2018 | AFC ACCOMPLISHMENTS 165 of restructuring is the movement of pores. Under large thermal gradients, pores introduced during fabrication are generally greater than 1 ┬Ám in size, and are uniformly distributed throughout the pellet. Pores move toward the center of the pellet where they eventually coalesce into a large central void. Speculation regarding the manner in which the central void forms has led to the concept of a vapor transport mechanism in which fuel at the surface of the hot side of a pore vaporizes, then condenses on the cool side of the pore.The result is a net flux of pores toward the pellet center.The emphasis in the present work is on the application of these models to engineering-scale finite element simulations. Accomplishments: Central void formation in oxide fuel is known to be a strong function of rod linear power.As shown in Figure 1a, the diameter of the central void increases with an increase of linear heat generation (LHGR).To investigate response of the newly implemented pore migration model in BISON, a series of calculations of radial porosity distribution were performed Figure 1. Top: micrographs of void formation at different linear powers. Bottom: BISON Calculation for the porosity field variable vs. normalized radial position from the 1D axially symmetric simulation of the fuel pellet at varying LHGRs. This shows the pore migration model adequately reproduces the trend of increasing void diameter with increasing power.