By Frank von Hippel
In January 2014, the U.S. Department of Energy's Office of Naval Reactors (ONR) submitted to Congress a Report on Low Enriched Uranium for Naval Reactor Cores (PDF).
The contrast to its 1995 Report on Use of Low Enriched Uranium in Naval Nuclear Propulsion, was striking. The 1995 report rejected LEU fuel brusquely: "The use of LEU for cores in U.S. nuclear powered warships offers no technical advantage to the Navy, provides no significant non-proliferation advantage, and is detrimental from environmental and cost perspectives." It argued that the only alternatives to using weapon-grade uranium fuel in U.S. submarine and aircraft carrier reactors would be to either abandon the lifetime cores that the U.S. and U.K. were on the verge of achieving or to build reactor cores with three times larger volume, which would increase the U.S. Navy's costs by about a billion dollars a year.
The new report opens the door a crack:
"recent work has shown that the potential exists to develop an advanced fuel system that could increase uranium loading beyond what is practical today while meeting the rigorous performance requirements for naval reactors. Success is not assured, but an advanced fuel system might enable either a higher energy naval core using HEU fuel, or allow using LEU fuel with less impact on reactor lifetime, size, and ship costs." [emphasis added]
The report hastened to add, however, that "Advanced fuel system development would be a long-term effort that must start well in advance of a ship application." In a briefing to Congressional staff, ONR officials talked about a 10 to 15 year program costing roughly a billion dollars.
The report made clear that part of the motivation of ONR for seeking funding to pursue this research and development was that it soon would have much less to do after a busy period of designing a new generation of reactor cores. The Virginia-class attack submarine is in production and plans are to continue its production for another 30 years. According to the Department of Energy's budget request to Congress for fiscal year 2015, the design of the reactors for the next-generation Ford-class aircraft carrier is 99% complete and the design of the reactor for the next U.S. ballistic missile submarine is progressing rapidly: currently 25% complete and projected to be 74% complete in five years.
Therefore, even if the U.S. decides that it can shift to LEU fuel as France already has, the actual construction of U.S. nuclear-powered submarines or ships with LEU cores may be decades in the future.
The implications of a U.S. commitment to shift to LEU fuel for its next naval reactor design would be significant, however.
The 53 heads of state who who attended the recent Nuclear Security Summit at The Hague agreed to the following: "We encourage States to continue to minimise the use of HEU through the conversion of reactor fuel from HEU to LEU, where technically and economically feasible, and in this regard welcome cooperation on technologies facilitating such conversion."
The heads of state who agreed to this statement included those of the four countries that currently use HEU for naval reactor fuel: the U.S., Russia, U.K. and India.
If the U.S. shifted, the U.K. would do so as well, since it depends upon U.S. naval reactor design expertise. That would leave Russia and India as the only countries with naval reactors using HEU fuel. They could shift more easily than the U.S. or U.K., however, since they are believed to use HEU enriched to less than 90 percent and design their naval reactors to be refueled. Russia already has designed the reactor for its next-generation nuclear-powered icebreaker to be LEU-fueled. The transition to low enriched uranium in naval cores in the United States has long been advocated as part of a strategy of minimizing HEU use worldwide.
Moving future naval propulsion reactors from HEU to LEU fuel would eliminate the processing into fuel of an average of over 3 tons of HEU -- about 100 weapon equivalents -- each year and would make it unnecessary to produce new HEU for naval reactors when the current stockpiles are exhausted. It would make it possible to remove these stockpiles as a potential obstacle to deeper cuts in the world's nuclear weapon stockpiles. In 2006, the U.S. assigned to a naval reserve about 150 tons of weapon-grade uranium being recovered from excess Cold War warheads. That is enough for 6,000 nuclear warheads. Such a stockpile could cast a long shadow if the U.S. and Russia, were, for example, to consider seriously reducing their nuclear-weapon stockpiles to 1,000 warheads each.