Several times a year, a convoy including an unmarked truck and heavily-armed chase vehicles moves from a government plant in Oak Ridge, Tennessee, along major highways to others in Irwin, Tennessee, or Lynchburg, Virginia. Later, similar convoys with special guards move from those sites to naval bases in King’s Bay, Georgia, or Kitsap, Washington. This is the nerve-wracking, but largely hidden dance of highly-enriched, weapons-usable uranium in the United States, a steady movement of nuclear explosive material along public routes from one protected government site to another, all to supply fuel for the reactors that power the U.S. Navy’s submarines and aircraft carriers. The Navy has been relying on such highly-enriched uranium (HEU) shipments since 1953, when the first nuclear-powered vessel, the USS Nautilus had its reactor core installed. Although the shipments are constantly monitored and the trucks are equipped with counterterror measures, it’s a fraught experience for many of those involved. HEU is generally considered a choice target for terrorists, since it can be readily used to create a devastating nuclear explosive. Now some experts are wondering: Does the U.S. Navy have to keep doing this? And if it does, will the Navy encourage military officials in other countries to do it as well –to build submarines and other vessels powered by nuclear reactors that consume HEU that has to be moved regularly from one place to another, rather than using a more benign fuel that cannot as readily fuel nuclear weapons? The experts say the issue is on the table now because countries like Iran, Argentina and Pakistan are claiming they intend to build nuclear-powered submarines – and any policy change by the U.S. military would take years to implement. A good way to reduce the terror risks posed by HEU would would be for the U.S. Navy to stop using it to power submarines and aircraft carriers and replace it with low-enriched uranium, which isn’t suitable for use in weapons, a group convened by the Federation of American Scientists said in a report released on March 19. For two decades, the Navy has refused this idea, insisting that the low-enriched fuel can’t match the superb performance of the HEU inside its shipborne reactors. It’s clear that to satisfy the Navy’s concerns, engineers would need to develop compact new reactors capable of operating more efficiently than existing reactors when fueled by low-enriched uranium, said the group, which included a physicist, four nuclear engineers — one of them a retired Navy vice admiral — and three nuclear policy experts. In a press conference in Washington, they recommended that the government begin a major effort to develop such a propulsion system next year, before an international summit meeting opens in Chicago in 2016, for the purpose of promoting nuclear security around the globe. While it’s already too late for the Navy to convert to low-enriched uranium for use in the Ohio-class ballistic and cruise missile subs, scheduled to begin construction in 2021, it could potentially produce a new reactor in time for the next generation of attack submarines and aircraft carriers, scheduled for deployment in the 2030s and 2040s, if it starts the program in 2017, the group said. The report said, moreover, that the United States is slowly but steadily using up its highly-enriched uranium set aside for naval nuclear fuels. By the 2060s, it said, the Navy will be faced a need to produce more of the weapons explosive, undercutting U.S. nonproliferation policy, unless it shifts gears. If the United States resumes production, said Alan Kuperman, coordinator of the Nuclear Proliferation Prevention Project at the University of Texas and an author of the report, “we won’t have a leg to stand on when we tell other countries not to produce highly-enriched uranium.” The report, “Naval Nuclear Propulsion: Assessing the Benefits and Risks,” was financed by the MacArthur Foundation, which has also funded work by the Center for Public Integrity. Officials from the Office of Naval Reactors – a part of the Energy Department — said in a report to Congress in January 2014, that substituting low-enriched for highly-enriched uranium would raise operating costs, cause more radiation exposure for crews and maintenance workers and generate more radioactive waste. But the report also said “the potential exists” to develop a new generation of more efficient low-enriched uranium naval reactors that could address these concerns. A spokeswoman for the Naval Nuclear Propulsion Program said this week that the service could not immediately comment further. The Navy estimated the effort could cost up to $2 billion over ten to fifteen years. Kuperman said that the figure, while large, was only a small portion of the overall nuclear Navy budget. The goal of this research, the task force report said, should be to match the longevity of the reactors currently in production for the Virginia-class attack submarines, which are designed to operate without refueling for the three-decade operating lifetime of the vessel. “The task force endorses this objective because of the downsides of refueling, in terms of operational and shipbuilding costs, and other issues such as minimizing radiation exposures to workers,” the report said. The task force said the threat of the theft or diversion of weapons-grade uranium intended for naval use is real, citing five separate reported thefts or diversions of naval fuels in Russia in the 1990s. In one of the Russian incidents, two Navy enlisted personnel were convicted of stealing two fuel rods containing a total of about four pounds of highly-enriched uranium from a storage facility in Murmansk. “Non-state actors such as terrorists groups or criminal gangs could steal, buy, or be given HEU that they could then form into improvised nuclear devices, which are crude but powerful nuclear explosives,” the report says. Five countries besides the United States already have nuclear-powered vessels: Russia, the United Kingdom, France, China and India. Of those, only the United States and the United Kingdom use uranium enriched to 90 percent or higher, the level preferred by weapons designers. The U.S. nuclear fleet is by far the largest, with 82 vessels, including 10 aircraft carriers, 14 ballistic missile submarines, four cruise missile submarines and 54 attack submarines. Russia, with the second-largest fleet, has a total of 54 nuclear-powered warships and six civilian nuclear-powered icebreakers. Overall, naval reactors consume a total of about three tons of highly-enriched uranium worldwide each year, the task force report says, about double the amount used for other non-weapons purposes. Charles Ferguson, the president of the Federation of American Scientists, an independent nonprofit group in Washington, said that the burden is on the Navy to prove that its nuclear vessels can’t be run on low-enriched fuel. “We’re saying, show us if it’s not technically feasible,” he said. “This is a serious issue.” Ferguson, a graduate of the Naval Academy who studied nuclear engineering and served on a ballistic missile sub, chaired the task force. The other members included retired U.S. Navy Vice Admiral Charles Leidig, who teaches engineering at the U.S. Naval Academy and has served on both attack and ballistic missile subs; Bethany Goldblum, a nuclear engineering professor at the University of California, Berkeley; Kuperman; Alireza Haghighat, professor of nuclear engineering at Virginia Tech; Paul Ingram, executive director of a London-based think tank, the British American Security Information Council; Nick Ritchie, a lecturer in international security at the University of York in Britain; and Bojan Petrovic, professor of nuclear and radiological engineering at the Georgia Institute of Technology.