the British government on the status of THORP and restated Government policy that the Sellafield facility should close.
"The Irish Government is turning the screw on Sellafield. With each turn of the screw, the ultimate objective of closing Sellafield moves nearer," Mr Cullen said. He said the Government's legal actions to date had been a step towards this ultimate goal.
"There is reason for cautious optimism. There is a realisation that nuclear reprocessing and discharges of nuclear waste into the Irish Sea is not viable. The Irish Government's campaign is paying dividends but we must keep the pressure applied."
He added: "Public confusion on Sellafield is not acceptable. Time and again we find that information on the operations at the Sellafield plant is muddled and unclear.
"This debate must be based on accurate reliable information from credible authoritative sources. How can we be confident that the plant is run in a secure safe and reliable manner when confusion reigns on a matter as fundamental as the life span of the installations on the site."
Mr Cullen said to use the Irish Sea to dump nuclear waste was "unacceptable" and that discharges must stop now and not in seven years' time.
The Green Party said the plant had difficulties from the start when BNFL lied over data on nuclear material that was being sent to Japan.
Green Party TD Mr Ciarán Cuffe said: "We are pleased at the proposal to close this white elephant that has cost the British taxpayer billions. We hope that this marks the beginning of the end for Sellafield and for technology that is dated, dangerous and past its sell-by date."
Fine Gael's environment spokesman, Mr Bernard Allen, called on the Irish Government to seek clarification from the British government on what he said were "conflicting reports" on the THORP closure.
"During a recent visit to Sellafield by a Fine Gael delegation . . . facts were uncovered proving that radioactive discharges into the Irish Sea, rather than reducing, will increase substantially over the next 20 years," he said.
Labour's environment spokesman, Mr Eamon Gilmore, said the Irish government must continue to exert "all possible pressure" to ensure that the plant not only closes, but closes at the earliest possible date.
"There is little doubt that the days of THORP are numbered as the deteriorating economics of the operation and enhanced environmental demands create a combination of circumstances that will make the plant non-viable," he said.