The Government has said a nuclear fuel plant at Sellafield in northern England could pollute the Irish Sea and be liable to terrorist attack.
The claims were made at the start of a two-day hearing at the Hamburg-based International Tribunal for the Law of the Sea.
The Government wants the tribunal, a United Nations body, to issue injunctions to prevent the start of operations at the mixed oxide (MOX) fuel plant and to stop ships transporting nuclear material to and from it pending arbitration.
Tribunal spokeswoman Ms Julia Pope said a judgment would be announced by December 9th.
The legal action in Hamburg is based on what the Government said are breeches by Britain of the 1982 United Nations Law of the Sea Convention (LOSC).
Ireland considers the process of authorisation of the MOX plant has been badly flawed and is inconsistent with the LOSC. The manufacture of MOX fuel at Sellafield involves significant risks for the Irish Sea, the Government said in a statement. Such manufacture will inevitably lead to some discharges of radioactive substances into the marine environment, via direct discharges and through the atmosphere, it said.
Manufacture is also vulnerable to accident and the MOX plant can only serve to increase the attractiveness of subjecting Sellafield to terrorist attack, it added.
In a response also released by the tribunal, Britain asked for the application to be dismissed.
It is a condition of jurisdiction that the parties should first have exchanged views with the aim of settling the dispute by negotiation. Ireland has, however, declined the United Kingdom's invitation to do so, the British response said.
The United Kingdom does not plan any action in the near or long term which will damage Ireland's rights under the law of the sea convention or cause serious harm to the marine environment, it added.
PA