Barium iodate, which is used as the vehicle for storing 129I in Portland cement concrete, is subject to radiolytic reduction to iodide. This could result in an increase in the leach rate of129I during storage due to the reduction of insoluble iodate to soluble iodide. The measured G value (ions of I- per 100 eV or per 1.602 × 10-17 J) was found to be 0.083 for concrete containing 9.05 wt% iodine. The reduction resulting from internal irradiation alone is quite small; only ∼0.21% of the stored 129I would be reduced in 1000 yr.