[normaljoe]

To godelski point yes there is low level stuff that really isn't a concern except to jandrese's point it's political. If I walk out of a reactor room and my gloves from my contamination suit pop too high they get put in a bag that is marked nuclear waste.

Granted the too high mark could still be perfectly fine to throw into a landfill and not impact anything, but nobody wants that in their neighborhood.

As to high level stuff which is what you are asking about, the spent stuff is really hot. To recycle, it would need to cool down first. Commercial plants place that in cooling pools, which is kind of bad if you have a Tsunami hit your plant (Japan), our something else.

So as to the waste element think I have 2% enriched object that is 100 cubic meters. The same in a highly enriched say 90% would only be about 2 cubic meters. This means my pools would be smaller, my overall size is smaller, and I can contain the smaller pool easier preventing the release.

On the politics side the idea of highly enriched is dangerous because it could be used for other purposes, however when those decisions were made I don't think anyone every imagined the concept of a dirty bomb in which enrichment is really going to matter one bit.