Self-healing ceramics for nuclear safety
Pacific Northwest National Laboratory (PNNL) researchers have used supercomputers to simulate how common ceramics could repair themselves after radiation-induced damages. This is an important discovery because 'materials that can resist radiation damage are needed to expand the use of nuclear energy.' These ceramics, which are able to handle high-radiation doses, could improve the durability of nuclear power plants. They also might help to solve the problem of nuclear waste storage. But read more...
You can see on the left the effects of radiation on two materials. "In yttria-stabilized zirconia (top), the defects produced by radiation are few and far between, having less impact on the properties of the material. In zircon (bottom), the defects are clustered, which could compromise the material's integrity." (Credit: PNNL) Here is a link to a larger version of this figure.
This research project has been led at PNNL by scientists Ram Devanathan and William Weber. Here are some of their comments about this research project. "'If you want a material to withstand radiation over millennia, you can't expect it to just sit there and take it. There must be a mechanism for self-healing,' said Devanathan. 'This research raises the possibility of engineering mobile defects in ceramics to enhance radiation tolerance,' Weber said. He noted that materials capable of handling high-radiation doses also 'could improve the durability of key equipment and reduce the costs of replacements.'"
The scientists performed "simulations of the interactions of millions of atoms on two massively parallel supercomputers. The computers were located at the Department of Energy's Environmental Molecular Sciences Laboratory at PNNL and National Energy Research Scientific Computer Center at Lawrence Berkeley National Laboratory."
Here is a description of their three-step approach. "First, they analyzed yttria-stabilized zirconia, a compound of yttrium and zirconium oxides that contains random structural defects called 'vacancies.' The defects occur because yttrium has a smaller electrical charge than zirconium. To correct the charge imbalance, zirconia gives up oxygen atoms. But the loss of these oxygen atoms leaves empty oxygen sites. The remaining oxygen atoms constantly jump in and out of those sites."
In the second step, the researchers simulated the behavior of an atom releasing an alpha particle. "An alpha particle shoots out of the atomic nucleus with such force that the remainder of the atom recoils in the opposite direction. The recoiling atom can cause significant damage to surrounding atomic structures."
The final step involves the analysis of interactions of millions of atoms, which is why the scientists needed supercomputers. "Using data analysis algorithms developed at PNNL, the researchers analyzed gigabytes of data, looking for atoms knocked out of place in fractions of a nanosecond after the recoiling atom hits the yttria-stabilized zirconia."
And what are the results of these simulations? "Although the self-healing activity does not completely repair the material, the defects are less apt to cause problems because they are spread out. This characteristic indicates that yttria-stabilized zirconia, which is used today in such items as solid oxide fuel cells and oxygen sensors, might be suitable for nuclear applications."
For more information, this research work appeared last month in the Journal of Materials Research, a publication of the Materials Research Society, under the name "Dynamic annealing of defects in irradiated zirconia-based ceramics" (Volume 23, Issue 3, Pages 593-597, March 2008). Here is a link to the abstract.
You also can read a previous article of PNNL Research Highlights about this project (March 2008).
So what's next? "The scientists now are refining the simulations and applying them to other materials." Does this mean that this can lead to less-risky nuclear plants and waste storage? Maybe yes, but certainly not before a while.
Sources: Pacific Northwest National Laboratory news release, April 17, 2008; and various websites
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