14 C leaching and speciation studies on Irradiated graphite from vandellós i Nuclear Power Plant

Abstract

The understanding of the 14 C 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 14 C 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 14 C activity was detected above the detection limits, and only leaching rates regarding beta-gamma emitters were observed: 2×10 -6 cm/day for 137 Cs and 1×10 -5 cm/day for 60 Co in granite/bentonite water media and 4×10 -6 cm/day for 137 Cs in pure water.