Specific helium-tungsten defect configurations suggested by Kornelsen to result from ion implantation following irradiation have been calculated. The calculations are atomistic in nature; those interatomic potentials involving the rare gases were determined from fist principles. The divacancy is found to be most stable in the second-neighbor configuration in the pure W lattice, but energetically prefers first-neighbors if it contains a Kr atom. We obtain good agreement with the experimental activation energies although we find certain configurations to differ slightly from those suggested by Kornelsen.