- 作者：S. Peuget ; J.-M. Delaye ; C. J茅gou
- 刊名：Journal of Nuclear Materials
- 出版年：January, 2014
- 年：2014
- 卷：444
- 期：1-3
- 页码：76-91
- 全文大小：2118 K
These studies have shown that some macroscopic properties vary with the accumulation of alpha decay, but then stabilize after integrated doses of the order of 4 脳 1018 伪 g鈭?. For example, the glass density diminishes by about 0.6%, its Young鈥檚 modulus by about 15%, and its hardness by about 30%, while its fracture toughness increases by around 50%. The SEM and TEM characterization showed that the glass is still homogeneous. No phase separation, crystallization or bubbles formation was noticed up to an alpha decay dose corresponding to several thousand years of disposal of nuclear glass canister. Moreover the initial alteration rate of the glass is not significantly affected by the glass damage induced by alpha decays or heavy ions irradiations.
The comparison of the macroscopic evolutions of the Cm doped glass with those obtained for glasses irradiated with light or heavy ions (from either experimental and molecular dynamic studies) suggests that the macroscopic evolutions are induced by the nuclear interactions induced by the recoil nuclei of alpha decay.
The analysis of the behavior of the glass structure subjected to ballistic effects with various spectroscopic studies, together with the results of atomistic modeling by molecular dynamics, have identified some slight changes in the local order around some cations. Moreover a modification of the medium-range order has also been demonstrated through changes in the bond angles between network formers and broadening of the ring size distributions, indicating increasing disorder of the glass structure. This structural evolution induced by alpha decays would be driven by the reconstruction of the glass disorganized by displacement cascades of the recoil nuclei, freezing a glass structure with a higher fictive temperature. This 鈥渂allistic disordering (BD) fast quenching鈥?event induces a new glassy state characterized by a higher enthalpy state. Accumulation of 伪 decays induce similar phenomena of 鈥淏D-fast quenching鈥? increasing the fraction of the sample volume characterized by a 鈥渉igh enthalpy state鈥? At dose around 4 脳 1018 伪 g鈭? the entire sample volume has been affected by 鈥淏D-fast quenching鈥?events at least once, which explain the stabilization of the evolutions of glass structure and properties.
Helium behavior was also studied by measuring the helium solubility constants and diffusion coefficients. Helium atoms are incorporated into the glass free volume with a solubility constant that varies less than 10% around a value of about 1011 at cm鈭? Pa鈭? and a density of solubility sites accessible for helium around 2 脳 1021 sites cm鈭? which is larger than helium production in a glass package. Helium diffusion experiments performed on infused and Cm doped SON68 glasses indicate that helium migration is controlled by a classical thermally activated diffusion process, whose activation energy (e.g. 0.6 卤 0.03 eV) is not affected by an alpha decay dose of around 1019 伪 g鈭?.
Helium implantation studies suggest that helium trapping could exist in nanometer size bubbles. SEM and TEM analysis performed on a Cm doped glass damaged by an alpha decay dose of around 1019 伪 g鈭?, showed a homogeneous glass without crystallization, phase separation or bubbles with a spatial resolution limit of 10 nm. Bubbles of significant size seem very unlikely to form at room temperatures. But, the ability to form helium bubbles of nanometer size, at temperature below the glass vitreous transition temperature cannot be excluded. However, all these studies agree on one point, the absence of macroscopic consequence on the glass integrity of accumulation of high helium concentration in the glass.