The Government's legal team will lodge papers today in relation to the case against the United Kingdom, claiming it has violated the UN Convention of the Law of the Sea by authorising the MOX (mixed oxide) nuclear fuel plant at Sellafield.
The team will travel to Hamburg in Germany where the International Tribunal for the Law of the Sea sits, to seek the injunction preventing the plant from starting operation. It will also seek a full hearing to determine the plant's future.
A spokesman also confirmed last night that the Government had instructed its legal team handling the Sellafield issue to give advice and assistance to Greenpeace and Friends of the Earth, whose legal challenge to try and prevent the start-up of the controversial plant began yesterday.
An Irish representative will be attending as an observer throughout the court case, he said.
The spokesman said last night "the gloves are now off" in relation to Sellafield. The Minister of State, Mr Joe Jacob, has accused the British government of violating numerous provisions of the UN Convention.
It had failed in its obligations to consult Ireland, to assess the plant's impact on the environment and to protect the marine environment, he said.
The Government formally served legal documents on the British government at the end of October.
The legal action follows years of reluctance to do so, despite long-standing concerns over the operation of the Sellafield plant just 60 miles from Dublin.
The change of attitude follows intense anger at the British decision this month to proceed with the new MOX fuel production plant, which would lead to the regular shipment of dangerous material through the Irish Sea.
The MOX plant is designed to process nuclear reactor fuel from uranium and plutonium imported from a large number of countries.
The Government is demanding an injunction preventing the plant from starting operations, and a full hearing then to determine the its future.
The papers are being lodged today in advance of the proposed opening of the MOX plant at the end of the month.
It hopes to obtain the injunction before that, unless Britain agrees to postpone activating the plant pending the full hearing, which would not reach a conclusion until the end of next year at the earliest.
At the five-member arbitration tribunal, according to Mr Jacob, Ireland will accuse the UK of failing to take adequate measures to prevent pollution from the plant; to assess properly the risk of terrorist attack; to prepare a plan to respond to such an attack; to co-operate with Ireland and share information and to carry out a full environmental impact assessment.
Ireland will seek a full environmental impact assessment and proof that the plant will bring no further radioactive pollution. It will also demand an agreed British-Irish strategy to prevent terrorist attacks or to respond to any terrorist attacks.
The international action will take place in parallel with arbitration proceedings started in June in under the OSPAR convention, which are intended to obtain certain information on the MOX plant which the British government has refused to provide.
The Government is also drafting papers with a view to taking a separate case against the UK in the European Court, claiming it is in breach of the Euratom Treaty.