Frank von Hippel and Sébastien Philippe

A July 2016 report by the U.S. Department of Energy's Office of Naval Reactors Conceptual Research and Development Plan for Low-Enriched Uranium Naval Fuel (PDF), sketches out a $1 billion, 15-year plan to develop, test and build a laboratory-scale line for production of high-density low-enriched uranium that could replace the highly enriched uranium currently used as fuel in U.S. naval reactors.

The report was requested by Congress in 2015 and follows on from the Office of Naval Reactors January 2014 Report on Low Enriched Uranium for Naval Reactor Cores (PDF), which concluded 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."

The report outlines an LEU naval fuel system development project that would involve "a laboratory scale manufacturing approach, and test data needed to engineer a reactor core design... with small fuel specimens to (1) establish basic manufacturing processes and (2) test irradiated fuel performance and properties." The proposed LEU fuel would be enriched to 19.75% U-235, in contrast to the existing HEU fuel that is enriched to over 90% and was produced originally for use in nuclear weapons.

The conceptual LEU fuel R&D plan would be launched in fiscal year 2018, which begins in October 2017. The effort is estimated to require 15 years and cost about $1 billion. The proposed budget level would be about 5% of the Office of Naval Reactors currently proposed budget for fiscal years 2018-21.

This report must now be critically examined to inform the public and Congress in taking its decision whether to support the program. This summer (2016), the JASON group of technical consultants carried out a classified review of the Office of Naval Reactors NR's proposed LEU fuel development program. It is important that an unclassified summary be made public.

LEU Fuel Development

In the preface of the new report, Director of Naval Reactors, Admiral James Caldwell, observes that the proposed R&D plan has "the potential to deliver a fuel that might enable an aircraft carrier reactor fueled with LEU in the 2040's... The fuel is unlikely to enable converting current life-of-ship submarine reactors to LEU." [emphasis added].

This leaves open the possibility that the new fuel could provide life-of-ship cores in redesigned submarine reactors. For the current submarine reactors, shifting from HEU to the new LEU fuel would require mid-life refueling, a complex and time consuming operation due to the exclusion of refueling hatches in U.S. nuclear submarines. France, which has been operating LEU fueled reactors for over 30 years, is now moving to LEU fuel that is less than 6% enriched (produced in a civilian facility), has refueling hatches in its submarines and refuels them during standard overhaul maintenance periods every ten years.

The Office of Naval Reactors report accepts that a lifetime core could be made out of the new fuel but suggests that such a core would have to be larger than current cores. It believes that current aircraft carrier reactors could accommodate the larger cores that would allow them to continue to have only one refueling at midlife but that current submarine reactors could not accommodate LEU cores large enough to avoid midlife refueling. The report argues further that a larger submarine reactor core would require a larger submarine. This assertion must be questioned since the cores are very small in comparison to the submarines: the hull diameter of the smallest U.S. nuclear submarines, the Virginia-class, is about 10 meters, while the cavity height of the M-140 cask that the Navy uses to ship spent submarine fuel is only about one meter.

LEU Fuel Deployment

If the initial 15-year program of fuel development is successful, the report provides estimates of the additional costs that would be associated with deployment. Deployment is projected to require at least an additional 10 years and cost several billion dollars. The projected costs of deployment include:

• $600 million for a fuel production line;
• "Several billion dollars" for a land-based reactor for testing a prototype core; and
• $1.5-2.4 billion for the first two cores to fuel the two reactors of a Ford-class aircraft carrier reactor. (Of this cost, $530 million is estimated to be in excess to the cost of HEU cores.)

These requirements and cost estimates should be critically examined.

The new report states that a "fuel development effort, such as this LEU work, is what builds, hones, and sustains [the Office of Naval Reactors' fuel development] expertise" between major reactor development efforts. It is important to the willingness of Congress to support the LEU fuel development program that the Office of Naval Reactors not attribute an undue share of the cost of refurbishing and upgrading its fuel development infrastructure to the LEU fuel development program.

For example, it is not clear why LEU fuel would require a several-billion-dollar new prototype reactor. The Office of Naval Reactors already has a prototype reactor at the Knolls Atomic Power Laboratory's Kesselring Site in West Milton, NY. It is currently being refueled to test fuel for the next class of U.S. ballistic missile submarines. Could it be used to test the new LEU fuel after that? The prototype reactor is too small to test a full aircraft carrier core but this need not be a constraint. The fuel for the Nimitz-class carriers was tested in a prototype reactor that was able to accommodate only one quarter of a Nimitz core. In any case, given the advanced state of computer simulations, prototypes of whole cores are becoming less necessary. Also, it is not obvious why an entirely new fuel production line should be required unless the new fuel design is a complete departure from that of the current fuel.

Benefits

According to the new Office of Naval Reactors report, "Development of an advanced naval fuel that uses LEU would demonstrate United States leadership toward reducing HEU and achieving nuclear non-proliferation goals." It is important to be clear that by itself LEU fuel development will not yield any reduction of HEU use or progress towards non-proliferation goals. That will require LEU fuel use. If the Navy's fuel fabrication facilities were shifted over completely to LEU, the report estimates a savings in security costs of about $30 million per year.