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More Should be Done to "Clean Out" Excess Weapons-Grade Nuclear Materials, Specialists say
Frank von Hippel and Charles Ferguson
Despite progress in reducing the worldwide supply of plutonium and highly enriched uranium (HEU), the essential ingredients for nuclear weapons, much needs to be done, including more attention to fuel from naval reactors and other reactors that have escaped general notice, according to a leading specialist on fissile materials.
Frank von Hippel, a professor of public and international affairs at Princeton University, discussed the status of the global effort to "clean out" nuclear-weapon materials at a 25 May Capitol Hill seminar sponsored by AAAS's Center for Science, Technology and Security Policy.
Reducing the amount of weapons-grade nuclear material and the number of locations where it can be found will reduce the threat that such material might fall into the hands of terrorist groups, von Hippel said. "In the end, it's all about having less of it in the world," he said. "To the extent that we can accomplish that, we'll make the world a safer place."
Charles Ferguson, a Fellow for Science and Technology at the Council on Foreign Relations, gave a primer on how to produce weapons-grade uranium and plutonium in the first place. He noted that the same technologies used to make reactor fuel—such as arrays of gas centrifuges to concentrate the amount of the chain-reacting uranium-235 isotope found in natural uranium—can also be used to make fissile material for a nuclear weapon.
While the low-enriched uranium used in civilian power plants is not directly usable in a nuclear weapon, Ferguson said, much of the work needed to produce weapons-grade uranium is accomplished as part of the process for making low-enriched uranium.
In one case of international interest, Iran now has at least eight linked "cascades" of centrifuges—each cascade with 164 centrifuges—and has plans to link upwards of 3,000 centrifuges in a pilot-scale enrichment facility, Ferguson said.
"You can set up a cascade so that it is optimized to produce low-enriched uranium for reactor fuel," he said. "That's what Iran is doing at this stage. But you can also set it up to be optimized to make high-enriched uranium used for bombs."
But even a cascade optimized for making low-enriched uranium can be a concern, Ferguson said, since the product can be recycled through the centrifuge cascade again and again to make highly-enriched uranium. The process would be inefficient, he said, but it is one reason why nuclear control experts worry about Iran's long-term intentions.
The resources of a nation-state, such as Iran, are needed to enrich uranium or extract plutonium from irradiated reactor fuel, Ferguson said. Terrorist groups do not have the resources to produce the materials, he said. But specialists worry about groups that might get access to HEU from a rogue state or by stealing it from a poorly secured storage facility. That is why von Hippel, Ferguson and others have been urging more aggressive measures to clean out dangerous nuclear materials from sites around the globe.
The U.S. and Russia are in the process of eliminating about one-third of their Cold War stockpiles of highly enriched uranium and have pledged to make similar reductions in their plutonium stockpiles. But von Hippel said the efforts do not go far enough and noted that civilian reprocessing of spent reactor fuel has been adding to the global supply of weapons-usable plutonium.
The most visible effort to reduce world HEU supplies is the blending down of Russia's excess weapons HEU into fuel suitable for burning in U.S. nuclear power reactors. Highly enriched uranium typically contains more than 90 percent of the uranium-235 isotope. The goal, by the year 2013, is to blend down 500 tons of Russian HEU to more benign low-enriched uranium containing no more than five percent U-235. Those 500 tons probably represent about 40 percent of the Russian stockpile, von Hippel said, although there remains uncertainty about just how much HEU the Russians have.
One ton of HEU can produce about 30 tons of low-enriched uranium, enough to fuel a 1 million-kilowatt power reactor for a year and a half, according to von Hippel. "About 10 percent of U.S. electricity is generated by surplus Soviet nuclear warheads," he said. "It's a great thing."
There is another effort underway to convert research reactors that use U.S.-supplied HEU to a low-enriched uranium fuel that cannot be used in nuclear weapons. Russia also has agreed to help clean out HEU fuel that it shipped to research reactors beyond its borders, but von Hippel said Russia has not yet decided whether to convert its own research reactors to low-enriched fuel. There are still about 140 operating HEU-fueled research reactors worldwide, about half of them in Russia, he said. Only about ten are being converted each year to low-enriched fuel.
Von Hippel also cited several types of HEU-fueled reactors, many of them in Russia, that also are candidates for cleanout and have largely escaped notice. They include so-called "critical assemblies" that serve as zero-power mockups for a variety of reactor types; pulsed reactors that are used in nuclear weapons labs and military testing facilities, some of them with enough HEU to make 15 Hiroshima-type bombs; and propulsion reactors, including 15 on nine Russian nuclear-fueled icebreakers.
Several Russian reactor operators have expressed an interest in switching to low-enriched fuels at their facilities, von Hippel said, but they have not received government permission to discuss alternatives.
Military naval reactors are likely to become an increasingly larger share of the HEU cleanout problem if the United States and Russia continue to reduce their nuclear weapons stockpiles of HEU, von Hippel said. Low-enriched uranium can be used as an alternative propulsion fuel, something the French navy already is doing. But the U.S. Navy has not been persuaded to follow suit, von Hippel said. The use of low-enriched fuel typically requires a larger reactor core, he said, and the Navy has argued that would require larger, more costly submarines.
When it comes to plutonium, the global stockpiles present a substantial disposal problem as well. There are some 500 tons of the material worldwide, von Hippel said, with about half of it produced by the reprocessing of spent fuel from civilian nuclear power plants. Britain and France have been the most active in producing civilian plutonium for use in "mixed-oxide" (MOX) fuels at suitable power plants. But such recycling has not kept up with the amount of civil plutonium being produced, von Hippel said.
The U.S. does not reprocess its spent reactor fuel to extract the plutonium. Instead, the waste has been piling up in storage casks at civilian power plants while the efforts to build a permanent underground disposal facility at Yucca Mountain in Nevada continue. The U.S. Department of Energy has proposed that spent fuel be reprocessed and the plutonium "burned" in fast-neutron reactors.
But von Hippel and others argue that such a solution makes little sense. The Energy Department has not yet been able to get rid of the 45 tons of weapons-grade plutonium that it has declared excess, von Hippel said, "but proposes to spend tens of billions of dollars to separate many hundreds of tons more" of the material from spent civilian reactor fuel.
The storage capacity for spent fuel at nuclear plants is sufficient for at least another 30 years, von Hippel argues, time enough to find more permanent disposal solutions. In the meantime, the spent fuel is highly radioactive and would quickly kill any terrorists who did not have the expertise and specialized equipment to handle it.
13 June 2007