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Policy Statement

If the U.S. continues to develop the HEU Kilopower reactor, it will provide justification for other countries to flout the HEU minimization norm. The watch list demonstrates that several states potentially could do so. To preserve its global HEU minimization efforts, the U.S. must commit to halt exploration of HEU-fueled space reactors. 


In 2020, the U.N. was scheduled to hold its quinquennial Nuclear Non-Proliferation Treaty Review Conference, but it has been temporarily postponed due to the global COVID-19 pandemic. Each conference produces a substantive final document, including conclusions, recommendations, and practical steps for the systematic and progressive implementation of decisions in the areas of nuclear disarmament, nuclear non-proliferation, and peaceful uses of nuclear energy. 


We propose that the United States introduce the following Draft Statement at the postponed 2020 NPT Review Conference to commit itself to research and develop only LEU-fueled space reactors while drawing attention to the failures of the current governance of nuclear materials in space. 

Draft Statement


HEU Minimization and Downblending/Reclassification

  1. Affirm the vital importance of minimizing the use of HEU in civilian applications and underscore the proliferation and terrorist risks associated with HEU use

  2. Reaffirm the responsibility of states to promote and abide by the HEU minimization norm 

  3. Commit to downblend to LEU or reclassify stocks of HEU designated for space reactor missions


LEU Alternatives to HEU Nuclear Reactors for Space 

  1. Convert existing HEU-fueled nuclear space reactor (SNR) designs to instead use LEU fuel, and halt planned launches of HEU SNRs 

  2. Focus efforts globally to ensure that SNR research is based on LEU fuel 

  3. Promote information sharing and research cooperation among national space programs on LEU alternatives to HEU space reactors


International legal basis

  1. Amend the “Principles Relevant to the Use of Nuclear Power Sources in Outer Space” resolution to clarify that the resolution extends to all civilian uses of nuclear reactors in space, including propulsion reactors

  2. Replace the current stipulation that “[space] nuclear reactors shall use only highly enriched uranium 235 as fuel” with a provision that states LEU is not only an acceptable fuel, but the preferred fuel for space reactors 

  3. Reiterate that civilian national space programs should not use plutonium to fuel space reactors, due to health concerns in a launch failure or reentry 


Secure access to LEU

  1. Guarantee access to LEU for national space programs developing LEU-fueled SNRs

  2. Coordinate with nuclear suppliers to ensure reliable supply of LEU for civilian space applications

The Draft Statement above would achieve three main objectives. First, it would commit the U.S. to research and develop only LEU-fueled space reactors. This would effectively end NASA’s attempts to fuel its planetary surface reactor with HEU and demonstrate that America’s higher priority is HEU minimization. Second, it would compensate national space programs for the loss of an HEU option. The Draft Statement offers signatories greater access to research and international assistance. It also guarantees that compliant countries will have a supply of LEU to fuel their space reactor missions. Finally, the Draft Statement reforms the international rules governing space reactors.


In 1972, the U.N.’s Committee on the Peaceful Uses of Outer Space (COPUOS) became increasingly concerned about the use of radioisotope generators and nuclear reactors in outer space. [1] Following the Soviet Union’s nuclear-powered Kosmos 954 satellite’s unprogrammed reentry in 1978, state members of COPUOS submitted a proposal to the Scientific and Technical Sub-committee of COPUOS urging development of the “technical base of a multilateral regime of strict and fully effective standards, safeguards, and limitations pertaining to the use of nuclear power sources in space.”  [2] Between 1978 and 1992, eleven principles were created to ensure the safe use of nuclear power sources in outer space. [3] In 1992, the U.N. General Assembly adopted the “Principles Relevant to the Use of Nuclear Power Sources in Outer Space.” [4]


The 1992 non-binding resolution “aimed to ban plutonium fuel” for space reactors. [5] Its literal reading also inadvertently prohibited the use LEU, stating that “[space] nuclear reactors shall use only highly enriched uranium 235 as fuel.” [6] To ensure that this drafting error does not discourage the research and development of LEU-fueled space reactors, our proposed Draft Statement clarifies that national space programs should actually favor LEU fuel. The 1992 resolution also was limited only to non-propulsion reactors. The Draft Statement proposes that the international regulation should apply to propulsion reactors as well. These fixes would convey to the international community that all future SNRs should use LEU fuel. 


The Draft Statement would provide major non-proliferation benefits. Most immediately, the statement would discourage Russia and the United States from further pursuing HEU SNRs while their sunk costs are still relatively low and the widespread deployment of SNRs is still decades away. Given that the United States and Russia both plan launches of HEU-fueled SNRs this decade, the window of opportunity is quickly closing to prevent precedents that could establish HEU space reactors as acceptable or even the norm in the international community. [7] Thus, the statement is a critical and timely step toward preventing the global spread of SNRs using HEU fuel, which would increase the risks of nuclear proliferation and terrorism.  



[1] Carl Q. Christol, “United Nations: General Assembly Resolution and Principles relevant to the Use of Nuclear Power Sources in Outer Space,” International Legal Materials 32, no. 3 (1993): 917.

[2] Ibid, 918.

[3] Ibid, 919.

[4] Ibid, 917.

[5] Alan J. Kuperman, “Avoiding Highly Enriched Uranium for Space Power,” Paper presented at ANS NETS – Nuclear and Emerging Technologies for Space, Las Vegas, NV, 2018. 

[6] 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), 214. 

[7] “ЦНИИмаш: Новый Транспортный Космической Модуль Появится в 2022-2023 Годах,” ТАСС, accessed November 29, 2019,

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