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Here's one startup that is using a design that can convert spent fuel: http://www.transatomicpower.com/the-science/

Plenty of retiring Nuclear plants. Just do a conversion on the same real-estate and use the waste as fuel.

[EDIT] For a deep dive into Thorium, check out any one of the "Thorium Remix" vids: http://thoriumremix.com/2015/

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Here's a list of other Gen IV reactor companies/projects (from Thorium Remix 2016):

Terrestrial Energy, Flibe Energy, Molten Energy, Transatomic, ThorCon Power, Copenhagen Atomics, Seaborg, Chinese Academy Of Sciences.

I uprooted unique_parrot2's comment, as it reflected my view about nuclear power, up until last year. Here is the documentary that changed my mind: http://pandoraspromise.com