The microstructure of nuclear fuel, UO2, is strongly modified under irradiation by the release of fission products, irradiation damage, and high operation temperature combined with poor thermal conductivity. Irradiation damage accumulation during nuclear plant operation reduces the thermal conductivity of UO2, which leads to reduced fuel lifetime and increased operation costs. Despite large empirical databases for thermal transport in UO2 exists, there is a lack of fundamental understanding between the irradiation microstructures and thermal transport properties. The main motivation of the proposed research is to develop a controlled microstructure in UO2 by He2+ and H+ ion irradiations and examine the effect of microstructure on the thermal conductivity. Low-dose (< 1 dpa) ion-irradiation microstructures of UO2 have been previously studied by indirect methods, such as X-ray diffraction (XRD) and Raman spectroscopy. The irradiation defects have been identified as (vacancy-interstitial) Frankel pairs and/or small defect clusters. However, the link between the thermal transport properties and the irradiation damage is yet undiscovered. By using ion irradiations (at UW), laser-based thermal conductivity measurements (at INL), advanced X-ray methods (SSRL at Stanford), and the proposed TEM/STEM work at CAES, state-of-the-art-knowledge from a well charachterized irradiation damage on thermal transport properties of UO2 will be obtained. The ion irradiations, X-ray charachterizations, and thermal transport measurements are under way and the first results are expected by June 2013.

The proposed reserch will contribute in "Developing technologies and other solutions that can improve the reliability, sustain the safety, and extend the life of current reactors" (one of the four reseach objectives of Office of Nuclear Energy program). An experimentally verified model for thermal conductivy of UO2 would improve the ability for predicting the nuclear fuel performance and would lead to improved fuel economy.



Eventually, the research will benefit DOE's goal of maintaining and enhanching Nation's nuclear infrastructure capacity to meet Nation's energy and environmental needs.