PARIS, Oct 25 (Reuters) - French grid operator RTE said next generation nuclear reactors offer an affordable path to shifting the country"s energy mix away from fossil fuels and make the aim of carbon neutrality by 2050 achievable. "Building new nuclear reactors is economically viable, especially as it makes it possible to maintain a fleet of around 40 gigawatts (GW) in 2050," said the RTE in a report examining the different pathways to meet the expected rise in electricity demand. Industry and government sources say the report is expected to help inform President Emmanuel Macron"s decision to go ahead with plans to build new nuclear plants. Le Figaro reported last week that Macron wants to announce the construction of six new EPR nuclear reactors by the end of the year. Achieving future carbon neutral goals without nuclear reactors would require a scale up of renewables faster than the most dynamic electric mixes in Europe, RTE said. France and several other European countries have pushed to label nuclear energy as green investments in the European Union"s upcoming sustainable finance rules. read more The carbon neutral goals will be "impossible" without a significant development of renewable energy, RTE said. Other supply options include the development of further interconnectors between countries, expanding hydraulic storage, and installing batteries to store renewable power. New thermal power plants that utilise carbon-free gases, such as "green hydrogen" which is produced through the use of renewable energy, can also be used in order to meet rising consumption forecasts, the operator said. RTE said the current energy crisis shows Europe"s dependence on hydro-carbons, such as gas and coal, has an economic cost and that low-carbon production in the country is an issue of energy independence. France"s nuclear safety watchdog ASN in February cleared more than half of the nuclear fleet to operate for a decade longer than originally planned after maintenance work, as 32-900 megawatt reactors are coming to the end of their lifespan. France currently has about 62.4 GW of nuclear generation capacity provided by 57 reactors, RTE data showed. REACTION Environmental groups decried the report"s emphasis on nuclear energy and supported calls for a quicker build out of renewable generation. Greenpeace focused on the three pathways which would see the grid operated on 100% renewable energy and called for debates on the energy transition. "This not only proves that nuclear power is not a necessary evil, but also that, whatever option is chosen, renewable energies need massive development to respond to the climate emergency," Greenpeace said. The RTE report said that scenarios with high shares of renewables, or those that extend reactor life beyond 60 years, would "involve heavy bets on technology" to meet carbon neutrality goals. French Green party members described the report as one-sided and an attempt to justify new nuclear projects while disregarding consumption control measures. "The goal of the president of the Republic and his government is clear: to justify the revival of nuclear power at any cost," said Matthieu Orphelin, who used to represent Macron"s party but who has joined the Greens. The French renewable energy union SER said the scenarios presented in the report represented "a major paradigm shift," as it is expected that renewables will need to cover at least 50% of demand by 2050.