Well, technically, nothing's really renewable. Limited but massive nuclear fusion in the sun is indirectly powering solar PV and wind and hydro for 4-10 billion more years. Limited nuclear alpha decay of Uranium inside Earth powers geothermal. The limited Earth-Moon gravitational system powers tidal.

So I think it's fair to actually consider nuclear fusion and nuclear fission in breeder reactors both to be renewable. B. Cohen said the same about breeder fission reactors in the 1980s [1].

Uranium in seawater can be extracted at 10x world energy scale for billions of years. It replenishes continuously through crustal erosion and plate tectonics. Sounds pretty renewable.

But according to policies we're writing today, the term renewable does not include fusion or fission in breeders. I consider this problematic. Thus I think we all should prefer either "sustainable energy" or "low-carbon energy".

[1] http://large.stanford.edu/publications/coal/references/docs/...

I prefer “sustainable”, as in “this technology can be used as some scale for X years without causing major problems”.

High-burnup nuclear power, under reasonable assumptions, is sustainable for hundreds of thousands of years. Fusion is presumably sustainable as long as the Earth exists, as are solar and wind. Coal is not sustainable at all.

Right on. Breeder fission reactors can power civilization for at least tens of millions of years, probably billions, thanks to seawater uranium extraction and renewal through plate tectonics.