You can calculate how much power is needed based on past data. That part is complicated, but not really unreliable, although of course the demand may look diffe

You can calculate how much power is needed based on past data. That part is complicated, but not really unreliable, although of course the demand may look different in 20 years. And yes, we're going to need extra longer-term storage, but less than you'd think (IIRC up to 10% for a large grid). Nobody knows the cost of that storage. You can calculate an upper bound by using today's prices, but once these things actually come in demand, new ideas are going to spring up and the prices are probably going to fall, just like it did for PV and wind turbines. It seems to me that investing in nuclear tech today is a really risky proposition.