The half-life for the 2 nu beta beta decay transition in ¹⁰⁰Mo is calculated by using a conventional proton-neutron quasiparticle random phase approximation method and a recently proposed particle number projected quasiparticle random phase approximation formalism. The calculations of the relevant matrix elements have been performed by using a realistic effective two-body interaction constructed from the Bonn one-boson exchange potential. Suppression of the 2 nu beta beta decay matrix element is found both in the unprojected and projected models. The collapse of the quasiparticle random phase approximation formalism, induced by renormalized particle-particle interactions, is found to play an important role in dealing with the numerical stability of the results. The particle number projected results are found to be more stable than those corresponding to the unprojected formalism although the particle number projection does not suffice for a complete elimination of spurious ground-state correlations near the collapse of the quasiparticle random phase approximation.