Whether it's more expensive or not depends on how you measure "cost", and including intermittency and storage costs for renewables seems to favor Nuclear in many cases[1][2]. Based on real-world examples of countries that traded one for the other, like Germany, renewables look quite bad economically. I know there's a lot of hand waving about how this has to do with how electric auctions work, but this seems like a convenient excuse.
[1] https://www.sciencedirect.com/science/article/abs/pii/S03605...
[2] https://en.wikipedia.org/wiki/Cost_of_electricity_by_source#...