This is a bit of an understatement. They are very high and I don't think anyone has been willing to do so without significant government subsidizing. I'm not anti nuclear by any means, but from what I recall the economics of it just don't pan out very well under current conditions. We have existing nuclear plants that aren't renewing their license and instead shutting down.
By far the startup costs are "high" because of environmentalists and lawyers, and irrational public fears. The licensing, regulatory, and legal costs are ENORMOUS.
Yes, a nuclear plant is "expensive" but it's raw energy output is staggering, to the point that any business, without all the neo-Luddite interference, can easily make a stable financial plan to recoup it's higher construction costs. Because the ratio of power produced to the expense of producing it is still so insanely high. Actually, the energy output is so high, that a nuclear plant can even afford the bureaucratic and legal costs, what the business or utility can't handle is the time, because the main tactic by the environmental Left is to drag them through the courts for decades until the project is abandoned.
And what's WORSE is that the environmentalist political pressures have made implementing newer, cheaper, and SAFER reactor designs impossible. Designs that are literally "walk away safe". i.e. you can throw every control and lever in the plant to it's worst possible setting and leave, and the core will never melt down or explode. Pebble bed reactors, LFTR's, passive gravity fed/cooled designs, all sorts of neat stuff like containerized modular sealed reactors that would need no servicing and can be transported and replaced intact. And some of these even address the nuclear weapon "proliferation concerns" so that we can "allow" less trustworthy countries to have them as well.
And even with the "old" designs (Fukushima is 1950's tech, built in the 60s, with only modest upgrades, and would never have melted down if Japan had built a 500-year tsunami seawall around the plant, or even simpler, just placed the backup pump generators up on a hill or stilts... or something. Even with the accidents, no "Western" commercial power nuclear plant has ever killed anyone with radiation. While the statistical increase in cancer from natural radioactivity released by coal plants does actually kill thousands of people every year.
God... everywhere I look around, there are more and more reasons for "physical removal" or Pinochet helicopter rides for the various strains of the Left. What they advocate and agitate for
actually does kill people, or at least degrade/harm all of society even when the Left is moderated by Western Constitutional Republics.
Imagine if we had so much energy we could do mass-desalinization of seawater, especially in poor arid countries. We could recycle most anything, no matter how energy intensive it was.
The real proof would be if/when fusion is perfected, and it's inherently "safe" in ways fission isn't, the Left will still fight it. Because they fight everything.