Earlier quoted context omitted.
So if we can process nuclear waste in fast reactors like this, why haven't we done so with existing nuclear waste? Scale? Cost? Something else?
The cost issue: Storing spent fuel is pretty cheap because it is not very voluminous. The USA has produced about 85k tons of spent fuel, which would fit into a single football stadium. This means the cheapest thing to do is just kick the can down the road. The proliferation issue: Waste burners require processing of spent fuel, which some states believe is a weapons proliferation risk. The sodium issue: Liquid sodium…
The US doesn't do this ostensibly due to proliferation risk [1] however, I am of the opinion that was due purely due to pressure from the coal lobby.
[1] https://en.wikipedia.org/wiki/Nuclear_reprocessing#History