Radioactive iodine wastes can be isolated in very concentrated form as insoluble barium io-date in concrete. Specimens containing from 2.9 to 11.9% by weight of iodine as barium iodate have been prepared and subjected to standard leaching tests with very satisfactory results. Incremental rates after 100 days leaching were ∼3 μm/day for specimens containing 9.05% iodine; specimens containing from 5.4 to 11.9% iodine showed surprisingly comparable leach rates. Lower leach rates can be obtained by the addition of butyl stearate or by treating the concrete with waterrepellent agents. The process as envisioned produces no contaminated waste side streams. A product containing 9.05% fission product iodine, of which ∼75% is 129I, will generate ∼3.3 μW/kg of product. The daily iodine product from a 5 × 103 kg/day liquid-metal fast breeder reactor fuel reprocessing plant can be contained in 9.49 × 10−3 m3 (0.335 ft3) of such concrete.