Nuclear is a fossil fuel range extender

The biggest challenge of nuclear power is - beyond the discussions about safety and long term storage of waste, which we don't want to comment - the fact that the majority of inputs into construction and operations are fossil fuels. Cement and steel, but equally uranium or thorium are mined and produced with large quantities of low-cost coal, natural gas and oil. If those inputs become scarce and potentially more expensive, so will building and operating nuclear technology. This is the biggest challenge with anything new: as long as we manufacture it mostly with raw materials extracted and refined using low-cost fossil fuels, output prices (e.g. a kWh from nuclear power plants) never shows the true cost.