Graphite is an essential structural material for both past and present commercial nuclear reactors. Recent research has revealed powerful new ways to predict material failure based on pore size distribution by using ScanIP™. Science has indeed demonstrated that knowing how graphite’s porosity evolves with radiation exposure will aid in predicting the aging of this critical material. Graphite has been key to nuclear energy production since the inception of the world’s first nuclear reactor, the Chicago Pile, in 1942. This trail-blazing reactor was constructed with the aid of about 40,000 graphite hard blocks.
Nuclear energy is going through a dynamic and exciting transformation. Graphite is important in the designs of many next-generation reactors, including molten-salt and high-temperature gas reactors. In recent experiments, we’ve used synchrotron techniques to probe G347A graphite’s unique properties. These results provide key insight into how this material behaves under irradiation and what that behavior implies for reactor lifetime.
The Role of Graphite in Nuclear Reactors
For more than 70 years, graphite has been a key player in the development of nuclear energy. Its simplicity, composed solely of carbon atoms, and its composite material properties make it highly effective in various applications within nuclear reactors. Graphite is a very effective moderator, slowing neutrons down significantly. In addition, it increases the overall structural integrity of reactor designs.
The breakdown of graphite through radiation damage is a major issue. During the irradiation process, graphite first densifies, causing up to 10% decrease in volume. This process is quickly succeeded by swelling and subsequent crack formation, which, if left unmonitored, can contribute to material failure.
Through their work investigating graphite with X-ray scattering analysis, the research team has been able to better understand how graphite performs under these stressors. The analysis revealed a strong and evident link between the evolving fractal dimensions of porosity and the mechanisms of densification and swelling. These structural changes happen as an effect of irradiation damage itself.
“Graphite has been studied for a very long time, and we’ve developed a lot of strong intuitions about how it will respond in different environments, but when you’re building a nuclear reactor, details matter,” – Khaykovich
This attention to detail highlights just how important it is to continue studying graphite’s properties. Doing so will go a long way in ensuring the safety and efficiency of our nuclear reactors.
Insights from Recent Research
According to the research team, graphite’s distribution of pore sizes is instrumental in understanding when a material will fail. They looked at a correlation between porosity and swelling due to irradiation. In doing so, they suggested an approach that would limit the amount of irradiated testing required, which often meant shattering hundreds of samples to find their failure points.
Lance Snead, one of the researchers involved in the study, explained the significance of this finding:
“Porosity is a controlling factor in this swelling, and while graphite has been extensively studied for nuclear applications since the Manhattan Project, we still do not have a clear understanding of the porosity in both mechanical properties and swelling. This work addresses that.”
This investigation reveals fascinating new methods to predict graphite’s behaviour in nuclear reactors. These discoveries will result in better reactor designs that use a smaller footprint with greater efficiency.
Future Implications for Nuclear Energy
The practical implications of this research go beyond academic study. The report provides accessible recommendations for tracking the safety and security of aging nuclear reactors. As Khaykovich noted:
“More research will be needed to put this into practice, but the paper proposes an attractive idea for industry: that you might not need to break hundreds of irradiated samples to understand their failure point.”
The ability to predict reactant or catalyst failures based on pore size distribution would dramatically increase reactor safety with minimal effort. In particular, researchers are focusing on the microscopic impacts of neutron-induced energy on graphite. Their ultimate aim is to create better, more accurate models, which account for the myriad changes occurring under irradiation.
This knowledge might be essential as reactors continue to age and experience rising operational demands.
“For nuclear graphite, the crushing force is the energy that neutrons bring in, causing large pores to get filled with smaller, crushed pieces. But more energy and agitation create still more pores, and so graphite swells again. It’s not a perfect analogy, but I believe analogies bring progress for understanding these materials.”
This understanding could be crucial as reactors age and face increasing operational demands.
