The Garda and inspectors from the State's radiation safety body will be allowed to visit the controversial Sellafield site in Cumbria under a deal signed by the Irish and British governments today.
The package of measures was signed by the Minister for the Environment, Mr Roche, and the British Ambassador to Ireland, Mr Stewart Eldon, at the Custom House in Dublin.
The action is being taken under the United Nations Convention on the Law of the Sea (UNCLOS).
Under the deal signed today, the Garda and the Radiological Protection Institute of Ireland (RPII) will be allowed to visit Sellafield.
The RPII will also be given access to Britain's radiation monitoring system. A series of initiatives to develop and improve existing co-operation agreements between the two governments is also included in the package.
Mr Roche said the agreement ensures both countries will co-operate fully in the event of a significant nuclear incident.
He said it was a "'positive development in our shared interest in managing our respective positions on the nuclear energy issue".
Mr Roche said the package was "about confidence building and improving communication, co-operation and co-ordination between friendly neighbouring States".
The Minister and the ambassador also said talks to date on a legal action being brought by Ireland against Britain over Sellafield had been "fruitful and constructive".