Radiation damages in nuclear waste glasses: a « NMR point of view »

Thibault Charpentier (1) , S. Peuget (2) , A. Le Gac (2, 3) , Bruno Boizot (3) , C.L. Rountree (4) , L. Martel (5) , J. Somers (5)

1 LSDRM - Laboratoire Structure et Dynamique par Résonance Magnétique (LCF)
2 LMPA - Laboratoire des Matériaux et Procédés Actifs
3 LSI - Laboratoire des Solides Irradiés - Irradiated Solids Laboratory
4 SPEC - UMR3680 - Service de physique de l'état condensé
5 ITU - JRC Institute for Transuranium Elements [Karlsruhe]

Borosilicate glasses have been recognized as valuable materials for the conditioning of nuclear wastes. An important issue for their long-term behaviour is radiation effects which may impact their performance and stability. To address these concerns, a fundamental understanding of the origin at the atomic scale of the macroscopic property evolutions must be established. Over the la st decade, magic-angle spinning nuclear magnetic resonance (MAS NMR) has firrrùy established itself as one of the most powerful tool to investigate a glass's structure. It offers several probes of the local structure, nuclei such as 11B, 23Na, 27 Al, 29Si and 17 0, to probe changes either in the glass network or in the alkali distribution. Recently, using external heavy ions irradiation (Xe, Au, Kr) ta simulate alpha decays,[1-3] dramatic changes in the local network structure were evidenced : conversion of tetrahedral B0 4 units into planar trigonal B0 3 units (l1B), appearance of high-coordination aluminum units (AlOs, AI0 6); glass depolymerisation e 9 Si) and changes in the distribution of alkali cations CZ 3 Na). Additionally, the spectra broaden globally which supports the hypothesis of an increased topological disorder after irradiation. AH these structural changes are similar to those observed with increasing the glass temperature or quenching rate and support therefore the model of ballistic disordering fast quenching events which induce a new glassy state with higher fictive temperature. Effects of external electronic (beta) irradiations will be also discussed. If NMR spectra variations show similar trends-but much less pronounced-they are mainly engendered by alkali migration phenomena and formation of molecular oxygen. Until recently, these studies were limited to externally irradiated samples (enabling the different components of irradiation to be dissociated for their precise investigation), but recently, the first MAS-NMR experiments could be performed on radioactive glass es (doped with 244Cm 0.1 % mol.) paving the way for future MAS NMR exarninations of self-irradiation damages in glasses. Experiments were performed at the Joint Research Centre Institute for Transuranium Elements (JRC-ITU) where a commercial NMR spectrometer were integrated with a radioactive glovebox and a MAS commercial probe. Pirst results will be presented. Competitive effects between the recoil nuclei and alpha decays were evidenced and the high resistance of the nuclear waste glasses corroborated.

Domaines: Matériaux

Thibault Charpentier, S. Peuget, A. Le Gac, Bruno Boizot, C.L. Rountree, et al.. Radiation damages in nuclear waste glasses: a « NMR point of view ». MRS Spring meeting, Mar 2016, Phoenix, United States. ⟨cea-02351146⟩