The lack of ductility of the B2 NiAl alloy stands in the way of promising applications. In an effort to understand the dislocation behavior, computer simulation of the planar faults involved in the core spreadings of <100> and <111> dislocations was carried out. Seven γ-surfaces were computed for different crystallographic planes ({110}, {112}, {123}, {210}, {100}, {111} and {122}). Stable APB's are observed in the {110} and {112} planes but they are deviated from the exact 1/2a<111> position. No other stable planar fault was observed. The dislocation core spreadings are explained by the energy balance among the directions of lowest restoring forces observed in the γ-surfaces. The complete <111> screw dislocation was stable in the simulation. According to the stable APB's, two dissociation reactions of the <111> screw dislocation in the {110} and {112} planes are proposed. The simulation of metastable superpartials shows that the dissociation in the {112} planes is very close to a stable dissociation. / Master of Science