By Sophia Macartney
Two non-nuclear weapon states are acquiring nuclear-powered submarines. The Australia-UK-US (AUKUS) alliance is providing Australia with nuclear-powered submarines by the 2040s, and Brazil has been seeking nuclear-powered submarines since the 1980s. Pessimists say AUKUS is a proliferation risk in contradiction of the spirit of the Nuclear Non-Proliferation Treaty (NPT) and could set a precedent; optimists say this is an opportunity to build cooperation among allies and counter Chinese aggression in the Asia Pacific. But what are the associated risks of non-nuclear weapons states acquiring such submarines and how can they be mitigated?
The thought of a non-nuclear weapon state acquiring nuclear weapons is alarming; fortunately, this is not what is happening. Instead, it is the type of technology that fuels the submarines that is being transferred. Most submarines are conventionally powered, or diesel-electric, but nuclear-powered submarines are often powered by fissile material enriched to levels that are dangerously close to or at the level necessary to create nuclear reactions in nuclear weapons. While nuclear-powered submarines are not themselves nuclear weapons, they can, under some circumstances, pose a proliferation risk.
In comparison to conventionally powered submarines, nuclear-powered submarines are faster, rarely need to be refueled and have longer endurance — but they are also larger, less nimble and expensive. Most importantly, the defining characteristic of a submarine is stealth, and nuclear-powered vessels are inherently less stealthy than electric ones given persistent reactor noise. Therefore, no naval power would employ a nuclear submarine unless longer range and endurance are the driving motivations.
Despite the expense and specialized utility of nuclear submarines, Brazil and Australia still want them, raising questions of why they might be justified. Both countries have limited budgets and competing militarization priorities, leading to questions about whether the capability to project naval power at a distance is worth the cost. For Brazil, it almost certainly is not, given the Brazilian Navy’s priority on coastal defense. For Australia, the answer is less clear, with concerns about Chinese intentions in the vast expanses of the Pacific driving uncertainty. Not being a nuclear state but owning nuclear submarines could also lead some to imagine a certain perverse sort of prestige deriving from being the next thing to a nuclear state, despite not having nuclear weapons.
The proliferation risks center around the potential proliferators using naval reactor programs, specifically the need to enrich uranium for fuel, as a potential facade for the development of nuclear weapons. Enriching uranium to fissile levels is the most significant barrier to building such weapons. The NPT does not prohibit non-nuclear weapon states from building nuclear-powered submarines or enriching uranium for naval use. The loophole of concern is that there is no way to determine that enrichment activity would be solely for naval propulsion. The International Atomic Energy Agency (IAEA), which monitors compliance with nuclear safeguards and best practices, cannot safeguard naval reactors and also permits non-nuclear weapon states to withdraw nuclear material from safeguards for use in “non-proscribed military activity.”
Naval reactors, which are not monitored by the IAEA, can either use low enriched uranium (LEU) or highly enriched uranium (HEU), which exacerbates the proliferation problem. LEU is uranium that has been enriched below 20% and is considered reactor-grade, as it is typically used in commercial reactors and for peaceful civilian purposes. HEU is uranium that has been enriched above 20% and is used in nuclear weapons and naval reactors. If the uranium becomes enriched above 90%, it is considered weapons-grade. Once uranium enrichment passes the 20% enrichment threshold, 90% of the work to enrich to weapons-grade uranium has been done, which is why using only LEU that has not passed that threshold in naval reactors is crucial to non-proliferation efforts.
Of the nine nuclear-weapon states, six have nuclear-powered submarines. China and France use LEU to fuel their nuclear-powered submarines, while the United States, Russia, India, and the United Kingdom use HEU. The use of HEU in naval reactors poses a significant proliferation risk because its diversion for use in nuclear weapons can go undetected as per the NPT and IAEA loophole.
Despite ongoing research and development efforts by the United States to convert to only LEU compatible naval reactors, a transition has yet to begin. Congress has ordered funding for the Navy’s research and development of LEU fuel for the past seven years, but it has been brushed aside and repeatedly delayed by the Navy. Working to prevent the spread of HEU by using LEU in naval reactors, therefore diminishing proliferation threats, should be a priority before moving forward with AUKUS plans. As of now, there is still time for the United States to design LEU reactors to transfer to Australia, but given the current AUKUS plan to use HEU, it seems unlikely.
In March 2023, the leaders met to solidify the timeline and announce the incorporation of UK and U.S. technology in nuclear-powered submarines for Australia, which was met with criticisms from China and former Australian Prime Ministers. Although the deal is intended to meet “the highest nuclear non-proliferation standard,” according to the White House statement, it is not clear what such a standard may entail. Australia has strong non-proliferation bona fides, but setting a precedent of a nuclear weapons state transferring HEU is cause for concern.
Most of the components of the AUKUS submarine fleet will be manufactured in the United Kingdom then transported to Australia. These submarines will be powered by the PWR-S nuclear reactor design, which uses HEU. To mitigate these proliferation concerns, AUKUS has plans to place UK and U.S. crews aboard Australian submariners so there is no need for training reactors to be in Australia. These steps, although in the right direction, still do not provide the level of confidence that using LEU would.
In July 2007, Brazil’s president, Luiz Inácio Lula da Silva, announced plans to fund construction of a nuclear-powered submarine. Brazil released the National Defense Strategy in December 2008, which laid out a weak justification of why nuclear-powered submarines would be a worthwhile investment, centering around the posited necessity to protect Brazil’s maritime coast — in an environment without specific threats.
Although it would be easy to dismiss Brazilian ambitions as not justifying the expense, the plan to build a nuclear-powered submarine has persisted and remains popular, due in large part to the perceived prestige of owning such a system. Brazil, however, is perceived as a responsible actor when it comes to proliferation — its government notably ended a nuclear weapons program when Brazil joined the NPT. The Brazilian submarine design is also reportedly derived from France, presumably to employ LEU. Therefore, there is relatively less international concern about the program.
The United States and United Kingdom should be seeking to limit production of more HEU, not setting precedents for excuses to make more. This could also potentially be a gateway to more acceptance of the Fissile Material Cutoff Treaty (FMCT), which would prohibit the production of fissile material needed for nuclear weapons: HEU and plutonium. Furthermore, if ever implemented, the FMCT should cover fissile material use in naval propulsion as well, eliminating the loophole. Stopping the spread of HEU use in naval propulsion in a developing treaty is much more viable than incorporating it into existing regulations, so this should be a prioritized consideration in future non-proliferation policies and treaties.
In the short term and on a case-by-case basis, AUKUS should only use LEU in Australian nuclear submarines, rather than HEU, while continuing to explore the possibility of converting U.S. and British subs to more sustainable LEU fuel. In the long term and on a permanent basis, the future of the FMCT, if ever implemented, should address the loophole and cover naval propulsion. The backlash and international wariness over the transfer of nuclear submarines is too far gone to take back, but there are still ways to prevent spreading HEU usage as a dangerous precedent.