The accumulation of boron within the porous nickel ferrite (NiFe2O4, NFO) deposits on nuclear fuel rods is a major technological problem with important safety and economical implications. In this work, first-principles results are combined with experimental thermochemical data to analyze the energetics of vacancy formation in NFO and the possibility of B incorporation into the structure of NFO. Under solid-solid equilibrium conditions, the calculations suggest that vacancy formation and B incorporation into the NFO structure is energetically unfavorable, the main limiting factors being the narrow stability domain of NFO and the precipitation of B2O3, Fe3BO5, and Ni3B2O6 as secondary phases. Assuming solid-liquid equilibrium between NFO and the surrounding aqueous solution saturated with respect to NFO, the calculations predict that in operating PWR environment, Ni vacancies are likely to form. Under these conditions the possibility of B incorporation at the Ni vacancy sites cannot be excluded.