The problem with this story is that it is being covered by reporters (and editors) who seem to have no grasp of the underlying technical and legal issues.
There is one paragraph in the lengthy Washington Post story that even touches upon on what the underlying difficulty is:
According to the Democratic report, Harvey’s NSC colleagues warned repeatedly that any plan to transfer nuclear technology had to comply with the Atomic Energy Act. The United States imposes limits on uranium enrichment and the reprocessing of spent fuel, both of which could be used to produce material for nuclear bombs. Saudi Arabia does not want to make those commitments.
We do not know what specifically was being proposed and the problems that experts on the subject in the government had with it.
Getting “nuclear power reactors” could be benign. Or it might not be, depending on a lot else riding along.
(The author of that piece by the way was Karen DeYoung who wrote a stunningly ignorant and laudatory report about the Trump-Kim summit last year.)