Reducing the Threat of HEU: Alternative Fuel for Naval Reactors

By: Cassandra Peterson

The Nuclear Nonproliferation Treaty ensures a country’s right to pursue peaceful nuclear energy projects in a verifiable manner, but a convenient loophole places enriched uranium intended for nautical use outside of the realm of accepted safeguards. This means that some highly enriched uranium (HEU) held by the U.S. and other countries isn’t regulated or monitored, making it susceptible to diversion for use in nuclear weapons programs. The significant risk begs the question: are there other options?

Consequently, the Nuclear Threat Initiative, in conjunction with the James Martin Center for Nonproliferation Studies, recently released a report entitled Replacing Highly Enriched Uranium in Naval Reactors. The expert report recognizes that eliminating stockpiles of HEU is a crucial step in reducing the risk of proliferation worldwide, and proposes that the solution might be found in converting naval reactors to use low enriched uranium (LEU) fuel.

Any concentration of uranium enriched above 20% qualifies as HEU, which is weapons-usable, but nuclear weapons typically operate on uranium enriched at a level of 90% or higher, a range known as weapons-grade. By contrast, LEU is uranium enriched below a level of 20% – too low for powering a nuclear bomb.

The uranium that many countries use in reactors onboard nuclear-powered submarines and – less frequently – aircraft carriers is often enriched above 90%, which means that any state with such vessels is potentially one step closer to nuclear weapons. Right now, those countries include the U.S., Russia, India, and the UK, which all use HEU in military vessels. While it’s worth noting that all of these countries already have nuclear weapons, the number of countries using HEU reactors could rise; Russia may be looking to lease out its HEU-fueled icebreakers, possibly spreading the technology and accompanying risk. Other nations are looking to build nuclear submarines, and there is no guarantee that they will choose LEU fuel.

However, some countries have already made the switch. France converted its nuclear powered vessels to LEU in 2008, China likely uses LEU in its submarines, and Russia has already designed an LEU-fueled reactor for future icebreakers. But change is slow in coming, and the threat of diversion is amplified when analyzing how much HEU is stockpiled for naval reactors.

For example, the United States is in possession of 585.6 metric tons of HEU, 499.5 metric tons of which are earmarked for military and civilian use. Of that number, it’s estimated that roughly 140 metric tons will be used in propulsion systems. Even though the U.S. halted production on HEU for naval activities in 1992, existing stockpiles are expected to last for approximately 50 more years.

Considering efforts the international community has made to restrict the path to nuclear weapons in other countries, perpetuating use of HEU in naval reactors seems counterintuitive. But LEU may not be an easy fix.

In 1995, the Navy prepared a study on the feasibility of converting naval reactors to LEU. The report implied that the change would have economic and environmental pitfalls, because the frequent refueling necessitated by LEU reactors would be detrimental in the long run. Reactor cores that were constructed to last for the entire life of a ship, which is sometimes as long as 42 years, presented less of an environmental impact, but would require more space.

A second report from the Navy in 2014 – this time lacking both supporting evidence and full transparency – concluded that LEU remains an unworkable alternative.

Outside experts challenge this notion. The NTI report suggests a new study on LEU feasibility, correlated by outside contractors. Other suggestions include promoting dialogue with the French government on their familiarity with LEU submarines and briefing Congress on the results. If successful, the report even suggests options for change, with the Ohio Class Replacement Program (SSBN-x) scheduled to begin construction in 2021.

Despite the limited timeframe with which to move forward, these are sensible measures. There’s no way to determine whether LEU is a viable option for the U.S. until it is examined in earnest. Other countries have pursued LEU fuel. It’s time for the United States to at least consider following suit.

*A special thanks to Dr. George Moore for providing PowerPoint slides from an event on the NTI report, which can be read here.