Fission gas bubble percolation on crystallographically consistent grain boundary networks

Unit mechanisms of fission gas release: Current understanding and future needs

“…There has been recent work considering explicit tunnel interlinkage through network percolation simulations by Millett et al [115,133], and Sabogal-Su arez et al [134], and examples are shown in Fig. 7.…”

“…7. Examples of grain edge tunnel simulations using network percolation models, where (a) shows a 3D simulation of a fuel pellet slice with radial cracks for a fixed fraction of open vs closed grain faces [133], (b) shows an 2D axisymmtric simulation with the grain face percolation evolving with time according to a 2-stage Booth equation after 1157 days [115], and (c) shows a 2D slice of a pellet with cracks and a crystallographically consistent grain boundary network [134].…”

“…Of these two gaseous elements, Xe has the highest fission yield and is found in UO 2 LWR fuels with the following isotopic composition (half-life, yield) [6,7]: 129 Xe (stable, 0.8%), 131 Xe (stable, 2.93%), 132 Xe (stable, 4.38%), 134 Xe (stable, 8.06%) and 136 Xe (2.11 Â 10 21 years, 6.46%). Kr is found with the following isotopic composition (half-life, yield): 83 Kr (stable, 0.54%), 84 Kr (stable, 1.00%), 85 Kr (10.78 year, 0.29%) and 86 Kr (stable, 2.02%).…”

Modelling of fine fragmentation and fission gas release of UO2 fuel in accident conditions

“…If the grain face bubbles grow to such an extent that they connect with the grain edges, where three grains meet, a continuous network may form, through which part of the intergranular gas inventory can be vented to the rod free volume. Significant venting will occur only if the grain faces and grain edges connect over a larger volume of the material than just a few grains; computational analyses based on percolation theory suggest that more than about 60 % of the grain faces must be permeable for a long-range network to form and considerable fission gas release to occur [77,78].…”

Microstructure-Level Modeling of Stage 3 Fission Gas Release in UO₂ Fuel

“…Models for the evolution of fission gas bubble microstructure and release processes have been developed in the past using analytical [2,3,4,5,6] and computational [7,8,9,10,11,12] methods. However, due to the complexity of the microstructures formed during Stage 3, few of these models have attempted to include the effects of grain edge bubbles and the need for a percolated pathway to the surface for fission gas release to occur.…”