Construction of the new reactor at Flamanville began in 2007 and was initially due for completion in 2012. Already six years late to open, the project is now being pushed back another year to 2019.
A string of development problems has tripped up the project, and France's EDF on Wednesday raised the expected construction costs by 400 million euros, from 10.5 to 10.9 billion euros more than three times the initial budget.
Problems were found in dozens of the roughly 150 welds in the reactor's "main secondary system", where steam produced by the generator is returned to the turbine.
Out of the 148 welds examined, 33 were found to have quality deficiencies, the company said, adding that it would delay by a year the loading of nuclear fuel to the fourth quarter of 2019.
EDF’s announcement comes just three weeks after a French parliamentary report found security “failings” in the defences of the country’s nuclear power plants.
New technology complications
Flamanville’s next-generation reactors, called European Pressurised Reactors (EPR), have promised advances in safety and efficiency over conventional reactors, while producing less waste.
But all three European plants being built with EPR, including Flamanville, have encountered delays and cost overruns. In Britain, two reactors being built by EDF for the Hinkley Point project are behind schedule and are expected to cost more than 22 billion euros. The Olkiluoto 3 reactor in western Finland, which was supposed to be the first EPR to go online, has been delayed for the last decade.
France is one of the world's most nuclear-dependent countries, with 58 reactors providing 75 percent of its electricity.