Here is the link to the Japanese language Sankei Shimbun story about a Japanese government study on developing nuclear weapons.
The story doesn’t have the document, but reproduces the “essence” in bullet points:
I gather (from a friendly translation) that this boils down to three points:
一 To trial manufacture a miniaturized nuclear warhead, the minimum time required is 3-5 years, and the cost is 200-300 billion yen.
一 To produce fissionable material, the expansion of uranium enrichment facilities is unrealistic; it is also impossible to reprocess spent fuel from light water reactors.
一 The extraction of plutonium from graphite-moderated reactor is the quickest route.
That’s not meant to be a literal translation and Japanese speaking readers are encourage to do better.
More later …
Robot Economist provides an “on the fly” translation in the comments section.