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Introduction
Preventing the proliferation of nuclear weapons has been a major focus of international policy for over 70 years. However, a growing interest in high-assay low-enriched uranium (HALEU), driven by billions of dollars in U.S. government funding, raises serious concerns about nuclear security. HALEU, enriched between 10% and 19.75% in uranium-235, is being hailed as a key fuel for next-generation reactors. Yet, critics warn that it could also pose unprecedented risks for nuclear proliferation and terrorism.
With the U.S. Department of Energy estimating a need for over 40 metric tonnes of HALEU before the end of the decade, the expansion of its production and use is accelerating. Companies like TerraPower, backed by Bill Gates, and Centrus Energy are working to commercialize HALEU-fueled reactors, aiming to provide carbon-free power and energy security. However, the potential consequences of making HALEU widely available—both domestically and internationally—must be carefully examined.
What Is HALEU and How Does It Compare to Other Nuclear Fuels?
High-Assay Low-Enriched Uranium (HALEU) is essential for many next-generation reactors, including small modular reactors (SMRs), molten salt reactors (MSRs), and fast neutron reactors. These reactors are designed to be more efficient than traditional nuclear plants, smaller and modular for flexible deployment, and safer by incorporating passive safety features. HALEU’s higher enrichment enables longer fuel cycles, reducing refueling needs and making reactors more practical for remote locations or military applications.
Low-Enriched Uranium (LEU) vs. HALEU vs. Highly Enriched Uranium (HEU)
- Low-Enriched Uranium (LEU): The standard fuel for commercial nuclear reactors, LEU is enriched to less than 5% uranium-235. It is not considered weapons-usable without further enrichment.
- High-Assay Low-Enriched Uranium (HALEU): HALEU is enriched between 10% and 19.75% uranium-235. While technically below the 20% threshold for highly enriched uranium (HEU), it is much closer to weapons-grade material than traditional LEU.
- Highly Enriched Uranium (HEU): At 20% uranium-235 and above, HEU is internationally recognized as directly usable for nuclear weapons. Some experts argue that HALEU, at its highest enrichment level (19.75%), is close enough to be a proliferation risk.
Unlike LEU, HALEU requires specialized handling, transport, and security measures due to its higher enrichment level. However, it does not currently face the same stringent safeguards as HEU, raising concerns about potential misuse.
Pros of HALEU Nuclear Fuel
HALEU is gaining attention as the preferred fuel for many next-generation reactors, including small modular reactors (SMRs) and advanced fast reactors. These reactors are designed to be more efficient, safer, and more flexible than traditional light-water reactors. However, HALEU’s higher enrichment level also brings potential security risks.
With increasing global demand for clean energy, HALEU-powered reactors are seen as a key solution. The U.S. Department of Energy (DOE) estimates that more than 40 metric tonnes of HALEU will be required before 2030 to support nuclear expansion. These reactors will play a significant role in helping the U.S. achieve its goal of 100% clean electricity by 2035. By providing a stable and carbon-free power source, HALEU could contribute to decarbonizing the energy sector.
1. Supports Advanced Nuclear Reactors
HALEU is crucial for many next-generation reactors, including small modular reactors (SMRs), molten salt reactors (MSRs), and fast neutron reactors. These designs offer:
- Greater efficiency than traditional nuclear plants
- Smaller, modular designs for flexible deployment
- Improved safety with passive cooling features
HALEU’s higher enrichment enables longer fuel cycles, reducing refueling needs and making reactors more practical for remote locations and military applications.
2. Enhances Clean Energy Goals
The U.S. aims to achieve 100% clean electricity by 2035, and HALEU-fueled reactors are a key component of that strategy. Advanced reactors using HALEU produce:
- Stable, carbon-free energy
- Lower greenhouse gas emissions
- More efficient use of nuclear fuel
With growing global energy demands, HALEU-powered reactors could help transition away from fossil fuels.
3. Reduces Dependence on Foreign Uranium Sources
The development of HALEU supports energy security by reducing reliance on foreign uranium sources. Domestic production efforts, such as those by Centrus Energy in Ohio, aim to establish a U.S.-based supply chain, decreasing dependence on uranium exports from countries like Russia. This shift strengthens national energy independence and ensures a reliable fuel source for advanced nuclear reactors.
4. Improves Reactor Performance
Compared to traditional low-enriched uranium (LEU) reactors, HALEU reactors offer improved performance and efficiency. They can operate at higher temperatures, have greater neutron efficiency leading to better fuel utilization, and produce less nuclear waste per unit of energy. These advantages make HALEU a key enabler of next-generation nuclear technology and a promising option for the future of nuclear energy.
HALEU is particularly relevant for next-generation reactors, including TerraPower’s sodium-cooled reactor (backed by Bill Gates) and the DRACO (Demonstration Rocket for Agile Cislunar Operations) space-based nuclear propulsion system. These projects require HALEU due to their reactor designs, which cannot operate efficiently with lower-enriched uranium (LEU). However, despite its perceived advantages, recent scientific studies raise concerns that HALEU could be used for nuclear weapons under the right conditions.
Cons of HALEU Nuclear Fuel
1. Increased Proliferation and Security Risks
Despite its benefits, HALEU presents several challenges and risks. One of the biggest concerns is its potential for nuclear proliferation. HALEU contains up to 19.75% uranium-235, which, while below the highly enriched uranium (HEU) threshold, still poses a security risk. Experts warn that a Hiroshima-like bomb could be built with approximately 1,000 kg (2,200 pounds) of HALEU. Unlike HEU, HALEU does not currently require the same level of international security safeguards, making it more vulnerable to theft or misuse. Expanding HALEU use without robust oversight could weaken global nonproliferation efforts.
A 1954 study by Los Alamos National Laboratory found that HALEU could be weaponized if available in sufficient quantities. This contradicts the assumption that 20% enrichment is the threshold distinguishing weapons-usable material from non-weapons-usable material. The study determined that uranium enriched up to 10% was ineffective for weapons, but HALEU (10–20% enrichment) was of “weapons significance” given a large enough supply.
According to recent analysis, between 700 kg and 1,000 kg of HALEU is enough to build a nuclear bomb with a yield of 15 kilotons—equivalent to the Hiroshima bomb (Little Boy). The DRACO space reactor alone will use 300 kg of HALEU, which, while marginal, could still be considered a proliferation risk. This raises concerns that large-scale HALEU production and usage could increase nuclear security threats, particularly if reactors and fuel are exported to countries with less stringent security measures.
Historically, HALEU has been used in research reactors in quantities too small for weaponization. However, the scale of its use is rapidly increasing with the development of new nuclear technologies.
For example, the Oklo 15MW microreactor is expected to require 5 metric tons of HALEU. Similarly, the TerraPower 345MW reactor will need 14 metric tons for its first core and 5 metric tons annually thereafter. These quantities far exceed the original Los Alamos comfort zone, which suggested that 100 kg of HALEU posed no nuclear threat.
2. Potential for International Precedents
If the U.S. and other nations normalize HALEU use, countries with weaker nuclear security protocols might adopt it as well. This increases the risk of HALEU stockpiles being used in nuclear weapons programs, particularly in politically unstable regions. The spread of HALEU technology without stringent safeguards could lead to increased availability of weapons-usable materials, heightening global security concerns.
3. Challenges in Handling and Transport
Handling and transportation of HALEU also present logistical and regulatory challenges. Due to its higher enrichment, HALEU requires specialized storage and handling, more stringent transportation security, and enhanced regulatory frameworks. The lack of existing infrastructure to manage HALEU safely makes its widespread deployment difficult. Currently, there is no large-scale commercial HALEU production facility in the U.S., and global supply chains remain underdeveloped.
4. Limited Current Production Capacity
Production capacity remains a major hurdle for HALEU adoption. The process of producing HALEU is expensive and technically demanding, and the U.S. currently lacks sufficient domestic enrichment facilities. Despite the growing demand for HALEU, its production remains limited. The U.S. and U.K. governments have invested billions in developing HALEU infrastructure. The Inflation Reduction Act (2022) allocated $700 million specifically for HALEU production. Additionally, the U.S. Department of Energy (DOE) has committed over $2 billion to the TerraPower reactor project.
With the U.S. Department of Energy estimating a need for over 40 metric tonnes of HALEU before the end of the decade, the expansion of its production and use is accelerating. Companies like TerraPower, backed by Bill Gates, and Centrus Energy are working to commercialize HALEU-fueled reactors, aiming to provide carbon-free power and energy security. Centrus Energy, the only U.S. company currently producing HALEU, is still in the early stages of scaling up. Without a stable and secure supply chain, the rapid deployment of HALEU-powered reactors may face significant delays.
However, a major challenge remains: Russia is currently the only country with the capability to produce HALEU at scale. Due to geopolitical tensions, the U.S. has banned HALEU imports from Russia until 2028, further complicating supply chains. Meanwhile, the only HALEU producer in the U.S. (contracted by the DOE) was expected to produce 900 kg of HALEU in 2024, but has so far managed only 200 kg.
This production bottleneck raises concerns about whether HALEU-based reactor projects will be viable in the near future and whether the U.S. can maintain secure control over HALEU fuel supplies.
However, the potential consequences of making HALEU widely available—both domestically and internationally—must be carefully examined.
5. Security Classification Gaps in HALEU Regulations
One of the biggest issues with HALEU lies in its security classification. The current uranium security framework categorizes materials based on their enrichment levels rather than their potential for weaponization.
- Category I: Applies to highly enriched uranium (HEU) and requires strict security, including armed guards, vaults, and access controls to prevent theft.
- Category II: Applies to HALEU, which only requires detection measures rather than actual theft prevention.
This means that facilities handling HALEU do not need advanced security measures such as paramilitary protection or reinforced storage vaults. Instead, they only require basic surveillance and local law enforcement backup. As a result, a large quantity of HALEU could be more vulnerable to theft or diversion, increasing the risk of unauthorized use in weapons development.
Proposed Security Measures and Policy Recommendations
Given the security risks associated with HALEU, nuclear safety experts are advocating for reclassifying HALEU as Category I material when used in quantities large enough for weaponization. This would bring HALEU under the same stringent security measures as highly enriched uranium, requiring:
- Armed paramilitary protection at HALEU facilities.
- Hardened vaults and physical barriers to prevent unauthorized access.
- Comprehensive security clearances for personnel handling HALEU.
Experts argue that failing to implement these safeguards could create serious security gaps if HALEU-powered reactors become widespread. The assumption that HALEU is not weapons-usable could lead to inadequate security measures, making it easier for rogue nations or terrorist organizations to obtain sufficient material for a nuclear weapon.
Conclusion
HALEU presents a paradox: it is an essential fuel for next-generation nuclear reactors that promise clean energy and efficiency, yet it also introduces new risks of nuclear proliferation and security threats. While its potential to support carbon-free power and energy independence is significant, the concerns over its use and global precedent cannot be ignored. While HALEU enables advanced reactor designs and offers an alternative to highly enriched uranium, its classification as a low-risk material is outdated.
The Los Alamos study and recent findings suggest that HALEU in large quantities is weapons-usable, contradicting the assumption that 20% enrichment is a clear-cut threshold for security risks. Current security regulations do not account for the scale of HALEU usage in modern reactors, creating potential vulnerabilities.
To mitigate these risks, HALEU should be reclassified as a Category I material when used in quantities sufficient for weaponization. Strengthening security protocols will be essential to prevent proliferation and ensure safe adoption of HALEU in the nuclear energy and space industries. Governments and regulators must weigh the benefits of HALEU against its risks, ensuring that strict security measures and nonproliferation safeguards are in place. The path forward must balance innovation in nuclear technology with the need for global security and stability.
