We designate Japan as a Tier 3 state because while it may not be considering it now, the state has the necessary components to develop a SNR in the future. Japan has the seventh largest government space budget and is ranked one of the best space agencies in the world. [1] While Japan does not produce HEU, it does have the ability to produce LEU. According to Dr. Hideki Nakashima, an expert in the field, “it is realistic [for Japan] to design a space reactor with 20% enrichment.” [2] If Japan did decide to pursue a nuclear reactor in the future, it would probably try to use LEU.

 

While there is no public information suggesting that Japan is considering the development of a SNR, there is a growing interest among Japanese researchers. In 2013, only one serious Japanese academic paper had been published on this topic. [2] The paper, published in 2009, was written by researchers from Kyushu University in Japan. Even though this research paper provided insight into the mechanics of using LEU for space reactors, one of the co-authors of the study, Dr. Nakashima, stated in 2013 that “[a] space nuclear reactor [sic] is not seriously considered by the Japanese government.” [3] Correspondence with Dr. Nakashima in 2020 suggests that he still believes that Japan is not currently pursuing the development of a SNR [4].

 

Since 2013, however, there seems to be a growing number of Japanese researchers exploring various aspects of space reactors. At the Atomic Energy Society of Japan’s 2016 fall meeting, researchers from two different universities presented on nuclear space reactors. [5] The researchers from Hokkaido University presented their findings from their “Core design study of space reactor with low excess reactivity” while researchers from the Tokyo Institute of Technology presented on “Optimization of Small CANDLE Burn-up Reactor for Space Nuclear Power.” [6] Even with the growing interest by Japanese researchers, the Japanese government has not yet publicly indicated its interest in the development of a SNR. 

 

However, this does not mean that the Japanese government will not change its mind in the future. JAXA, Japan's space agency, has the seventh largest government space budget and is ranked one of the best space agencies in the world. [7] Japan also contains the largest stockpile of civilian HEU among the Non-Nuclear Weapon States, estimated at nearly 1,800 kg. [8] Japan does not produce HEU, but it does produce low-enriched uranium (LEU). [9] While most of Japan's enrichment services are imported, Japan Nuclear Fuel Limited (JNFL) is licensed to enrich uranium. However, it currently limits its enrichment to 5%. [10] According to Dr. Nakashima, however, “enrichment to 20% is permitted by [the] U.S.-Japan treaty. So in Japan, it is realistic to design a space reactor with 20% enrichment.” For Japan to enrich above that level would require U.S. consent under a 1988 bilateral agreement. [11 ] When asked whether there is any indication that the Japanese government is actively considering developing a SNR, Dr. Nakashima responded that he was inspired to research this topic due to his interest in fusion space propulsion and not because there is an interest by the Japanese government [11]. 

 

It is important to highlight Japan’s dedicated efforts in both nuclear disarmament and non-proliferation. Japan has actively assisted other Asian countries to fulfill their obligations of creating and implementing domestic regulations to combat the proliferation of weapons-grade material to non-state actors. [10] It has hosted non-proliferation conferences centered around enhancing regional security and non-proliferation efforts. As the only country to have suffered from atomic bombings, Japan understands the danger of proliferation and has been actively advocating for global disarmament. [11] This, paired with the fact that Japan is limited by a bilateral agreement to enriching below 20%, suggests that if Japan did become interested in developing a SNR, it would likely choose a LEU-fuel design.

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[1] Nicolas Nelson, “Which Space Agencies Are Considered The Best In The World,” Forbes, May 22, 2017, https://www.forbes.com/sites/quora/2017/05/22/which-space-agencies-are-considered-the-best-in-the-world/#3159ab235245; https://spacenews.com/op-ed-global-government-space-budgets-continues-multiyear-rebound/.

[2] H. Nakashima, "Correspondence." Email. 2020. 

[3] R. Blake Messer, “Space Reactors,” in Nuclear Terrorism and Global Security: The Challenge of Phasing out Highly Enriched Uranium, ed. Alan J. Kuperman (Routledge, 2013), 215.

[4] Ibid, 217.

[5] H. Nakashima, "Correspondence." Email. 2020. 

[6] “Atomic Energy Society of Japan 2016 Fall Meeting,” Atomic Energy Society of Japan, accessed November 18, 2019, https://confit.atlas.jp/guide/event/aesj2016f/session/1L08-12/detail?lang=en.

[7] Ibid.

[8] Simon Seminari, “Global government space budges continues multiyear rebound,” Space News, November 24, 2019, https://www.forbes.com/sites/quora/2017/05/22/which-space-agencies-are-considered-the-best-in-the-world/#3159ab235245; https://spacenews.com/op-ed-global-government-space-budgets-continues-multiyear-rebound/.

[9] “Civilian HEU: Japan,” Nuclear Threat Initiative, July 1, 2019, https://www.nti.org/analysis/articles/civilian-heu-japan/.

[10] Ibid.

[11] US Nuclear Regulatory Commission, "Article 6: Proposed agreement between the US and Japan concerning peaceful uses of nuclear energy," 1987. https://www.nrc.gov/docs/ML0413/ML041350444.pdf. 

[12] “Japan’s Nuclear Fuel Cycle,” World Nuclear Association, updated October 2019, https://www.world-nuclear.org/information-library/country-profiles/countries-g-n/japan-nuclear-fuel-cycle.aspx; “Uranium Enrichment,” Japan Nuclear Fuel Limited, accessed November 16, 2019, https://www.jnfl.co.jp/en/business/uran/.

[13] H. Nakashima, "Correspondence." Email. 2020. 

[14] Disarmament, Non-Proliferation and Science Department Ministry of Foreign Affairs, Japan’s Disarmament and Non-Proliferation Policy (Fifth Edition), March 2012, https://www.mofa.go.jp/policy/un/disarmament/policy/pdfs/pamph1103.pdf.

[15] Ibid.