Effect of Alpha Decay on Nuclear Borosilicate Glass Properties
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Effect of Alpha Decay on Nuclear Borosilicate Glass Properties Sylvain Peuget, Christophe Jégou, Véronique Broudic, Danièle Roudil, Xavier Deschanels, Jean-Michel Bart Commissariat à l’Énergie Atomique, CEA Marcoule, DEN/DTCD, BP 17171, 30207 Bagnols-sur-Cèze Cedex, France ABSTRACT The properties of actinide glasses are studied in the context of high-level waste management programs. Reprocessing high burnup fuels in particular will increase the minor actinide content in the glass package, resulting in higher cumulative alpha decay doses in the glass, and raising the question of the glass matrix behavior and especially its containment properties. The effect of alpha self-irradiation on the glass behavior is evaluated by doping the glass with a short-lived actinide (244Cm) to reach in several years the alpha dose received by the future glass packages over several thousand years. “R7T7” borosilicate glasses were doped with 3 different curium contents (0.04 wt%, 0.4 wt% and 1.2 wt% 244CmO2). The glass homogeneity was characterized by SEM and XRD. Chemical analysis after dissolution of the glass confirmed the chemical composition. The curium content and its distribution in the glass specimens were checked by calorimetry measurements and gamma spectrometry on 243Cm and 245Cm isotopes. The density and mechanical properties of the curium-doped glasses were characterized up to 2 × 1018 α/g, revealing only a slight evolution of the macroscopic behavior of R7T7 glass in this range. The leaching behavior of curium-doped glass was also studied by Soxhlet tests. The results do not show any significant evolution of the initial alteration rate with the alpha dose. INTRODUCTION Fission products and minor actinides are currently stabilized and immobilized by vitrification in France; this is the French reference process for industrial management of such high-level wasteforms. “R7T7” glass, named after the COGEMA La Hague vitrification units, is the reference glass selected to immobilize the radioelements arising from reprocessing light-water reactor fuel with a burnup of 33 GWd·t-1. Developments in the characteristics—and notably the burnup—of the fuel used in nuclear power plants modify the isotopic composition of the radioactive elements to be immobilized. Depending on the glass loading factor, this will result in a higher concentration of minor actinides in the glass, and thus an increase in the cumulative alpha decay accumulated by the material. As alpha decay is the main cause of atom displacements after disposal [1-4], a research program was undertaken on the effect of alpha decay on the glass containment properties. The aim of this program is to improve our understanding of the glass behavior, so as to consolidate the stabilization of the macroscopic properties observed in the past between 2 and 5 × 1018 α/g [1-4]. R7T7-type glass samples doped with a short-lived actinide (244Cm) were fabricated to obtain within a few years the cumulative alpha decay equivalent to that of an industrial glass package tens of thousands o
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