When the U.S.–Japan Nuclear Cooperation Agreement was automatically extended in 2018, media reports repeatedly described Japan’s approximately 47 tons of separated plutonium as sufficient for roughly 6,000 atomic bombs.
Most of that material, however, was stored in the United Kingdom and France, while all Japanese-held nuclear material remained subject to IAEA safeguards and strict material-accountancy controls.
This article examines the Rokkasho Reprocessing Plant, pluthermal generation and the nuclear fuel cycle and asks whether reporting driven by fear, rather than technical facts and actual utilization plans, enables the public to make informed judgments.

This article republishes a chapter based on an essay by Yoshiko Sakurai originally presented on August 6, 2018 and reissued on January 17 and August 3, 2020.
Sakurai’s essay was entitled “Is the Abe Administration’s Energy Policy Identical to That of the Naoto Kan Administration?” and criticized Japanese policy and media reporting concerning the nuclear fuel cycle, the Rokkasho Reprocessing Plant, plutonium holdings and the U.S.–Japan Nuclear Cooperation Agreement.
The agreement entered into force in 1988 and was automatically extended in July 2018 when its initial thirty-year period expired without either side terminating it.
Foreign Minister Taro Kono stated at the time that the agreement formed a foundation of Japan’s nuclear industry, while also emphasizing the need to reduce Japan’s plutonium holdings.
At the end of 2017, Japan managed approximately 47.3 metric tons of separated plutonium.
Approximately 10.5 tons was stored domestically, while approximately 36.7 tons was stored in the United Kingdom and France.
The latest report published by Japan’s Atomic Energy Commission shows that the total had declined to approximately 44.4 tons by the end of 2024, consisting of approximately 8.6 tons in Japan and 35.8 tons overseas.
When the Rokkasho Reprocessing Plant is operating, national and IAEA inspectors are to remain on site around the clock.
Its safeguards system includes material accountancy, inventory verification, continuous monitoring and on-site sample analysis.
Strict safeguards against military diversion do not, however, mean that reactor-grade plutonium is physically incapable of use in a nuclear explosive device.
United States Department of Energy material explains that reactor-grade plutonium creates serious heat and neutron problems for weapon designers but is not physically unusable in a nuclear weapon.
The central question raised by this article is whether describing Japanese material only as “enough for thousands of atomic bombs,” while omitting its location, composition, intended use and safeguards, constitutes accurate public-interest reporting.
August 3, 2020
IAEA inspectors are also permanently stationed at the Rokkasho Reprocessing Plant, and Japan is subject to strict controls.
It is scientifically and physically impossible for Japan to build an atomic bomb.
I am republishing the chapter first issued on January 17, 2020 under the title: “As Soon as the U.S.–Japan Nuclear Cooperation Agreement Was Automatically Extended, the Media Began Reporting ‘International Concern.’”
The following explains why.
I now either watch NHK news only in passing or skip it altogether.
In particular, I truly do not want to watch News Watch 9.
The other night, however, I happened to see it.
It reported negatively on the strategic road map for fast-reactor development while explaining almost none of the information presented on the Agency for Natural Resources and Energy’s website.
What I found amusing was the expression of Arima, who presumably wanted to advocate opposition to nuclear power.
Perhaps senior management had finally warned him about excessively arbitrary reporting.
He appeared desperate to make an anti-nuclear comment but was forcing himself, with a childlike expression, to hold back what he wanted to say.
Even when reporting on the Monju accidents, they provide no concrete explanation and merely refer to “repeated accidents.”
They are the real villains.
They are all the more malicious because they speak as though they represented good sense or were conveying the truth.
The preceding passage is omitted.
Japan’s nuclear-energy policy is literally on the verge of being destroyed at its foundations.
Japan imports uranium for nuclear fuel from the United States and other countries and has reprocessed uranium fuel used in reactors to recover plutonium.
The nuclear fuel cycle consists of reusing this material in the Monju prototype fast breeder reactor in Fukui Prefecture and in ordinary light-water reactors through pluthermal generation.
Japan’s nuclear policy rests upon this foundation.
Monju, however, was assigned to decommissioning.
The only remaining means of maintaining the nuclear fuel cycle is pluthermal generation.
Among the reactors that had restarted, only four were capable of pluthermal operation.
Each reactor consumes approximately 0.4 metric tons of plutonium annually.
If the Rokkasho Reprocessing Plant in Aomori Prefecture, then expected to be completed within three years, began operating, the reprocessing of spent fuel would recover approximately eight metric tons of plutonium annually.
Discussion therefore arose about suspending or limiting spent-fuel reprocessing in order to carry out the Atomic Energy Commission’s “commitment” to reduce Japan’s plutonium holdings.
The commission’s policy can be read as an attempt to sever Japan’s nuclear fuel cycle and bring the nuclear industry toward its end.
Does this not correspond perfectly with Naoto Kan’s scheme?
It would force the public to bear the enormous costs of renewable energy, cause nuclear policy to fail, leave Japan excessively dependent on coal and other fossil fuels and turn the country into a major emitter of CO2.
Why is Japan being driven down such a foolish path?
During the process leading to the automatic extension of the U.S.–Japan Nuclear Cooperation Agreement, information circulated in both Japan and the United States describing Japan as possessing “47 tons of plutonium,” “enough for approximately 6,000 atomic bombs,” and presenting a “danger of nuclear proliferation.”
These descriptions, however, were inaccurate.
The 47 tons held by Japan was reactor-grade plutonium, with a different isotopic composition and markedly lower purity than the weapons-grade plutonium used in nuclear weapons.
Approximately 36 tons of Japan’s plutonium had been recovered under contracts with the United Kingdom and France and remained stored in those two countries.
IAEA inspectors were also permanently stationed at the Rokkasho Reprocessing Plant, and Japan was subject to strict controls.
It was scientifically and physically impossible for Japan to build an atomic bomb.
There was no problem with Japan’s plutonium holdings.
The only solution was to operate the reprocessing plant and complete the nuclear fuel cycle.
Nevertheless, Japan as a whole shrank before inaccurate information—or information containing a particular political purpose.
As soon as the U.S.–Japan Nuclear Cooperation Agreement was automatically extended, the media began reporting “international concern.”
NHK commentator Noriyuki Mizuno went so far as to criticize Japan by saying that “China and North Korea have specifically identified Japan and pointed to the possibility of nuclear development” on the August 1 edition of Jiron Koron.
The objective of such information was to force the abandonment of the reprocessing plant, destroy the nuclear fuel cycle and bury the whole of Japan’s nuclear industry.
The Abe administration, which bore responsibility for Japan’s energy policy, should have recognized that anti-nuclear information was placing Japan’s future in danger and begun rebuilding the nation’s energy policy.