Why is nuclear energy non-renewable?
It is produced from a fixed supply of raw material that cannot be “renewed”.
All energy is actually “non-renewable” because the law of thermodynamics says that entropy is always increasing, and energy cannot be created or destroyed – only changed in form. However, in terms of available energy sources on earth we think of any directly solar-derived sources as “renewable”. Included are wave,water, wind, biomass conversion and direct photo-voltaic electrical production.
While nuclear power production may be considered “cleaner” - at least with respect to greenhouse gas generation – than “fossil fuels” (hydrocarbons), it still requires the use of a limited mineral resource. The uranium ores necessary for nuclear fuel production only exist in finite amounts in the earth, and they are not renewable, although they may have very long lifetimes.
Even fusion power will consume net physical resources, even though the output is much more, and cleaner environmentally overall than fission-produced power.