New research could help increase the efficiency of nuclear power plants in the near future

New research from scientists at Texas A&M University could help make nuclear power plants more efficient in the near future. Using a combination of physics-based modeling and advanced simulations, they found the key underlying factors causing radiation damage to nuclear reactors, which could then provide insights into the development of more radiation-tolerant, high-performance materials.

“Reactors either have to run at a higher output or consume fuel longer in order to increase their output. With these settings, however, the risk of wear also increases, ”says Dr. Karim Ahmed, Assistant Professor at the Institute for Nuclear Technology. “So there is an urgent need for better reactor designs, and one way to achieve that goal is to optimize the materials used to build the nuclear reactors.”

The results of the study will be published in the journal Frontiers in Materials.

A study by Dr. Karim Ahmed and his team could help optimize materials for modern nuclear reactors in a safer, more efficient and more economical manner.

According to the Department of Energy, nuclear power outperforms all other natural resources in electricity production and accounts for 20% of the United States’ electricity production. The source of nuclear energy are fission reactions, in which a uranium isotope splits into daughter elements after being hit by fast-moving neutrons. These reactions generate enormous heat, so the parts of nuclear reactors, especially the pumps and pipes, are made from materials with exceptional strength and corrosion resistance.

However, fission reactions also generate intense radiation that causes deterioration in the structural materials of the nuclear reactor. When high-energy radiation penetrates these materials at the atomic level, it can either repel atoms from their positions, leading to point defects, or force atoms to occupy vacant spaces, creating interstitial defects. Both imperfections disrupt the regular arrangement of the atoms within the metal crystal structure. And what then starts with tiny imperfections growing to form voids and dislocation loops that affect the mechanical properties of the material over time.

While there is some understanding of the type of defects that occur in these materials upon exposure to radiation, Ahmed said it was tedious to model the radiation along with other factors such as the temperature of the reactor and the microstructure of the material together to create the formation defects and contribute to their growth.

“The challenge is the computational cost,” he said. “In the past, simulations were limited to certain materials and areas with a size of a few micrometers, but if the domain size is increased to 10 micrometers, the computing load jumps dramatically.”

In particular, the researchers said, previous studies have compromised the number of parameters in the simulation’s differential equations to account for larger domain sizes. However, an undesirable consequence of ignoring some parameters over others is an inaccurate description of radiation damage.

To overcome these limitations, Ahmed and his team designed their simulation with all parameters and made no assumptions about whether any of them were more relevant than the other. They also used the resources of the Texas A&M High Performance Research Computing Group to carry out the now computationally intensive tasks.

When performing the simulation, their analysis showed that the use of all parameters in non-linear combinations provides an accurate description of the radiation damage. In addition to the microstructure of the material, the radiation conditions in the reactor, the reactor design and the temperature are particularly important in order to predict the instability of materials due to radiation.

On the other hand, the researchers’ work also sheds light on why specialized nanomaterials are more tolerant of cavities and dislocation loops. They found that instabilities are only triggered if the cluster of co-oriented atomic crystals surrounding the boundary or the grain boundary is above a critical size. With their extremely fine grain sizes, nanomaterials suppress instabilities and become more radiation-tolerant.

“Although our study is a fundamental theoretical and modeling study, we believe it will help the nuclear community optimize materials for different types of nuclear power applications, especially new materials for reactors that are safer, more efficient and more economical” said Ahmed. “This advancement will ultimately increase our contribution to clean, carbon-free energy.”

Reference: “Surface and size effects on the behavior of point defects in irradiated crystalline solids” by Abdurrahman Ozturk, Merve Gencturk and Karim Ahmed, August 10, 2021, Frontiers in Materials.
DOI: 10.3389 / fmats.2021.684862

The first author of this work is Dr. Abdurrahman Ozturk, research associate in the nuclear technology department. Merve Gencturk, PhD student in the nuclear engineering department, also contributed to this research.