Predicting Thermal Conductivity Evolution of Polycrystalline Materials Under Irradiation Using Multiscale Approach
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AFTER several decades of stagnation, there is renewed interest in nuclear power.[1–3] Compared with other energy, nuclear power is reliable and dependable to meet the rising electricity thirst on a large scale. The second advantage of nuclear energy is supply security. Geopolitical instability, disruptions of supplies, and increasing prices have raised concerns in fuel import countries. Moreover, nuclear power is crucial to achieving the carbon goal. The renaissance of nuclear power is still facing two challenges: economics and waste management. To overcome these two barriers, it is important to develop a methodology to predict properties and evaluate performance of nuclear materials, including fuel and waste forms, accurately and efficiently based on physical science. Thermal conductivity is one of the properties important to the performance of fuel and waste forms. The primary concern for present commercial oxide nuclear fuel uranium dioxide (UO2) systems is poor thermal conductivity,[4] resulting in high fuel temperature, fission gas release during irradiation, and decreasing safety margins in accident scenarios.[5] The
DONGSHENG LI, YULAN LI, SHENYANG HU, XIN SUN, and MOHAMMAD KHALEEL, Scientists, are with the Fundamental and Computational Science Directorate, Pacific Northwest National Laboratory, Richland, WA 99352. Contact e-mail: [email protected] Manuscript submitted March 21, 2011. Article published online November 12, 2011 1060—VOLUME 43A, MARCH 2012
temperature distribution within fuel pellets is vital to reactor performance, including effects on heat transfer, grain growth/restructuring, mechanical behavior, pellet/ clad interactions, fission product migration, and fission gas release.[6] In the case of waste form, thermal conductivity is also crucial to predicting performance and life.[7] It is the same for cladding and other structural materials used in an irradiation environment.[8] In predicting the thermal conductivity of materials under irradiation, the influence of molecular structure, lattice parameters, and conductive mechanisms has been investigated thoroughly, and several empirical and theoretical laws have been proposed.[9–11] While several sophisticated techniques have been developed to predict the thermal conductivity of fuel and waste forms, most of the current models do not consider the microstructure evolution under irradiation or anisotropy in a microstructure. The influence of microstructure, however, has not been addressed in the modeling of thermal conductivity, because traditional fuel pellets exhibit random microstructures and thus possess isotropic properties. Such randomness, a hidden assumption in most current models, does not facilitate the prediction of thermal conductivity in fuels with engineered microstructures, which can be designed with anisotropic properties that may ultimately be preferred. This is the same in the application of waste form. Most pure waste form packages fabricated are isotropic. However, the loaded and irradiated waste forms usually do not keep the sa
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