* Minister had been an obstacle to EDF's nuclear plans
* Break up of EDF now seen less likely
* Resignation frees up Macron to shift nuclear policy
* President seen picking more pragmatic environment minister
PARIS, Aug 28 (Reuters) - The shock resignation of the French environment minister may mean that EDF can not only extend the lifespan of its ageing reactors but could even build new reactors in France, the world's most nuclear-reliant nation.
The nuclear lobby has for decades had a powerful influence on French energy policy and Nicolas Hulot, who quit on Monday night, was widely viewed as an impediment to the industry's drive to maintain nuclear as France's main power source.
Even when announcing his resignation live on French radio, the former ecological activist branded nuclear a "useless folly".
EDF shares rose more than 2 percent on news about the exit of Hulot, who had wanted EDF to close up to a third of the utility's 58 nuclear reactors and shift to renewable energy.
"EDF leadership will be drinking champagne," said Gerard Magnin, who in 2016 resigned from EDF's board in disagreement over its all-nuclear strategy.
"Hulot was the last remaining obstacle to a strategy with nuclear as the sole option for security of supply and carbon-free energy," he told Reuters by phone.
EDF declined comment on the resignation of Hulot.
French President Emmanuel Macron is an advocate of nuclear but the popular Hulot served as a counterbalance. The utility's shares slid 7 percent when he was appointed last year.
Macron had campaigned on a promise to respect the previous Socialist government's energy law to cut France's reliance on nuclear energy to 50 percent by 2025 from 75 percent now, the highest level in the world. https://bit.ly/2LwOEiM
Hulot had been a strong backer of the plan. But within six months of taking office, the minister was sent out to announce that the target was being pushed back a decade. He said France would set a new timeline in early 2019.
Hulot's exit may buy the nuclear industry more time.
"We believe (Hulot) would not have wished to present a new energy strategy which extends the role of nuclear in France," wrote UBS head of utilities research Sam Arie, who rates EDF "buy".
Arie said his resignation suggested a decision on extending the lifespan of France's nuclear plants was on the way and made it less likely EDF would be split into nuclear and non-nuclear units, as Hulot proposed.
Most of EDF's nuclear fleet was built in the 1980s and the firm wanted to extend their 40-year lifespan by 10 to 20 years, which is key to its profitability, as the value of the plants is largely written off and they generate the bulk of EDF's profits.
EDF had core earnings of 13.7 billion euros ($15.7 billion)in 2017 on revenue of 70 billion euros.
Macron's government is awaiting recommendations from nuclear regulator ASN, due by 2020-21, before deciding.
But EDF internal documents show it plans to build two new reactors by 2030 to renew its fleet. EDF CEO Jean-Bernard Levy has said publicly he expects France will eventually build 30 new-generation reactors in decades ahead.
Hulot told the daily Liberation before his resignation that Macron was likely to support those plans. "If I leave, there will be three more reactors in the coming years," he said in the interview, which was published on Tuesday after he had quit.
Hulot joins a long list of environment ministers who have rued their inability to influence energy policy and left early. France has had 13 environment ministers in the last 20 years.
Delphine Batho, minister under former president Francois Hollande, described in 2014 how the EDF chief executive acts as a "shadow energy minister" who "doesn't sit at cabinet meetings, but who nonetheless decides France's energy policy".
France has long championed nuclear to secure its energy independence. Its scientists have had a leading role in the study of radioactivity.
Industry experts expect a new minister to be more pliable. "He or she will be a doormat," said one source familiar with French energy policy, asking not to be identified.
Macron could chose between several environment specialists in his LREM party, including Hulot's deputies Brune Poirson and Nicolas Lecornu, both seen as pragmatists, as well as ADEME state environment agency chief Arnaud Leroy, who helped Macron write his energy programme.
He could also pick parliament chair Francois de Rugy or lawmaker Barbara Pompili, who come from the ecology movement.
($1 = 0.8744 euros) (Writing by Geert De Clercq Editing by Richard Lough, Georgina Prodhan and Edmund Blair)