Nobody challenges it, but when someone says "I wonder how we'll get rid of the byproducts of solar", it obviously frames the discussion differently than "I wonder how much less impact the byproducts of solar have on the environment than those of coal".
How do we get rid of a fast reactor's spent parts?
(Yeah, it should be possible to design a reactor so it consumes more long-lived waste than it creates. But I don't think anybody ever bothered to do that.)
