Nuclear energy is expensive. This is true of all rankine cycle style generators, which use heat to generate steam to turn a turbine. In most places, the cost of new renewable energy is cheaper than the ongoing operation and maintenance cost of rankine cycle generators. Nuclear is particularly expensive among rankine style generators, as it requires lots of capital and long build times, and is the only major generating technology with a negative learning curve over the past several decades. The cost issue is the main problem with nuclear power.
https://www.lazard.com/perspective/levelized-cost-of-energy-levelized-cost-of-storage-and-levelized-cost-of-hydrogen/
https://atb.nrel.gov/electricity/2021/index
While rankine cycle generators can't compete on cost with renewable energy now, there is a need for excess renewable energy, storage, or other firm capacity at high levels of variable renewable energy (80%+) on the grid. This is decades away. Ideally, you'd want a technology with a low capital cost and high ramp rate. The theory supported by nuclear advocates is that smaller modular nuclear reactors (SMRs) may be cheaper to build than existing light water reactors and can provide that firm capacity. Nuclear however, is just one of many competitors to provide that grid service. It has to compete with hydropower, high capacity factor offshore wind, various forms of storage, targeted building efficiency, demand response, expanded transmission, and even overbuilt renewable energy with curtailment as costs get cheap enough. Nuclear isn't the ideal solution to firm capacity, as it is expensive and has low ramp rates. Optimistic cost projections for SMRs are still multiple times that of renewables. Nuclear plants want to run at high capacity factors (85%+) to offset their cost, and take many hours to ramp up or down. Some have suggested pairing electrolyzers onsite with nuclear to convert the constant power output into a one with more variable energy and higher ramp rate. But it's almost certain that renewable energy paired with electrolyzers or other renewable gas will be cheaper and do the same thing. Here is an example case study comparing generating technology mixes for a 100% renewable U.S. power grid: https://www.sciencedirect.com/science/article/pii/S2542435121002464. In all decarbonization scenarios, VRE accounts for 70%+ of capacity and 90% generation. Nuclear and coal phase out as the highest-cost generating options.
Compounding the cost problem is that the nuclear industry has had significant issues of corruption, fraud, and other criminal activities which undermine safety and increase costs. Some of these issues are nuclear-specific, but most are related to having vertically-integrated or state run utilities building large generators instead of cheaper alternatives and having to have some mechanism of public debt repayment to make up the cost. The safety issues that arise from this are unique to nuclear power, and justifiably worry anti-nuclear activists.
https://www.worldnuclearreport.org/
Nuclear, even some SMRs, will likely be part of the grid in 30 years, if for no other reason than because the utility and nuclear lobbies are quite politically powerful and engage in both legal and illegal bribery. Even coal CCS is getting substantial government R&D investment, which will never be economically viable. But SMRs will never play more than a supporting role for the grid, at best reducing capacity costs ~20% for a 100% RE scenario several decades from now. Beyond keeping existing nuclear plants open that are still in good operating condition, there isn't much of a role for nuclear in the next several decades. The most important thing to focus on in the next several decades is building lots more wind and solar, electrifying heating and transport, and building efficiency. Everything else is secondary.