title: β-Irradiation Effects on the Formation and Stability of CaMoO4in a Soda Lime Borosilicate Glass Ceramic for Nuclear Waste Storage.
abstract: Molybdenum solubility is a limiting factor to actinide loading in nuclear waste glasses, as it initiates the formation of water-soluble crystalline phases such as alkali molybdates. To increase waste loading efficiency, alternative glass ceramic structures are sought that prove resistant to internal radiation resulting from radioisotope decay. In this study, selective formation of water-durable CaMoO4in a soda lime borosilicate is achieved by introducing up to 10 mol % MoO3in a 1:1 ratio to CaO using a sintering process. The resulting homogeneously dispersed spherical CaMoO4nanocrystallites were analyzed using electron microscopy, X-ray diffraction (XRD), Raman and electron paramagnetic resonance (EPR) spectroscopies prior to and post irradiation, which replicated internal β-irradiation damage on an accelerated scale. Following 0.77 to 1.34 GGy of 2.5 MeV electron radiation CaMoO4does not exhibit amorphization or significant transformation. Nor does irradiation induce glass-in-glass phase separation in the surrounding amorphous matrix, or the precipitation of other molybdates, thus proving that excess molybdenum can be successfully incorporated into a structure that it is resistant to β-irradiation proportional to 1000 years of storage without water-soluble byproducts. The CaMoO4crystallites do however exhibit a nonlinear Scherrer crystallite size pattern with dose, as determined by a Rietveld refinement of XRD patterns and an alteration in crystal quality as deduced by anisotropic peak changes in both XRD and Raman spectroscopy. Radiation-induced modifications in the CaMoO4tetragonal unit cell occurred primarily along the c-axis indicating relaxation of stacked calcium polyhedra. Concurrently, a strong reduction of Mo6+to Mo5+during irradiation is observed by EPR, which is believed to enhance Ca mobility. These combined results are used to hypothesize a crystallite size alteration model based on a combination of relaxation and diffusion-based processes initiated by added energy from β-impingement and second-order structural modifications induced by defect accumulation.
authors.affiliation: Department of Earth Sciences, University of Cambridge , Downing Street, Cambridge CB23EQ, U.K.
authors.forename: Karishma B
authors.identifier: http://orcid.org/0000-0001-5787-2422
authors.initials: KB
authors.lastname: Patel
authors.affiliation: Ecole Polytechnique, Laboratoire des Solides Irradiés, CEA/DSM/IRAMIS, CNRS , 91128 Palaiseau Cedex, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Boizot
authors.affiliation: Department of Earth Sciences, University of Cambridge , Downing Street, Cambridge CB23EQ, U.K.
authors.forename: Sébastien P
authors.initials: SP
authors.lastname: Facq
authors.affiliation: Department of Earth Sciences, University of Cambridge , Downing Street, Cambridge CB23EQ, U.K.
authors.forename: Giulio I
authors.initials: GI
authors.lastname: Lampronti
authors.affiliation: CEA, DEN, DTCD, SECM, LMPA, Marcoule , F-30207 Bagnols-sur-Cèze, France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Peuget
authors.affiliation: CEA, DEN, DTCD, SCDV, LDPV, Marcoule , F-30207 Bagnols-sur-Cèze, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Schuller
authors.affiliation: Department of Earth Sciences, University of Cambridge , Downing Street, Cambridge CB23EQ, U.K.
authors.forename: Ian
authors.initials: I
authors.lastname: Farnan