Abstract
ABSTRACTThe understanding of the 14C behavior in waste packages could lead, in the Spanish context, to a revision of the management strategies for radioactive waste and a revaluation of the near surface repository devoted to the disposal of waste containing this radionuclide in high concentrations. To achieve this objective, and in the context of the EU project Carbon-14 Source Term (CAST), the authors of the work presented in this paper have performed leaching experiments with irradiated graphite considering two different scenarios. One, in which the leaching solution simulates some of the expected conditions in a repository where a granite/bentonite mixture has been used as backfill material, and the other, using deionized water as a high efficiency chemical removal agent and for comparison purposes. The analytical approach to measure the release rate and speciation of 14C from irradiated graphite samples in the aqueous and gaseous phase is also described. The main results obtained shows that, after 359 days of leaching, no 14C activity was detected above the detection limits, and only leaching rates regarding beta-gamma emitters were observed: 2×10–6 cm/day for 137Cs and 1×10–5 cm/day for 60Co in granite/bentonite water media and 4×10–6 cm/day for 137Cs in pure water.
Highlights
The disposal of radioactive waste from nuclear power plants (NPP) containing 14C implies considerations that are different from those encountered with other usual isotopes
The understanding of the 14C behavior in waste packages could lead, in the Spanish context, to a revision of the management strategies for radioactive waste and a revaluation of the near surface repository devoted to the disposal of waste containing this radionuclide in high concentrations
In the context of the EU project Carbon-14 Source Term (CAST), the authors of the work presented in this paper have performed leaching experiments with irradiated graphite considering two different scenarios
Summary
The disposal of radioactive waste from nuclear power plants (NPP) containing 14C implies considerations that are different from those encountered with other usual isotopes. Several works at international (Banford et al 2008; Von Lensa et al 2011) and national level (Esteban-Duque et al 1996; Rodríguez 1997) were performed aiming to provide data on the content and distribution of 14C in radioactive waste mainly coming from nuclear reactors Within this framework, the understanding of the 14C behavior in waste packages could lead to a revaluation of the near surface repository for the disposal of waste containing this radionuclide in high concentrations. 14C Inventory The 14C content of the leachates was analyzed twice, first by means of a conventional LSC system (Packard Tricarb 3110 TR/LL) and, after a preliminary evaluation of the results (where no 14C activity was detected above the detection limits), with an ultra-low level LSC equipment (Quantulus) For these analyses, 0.5 mL of sample was introduced in the combustion oven, following the same methodology as was used for the characterization of the initial graphite. Specimen geometry Leachant Temperature (°C) Vessel / Stirring Vleachate/Sspecimen Initial gas phase composition Regime Sampling Analyses
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