A small Ukrainian town, standing on the path of war, is preparing for the Russian offensive.

PARIS. On the windswept coastline of Flamanville, an industrial city in northwestern France overlooking the turbulent waters of the English Channel, one of the world’s most powerful nuclear reactors sits under a soaring concrete dome.

But when this lumbering giant will start supplying electricity to the French electricity grid is anyone’s guess.

Construction for a decade be behind schedule and 12 billion euros, or $13 billion, over budget. Plans to begin operations this year have again been pushed back to 2024. And the problems in Flamanville are not unique. The newest nuclear power plant in Finland, which started working last monthwas supposed to be completed in 2009.

As President Vladimir V. Putin’s war in Ukraine pushes Europe to end its dependence on Russian natural gas and oil, nuclear power is growing in importance, promising both home-grown power and reliable power.

Proponents say nuclear power could help solve Europe’s looming energy crisis, complementing a major pivot already under way before the war to bring solar, wind and other renewable technologies to meet ambitious climate change targets.

“Putin’s invasion has changed our views on energy security in Europe,” said Fatih Birol, head of the International Energy Agency. He added: “I expect nuclear power may well take a step back in Europe and elsewhere as a result of energy insecurity.”

But making the nuclear renaissance a reality is fraught with problems.

The desire to find ready-made alternatives to Russian fuel has deepened the political divide in Europe over nuclear energy, as a bloc of pro-nuclear countries led by France, largest producer of nuclear energy, is pushing for a build-up while Germany and other like-minded countries are opposed, citing the danger of radioactive waste. The European Commission’s recent plan to reduce dependence on Russia defiantly excluded nuclear energy from the list energy sources to consider.

Credit…Pool photo by Finnbarr Webster

The long delays and cost overruns that have plagued the huge Flamanville-3 project, a state-of-the-art pressurized water reactor designed to produce 1,600 megawatts of power, are emblematic of the broader technical, logistical and financial challenges facing expansion.

BUT a quarter of all electricity in the European Union comes from nuclear power produced in a dozen countries from an aging fleet that was mostly built in the 1980s. France, with 56 reactors, produces more than half of the total.

A fleet of 13 next-generation nuclear reactors planned in France, using a different design than Flamanville, will not be ready until at least 2035, too late to make a difference in the current energy crisis.

Through the channel, the UK recently announced ambitions to build as many as eight new nuclear power plants, but the reality is more sobering. Five of the six existing UK reactors are expected to be decommissioned within ten years due to their age, while only one new nuclear plant, the gigantic £20bn French nuclear plant at Hinckley Point in the southwest England, is under construction. Its first part is expected to appear online in 2026.

Others being considered in Eastern Europe are not expected to appear online until 2030.

“Nuclear power will take so long” because it takes at least 10 years to complete projects, said Jonathan Stern, senior fellow at the independent Oxford Institute for Energy Studies.

“The big problem is to get Russian gas, and this problem is now, and not in a decade, when we may build new generation nuclear reactors,” he added.

Proponents say nuclear power could be a solution if there is political will.

The Government of Belgium, in agreement with the country’s Green Party, reversed the decision phase out nuclear power by 2025 and extend the life of two reactors by another ten years as Russia stepped up its offensive against Ukraine last month. The energy will help Belgium avoid dependence on Russian gas as it creates renewable energy sources, including wind turbines and solar panels, to meet European climate targets by 2035.

Credit…Gianfranco Tripodo for The New York Times

“The invasion of Ukraine has changed lives,” Belgian energy minister Tienne van der Straeten said last week, explaining the government’s turnaround. “We wanted to reduce our imports from Russia.”

But in Germany, which is more dependent on Russian gas and coal than any other European country, the idea of ​​using nuclear energy to overcome the energy crisis does not seem to be going anywhere.

Germany plans to shut down its last three nuclear power plants by the end of the year, the latest chapter in a program approved by lawmakers to phase out the country’s fleet of 17 reactors following the 2011 nuclear disaster in Fukushima, Japan.

Germany’s two largest energy companies have said they are prepared to delay the shutdown to reduce the country’s dependence on Russia. But the Green Party, which is part of Berlin’s ruling coalition, has ruled out continuing to operate them, let alone reopening three nuclear plants that closed in December.

“For reasons that I think are very good and right, we have decided to phase them out,” Chancellor Olaf Scholz told Parliament this month, adding that the idea of ​​postponing Germany’s nuclear exit was “not a good plan.”

Credit…Martin Meisner/Associated Press

Even in countries that see nuclear power as a valuable option, there are many obstacles in the way. “It won’t happen overnight,” said Mark Hibbs, a nuclear expert at the Carnegie Endowment for International Peace research organization.

President Emmanuel Macron’s plans to revive nuclear power in France include the construction of new generation large and small nuclear reactors at an estimated starting price of 50 billion euros ($57 billion), a staggering cost that other European countries cannot or cannot afford. t take over. He acknowledged that the build-up will not be quick, in part because the industry also needs to train a new generation of nuclear engineers.

“Most governments push and push, and even if they start building, it takes a long time,” said Mr Stern of the Oxford Institute for Energy Studies. “All these other technologies are rapidly developing and getting cheaper, while nuclear is not developing and getting more expensive.”

Meanwhile, many of France’s aging reactors built to achieve energy independence in the aftermath of the 1970s oil crisis have been shut down for safety checks, making it difficult for French nuclear power to help deal with Russia’s energy shortfall, said Anne-Sophie Corbeau of the Center global energy policy Columbia University.

“Nuclear power production in France will decline this year unless you find a magic solution, but there is no magic solution,” she said.

However, Moscow’s aggression could help reverse the arc of the industry’s gradual decline.

There have been a number of optimistic statements lately. In addition to the UK’s announcement this month to expand its nuclear capacity, the single-reactor Netherlands plans build two more in addition to solar, wind and geothermal energy.

And in Eastern Europe, a number of countries in Russia’s shadow have been making plans to build a fleet of nuclear reactors, a move that supporters say seems prescient in the wake of Russia’s invasion of Ukraine.

NuScale Power, an Oregon company selling a new reactor design that it claims will be cheaper and faster to build because major components are assembled in factories, has signed tentative contracts in Romania and Poland.

The Russian incursion has reinforced “clients’ desire to see nuclear power as part of the overall energy mix for their portfolios,” said Tom Mundy, the company’s chief commercial officer.

Nuclearelectrica, a Romanian energy company, is moving ahead with both the NuScale plant and two Canadian reactors to complement a pair of nuclear plants that generate about 20 percent of the country’s electricity, said Cosmin Gita, chief executive.

“The Ukrainian crisis has definitely shown us the need to strengthen energy security,” Mr. Gita said. “We are gaining more momentum for our projects.”

Maike Becker, a utilities analyst at research firm Bernstein, said that in the long run, a Russian war would likely “help the European idea” of greater energy independence.

“This is what nuclear energy can provide,” she added.

Liz Alderman reported from Paris and Stanley Reed from London.

Correction:

April 26, 2022

An earlier version of this article incorrectly stated the amount of power that the Flamanville-3 nuclear power plant would generate. It is designed to generate 1,600 megawatts, not 1,600 gigawatts.