Well, the french reactors are not processing old fuel. Spent fuel is taken out, brought to some other place (La Hague), replenished and then transferred back to the nuclear plant. This stretches the effectiveness of the nuclear fuel by a few percent but does not at all solve the problem of final storage of nuclear waste.

If this is, what the original poster meant with - "Reactor technologies have advanced, we just haven't built enough. We can actually reprocess the tons of old fuel we have for trillions of MWh." - I am a little disappointed.

By the way: La Hague had nuclear accidents, including exposure of Iodium-131 and Caesium-137, explosions, tritium contaminations of the ocean, leaks, a catastrophic fire in the storage facilities of graphite elements and uranium parts, continuous contamination with Strontium-90 and others from 1968 until 2013.

https://fr.wikipedia.org/wiki/Usine_de_retraitement_de_la_Ha...

I just mentioned this because of:

"Anti-nuclear fear mongering has proved baseless. The French have recycled fuel like this for 30 years without incident: no terrorist attack, no bad guys stealing uranium, no contribution toward nuclear weapons proliferaton, and o accidental explosions."

in the linked article of the parent post.