Could low-enriched uranium be used in naval reactors? Don’t ask the Navy

The Navy’s 1995 approach

In 1995, the Navy’s analysis considered two tracks or options: The first was replacement of HEU cores in submarines and aircraft carriers ⁷ with LEU cores that would fit in the existing design space—an option considered technically feasible but not superior to HEU fueling. The shorter life of LEU reactor cores that could fit in that space would mean they’d need a number of refuelings during the life of each vessel. The second option was the development of larger LEU cores that would last for the design life of the vessel. The larger, life-of-the-ship reactor cores would require more space and larger compartments and increase the weight of shielding for the cores; therefore, most vessels would have to be larger. ⁸

Both options would have had one-time costs for development of new LEU core designs. But the initial cost of the LEU life-of-the-ship option was projected to be much greater because the vessels themselves would also need to be redesigned. In addition, there were concerns that the increased vessel size would lead to a decrease in operational capabilities and perhaps safety. By comparison, the multiple-refueling LEU option that could stay within current design space probably would have little effect on performance, but it was far more costly over time. The higher costs are related to the need to purchase multiple cores for each vessel, and to refueling outages which would require the Navy to purchase more ships to keep the same number of ships at sea.

Although the Navy’s overall conclusion in 1995 was that neither LEU option was palatable, it did express an offhand preference for the LEU life-of-the-ship option, noting that “the case in which ships would be redesigned to accommodate larger life-of-the-ship LEU cores clearly would have the lesser long-term impact in both cost and ability of the industrial infrastructure to maintain the ship” (Director, Naval Nuclear Propulsion, 1995: 27).

So, is there anything in the 2014 report that indicates a change in the negative assessment of LEU that the Navy made in 1995?

Technical considerations

Both the 1995 and 2014 reports contain similar laudatory background descriptions of the US Naval Nuclear Propulsion Program from its inception in 1948. The 2014 report notes that the Navy has used more than 30 different reactor designs (the same comment also appears in the 1995 report) and that the Navy’s design objective is to produce cores using a conservative approach that “ensures reliability and safety to the crew, the public, and the environment” (Director, Naval Nuclear Propulsion, 1995: 1).

The 1995 report set forth eight criteria that are unique to naval reactors and distinguish them from land-based civilian reactors: compactness, crew protection, public safety, reliability, ruggedness, maneuverability, endurance, and quietness. Although the 2014 report explicitly mentions only compactness, ruggedness, maneuverability, and endurance, it addresses the other criteria by implication. ⁹

The issue of long-lived fuel integrity does seem to be handled differently in the 1995 and 2014 reports. In the 1995 report, the Navy apparently did not consider that the life-of-the-ship fuel integrity problem had been resolved, even for HEU cores. For aircraft carrier cores, the earlier report said, “the limiting technical consideration is corrosion of the [fuel] cladding. Advanced cladding materials are in development and testing with the goal of realizing core lifetimes as long as 45 years” (Director, Naval Nuclear Propulsion, 1995: 9–10). By failing to mention the issue in the 2014 report the Navy seems to suggest that the fuel integrity issue, at least for HEU cores, was resolved by 2014. ¹⁰

There are also some subtle differences between the 1995 and 2014 reports in their respective time estimates for development of LEU systems for naval propulsion. The 1995 report estimated about 15 years would be needed, with at least 10 years for development and testing and five more years for building and qualifying the core. The 2014 report is less optimistic, suggesting a development period of as long as 25 years (Office of Naval Reactors, 2014: 3).

Both reports find that LEU cores would increase the number of times Navy ships needed refueling unless ships were redesigned for larger life-of-the-ship LEU cores. According to the 2014 report, for example, if LEU cores were used a Virginia-class submarine would require three refuelings in its 33-year life instead of none, and a Ford-class carrier would require two refuelings instead of one in its lifetime.

Both reports also address the option of increasing LEU core size so that the initial loading of fuel would last the projected life of the ship. The 1995 report estimated that LEU life-of-the-ship cores would be larger than HEU cores by about a factor of three. The 2014 report echoes the earlier report’s assessment of the necessary increase in size.

So although there are differences between the 1995 and 2014 reports on some technical details, the reports come to similar conclusions regarding the technical merits of the options of LEU cores in current designs (requiring refuelings) or development of larger LEU life-of-the-ship cores. The 2014 report states:

Either of these options would require billions of dollars of investment to develop and deploy. These options would also lead to sustained increases in lifecycle and operating costs … In summary, substituting LEU for HEU in a current naval fuel system offers no operational advantage, is impractical, and is not cost-effective. (Office of Naval Reactors, 2014: 3–4)

Environmental considerations

The 1995 report suggests that use of LEU fuel would cause negative environmental impacts because there would be an increase in the number of shipments of spent fuel if LEU were used, the use of LEU fuel would create an increase in the volume of spent fuel requiring disposal, and the increased number of refuelings needed with LEU fuel would potentially increase the occupational radiation exposure of shipyard workers (Director, Naval Nuclear Propulsion, 1995: 15).

The 2014 report on environmental issues appears to shift focus. Perhaps recognizing that some of the environmental concerns raised in the 1995 report are subjective and subject to criticism, the 2014 report stresses the cost required to deal with environmental impacts. Increased costs for newly designed used fuel storage containers, for example, seem to dominate the environmental focus, replacing the 1995 report’s concentration on increased hazards to shipyard workers.

Overall though, the Navy’s position on the environmental impact of LEU does not seem to have changed at all from the 1995 to 2014 reports. Both stress the negative environmental consequences of the use of LEU fuel and are somewhat simplistic in their arguments. ¹¹ Admittedly, the use of LEU cores, even life-of-the-ship LEU cores, would generate more radioactive waste (both in volume and level of radioactivity) due to the increased volume of fuel and to the increased presence of uranium 238 in the spent fuel. However, one cannot escape the impression, particularly in the 1995 report, that the Navy’s analysis of the increased environmental impact of LEU is not balanced by an assessment of the risks of potential loss of control of HEU and subsequent misuse.

Economics

The 1995 report contained a rather detailed analysis of the economic impacts of the two options for use of LEU cores in the Navy’s nuclear ship program, albeit without substantiation of the cost estimates. The Navy concluded that “either option would be extremely costly. Of two unattractive choices, the case in which ships would be redesigned to accommodate larger life-of-the-ship LEU cores clearly would have the lesser long-term impact in both cost and ability of the industrial infrastructure to maintain the ships” (Director, Naval Nuclear Propulsion, 1995: 27).

Obviously, the absolute dollar numbers required to make the switch from HEU to LEU would have changed by 2014—but the 2014 report fails to address specifics on research and development costs, core and refueling infrastructure costs, ship maintenance costs, and so on, as requested by Congress.

Rather than updating the cost estimates, the 2014 report focuses a significant portion of its economic considerations on the health of the naval reactor research and development program. It says that that program has remained healthy, citing the development of the 40-plus-year core life of the Ohio replacement ballistic missile submarine, but that funding cutbacks may jeopardize the program’s future (Office of Naval Reactors, 2014: 5).

The 2014 report is virtually devoid of substantive economic analysis beyond brief references to increased costs and a final statement that “substituting LEU for HEU … is not cost-effective” (Office of Naval Reactors, 2014: 4). Beyond that generalized statement, there is little indication that the Navy did a current cost assessment of the two options in 2014. One can assume, however, that the Navy’s summary statement indicates that there is no real change in the Navy’s opinion that LEU replacement of HEU would be a costly option and that there is little, if any, change in the Navy’s 1995 position on LEU based on any new cost factors.

What about proliferation?

The Navy’s 1995 report considers the LEU fuel cycle, US nonproliferation policy, and the security implications of using LEU fuel instead of HEU fuel. In reviewing the Navy’s arguments, it’s helpful to remember that there are essentially two types of HEU considered as useful for fuel. Historically, naval HEU fuel was a specific enrichment level reportedly higher than the enrichment used in nuclear weapons. With the drawdown of nuclear weapons, a large amount of HEU that was removed from weapons was made available for the Navy’s use. Although this fuel might not be as efficient as the special-purpose higher-enrichment fuel, it has successfully powered some naval propulsion reactors.

In 2014, the Navy told Congress that the use of weapons-surplus HEU fuel “provides a safe, economical way of removing this material from the threat of diversion and postpones the need to obtain a new, costly enrichment facility for HEU” (Office of Naval Reactors, 2014: 4). ¹² Certainly the cost savings of burning surplus weapons HEU are significant, but the HEU scavenged from retired weapons could also have been downblended and consumed in commercial nuclear power plants, ¹³ as in the Megatons to Megawatts program. ¹⁴

The 1995 report does not explicitly mention the proposed Fissile Material Cutoff Treaty which many in the nonproliferation community think is essential to control future proliferation. While burning weapons-grade HEU scavenged from dismantled nuclear weapons puts off the need to produce HEU for propulsion reactors “for many decades” (Director, Naval Nuclear Propulsion, 1995: 28), ultimately the need to produce HEU would be in conflict with a proposed fissile material treaty that would prohibit production of the two main components of nuclear weapons, HEU and plutonium. The impact of a potential treaty on the decisions made about the use of the LEU fuel is an issue that the Navy should arguably have addressed in the 1995 report. Unfortunately, both it and the 2014 report are essentially silent on the issue and how it relates to overall US nonproliferation policy.

Unquestionably, use of LEU fuel in naval reactors would produce more plutonium in used fuel than would HEU. ¹⁵ The 1995 report raises the production of plutonium in LEU fuel and concerns about its diversion for use in nuclear weapons as examples of LEU use causing increased proliferation and security concerns (Director, Naval Nuclear Propulsion, 1995: 29). In a glaring omission, however, the 1995 report almost totally ignores the proliferation and security risks of HEU and, perhaps more important, the terrorism risk that naval HEU could be stolen and fashioned into an improvised nuclear device. The 2014 report also fails to address the issue.

Although the Navy’s assessment of the proliferation considerations about the use of LEU fuel is open to significant criticism, in the end the Navy’s position on the issue does not appear to have changed. In fact, in its new report it appears the Navy attempted to buttress its support for HEU by adding minor details to enhance its argument that LEU cores offer no nonproliferation advantages.

Another study is needed

It still appears that the Navy will need to be pulled or pushed into a shift of position on LEU use in naval reactors, either by domestic or international political pressures. Although such pressures may be mounting, they are insufficient at the present time to force changes, despite the possible benefits—including reduction of proliferation and terrorism threats—that could result from LEU use. Further, although the Navy’s 1995 and 2014 reports are inadequate, there may be considerations not mentioned in these reports that need to be addressed.

Since the 2014 report failed to address the issues it was asked to examine and has proved to be deficient in a number of ways, ¹⁶ and the Navy seems to have proved to be incapable of providing a transparent assessment of the potential for LEU use in its reactors, Congress should demand an impartial review by technically qualified experts who should be given access to all the Navy’s studies and research and development efforts in order to produce a thorough analysis at both the classified and unclassified levels upon which future decisions on LEU use can be based. These expert inquiries should expand beyond the Navy’s prior reports and address all considerations affecting LEU use in naval reactors, paying particular attention to any performance impacts that might result from LEU use.

Without prejudging the results of such studies, it should be noted that Congress would be, and probably should be, reluctant to mandate a use of LEU if it would put the Navy’s vessels, particularly submarines, at technical disadvantage vis-à-vis similar vessels in other navies. Therefore, beyond the impartial review this article recommends, the executive branch and Congress should consider whether an enforceable international ban on HEU use in naval propulsion reactors is achievable. Such an agreement would eliminate any considerations that other navies could gain a technical advantage by using HEU fuel. Naval construction agreements were effectively negotiated during the 1920s and 1930s in part because the participating states wanted to limit costly naval arms races. Could a naval treaty concept return in the form of agreements on HEU use in naval reactors? If so, it would be a huge step toward lessening the nonproliferation and terrorism risks that are inherent in the use of HEU as naval fuel.