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Microstructural Evolution of Nuclear Fuel Under Irradiation


Investigators: Di Yun

The objective of this research program is to address major nuclear fuels performance issues for the design and use of oxide-type fuels in the proposed Global Nuclear Energy Partnership (GNEP) a fast-spectrum Advanced Burner Test Reactor (ABTR) concept. [1] This research program provides a synergy between the high-level materials modeling and a well-rounded experimental effort. The program will address radiation effects and fission product transport processes in oxide-type nuclear fuels to establish a fundamental understanding of fuel performance.  These objectives will be pursued by examining and modeling irradiation effects in CeO2+x, UO2+x and (CeU)O2+x surrogate fuel types, the latter to initiate studies on mixed oxide systems for comparison with performance of MOX-type fuels.  The irradiation effects will be induced by ion implantation over a range on ion energies and to a range of ion doses to simulate the effects of fission product damage.  In addition, transport and trapping of simulated fission products will be examined.  In the early stages of the program, this work will be carried out using inert gas ions (e.g. Kr and Xe) for both ion implantation to cause irradiation damage, and for dynamic transport studies to understand both trapping and defect mobility processes in these fuel forms.  In the later stages of the work, ion which simulate fission products which can act as substitutional atoms for U or Ce in the oxide structure (e.g. Mo and Cs) will be examined.

The experimental studies will compliment modeling work using both molecular dynamics (MD) simulations of damage cascades in the oxide lattice as well as kinetic Monte Carlo (kMC) to study defect dynamics.  The MD approach is extremely useful to understand the very early stages of irradiation damage defect structures during energetic displacement cascades under irradiation and kMC is very useful for using the defect configuration energies from MD to examine the defect and fission product transport mechanisms.

This combination of experimental and modeling efforts have been extremely productive in understanding atomic displacement damage and effects in metal and metal alloy systems.  The proposed program will employ these techniques to provide a new and extremely valuable understanding of oxide-type nuclear fuel performance.

In addition to the specific technical objectives stated above, the program also directly addresses the other NERI objectives. The work is tied closely into ongoing national laboratory programs and interests, and thus meets the objective of “Integrat[ing] … universities into the Department of Energy’s mainline nuclear R&D programs.” The work also involves graduate students, thus “assuring a new generation of engineers and scientists for the nuclear future.”  As stated in the Report to Congress [1], the FY 2007 GNEP program with Universities will be funded primarily through the NERI proposal process.

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