Influence of Platinum-Group Metals on Nuclear Glass Properties: Viscosity, Thermal Stability and Alterability
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Influence of Platinum-Group Metals on Nuclear Glass Properties: Viscosity, Thermal Stability and Alterability F. Bart, J.L. Dussossoy and C. Fillet Commissariat à l’Énergie Atomique (CEA/MARCOULE), DCC/DRRV/SCD BP 17171, 30207 Bagnols-sur-Cèze Cedex, France ABSTRACT The fission products resulting from reprocessing of commercial spent fuel are currently vitrified industrially by COGEMA at La Hague. The properties of 21 non-radioactive borosilicate glass samples containing between 4 and 6% of the platinum-group metals (PGM: Pd and Ru) compared with 1.6% in the industrial glass were investigated for chemical composition variations covering the full specification range. After a brief morphological description of the undissolved PGM in the glass, the viscosity variations at temperatures ranging from 1100 to 1200°C are discussed with emphasis on the effects of the particle inclusions on the rheological properties of the glass. Variations in the chemical durability of quenched glass specimens are then discussed. The initial leach rate V0 at 100°C remained near the values obtained for the reference glass. The same tests were repeated on glass heat-treated to obtain maximum crystallization, and the results confirmed that the chemical durability of the glass is practically unaffected by the crystallization observed in this type of glass. INTRODUCTION The fission products resulting from reprocessing of commercial spent fuel are currently vitrified industrially by COGEMA at La Hague. An aluminoborosilicate glass fabricated at 1100°C was developed to ensure durable containment of the high-level radioactive waste from light-water reactor fuel. It is tailored to ensure uniform incorporation in the glass network of all the fission products (some thirty different chemical elements) with the exception of the platinumgroup metals (PGM: Pd, Rh and Ru), which precipitate in the glass forming particle clusters. The influence of the platinum-group metals Ru and Pd* on the major nuclear glass properties (viscosity, thermal stability and alterability) was assessed over the entire guaranteed composition range. The quantity of inclusions was three times higher than in the industrial glass to accentuate any PGM particle effects. QUENCHED GLASS FABRICATION AND HOMOGENEITY ANALYSIS The glass composition range guaranteed by COGEMA and used in this study is shown in Table I. Twenty one glass compositions within this composition range were fabricated for this * The platinum-group metals actually consist of three fission products: Ru, Pd and Rh. In the inactive laboratory tests, Rh is simulated by Pd since both elements are present in the same reduced chemical form, unlike Ru, which is present as RuO2.
study by melting oxides, nitrates and carbonates at 1200°C in platinum crucibles with mechanical stirring to maintain the PGM in suspension in the melt. After refining for three hours, the glass specimens were poured into graphite molds, then annealed for one hour at 520°C to relax the mechanical stresses due to quenching. Table I. Reference chemica
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