Abstract
ABSTRACTThe radiocarbon (14C) content of irradiated graphite is the most important problem for the management of Spanish irradiated graphite (Vandellós I NPP) as L&ILW, due to this material exceeding the maximum14C inventory for the C.A. El Cabril repository. Therefore, the encapsulation of graphite in an impermeable matrix and making an appropriate waste form are indicated as potential management options to be studied. The conversion of the graphite to a long-term stable glass matrix, called IGM (impermeable graphite matrix), uses a long-term stable inorganic binder which additionally encloses the graphite pore system. The world’s first IGM samples made with irradiated graphite have been manufactured in CIEMAT facilities. The durability of the matrix is investigated in leaching experiments in deionized water and granitic bentonite water. The results show that ∼0.05% of14C is leached. A species of organic carbon was found as formate and oxalate (∼10–1mg/L). CO was detected as volatile specie in both media in the first leaching steps; for deionized water (∼3.101mg/L) and in granitic bentonite water (ranging 1.101–3.101mg/L). These low values demonstrated the durability of the IGM glass matrix for final disposal.
Highlights
Reactor-grade graphite is a material fabricated for having high purity, high thermal conductivity, and in so far as possible, high resistance to irradiation damage.Any reactor-grade graphite has a pore structure that enables the penetration of aqueous and gaseous phases and radionuclides, which are not intrinsically bound in the graphite, could be leached
The leaching process (Carpentiero et al 2004; ISO 6961-1982(E)) of the IMPERMEABLE GRAPHITE MATRIX (IGM) specimens was performed at room temperature. ∙ The specimen is suspended in 100 mL of leachant by means of a PTFE (PolyTetraFluoroEthylene) thread and surrounded by at least 1 cm of liquid in any direction (Figure 4). ∙ The initial gas phase composition consists of synthetic air supplied from a high-pressure gas bottle
Ionic species with organic carbon are not detected in the granitic-bentonite water leachant, due to the presence of high concentrations of other anions that mask the detection of carboxylic acids
Summary
Reactor-grade graphite is a material fabricated for having high purity, high thermal conductivity, and in so far as possible, high resistance to irradiation damage (density, minimum gas content, nuclear graphite [prepared under the auspices of the Division of Technical Information, United States Atomic Energy Commission; Nichols and Woodruff 1962]). Any reactor-grade graphite has a pore structure that enables the penetration of aqueous and gaseous phases and radionuclides, which are not intrinsically bound in the graphite (crystalline structure), could be leached. Besides the usage of a long-term stable inorganic binder matrix, the resulting material is homogeneously filled and mechanical damage would not reopen a sealed pore system. Leached gaseous and aqueous species have to be studied in order to determine the mobility of radiocarbon (14C) in the repository environment
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