Not only could they take 20 years to build, you have to consider how long they will actually be useful for. If we over-provision solar, wind, and batteries for the next 50 years (to deal with intermittency), then the nuclear plants may only have 30 years of operational life to amoritise their huge upfront costs over.

If you consider the cost trends of these technologies, then nuclear energy looks like an economic dead-end[0], and that's before you factor in the costs of long-term waste management, possible large scale contamination in the event of an accident or attack, and the small but potentially significant increased risk of nuclear proliferation or breakout.

[0] https://ourworldindata.org/uploads/2021/02/Price-of-electric...

No, we screwed it up so much that it would take decades to fix. Building a traditional reactor takes over ten years, while advanced reactors need ten more years of R&D. By that time, renewables may be cheaper than even next-generation reactors.

Nuclear and short term don't really go together. Especially with the currenr regulatory climate. Looking at a couple plants in China, it looks like about 5 years between construction start and utility connection, and you probably can't get things built any faster than that. If you add in site selection and design work, that's longer too. And there's likely only a limited capacity for manufacturing.