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Microstructurally Explicit Simulation of Intergranular Mass Transport in Oxide Nuclear Fuels

Harn Chyi Lim, Karin Rudman, Kapil Krishnan, Robert McDonald, Patricia Dickerson, Darrin Byler, Pedro Peralta, Chris Stanek, Kenneth McClellan

Nuclear Technology / Volume 182 / Number 2 / May 2013 / Pages 155-163

Technical Paper / Special Issue on the Symposium on Radiation Effects in Ceramic Oxide and Novel LWR Fuels / Fuel Cycle and Management /

Transport of fission products (FPs) inside fuel pellets is an important mechanism that affects microstructure evolution as well as fuel performance. To study this phenomenon for low fuel burnups, when solid-state diffusion is likely to be the controlling mechanism that sets the stage for subsequent phenomena, e.g., fission gas bubble formation and linkage, we created a three-dimensional (3-D) finite element model based on the real microstructure of a depleted UO2 sample. The model couples grain bulk, grain boundary (GB), and triple junction (TJ) diffusion by using 3-D elements for grain bulks, two-dimensional elements for GBs, and one-dimensional elements for TJs. Grain boundary percolation theory is applied in one case study, and the result shows that the presence of high-diffusivity TJs reduces the effect of GB percolation. The model is also used with mass generation from grain bulks, and it is found that localized regions with a high concentration of FPs can form in the presence of a dominant GB percolation path. The work introduces an approach to model diffusion through GBs and TJs at a fair computational cost that can be applied to study the effects of microstructure on FP transport.

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