Evaluation of a radioactive concrete waste form recovered from an ocean dumpsite

Little dissolution of the concrete waste form in the ocean environment occurred as evidenced by a maximum waste package weight loss of approximately 5%. Water loss through evaporation during curing and dissolution of calcium hydroxide in disposal or inaccuracy of the initial weighing are believed to be responsible for the apparent weight loss. A conservative estimate that assumes a constant 0.33%/yr weight loss due solely to cement-phase dissolution predicts that it would require a minimum of 300 years in this environment before the concrete waste form would lose its integrity. The measured compression strength of the concrete waste form is in the range expected for concrete formulations. This indicates the absence of appreciable attack which is also supported by the observation that negligible deterioration of the waste form surface has occurred. The concrete waste form contained Cs-137, Cs-134, and Co-60. Based on the assumed initial Cs-137 distribution in the waste form, a bulk leach rate for this radionuclide of 2.4x10-3 g/(cm2-day) was calculated. This corresponds to an average fractional activity loss rate of 3.7x10-2 per year (neglecting decay). 7 figures, 1 table