Depending on how countries classify waste, only about 0.2–3% by volume is high-level waste, according to the World Nuclear Association (WNA), a London-based industry group that promotes nuclear power.
Mostly derived from civil reactor fuel, this is some of the most dangerous material known on Earth, remaining radioactive for tens of thousands of years. It requires cooling and shielding indefinitely and contains 95% of the radioactivity related to nuclear power generation.
Well, no, not really.
But the idea was boosted in December 2018 by French Nobel prize–winning physicist Gérard Mourou, who, in his acceptance lecture, said laser beams millions of times brighter than the surface of the sun in bursts that last a millionth of a billionth of a second had the potential to neutralise nuclear waste, reducing its half-life to a few years and its radioactivity to very little.
Largely speaking and not wholly and exactly the higher the radiation danger now the shorter the period of time for which it is dangerous. And vice versa. The not wholly is because plutonium is nastily poisonous without radioactivity etc. Thorium poses heavy metal poisoning dangers rather greater than its radioactivity etc.