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January 2012

The Evolution of Radiation-Induced Defects in Iron

Novel simulation techniques provide insight into the effects of radiation on iron

Maria Luckyanova

This 9826-atom simulation shows how radiation can cause a disturbance in the normal magnetic distribution of iron. Notably, the magnitude of the magnetic enhancement is largest in the middle and smaller at the edges. The smaller enhancement corresponds to a higher density of physically displaced atoms, as indicated by the green and red atom pairs in the inset which are more dense around the edges than the center. Atomic pairs that have not been displaced are not shown in the figure.

Iron, in its role as a key building material of nuclear fuel containers, must withstand both natural forces from the outside and large amounts of radiation from nuclear reactions on the inside. In the past year, after the tragic earthquake and subsequent nuclear disaster that struck the Fukushima prefecture on the east coast of Japan, it has become obvious that understanding the integrity of these housing structures is absolutely essential to guaranteeing the safety of local populations. Using advanced simulation techniques, researchers in the Center for Defect Physics in Structural Materials have modeled the evolution of a radiation-induced defect in iron. These predictions enrich existing knowledge about the fundamental properties of iron and will help engineers design safer and more robust structures in the future.

Magnetism in iron

Individual iron atoms align and distribute themselves in particular ways to give bulk iron its well-known magnetism. This magnetism influences many mechanical characteristics of iron, including its durability and brittleness. The Center is taking advantage of the leaps made in simulation science and computing power to study the evolution and consequences of atomic-scale defects in the magnetic signature of iron as a result of the radiation released during nuclear reactions. Such simulations have been performed, but never with the inclusion of temperature effects, which have the potential to have a large influence on the outcome of radiation-induced defects.

Modeling defect evolution with atomic-scale simulations

By imposing a set of conditions on a group of atoms and modeling the resulting dynamics, the response of a material to these conditions can be determined at the most fundamental level.The temperature dependence of the radiation-induced defect formation has not been previously theoretically modeled. Including the effects of temperature on the material shows how lattice vibrations and the volume of the lattice, properties which are both highly temperature dependent, affect the magnetic state of the iron. By adding this dimension to the simulation of radiation-induced defects in iron, a more complete understanding of these effects is possible.

Lasting defects in iron due to radiation

The simulations performed for this study show that when iron is struck by radiation, there is a momentary disruption in the typical magnetic distribution of the material. The magnitude of this disruption turns out to be highly temperature-dependent. Although this momentary fluctuation from the normal magnetic distribution eventually relaxes, the material undergoes certain lasting structural defects, most notably the formation of vacancies in the normal lattice of iron. These results have previously been observed experimentally. Further study is necessary to fully understand the implications of this result, according to lead author Yang Wang. He adds, “[in time], this study will give guidelines for building a better theoretical model for magnetic materials.”

More Information

Wang Y, DMC Nicholson, GM Stocks, A Rusanu, M Eisenbach and RE Stoller. 2011. “A Study of Radiation Damage Effects on the Magnetic Structure of Bulk Iron.” Journal of Applied Physics 109(7): Art. No. 07E120. DOI: 10.1063/1.3553937.

IAEA Nuclear Energy Series. 2009. “Integrity of Reactor Pressure Vessels in Nuclear Power Plants: Assessment of Irradiation Embrittlement Effects in Reactor Pressure Vessel Steels.” No. NP-T- 3.11.

Acknowledgments

This work was supported by the Center for Defect Physics in Structural Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

About the author(s):

  • Maria Luckyanova is in her third year of graduate studies at the Massachusetts Institute of Technology under Professor Gang Chen in the Nanoengineering Lab, a part of the Mechanical Engineering Department. She studies heat transfer through nanostructures using an optical pump and probe technique. She is a member of the Solid State Solar Thermal Energy Conversion EFRC. In her spare time she loves to conduct imaginary symphony orchestras and ride her bike.

How Iron’s Magnetic Structure Responds to Radiation

Iron-based materials are exposed to powerful radiation levels inside nuclear reactors. Safely operating these reactors benefits from understanding how iron structures in containment vessels and other structures respond to the intense radiation they encounter. Using advanced simulation techniques, researchers found the iron experiences a short-lived disruption to its magnetic structure that accompanies the well-known disruption to the atomic structure. How large the disruption is depends on the temperature of the iron when it encounters the radiation. Although the iron’s magnetic structure returns to normal, the material undergoes lasting changes at the atomic level after the disrupted area expands and then shrinks back. This correlation between magnetic and atomic (previously seen experimentally) disruption does not appear to alter the iron on a wider scale and holds promise for innovative iron-based materials. This research was done by the Center for Defect Physics in Structural Materials, led by Oak Ridge National Laboratory.

Written by Maria Luckyanova and Kristin Manke

More Information

Wang Y, DMC Nicholson, GM Stocks, A Rusanu, M Eisenbach and RE Stoller. 2011. “A Study of Radiation Damage Effects on the Magnetic Structure of Bulk Iron.” Journal of Applied Physics 109(7): Art. No. 07E120. DOI: 10.1063/1.3553937.

IAEA Nuclear Energy Series. 2009. “Integrity of Reactor Pressure Vessels in Nuclear Power Plants: Assessment of Irradiation Embrittlement Effects in Reactor Pressure Vessel Steels.” No. NP-T- 3.11.

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.