The gamma radiolysis of water was investigated for conditions relevant to studies of the geological disposal of nuclear fuel waste. Chemical kinetic calculations were carried out for seven systems: argon-purged water; O2-purged water; N2O-purged water; O2-purged solution containing 0.01 mol/ℓ sodium formate; O2-purged solution containing 0.01 mol/ℓ t-butanol; N2O-purged solution containing 0.01 mol/ℓ Na2CO3; and argon-purged solution containing 0.169 mol/ℓ Cl− ions. The initial pH in all systems was set at 9.5. The concentrations of the important oxidants and reductants, both molecular and radical species, are presented as a function of the dose rate and the radiolysis time. In almost all cases, radical species are at steady state after 20 h of irradiation. In argon-saturated solutions, concentrations of all radiolysis products are low (<4 × 10−8 mol/ℓ). In oxygen-saturated solutions containing formate, an H2O2 concentration as high as 1.7 × 10−3 mol/ℓ was calculated after 20 h of irradiation at a dose rate of 280 Gy/h.