Construction of the U.K.'s 3,300-MW Hinkley Point C nuclear power plant could run 15 months beyond the original 2025 completion deadline and cost 25% more than originally budgeted in 2015. That could drive the cost to as much as $27.9 billion.

Europe’s two other plants based on the same French Evolutionary Power Reactor (EPR) are both more than 10 years late in Finland and France.

Implementing the completed functional design, which has been adapted for a first-of-a-kind application in the U.K., also added costs.

Paris-based EDF, which leads and co-owns the Hinkley pressurized water reactor plant in Somerset, cites difficult ground conditions among causes of the price hike. "Extra costs needed to implement the completed functional design, which has been adapted for a first-of-a-kind application in the U.K. context," also contributes, adds the company.

The project has been difficult for years.

EDF's flagship 2,660 EPR plant in Flamanville, in northern France, is now not expected to start generating  before the end of 2020. Rectifying faulty welds is the latest cause of delay, putting completion back from the 2012 target when work began in 2007. Even later is Finland's 1,600-MW Olkiluoto lll plant, the completion of which has slipped from April 2009 to June 2020, according to its utility owner TVO.