According to a press release from the Luxembourg government published the same day, the aim of the exercise was to test communication and operational dialogue between French services, the French crisis unit and their equivalents in Germany, Luxembourg and Belgium.

As part of the procedure, a representative of the Luxembourg division of radiation protection of the directorate of health was sent to the nuclear safety authority in Paris, while a liaison officer from the office of the high commissioner for national protection was dispatched to the Metz prefecture.

On 12 October, Greenpeace France activists breached the perimeter fence of the site and released fireworks next to the spent fuel storage pool to highlight weaknesses in the site’s security.

EDF, which operates the site, said the break-in had “no impact on the safety of the installations”, however it prompted Luxembourg environment minister Carole Dieschbourg and health minister Lydia Mutsch to call for an investigation.

In a government press release published the same day, Dieschbourg and Mutsch called for a “detailed investigation which will examine the circumstances of this incident and will challenge the French Minister of Ecological and Solidarity Transition Nicolas Hulot on this intrusion.”

The statement further explained that the incident prompted the foreign affairs ministry to call an extraordinary meeting of the Franco-Luxembourg joint committee on nuclear safety.

Located just 22 kilometres from Luxembourg City, Cattenom’s four pressurised water reactors were constructed between 1979 and 1991.

A damning 2016 German report by investigating chief and nuclear engineering expert Manfred Mertins pointed out “serious shortcomings” at the site in relation to international safety standards. His report said that the plant could not be safely secured in the event of an external disaster such as a plane crash, earthquake or flood.