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September 2011

Increasing Predictability in Thorium-based Fuels

Replacing uranium with new fuel could resolve atomic power security and safety concerns

Jessica Morrison

The preferred location for incorporation of cesium in ThO2 is on a vacant thorium lattice site.

The uranium-based nuclear fuel cycle has a strong legacy in the United States — we first learned about controlling chain reactions during the Manhattan Project, and uranium has since become the prime choice for fuel in nuclear reactors. With concerns of proliferation and long-term storage ever-present, scientists in the Materials Science of Actinides Energy Frontier Research Center are looking in another direction: thorium-based fuels.

Looking past the legacy of a uranium-based fuel cycle: Solving a major concern, the thorium-based fuel cycle offers more proliferation resistance because plutonium-239, which can be used in the production of a nuclear weapon, is not created.

“Worldwide thorium reserves are much larger than uranium reserves, and the production of plutonium and other long-lived actinides is greatly reduced by the thorium fuel cycle, so there is both proliferation resistance and less concern environmentally for long-term waste disposal,” says William Weber, senior author on the recent thorium study published in the Journal of Nuclear Materials.

Nuclear fission, an important part of the nuclear fuel cycle, occurs when heavier atoms are split into lighter ones. The thorium nuclear fuel cycle results in the buildup of lighter fission products — Kr, Xe, Br, Rb, Cs and I, for example — that decrease fuel performance. By exploring how these fission products are incorporated and migrate in thorium fuel materials, through a computational study, Weber’s group hopes to allow better prediction of the structural evolution, properties, and performance of thorium fuels.

According to Weber, volatile fission products not only affect the thermal conductivity of fuel in a reactor, but they also contribute to the performance and safety of used fuel held in interim storage. Increasing the understanding of fission product behavior is valuable for both long-term safety and performance.

Calculating efficiency in experimental trials: This study contributes to the efficiency of proposed experimental trials by suggesting that rubidium is the fission product most likely to be incorporated and that xenon is the least.

“Theory provides guidance on which experiments to do, allowing us to investigate the most mobile fission product first,” says Weber.

More Information

Xiao HY, Y Zhang, and WJ Weber. 2011. "Trapping and Diffusion of Fission Products in ThO2 and CeO2." Journal of Nuclear Materials 414, 464-470. DOI: 10.1016/j.jnucmat.2011.05.037.

Acknowledgments

This work was supported as part of the Materials Science of Actinides, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Basic Energy Sciences. Theoretical calculations were performed using the supercomputer resources at the Environmental Molecular Sciences Laboratory located at Pacific Northwest National Laboratory and at the National Energy Research Scientific Computing Center located at Lawrence Berkeley National Laboratory.

About the author(s):

Trading in Uranium for Thorium

New type of nuclear fuel could solve security, storage issues

Cesium is very mobile in thorium fuel and has strong preferences regarding where it rests in the fuel’s molecular structure.

When removed from nuclear power stations, uranium-fuel rods contain plutonium and other elements that present security and environmental concerns. To prevent it from being acquired for weapons, the fuel must be secured. However, the storage system also must protect the environment for generations. So, the stakes are pretty high. But, what if the stakes weren’t so high? Enter thorium-based fuel. This fuel provides the necessary energy with fewer troubling by-products. One challenge in using thorium fuels is that performance falls off as certain elements build up and move around in the fuel. To lessen the impact of these troubling elements, aka “fission products,” scientists conducted advanced computational studies to select the fission products that cause the greatest performance issues. They followed up by determining where and how the elements migrated. The Materials Science of Actinides, led by Notre Dame University, conducted the study.

More Information

Xiao HY, Y Zhang, and WJ Weber. 2011. "Trapping and Diffusion of Fission Products in ThO2 and CeO2." Journal of Nuclear Materials 414, 464-470. DOI: 10.1016/j.jnucmat.2011.05.037.

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.