Maybe Iran can sell us some Plutonium.
Of course, we could reverse Carter’s executive order and start reprocessing spent nuclear fuel.
Other than small scale use of radioactive material in space (like this and other probes), large scale use is a non-starter. Even just going this far, the enviro-wackos throw up huge lawsuits to prevent any such usage - everything from danger of falling back to earth and killing millions to contaminating pristine space with radioactivity (yes, they are really that nuts).
So contrary to the author’s contention, using radioactive material in space is just as controversial as building a nuclear reactor in the US (other countries are no so short-sighted).