A new report says Europe’s fleet of nuclear power plants poses an increasing risk to millions of Europeans as the facilities age, and as governments decide to extend the operation of plants beyond their originally intended lifetimes.

The nearly 150-page report, commissioned by Greenpeace, synthesizes the research of eight European nuclear energy experts. It concludes that because of Europe’s heavy dependence on nuclear energy, governments are likely to extend plant operations 20 years or more past their designed limits, and recommends that European Union policies be changed to incentivize repairs and discourage the construction of new plants.

As is the case with most nuclear plants worldwide, European reactors were built with a 40-year expected lifetime. As they age, operators usually have two options: shut down or make repairs in order to extend operations 20 years or more into the future. While many critics would prefer that the plants be shut down, it seems regulators in Europe — where nuclear energy accounts for about 15 percent of total energy production, and much more in some countries — are increasingly going with the second option.

The average age of a nuclear plant in Europe is 29 years, according to the Greenpeace report. Nearly half are more than 30 years old, and several are already over 40 years old. But the report found that only a few of those older plants are scheduled to be shut down, and many have already had their operating licenses extended another 20 years, which experts say poses an increased safety risk for all of Europe.

Despite these perceived risks, the experts who crafted the report say European policies that cap liability for nuclear accidents are disincentivizing plant operators from making much-needed repairs as the plants age. The report found that each plant’s legal liability is 100 to 1,000 times lower than the cost of a potential disaster.

A similar structure exists in the United States, where nuclear industry liability has been capped at low levels since 1957 by the Price-Anderson Act.

“The whole problem is you’re not liable for the full damage … and as a result of that, plants are able to externalize the damage,” said Michael Faure, a professor of international environmental law at Maastricht University and one of the authors of the report. “Because it’s the states that would pay, (nuclear operators’) incentives for prevention aren’t so great.”

But with many European countries relying so heavily on nuclear energy, industry watchdogs fear any countrywide or EU-wide policy change that could increase regulation is unlikely.

France, for example, gets nearly 80 percent of its energy from nuclear plants. And as the economies of some Eastern European countries increase, so does the appetite for nuclear energy.

There’s one silver lining for the nuclear energy naysayers: Building and repairing plants is getting more expensive. Stephen Thomas, a professor of business and energy policy at the University of Greenwich and another author of the Greenpeace report, said building new plants costs about three times as much today as it would have 40 years ago.

Those increased costs are already proving problematic. Several planned plants in France, Finland, England and elsewhere have struggled with cost overruns, extensive delays and safety issues. That gives hope to some experts that despite Europe’s current reliance on nuclear energy, its heyday may be waning.

“Looking at history, what determines the life of the plant is very seldom the regulatory side,” Thomas said. “What closes plants mostly is economics — the cost of running or repairing them. That’s what knocks them offline. That’s why plants are going.”