The solubility of nickel and its migration through the cementitious backfill of a geological disposal facility for nuclear waste

[Display omitted] •The solubility limiting phase under the conditions of a cementitious waste repository was Ni(OH)2.•Cellulose degradation products increase the advective transport of Ni through cement.•Transport of Ni is controlled by solubility and not sorption or incorporation to cement phases. This work describes the solubility of nickel under the alkaline conditions anticipated in the near field of a cementitious repository for intermediate level nuclear waste. The measured solubility of Ni in 95%-saturated Ca(OH)2 solution is similar to values obtained in water equilibrated with a bespoke cementitious backfill material, on the order of 5×10−7M. Solubility in 0.02M NaOH is one order of magnitude lower. For all solutions, the solubility limiting phase is Ni(OH)2; powder X-ray diffraction and scanning transmission electron microscopy indicate that differences in crystallinity are the likely cause of the lower solubility observed in NaOH. The presence of cellulose degradation products causes an increase in the solubility of Ni by approximately one order of magnitude. The organic compounds significantly increase the rate of Ni transport under advective conditions and show measurable diffusive transport through intact monoliths of the cementitious backfill material.