Tuesday, November 27, 2007

Cleaner Nuclear Power?

Congress pushes for another look at thorium fuel, saying it could reduce the amount of high-level nuclear waste produced by reactors.

By Peter Fairley

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A cleaner glow: Thorium and uranium fuel capsules in this research reactor at Russia’s Kurchatov Institute could help reduce waste from existing and future nuclear power plants. Kurchatov and Thorium Power, based in McLean, VA, are scaling up the capsules into 3.5-meter fuel rods for use in commercial power plants.
Credit: Thorium Power

Senators representing several Western states, including Utah's Orrin Hatch and Senate Majority leader Harry Reid, of Nevada, are working on legislation to promote thorium. They say it's a cleaner-burning fuel for nuclear-power plants, with the potential to cut high-level nuclear-waste volumes in half.

"They're concerned about the spent fuel from nuclear reactors ending up in their states," says Seth Grae, president of thorium-fuel technology developer Thorium Power, based in McLean, VA.

Nuclear watchdogs say that Thorium Power's technology has real potential. Moreover, they say that the legislation is needed. It would force the Department of Energy (DOE) and the Nuclear Regulatory Commission, which regulates the nuclear industry, to create new offices at the agencies to study thorium-fuel options and promote their use abroad.

"It makes a lot of sense in my view," says Thomas Cochran, director of the nuclear program at the Natural Resources Defense Council, in Washington. He says that congressional action is needed to overcome resistance within the DOE to exploring thorium.

Using thorium in existing reactors means rethinking the "once through" nuclear fuel cycle employed today in most countries, including the United States. The cycle starts with uranium-oxide fuel enriched in the fissile uranium isotope U235. Fission of the uranium in a reactor generates heat to drive a nuclear power plant's turbines, and it produces a highly radioactive blend of fission breakdown products, including plutonium that can be recovered to make nuclear weapons. Other fission products slow the chain reaction, requiring replacement of fuel every one or two years. The spent fuel is removed and stored on site, awaiting burial.

The DOE is working on a high-level waste repository at Yucca Mountain, in Nevada. But the facility won't open for at least another decade, and there is little political will to build more such sites. Meanwhile, Private Fuel Storage, based in Salt Lake City, is proceeding with a controversial interim storage site on Native American land, with a 20-year license and an option to renew. "That's quite a stopover," says Grae.

Thorium Power was launched in 1992 to commercialize a process that reduces the amount of toxic waste produced by traditional reactors. The process was developed by the late nuclear scientist Alvin Radkowsky, a seminal designer of the U.S. Navy's reactors and early commercial nuclear plants. Radkowsky's scheme relies on both thorium and uranium fuels, making it more complex on the front end. But doing so keeps most of the fuel in the reactor longer, and it produces waste that's less toxic.

Each fuel assembly carries a mix of two different fuel rods. The majority are rods containing pellets of thorium oxide. The thorium can't sustain a chain reaction on its own like U235 can, but it can absorb neutrons to form another fissile isotope of uranium that will: U233. In Thorium Power's design, these neutrons are supplied by the remaining rods, which are solid alloys of zirconium and fissile U235-enriched uranium.

Grae says that Thorium Power's hybrid-fuel assemblies are designed to perform as drop-in replacements for uranium-oxide fuel in pressurized water reactors, the most common reactor design worldwide. The reactors require only minimal modifications. The most important adjustment is the use of more-precise cranes to insert and remove fuel assemblies to enable separate extraction of the uranium rods. Grae says that this is key to the waste reduction because most of the thorium stays in the reactor core for nine years. (The uranium rods, like conventional uranium-oxide fuel, are swapped out more frequently.)

Cleaner Nuclear Power?

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