Maybe this is a dumb question, but why can't nuclear waste be diluted? You get U-235 though enrichment of naturally occurring uranium. Why is there no way to reverse this process?
Well, natural U-235 is pretty radioactive too. But I think it's mostly chemistry: you can dilute Uranium only in things like chlorine, and then you have lot of chlorine that you have to store instead.
It makes more sense to just put it all in a deep hole, only it's hard to make a really stable hole things won't leak out of.
You can dilute uranium that way. The issue is the radioactive material is all other place, not concentrated. You need to dilute cements and wood, and paper, and glass, and other materials the lab is made from.
I hope to god the goal of any remediation is in the service of conserving the site and the artifacts for their historical value. If Marie Curie's notebooks eventually end up encased in concrete somewhere "because they're contaminated"--
It makes more sense to just put it all in a deep hole, only it's hard to make a really stable hole things won't leak out of.