The report also endorsed Japan’s ambitious pursuit of a nuclear fuel cycle program using plutonium, despite a decision last year to scrap the Monju reactor, a centerpiece of the plutonium fuel program, following decades of poor safety records and technical problems. Japan faces growing international scrutiny over its plutonium stockpile because the element can be used to make atomic weapons.

Japan currently has a stockpile of 47 tons of plutonium — 10 tons at home and the rest in Britain and France, which reprocess and store spent fuel for Japan. Japan plans to start up its controversial Rokkasho reprocessing plant next year, but critics say that would only add to the problem.

Without the prospect of achieving a plutonium-burning fast reactor, Japan has resorted to burning a mixture of plutonium and uranium fuel called MOX in conventional reactors as a last ditch measure to consume plutonium. The report calls it “the only realistic method of making use of plutonium.”

The need to reduce its plutonium stockpile adds to Japan’s push for reactor restarts. It would require 16 to 18 reactors to burn enough MOX to keep its plutonium stockpile from growing, according to a pre-Fukushima accident target set by the Federation of Electric Power Companies of Japan, an umbrella group for Japanese utilities. The target is unchanged, though widely seen as too optimistic.