Is this actually a significant source of rare earth elements? My understanding is that they’re rare compared with things like carbon, nitrogen, etc. Cerium, one

Is this actually a significant source of rare earth elements? My understanding is that they’re rare compared with things like carbon, nitrogen, etc. Cerium, one of the rare earths, is apparently more common than copper, even. Seems like extracting them from spent nuclear fuel would be much less economic than just grinding them out of rocks, but IANANE.