The evolution of intergranular fission gas bubbles, including growth, percolation through the fuel matrix, venting and tunnel collapse is simulated using the Included Phase Model (IPM). The model accounts for the effects of vacancy and fission gas species on bubble growth and morphology, which ultimately lead to tunnel formation, venting of fission gas, and subsequent tunnel collapse. A simplified two-dimension bubble model is implemented on a randomly generated irregular, equiangular hexagonal network of grain boundaries and coupled to an intragranular diffusion model. A set of 28 simulations were conducted on a 20 by 15 grid of hexagons with an open surface at one end to permit venting and ensuing tunnel collapse. Results are post-processed and considered statistically to investigate macroscopic fission gas release parameters and the percolation of the network. The behaviors of individual grains and edges are further investigated as a function of edge length, equivalent grain size, and proximity to the free surface. This analysis revealed discrete growth modes corresponding to the number of bubbles on each edge. These modes emerge because edge lengths vary continuously but only an integer number of bubbles precipitate on them, leading to an unequal number of bubbles per unit length for different grains, and corresponding difference in vacancy potential. This result may improve edge percolation conditions utilized in other models. Limitations resulting from the two-dimensional model and avenues future development of more quantitative models are also discussed.

使用包括相模型（IPM）模拟了晶间裂变气泡的演化，包括生长，通过燃料基体的渗滤，排气和隧道塌陷。该模型说明了空位和裂变气体种类对气泡生长和形态的影响，最终导致了隧道的形成，裂变气体的排放以及随后的隧道坍塌。在随机生成的不规则，等角六边形的晶界网络上实现了简化的二维气泡模型，并耦合到了颗粒内扩散模型。在一个20 x 15的六边形网格上进行了一组28次模拟，该网格的一端有一个敞开的表面，以便通风并确保隧道塌陷。对结果进行后处理并进行统计考虑，以研究宏观裂变气体释放参数和网络的渗流。进一步研究了单个晶粒和边缘的行为，这些行为是边缘长度，等效晶粒尺寸以及与自由表面的接近程度的函数。该分析揭示了与每个边缘上的气泡数相对应的离散生长模式。之所以出现这些模式，是因为边长连续变化，但气泡上只有整数个气泡沉淀，导致不同晶粒的每单位长度气泡数不相等，并且空位势也相应不同。该结果可以改善在其他模型中使用的边缘渗透条件。