Which is nowhere near as big a deal as it sounds. The damage it will do (on average) if glassed and buried 100ft under ground is absolutely negligible at the scale we are talking about (global climate change and energy in general).

Yes, there's a 1 in 10000000 chance that 2000 years from now industrial age humans recovering from the apocalypse might dig a well in exactly that location and thousands will get sick with hundreds of deaths. You could multiply that by a hundred thousand cores and it would still be negligible compared to the hundreds of millions likely to die due to climate change in the next century

I really liked how you framed the danger.

But what about if we had a Reactor Dump storing 100's of these reactors, and then something happened to that dump, either it was hit by a meter or it was intentionally attacked in some way. Could that result in an apocalyptical type event?

No, it couldn't.

It would basically be a few Chernobyls in the worst case (a 1 in 1000 year asteroid impact winning the 1 in 100 million lottery and hitting the dump) and that mostly means extra birth defects and cancer (you wouldn't want to live somewhere that gave you a 10% chance if dying due to cancer age 40, but you could still have a civilization in such a location). It doesn't end life in the impacted area.

For intentional attacks there are much much easier ways of killing a lot of people.

So you have a large dump that must remain secure for 200k years.

You cannot do that. There is no place on Earth that we can be sure is geologically stable over that time period.

What a selfish thing to do: Make future generations pay for our current consumption for millennia.

Molten salt reactor waste should have a dramatically shorter half-life than waste from a light water reactor. MSR waste only needs a few hundred years of containment, not hundreds of thousands of years.

Explain that.

Makes no sense to me, but my physics education was decades ago

Well I'm not a physicist, so take everything I say with a grain of (molten) salt, but it has to do with the kind of fuel used, which produces different waste products.

The half life of most of the waste product from a gen-3 uranium reactor is measured in millions of years (235U's half life is ~700 million years, for example).

In some gen-4 molten salt reactor designs, most of the waste product would have a half life measured in hours, so they wouldn't need to be put into long-term containment at all. And the rest of the waste products would only require a few hundred years before they are emitting only background level radiation.

Hopefully someone with actual education on this can give a more complete answer, but that's my Reader's Digest understanding.

The molten salt will be quite radioactive, yes. It is part of the radioactive waste generated by a molten salt reactor. Some types of molten salt reactors do not have this problem, but I don't think they are the most practical.

The metal containing the molten salts might become somewhat radioactive too.

All in all, this is still comparable in amount of waste to water cooled reactors.