A request for the prescription of provisional measures, pending the constitution of an arbitral tribunal to be established under Annex VII of the United Nations Convention on the Law of the Sea, was submitted to the International Tribunal for the Law of the Sea on 9 November 2001 by Ireland against the United Kingdom. The dispute concerns the MOX plant, located at Sellafield, Cumbria, the international movement of radioactive materials, and the protection of the marine environment of the Irish Sea. 

According to the request for provisional measures, the dispute stems from the authorisation of the United Kingdom to open a new MOX facility in Sellafield. The facility is designed to reprocess spent nuclear fuel, containing a mixture of plutonium dioxide and uranium dioxide, into a new fuel which is known as mixed oxide fuel, or MOX.

The Irish Government is concerned that the operation of the plant will contribute to the pollution of the Irish Sea and underlines the potential risks involved in the transportation of radioactive material to and from the plant.