We utilize a novel computational approach to model the problem of impurity segregation at grain boundaries in nanophase materials. It is based on a parallel MonteCarlo algorithm that places the impurities according to the local chemical potential for the species, following the thermodynamic driving force for segregation. This technique is combined with molecular dynamics techniques to study the role played by Fe impurities in the properties of nanocrystalline Cu grain boundary properties. The impurities were found to improve microstructural stability as studied by high temperature annealing simulations, and grain boundary cohesion as studied via spall resistance high stresses produced by simulated laser irradiation. Virtual tensile tests of samples with and without impurities revealed that the impurities did not affect the high flow stress typical of nanostructured material. We interpret these results in terms of impurity dragging and grain boundary sliding.