As I understand it, Nuclear energy is not sustainable because there is not enough high grade Uranium that is easy to mine. Read B's excellent article on this here: https://link.medium.com/DHKXeYAnmzb

Additionally, nuclear co2 emissions is more like 60 g/kWh when you take into consideration mining, fuel prep, logistics, waste storage and plant decommissioning. https://theconversation.com/is-nuclear-power-zero-emission-no-but-it-isnt-high-emission-either-41615