Yucca alternatives could be problematic

By SCOTT R. BURNELL, UPI Science News   |   April 17, 2002 at 10:50 AM

WASHINGTON, April 17 (UPI) -- (Editor's note: This is the third article in a four-part series from United Press International examining some of the scientific issues related to using Nevada's Yucca Mountain as a nuclear waste repository site. Congress has started a 90-legislative-business-day period where it must vote to override the state's objections to continue the project. The House Energy and Commerce Committee is to hold a hearing on the project on April 18.)


The proposed nuclear waste storage site at Yucca Mountain continues to face vociferous and determined opposition but other avenues for handling the deadly waste also must deal with many of the same scientific and societal obstacles.

Spent fuel from nuclear power plants and other waste components must be secured in some shape or form, given the thousands of years the material will remain dangerous. Isolating the waste in a stable geological formation remains the favored option among scientific groups, but current technology offers other solutions, scientists told United Press International.

The most intriguing possibility is called transmutation. Not the alchemist's dream of turning lead to gold, rather it involves artificially inducing radioactive elements to decay hundreds or thousands of times faster than normal.

Atomic nuclei contain a set number of subatomic particles called protons and neutrons. If the nuclei somehow acquire extra neutrons, they become unstable and give off radiation as they try to return to their proper proton/neutron balance. This is what causes elements to become radioactive.

Transmuting nuclear waste involves injecting energy into radioactive material, said Patrick Herda, a vice president of Nuclear Solutions, an Idaho-based company attempting to commercialize the process.

"The nuclei are excited by something called a gamma-neutron reaction," Herda told UPI. "Gamma photons at certain energy levels can excite the nucleus of an atom to cause it to give off one or more neutrons."

The gamma or high-energy photons -- the particles that carry light and other electromagnetic energy -- accelerate the radioactive decay of nuclear waste, Herda said. The materials either become stable or change into other elements with much shorter radioactive lifetimes.

Herda said transmutation poses no risk of starting a nuclear chain reaction, something that also relies on the presence of extra neutrons. This is because transmutation does not generate particles with enough energy to support a chain reaction, he said.

David Bannon, a physics professor at Oregon State University, believes transmuting waste is technically feasible as long as some of the photons arrive at the radioactive nuclei with the proper energy level.

"If you can get the nucleus to (react) at that (energy level), the probability of its decay in certain cases may increase exponentially," Bannon told UPI. "If the waste contains lots of isotopes, the problem becomes much more difficult (because different isotopes react to different energy levels)."

One way to deal with that challenge is to separate the various isotopes before transmuting them, Bannon said. But that would create an additional low-level waste problem in the form of contaminated equipment. As long as the entire procedure is cost-effective, however, transmutation could be preferable to storage, he said.

Herda said his company's approach would avoid the separation problem by bombarding the waste with photons across a broad range of energy levels to affect all the isotopes at the same time.

Transmutation's other primary challenge lies in efficiently generating the power necessary to create the high-energy photons. Government-operated research facilities have particle accelerators that can reach billions of electron volts, Herda said. Scientific panels, however, consistently have said the approach would consume too much electricity to be considered feasible.

Japanese researchers are looking at a "gamma laser" approach that could be as effective as particle accelerators while using less power, Herda said, and Nuclear Solutions wants to refine that approach even more.

The transmutation reaction generates enough heat to potentially run a steam turbine that could further reduce the drain on outside electricity grids, said John Dempsey, another company executive.

Although the procedure would drastically reduce the radioactive lifetime of the waste, transporting and storing the remains still would be necessary, according to a National Academy of Sciences report released in 2001. Transmutation's main benefit would be reducing the volume of waste needing storage, thereby increasing the holding capacity of a geological repository, the report said.

Another means of disposing of nuclear waste -- sending it into space -- is a relative walk in the technological park compared to transmutation. The waste would be placed on a rocket booster and launched on a trajectory toward either the Sun or deep space, according to the NAS report.

Such an approach hits a nearly insurmountable wall when it comes to safety, however. The not-uncommon satellite launch failures, not to mention the space shuttle Challenger explosion, raise the risk of space disposal to unacceptable levels, the report said. The launch energy needed to reach the Sun also would substantially increase the option's cost.

Some Yucca opponents say there is no need to rush into picking a long-term solution, given the ability to store spent nuclear fuel in "dry cask" containers at reactor sites. Victor Gilinsky, a former Nuclear Regulatory Commission chairman now advising Nevada in its anti-Yucca effort, said current regulations allow such storage for decades.

"The Department of Energy and the nuclear industry think a 'permanent solution' to the nuclear waste issue is the key to getting permission for more reactors," Gilinsky told a group of reporters recently. "Despite DOE's current efforts to stampede the approval process, there's plenty of time to do much better."

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