> So "thousands of years" is a popular misunderstanding, in my view.

"Thousands of years" comes from the half life of Plutonium-239, which is 24,000 years.

Pu-239 isn't unusually dangerous for an isotope. It's chemically toxic and somewhat radioactive but so is tons of stuff. The biggest problem with it is that you can make nuclear weapons from it.

Most commercial reactors make both Pu-239 and Pu-240. They're infeasible to separate (harder than separating U-235 from natural uranium) and enough Pu-240 makes the plutonium unsuitable for weapons.

But Pu-240 has a shorter half life than Pu-239. So if you take the plutonium out of a legacy reactor and bury it in the ground for a long time, it turns into weapons-grade plutonium. Burying it in the ground is very stupid because then you have to guard it for tens of thousands of years to keep anyone from going in and taking it to make nuclear weapons from.

But that ship has sailed. We have a half century of the stuff already. Half again as much or not makes no difference, we need a solution for what do with what we already have regardless of whether we make any more.

The solution is that newer reactors can use plutonium as fuel, which permanently eliminates it. So far from nuclear waste being a reason not to build newer reactors, it's the reason we should, so we can get rid of what we already have before it becomes suitable for weapons.