* First time minister clearly approved new nuclear plants
* Says some of EDF's plants can operate more than 40 years
* EDF shares climb more than 5 percent (Adds shares, trader comment)
By Michel Rose
PARIS, Jan 13 (Reuters) - France should build a new generation of nuclear reactors to replace the country's ageing plants, Energy Minister Segolene Royal said on Tuesday, the first time a government member has clearly approved this option.
France, the country most reliant on nuclear power, must decide in the next few years whether to continue down the nuclear route as about half of its 58 reactors will reach their designed 40-year age limit in the 2020s.
Royal's so-called energy transition bill, which is being reviewed by the Senate after parliament's lower house passed a first version last year, aims to cut the share of nuclear energy in France's electricity mix to 50 percent from 75 percent.
But that does not mean France wants to exit atomic energy, as it is part of the country's history and expertise, Royal told L'Usine Nouvelle magazine in an interview, in contrast with Germany's decision to phase out nuclear power.
"EDF's board has adopted part of its big maintenance plan with my agreement," Royal said.
"We must now also programme the construction of a new generation of reactors, which will replace old plants when these cannot be renovated anymore."
Shares in EDF rose as much as 5.6 percent, the biggest gainer on France's CAC 40 index of blue chip stocks.
Clarinvest fund manager Ion-Marc Valahu, who owns EDF shares, said Royal's comments had given the stock a boost.
Traders also mentioned that European utilities had been buoyed by a Morgan Stanley upgrade to British energy company Centrica, as well as positive comments about the sector from Citigroup.
Mark Lewis, a senior analyst at Kepler Cheuvreux in Paris, said it was a big shift in Royal's stance.
"The problem in my view is that new nuclear build is just not economic at prices below 100 euros per megawatt-hour, just look at the guarantee the UK government had to give EDF for Hinkley C," he said.
Britain has guaranteed the price of power from the Hinkley Point C nuclear power station that is to be operated by French utility EDF.
State-owned EDF, which operates all of France's nuclear reactors, faces a 55 billion euro ($65 billion) upgrade of its existing plants by 2025, including work decided in the light of the Fukushima nuclear meltdown in Japan.
To finance this investment, EDF has advocated an extension of reactor lifespan to 50 or 60 years, arguing that the power stations were modelled on similar reactors in the United States which have been granted 60-year licences.
"I didn't include a 40-year age limit in the energy transition bill like ecologists wanted. Some nuclear plants can live longer," Royal said in the interview.
This was also the first time the former partner of President Francois Hollande, and a powerful voice in the cabinet, had approved an extension beyond 40 years.
However, the ultimate decision for a lifespan extension will be for the country's independent nuclear watchdog, the ASN, which is set to give a preliminary opinion on the question this year and make a final decision in 2018-2019.
$1 = 0.8473 euros Additional reporting by Sudip Kar-Gupta in London and Raoul Sachs; editing by Sybille de La Hamaide and David Clarke