  We address the issue of interaction between zero-point vacancies in solid 4He
as described within the shadow wave-function model. Applying the
reversible-work method and taking into account finite-size effects, we obtain a
zero-point monovacancy concentration of (2.03 +- 0.02) 10^{-3}, which is
slightly higher than the result due to Reatto et al. for the same model.
Utilizing the same methodology, we then consider the divacancy, taking into
account both the in-plane as well as out-of-plane configurations with respect
to the basal plane. We find no significant anisotropy between both
conformation. Furthermore, although there is a small binding tendency, the
expected divacancy concentration is only ~4-5 times larger than the value
expected in the absence of any clustering propensity, 2.5 10^{-5}. This result
suggests that, within the employed model description, no vacancy aggregation
leading to phase separation is to be expected in the ground state.
