True, after a few years, the most radioactive species decay, reducing much of the thermal output. But what is left is still a highly lethal cocktail of very long-lived isotopes and chemical poisons which if released into the environment by accident or deliberate sabotage would constitute a tragedy of unimaginable proportions. These products are radioactive isotopes of normal nuclei and chemically indistinguishable from them. They would enter food chains and other biological pathways where they would be potentially carried far and wide while simultaneously being concentrated by biological and geological processes into eternal pockets of death.

In addition to the fission products, we have Plutonium, the most toxic substance known to man as well as prime bomb-making material. Also in this deadly mix is Uranium 238, which is only slightly radioactive but highly toxic chemically, and Uranium 235 which is an irreplaceable resource and should not be just thrown away simply because we can't afford to invest in the means to recover it.

One of the reasons salt mines were proposed for the disposal of vitreous waste was because salt has a high thermal conductivity and can help disperse the heat generated even by completely processed waste in its final, "safest" form. If they were buried in an efficient thermal insulator they would eventually melt.

At least, Pandora had the excuse that she really didn't know what she was getting the rest of us into.