You can't build them one-at-a-time, much less one every few decades and expect them to be anywhere near cost competitive. First off, you get no economies of scale, something that was hard enough to come by in the 1960's and 1970's much less today.* Secondly, as with military/defense industries, if you don't have a minimum level of production you lose the workers who have the skills and institutional memory, two factors of production that are very expensive to develop from scratch.
From The Associated Press, July 31:
The first American nuclear reactor to be built from scratch in decades is sending electricity reliably to the grid, but the cost of the Georgia power plant could discourage utilities from pursuing nuclear power as a path to a carbon-free future.
Georgia Power Co. announced Monday that Unit 3 at Plant Vogtle, southeast of Augusta, has completed testing and is now in commercial operation, seven years late and $17 billion over budget.
At its full output of 1,100 megawatts of electricity, Unit 3 can power 500,000 homes and businesses. A number of other utilities in Georgia, Florida and Alabama are receiving the electricity, in addition to the 2.7 million customers of Southern Co. subsidiary Georgia Power.
“This hadn’t been done in this country from start to finish in some 30-plus years,” Chris Womack, CEO of Atlanta-based Southern Co. said Monday in a telephone interview. “So to do this, to get this done, to get this done right, is a wonderful accomplishment for our company, for the state and for the customers here in Georgia.”
A fourth reactor is also nearing completion at the site, where two earlier reactors have been generating electricity for decades. The Nuclear Regulatory Commission on Friday said radioactive fuel could be loaded into Unit 4, a step expected to take place before the end of September. Unit 4 is scheduled to enter commercial operation by March.....
....To understand France’s nuclear predicament consider its roots in the oil shock of 1973. At the time, most French power plants ran on petroleum. As the fuel became scarce, French politicians concluded that true sovereignty required an energy source France could control. Nuclear power fitted the bill. France knew something about the technology, having built an atom bomb and nuclear submarines. It boasted a cohesive corps of engineers, most of whom attended the same university, the École Polytechnique. And a centralised political system allowed the powerful executive branch to ram through the ambitious programme with little input from the French public or their elected representatives.
This rapid ramp-up enabled France to enjoy what industry types call the “fleet effect”. Building a reactor is complex and requires a lot of learning by doing. So long as you keep doing, the expertise grows, making each new project easier. Between 1974 and the late 1980s EDF brought reactors online at a rhythm of up to six a year, with construction crews moving swiftly from one plant to another (see chart).
However, the French approach has created lingering problems. On the technical side, squeezing a lot of construction into a few years means that reactors undergo their big decennial refit (le grand carénage) around the same time. And since they are built to the same standard, problems found in one trigger repairs in others. As a result, French reactors’ “load factor”, a measure of whether a plant is running at full capacity, hovers at 60% or so, compared with more than 90% in America....
