PubMed · 13820249
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J W ENDERS. 1960. Radioactive trash disposal at Los Alamos.. https://doi.org/10.1080/00028896009343329
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In several countries, low-level radioactive wastes are treated and stored awaiting construction and operation of a final repository. In some cases, interim storage may be extended for decades requiring special attention regarding security issues. The International Atomic Energy Agency (IAEA) recommends segregation of wastes that may be exempted from interim storage or ultimate disposal. The paper presents a method to optimize the decision making process regarding exemption vs. interim storage or ultimate disposal of these wastes.
Release of U and 99Tc from residual sludge in Hanford waste tanks 241-C-203 and 241-C-204 atthe U.S. Department of Energy's (DOE) Hanford Site in southeastern Washington state was quantified by water-leaching, selective extractions, empirical solubility measurements, and thermodynamic modeling. A contaminant release model was developed based on these experimental results and solid-phase characterization results presented elsewhere. Uranium release was determined to be controlled by two phases and occurred in three stages. In the first stage, U release is controlled by the solubility of tejkaite, which is suppressed by high concentrations of sodium released from the dissolution of NaNO3 in the residual sludges. Equilibrium solubility calculations indicate the U released during this stage will have a maximum concentration of 0.021 M. When all the NaNO3 has dissolved from the sludge, the solubility of the remaining cejkaite will increase to 0.28 M. After cejkaite has completely dissolved, the majority of the remaining U is in the form of poorly crystalline Na2U2O7 [or clarkeite Na[(UO2)O(OH)](H20)0-1]. In contact with Hanford groundwater this phase is not stable, and becquerelite becomes the U solubility controlling phase, with a calculated equilibrium concentration of 1.2 x 10(-4) M. For Tc, a significant fraction of its concentration in the residual sludge was determined to be relatively insoluble (20 wt % for C-203 and 80 wt % for C-204). Because of the low concentrations of Tc in these sludge materials, the characterization studies did not identify any discrete Tc solids phases. Release of the soluble fraction of Tc was found to occur concomitantly with NO3-. It was postulated that a NaNO3-NaTcO4 solid solution could be responsible for this behavior. The Tc release concentrations for the soluble fraction were estimated to be 2.4 x 10-6 M for C-203 and 2.7 x 10(-5) M for C-204. Selective extraction results indicated that the recalcitrant fraction of Tc was associated with Fe oxides. Release of the recalcitrant fraction of Tc was assumed to be controlled by dissolution of Fe oxide in the form of ferrihydrite. Based on this assumption and measured values for the ratio of recalcitrant Tc to total Fe in each bulk sludge, the release concentration of the recalcitrant fraction of Tc was calculated to be 3.9 x 10(-12) M for C-203 and 10.0 x 10(-12) M for C-204.
3H and 99Tc are important nuclides in low and intermediate level radioactive wastes, and in safety assessment of near surface repository their migration characteristic usually determines the computing result. The medium of loess appears to possess the characteristic of weak adsorption ability to 3H and 99Tc when they are migrating in it, so the adsorption ability are often neglected, and 3H are used to identify groundwater velocity. But in the field test it was showed that in the aerated zone loess possesses stronger adsorption ability to 99Tc than to 3H, and in the aquifer the stronger adsorption ability to 3H than to 99Tc. In this paper the migration tests of 3H and 99Tc were simulated by NESOR program of non-equilibrium adsorption model. The results show: 99Tc distribution coefficient ranges 0.05-0.055 mL/g in the aerated zone, 3H distribution coefficient is 0.116 mL/g in the aquifer, and the parameter reflects integrated impact of loess on 3H and 99Tc, and the mechanism of them being retarded still need proving.