Japan and Nuclear Power: The Atomic-Bombed Nation, Advanced Nuclear Technology Nation, and Potential Nuclear-Armed State

Japan's stance of rejecting nuclear weapons as an atomic-bombed nation

In August 1945, Japan became the only nation in history to suffer atomic bombings, following the dropping of atomic bombs on Hiroshima and Nagasaki. Having experienced such devastation, Japan has consistently advocated for the abolition of nuclear weapons since the war and has upheld the 'Three Non-Nuclear Principles'—not possessing, not manufacturing, and not permitting the introduction of nuclear weapons—as a national policy. Furthermore, Japan has maintained a strong stance of 'opposing all nuclear tests' and has made repeated diplomatic efforts to call for a comprehensive ban on nuclear testing, including underground tests (1). Given this historical background, there is a deep-seated negative sentiment toward nuclear weapons in Japanese society, and the government prides itself on being a standard-bearer for nuclear non-proliferation and disarmament. However, at the same time, Japan relies on the U.S. 'nuclear umbrella' for its security, and a dilemma has been pointed out between its position as an atomic-bombed nation advocating for anti-nuclear policies and its position as an ally relying on nuclear deterrence (2)(3). As an atomic-bombed nation that is also in an alliance with a nuclear-armed state, Japan is placed in a unique position of exploring both nuclear disarmament and nuclear deterrence.

The dawn of 'peaceful use of nuclear energy': Nuclear research since the 1950s

After World War II, while aversion to nuclear weapons spread, the concept of the 'peaceful use of nuclear energy' began to be promoted globally in the 1950s. U.S. President Dwight D. Eisenhower's famous 'Atoms for Peace' speech was delivered at the UN General Assembly in 1953, and Japan embarked on nuclear research and development in response to this trend (4). In 1955, the Atomic Energy Basic Act was enacted, and the use of nuclear energy in Japan began in earnest. The act stipulates that the research, development, and use of nuclear energy shall be 'limited to peaceful purposes' and based on the three principles of 'democratic, autonomous, and transparent' management (4). This was also a pledge not to divert nuclear technology for military purposes, and it became a prerequisite for Japan, an atomic-bombed nation, to engage in nuclear energy.

Eventually, with the cooperation of various countries, the introduction of research reactors progressed, and in 1966, Japan's first commercial nuclear power plant, the 'Tokai Power Station,' was built and began operation in Tokai Village, Ibaraki Prefecture (5). This Tokai Power Station (operated by the Japan Atomic Power Company) was a graphite-moderated gas-cooled reactor (GCR) introduced from the UK, which was the latest technology at the time. With the start of operations at the Tokai Power Station, the transfer of nuclear technology from overseas to Japan accelerated, leading to the domestic production and expansion of light water reactors (boiling water and pressurized water types) through the 1970s (6). During Japan's period of rapid economic growth, nuclear power was expected to be a future energy source, and the perception of 'nuclear energy that can be used for power generation' permeated society.

The U.S.-Japan Nuclear Cooperation Agreement and the nuclear fuel cycle: The only exception among non-nuclear-weapon states

Japan was granted an exception as a non-nuclear-weapon state to perform spent fuel reprocessing on its own soil in the form of comprehensive prior consent(7). This is a highly unusual measure from the perspective of nuclear non-proliferation, and thanks to this comprehensive consent, Japan has been able to operate reprocessing plants and separate and accumulate plutonium. In fact, Japan isthe only non-nuclear-weapon state to have established nuclear fuel cycle technology (including reprocessing, uranium enrichment, and the use of MOX fuel) and has contributed to the management of nuclear materials while cooperating with the International Atomic Energy Agency (IAEA) (8). It is said that this exceptional position stems from both Japan's aim to effectively utilize nuclear resources while being resource-poor, and its desire to maintain future autonomy in nuclear technology.

However, the existence of separated plutonium resulting from the promotion of the nuclear fuel cycle has also become a cause for concern regarding nuclear proliferation in the international community (9). The U.S.-Japan Nuclear Cooperation Agreement was initially concluded with a 30-year term, and it was automatically extended in 2018 without major turmoil. However, the international community, including the United States, continues to keep a close watch on the large amount of nuclear material held by Japan. The Japanese government also strives to manage plutonium under the strict safeguards of the Atomic Energy Basic Act, which limits use to 'peaceful purposes,' and the IAEA, and has expressed a policy of 'not holding excess plutonium' so as not to invite suspicion of diversion to nuclear weapons. Even so, in the current situation where no other non-nuclear-weapon state engages in the nuclear fuel cycle like Japan, meticulous care is required so that this special treatment itself does not create distrust or misunderstanding from other countries.

Expansion of nuclear power due to the oil shock and energy security

In the 1970s, the introduction of nuclear power in Japan reached a major turning point in energy policy. The first oil shock in 1973 and the subsequent second oil shock in 1978 made the whole world keenly aware of the dangers of oil dependence (10). Japan also experienced serious confusion due to the disruption of oil supplies, and the government and companies alike came to recognize the importance of 'stable energy supply.' One of the solutions that attracted attention was the expansion of nuclear power generation. As a domestic energy source to replace oil, the active introduction of nuclear power plants was promoted at the national policy level.

Then-Prime Minister Kakuei Tanaka stated in the Diet in 1973 that he 'wants to promote nuclear power with a serious determination,' and in 1974, policies such as the creation of a grant system for regions hosting nuclear power plants were implemented (11). With this government backing, the construction of nuclear power plants accelerated across the country from the late 1970s through the 1980s. This is thought to be due to the urgent need for energy security, as well as increased social understanding of nuclear power and rising electricity demand (12). As a result, Japan came to possess so many reactors that it was called a 'nuclear power giant,' andnuclear power generation temporarily became a major power source, accounting for nearly 30% of Japan's total power generation (13). However, after the 1986 Chernobyl nuclear accident, anxiety about nuclear power increased, and in the 1990s and 2000s, troubles occurred one after another in Japan, such as the accident at the 'Monju' fast breeder reactor (1995) and the JCO criticality accident in Tokai Village (1999) (14). Amidst this, distrust in safety spread and nuclear policy wavered, but the trend of dependence on nuclear power triggered by the oil shock remained the mainstream until the beginning of the 21st century.

The forefront of nuclear fusion research: The ITER project and 'modern alchemy'

On the other hand, apart from nuclear power generation via fission, expectations fornuclear fusion as a future energy source are also rising. Nuclear fusion is a technology that obtains enormous energy by fusing hydrogen isotopes, the same principle as the reactions occurring in the sun and stars. Japan is in a leading position in this nuclear fusion research as well, and is providing technical cooperation as a major participant in the International Thermonuclear Experimental Reactor (ITER) project. Also, in Naka City, Ibaraki Prefecture, there is the 'JT-60SA,' a state-of-the-art nuclear fusion experimental device built jointly by Japan and Europe. JT-60SA successfully generated plasma for the first time in October 2023, and is currently operating asone of the world's largest tokamak-type nuclear fusion reactors with a plasma volume of 160 cubic meters (15)(16). At this point before the operation of ITER, JT-60SA is the world's largest nuclear fusion experimental device, and its results are expected to provide important knowledge directly linked to the design and operation of future ITER and demonstration reactors (DEMO).

If nuclear fusion is put to practical use, it could become a 'dream energy source' that is safe, clean, and fuel-rich, so countries including Japan are competing fiercely. Furthermore, recently, a bold idea that could be called an 'alchemical' application of nuclear fusion technology has also emerged.(17)(18)(18)(19)(20)(21)(22). Japan's technological prowess will likely contribute significantly to a future where nuclear fusion reactors become a place for material conversion, not just power generation—a scenario where the peaceful use of 'nuclear' expands to a new dimension.

Rocket technology and plutonium holdings: The aspect of a potential nuclear-armed state

Although Japan has a policy of not possessing nuclear weapons in its constitution and policies, it is sometimes evaluated as havingthe technical potential to 'build nuclear weapons if it wanted to.' In fact, Japan's space development is highly advanced, and the technology for satellite launch vehicles (such as the H-IIA/B and Epsilon) shares basic parts with long-range ballistic missiles. Also, as mentioned above, Japan has recovered and held plutonium through the reprocessing of spent nuclear fuel. The accumulated amount currently reaches about 45 tons (23), which is calculated to be enough fissile material for thousands of nuclear weapons. There is no other country besides nuclear-armed states that holds such a large amount of plutonium, which is why there is an international view that Japan is a 'potential nuclear-armed state' (23).

For example, during the Obama administration in the U.S., there was an incident where Japan was strongly requested to hand over weapons-grade plutonium and highly enriched uranium that it had been storing for research purposes to the U.S. Ostensibly, it was in the name of counter-terrorism, but it is also reported that the background included distrust of the 'break from the post-war regime' advocated by the Abe administration at the time, and vigilance against Japan attempting to be a potential nuclear-armed state under the pretext of 'peaceful use' (24). In fact, the U.S. did not accept the plan to strictly manage it within Japan and insisted on the measure of 'transferring nuclear materials to the U.S.' (25). In this way, Japan's nuclear technology potential is sometimes a sensitive issue even from the perspective of its ally, the United States, and can become material for delicate maneuvering in international politics.

The Japanese government maintains the Three Non-Nuclear Principles of 'not possessing, not manufacturing, and not permitting the introduction of nuclear weapons,' and has clearly stated that it does not intend to pursue nuclear armament itself. However, due to the combination of factors such as rocket technology and vast plutonium stockpiles, Japan is viewed by various countries as havingthe potential to develop nuclear weapons in a short period of time. As the nuclear armament of neighboring countries like North Korea progresses, discussions such as 'shouldn't Japan also have nuclear deterrence' sometimes emerge domestically, but since that choice would entail extremely large diplomatic and economic costs, the reality is that it continues to rely on America's extended nuclear deterrence (the nuclear umbrella) (26). Nevertheless, it is a fact that Japan's maintenance of the nuclear fuel cycle and its pursuit of advanced rocket technology are sometimes viewed with suspicion by neighboring countries. Since Japan itself advocates for nuclear non-proliferation, it is essential to ensure highly transparent operations and build trust so as not to be criticized for a double standard of 'it's okay for Japan but not for other countries.'

Plutonium management and IAEA monitoring: Maintaining international trust

As mentioned above, the approximately 45 tons of plutonium held by Japan is also a source of concern in the international community. Therefore, Japan continues to make efforts to strictly manage all nuclear materials, including this plutonium, and to demonstrate to the world that it will not be diverted for military purposes. Specifically, under the Treaty on the Non-Proliferation of Nuclear Weapons (NPT), Japan has concluded a comprehensive safeguards agreement with the IAEA, and(27). IAEA inspectors regularly verify each of Japan's nuclear facilities and confirm that nuclear materials are being used for peaceful purposes as declared. The Japanese government also thoroughly implements the measurement, management, and transport security of nuclear materials based on domestic law, and takes every possible measure to ensure that no unauthorized removal or diversion of plutonium occurs. In the nuclear agreement with the U.S., high transparency and strict management are also imposed as a prerequisite for Japan to proceed with the nuclear fuel cycle.

Even so, it is not easy to completely dispel international distrust. Regarding the plutonium that Japan has accumulated over many years, speculation has been openly voiced by countries such as China that "Japan may have ambitions to manufacture nuclear weapons"(26). Although Japan itself denies any intention to manufacture nuclear weapons, there is also criticism that this possession of a large amount of plutonium is a contradiction that runs counter to the cause of nuclear non-proliferation(23)(28). In fact, it has been pointed out that there is a risk of being countered with "Why is Japan the only one treated specially?" when demanding that Iran or North Korea stop their nuclear development(29). To address such points, the Japanese government, while repeatedly emphasizing its position of "devotion to peaceful use," has launched plans to consume plutonium as MOX fuel in nuclear power plants and policies to adjust the pace of reprocessing so that no surplus is generated. Furthermore, the possibility of transitioning to an international management framework in which countries other than Japan participate is also being discussed for the future(30). It is essential for Japan to accumulate a track record of nuclear material management under the IAEA system and maintain international trust. It can be said that it is Japan's duty to continue to explore contributions to nuclear non-proliferation that can only be achieved because it is the only country to have suffered atomic bombings.

Between the Peaceful and Military Use of Nuclear Energy: Japan's Choice at a Crossroads

As described above, Japan has a multifaceted face regarding "nuclear." The aspiration for the abolition of nuclear weapons as a victim of atomic bombings, the development of nuclear power and nuclear fusion as an advanced scientific and technological nation, and its strategic value as a nation harboring potential nuclear deterrence—these are intricately intertwined, and Japan's nuclear policy is always built on a difficult balance. Currently, in the international community, movements for nuclear expansion and efforts for nuclear disarmament are intersecting, and the nuclear non-proliferation regime is also at a crossroads. As the gap between nuclear-armed states and non-nuclear states deepens, how Japan chooses to face "nuclear" in the future is extremely important.

Will Japan continue to walk the path of not possessing nuclear weapons and sticking to peaceful use as it has done so far, or will it lean toward possessing its own nuclear deterrent due to changes in the security environment (for example, the nuclear threat from neighboring countries)?—to put it to the extreme, there are two choices. However, choosing the latter would fundamentally overturn the long-standing beliefs and international reputation of Japan as a victim of atomic bombings, and in reality, the hurdles would be extremely high. Therefore, it is thought that Japan will continue to face the dilemma of upholding the ideal of a "world without nuclear weapons" while simultaneously reconciling it with real security(2)(3). Standing at the crossroads of military and peaceful use of nuclear energy, Japan is required to play a unique role based on its own history and international responsibilities. As the only country to have suffered atomic bombings, it will continue to appeal against the tragedy of nuclear weapons, and as a country with advanced nuclear technology, it will continue to demonstrate a model for nuclear non-proliferation and peaceful use—while balancing these two, Japan will likely continue to explore and take on challenges.

References/Sources:

• Ministry of Foreign Affairs, "From the Diet Resolution on the Three Non-Nuclear Principles" (1976 House of Representatives Committee on Foreign Affairs Resolution) mofa.go.jp (1)

• Agency for Natural Resources and Energy, "The Past and Future of the Peaceful Use of Nuclear Energy in Japan" (2018) enecho.meti.go.jpenecho.meti.go.jp (4)(5)(6)(10)(11)(12)(14)

• Sasakawa Peace Foundation, Yuki Kobayashi, "Marking the 10th Anniversary of the Fukushima Nuclear Accident: Contributing to Nuclear Non-Proliferation to Maintain Nuclear Technology" (2021) spf.org (8)(13)

• National Diet Library, Research and Information No. 980, "Overview of the Japan-US Nuclear Cooperation Agreement and Its Future" (2017) dl.ndl.go.jp (7)(9)

• JT-60SA Official Website, "JT-60SA certified as world’s largest tokamak" News Release (2024) jt60sa.org (15)

• Paving the way for ITER, the world's largest nuclear fusion reactor begins operation in Japan | TechNews (16)

• Nazology, "Mechanism for 'putting mercury into a nuclear fusion reactor to turn it into gold' announced" (August 6, 2025) nazology.kusuguru.co.jpnazology.kusuguru.co.jp (17)(18)(19)(20)(21)(22)

• Asahi Shimbun GLOBE, "Japan's contradiction: hoarding plutonium while appealing to the world for denuclearization" (September 6, 2019) globe.asahi.comglobe.asahi.com (23)(26)(28)(29)

• Diamond Online, Atsushi Yamada, "Distrust of 'Potential Nuclear-Armed State Japan'" (March 27, 2014) diamond.jp (24)(25)

• Japan Atomic Energy Agency 'Agreement between Japan and the IAEA for the Application of Safeguards' (1977)jaea.go.jp (27)

• SYNODOS, Ryoya Ishimoto, 'Japan's Position on the Nuclear Weapons Issue' (January 7, 2025)synodos.jpsynodos.jp (30)