[saulrh]

You have to store high-level waste for hundreds or thousands of years before it's safe.

Heavy metal wastes never become safe. A dump site for cadmium or chromium or lead or arsenic waste will be exactly as hostile to life around it in ten thousand years as it is today. The only way for it to "become safe" over time is for it to leak into the environment and distribute the damage over time. In practice, the "solution" for heavy metal industrial waste is to store it where it's produced and ignore it. Usually in huge open pits, which are just great for the environment around them /s.