PARIS (Reuters) - Greenpeace activists broke into an ageing Tricastin nuclear plant in France on Friday to demand its closure, a day ahead of the planned shutdown the country’s oldest nuclear reactor at Fessenheim near the German border.

FILE PHOTO: The EDF logo is seen on a reactor building at the Tricastin nuclear power plant site in Saint-Paul-Trois-Chateaux, France, June 27, 2019. REUTERS/Benjamin Mallet/File Photo

About 50 Greenpeace militants broke into the grounds of the Tricastin power station in southern France armed with jackhammers made from foam for a mock dismantling of the plant.

State-run utility EDFPA> confirmed there had been an unauthorised entry into the administrative area of Tricastin, and said 18 activists were arrested. EDF said there was no intrusion into the nuclear part of the plant and its safety was not compromised.

All four reactors at the Tricastin nuclear power plant with a total capacity of 3,600 MW , were online at 0950 GMT, according data from French electricity grid operator RTE.

France gets about 75% of its electricity from nuclear plants, but many are old and the country has set a target of reducing this to 50% by 2035, bringing in more renewable power.

“We are protesting and drawing attention to an aging nuclear power plant that is dangerous and should be shut down,” said Greenpeace spokeswoman Cecile Genot.

Greenpeace said in a statement Tricastin, like Fessenheim’s number 1 reactor, would reach its 40-year lifespan this year and should be unplugged.

“40 years is the maximum operating time for which French reactors have been designed and tested,” Greenpeace said. “Beyond 40 years, the consequences of aging power plants are unpredictable.”

Last June, EDF carried out maintenance and upgrade works at the Tricastin’s 900-megawatt (MW) reactor number 1, which it said would enable it operate for another ten years.

French nuclear safety authority ASN, will rule by the end of the year on the potential lifespan extension of 32 of EDF’s 900-megawatt capacity reactors. This would be followed by in depth assessment, reactor by reactor starting with Tricastin 1.

The closure of Fessenheim comes at a time of intense debate in France over the future role of nuclear in the country’s energy mix as well as efforts to curb carbon emissions while ensuring power supply.

After 43 years of service, Fessenheim’s number 1 reactor will be powered down and disconnected from the electricity grid on Saturday. Fessenheim 2 will shutdown on June 30.

Those against the shutdown of Fessenheim, particularly from nuclear industry, France’s third largest industrial sector, say the move could jeopardise the security of electricity supply, and the availability of cheap low-carbon energy.

Fessenheim’s two reactors produce around 12 terawatt hour (TWh) of electricity per year, equivalent to about 3% of output.

At the plant’s entrance on Friday, a trade union banner read: “No! To closing Fessenheim”.