The goal of this INCITE project is to make a breakthrough in our understanding of the brittle failure and plastic flow behavior of tungsten polycrystals, through exascale molecular dynamics simulations. The fundamental scientific discoveries revealed by the simulations are expected to be published in top-tier journals. The results of this research will also impact the broader Fusion Energy Science (FES) program through modeling of additively manufactured tungsten alloys. The team’s cross-scale simulation approach will study tensile deformation of bulk crystals, high-angle tungsten GBs as a function of temperature, alloy segregation, and dislocation content in the bulk as well as in the GB plane. The researchers will coordinate these modeling efforts with the experimental additive manufacturing (AM) work at Lawrence Livermore National Laboratory and UCLA, funded through the GAMOW project, as well as with micromechanical tensile tests of AM W polycrystals performed at Lawrence Berkeley National Laboratory. These simulations are aimed at identifying the key parameters that can influence ductile or brittle failure of tungsten and suggest new strategies for mitigation of crack formation during additive manufacturing of tungsten alloys.