Hostname: page-component-848d4c4894-x5gtn Total loading time: 0 Render date: 2024-05-08T02:16:17.535Z Has data issue: false hasContentIssue false
  • English
  • Français

Protective Effect of the Alteration Gel: A Key Mechanism in the Long-Term Behavior of Nuclear Waste Glass

Published online by Cambridge University Press:  21 March 2011

S. Gin
S. Gin*
Affiliation:
Commissariat à l'Énergie Atomique (CEA), Rhône Valley Research Center, DRRV/SCD, BP 171, 30207 Bagnols-sur-Céze Cedex, France Email: stephane.gin@cea.fr
Get access

Abstract

Experimental alteration results are presented in which a French SON 68 (R7T7-type) nuclear containment glass specimen was first altered under static conditions for 600 days at an S/V ratio of 5000 m−1 before transferring it to pure water. The experiment was designed to assess the diffusion barrier properties of the gel formed during the preliminary alteration phase. Contrary to predictions by kinetic models based only on chemical affinity, the renewed alteration of the specimen in pure water was very limited. Measurements at close intervals showed that the maximum alteration rate under these conditions was 7 ×10−3 g·m−2d−1, or about r0/300, whereas a pristine glass coupon in contact with pure water is altered at r0.

The renewed alteration behavior is attributed to partial (5–10%) dissolution of the existing gel, resulting in a slight degradation of its protective properties. Saturation conditions, at a different level than in the preliminary phase, were reached within a few days. The saturation of the solution with respect to silicon, generally interpreted as a glass/solution (Grambow) or gel/solution (Bourcier) equilibrium, is shown to depend not only on the alteration conditions, but also on the specimen leaching history, and is thus not an inherent glass property.

This experiment confirms the idea that the gel formed under saturation conditions controls the kinetics of SON 68 glass alteration by means of a diffusion barrier effect. It also raises a number of issues concerning the concept of a “residual rate” and the possible relations between the quasi steady-state Si concentrations observed in solution and the protective properties of the gel.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 663: Symposium – Scientific Basis for Nuclear Waste management XXIV , 2000 , 207
Copyright
Copyright © Materials Research Society 2001

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

1. Vernaz, E.Y. and Dussossoy, J.L. (1992), Current State of Knowledge of Nuclear Waste Glass Corrosion Mechanisms: the Case of R7T7 Glass. Applied Geochemistry, Suppl. Issue No. 1, pp. 13–22.Google Scholar
2. Berger, G., Claparols, C., Guy, C. and Daux, V. (1994), Geochim. Cosmochim. Acta vol. 58, pp. 4875–4886.Google Scholar
3. Daux, V., Guy, C., Advocat, T., Crovisier, J.L. and Stille, P. (1997), Chemical Geology, vol. 142, pp. 109–126.Google Scholar
4. Grambow, B. (1985), A General Rate Equation for Nuclear Waste Glass Corrosion. In Scientific Basis for Nuclear Waste Management., Mat. Res. Soc. Symp. Proc., 44, 15–27.Google Scholar
5. Lasaga, A.C. (1995) Fundamental Approaches in Describing Mineral Dissolution and Precipitation Rates. In: White, A.F., Brantley, S.L., (eds.), Chemical Weathering Rates of Silicate Minerals. Rev. Mineral. vol. 31, pp. 23–86.Google Scholar
6. Aagaard, P. and Helgeson, H.C. (1982) Thermodynamic and Kinetic Constraints on Reaction Rates among Minerals and Aqueous Solutions. 1 – Theoretical Considerations. American Journal of Science, 282, 237–285.Google Scholar
7. Chick, L.A. and Pederson, L.R. (1984), The Relationship between Reaction Layer Thickness and Leach Rate for Nuclear Waste Glasses. In Scientific Basis for Nuclear Waste Management. Mat. Res. Soc. Symp. Proc., 26, 635–642.Google Scholar
8. Jégou, C. (1998), Mise en évidence expérimentale des mécanismes limitant la cinétique d'altération du verre R7T7 en milieu aqueux: Critique et proposition d'évolution du formalisme cinétique. Ph.D. thesis. Université de Montpellier II, France.Google Scholar
9. Pacaud, F., Jacquet-Francillon, N., Terki, A. and Fillet, C. (1989), R7T7 Light Water Glass Sensitivity to Variations in Chemical Composition and Operating Parameters. In Scientific Basis for Nuclear Waste Management., Mat. Res. Soc. Symp. Proc., 127, 105–112.Google Scholar
10. Advocat, T., Crovisier, J.L., Vernaz, E.Y., Ehret, G. and Charpentier, H. (1991), Hydrolysis of R7T7 Nuclear Waste Glass in Dilute Media: Mechanisms and Rate as a Function of pH. In Scientific Basis for Nuclear Waste Management XIV. Mat. Res. Soc. Symp. Proc. 212, 57–64.Google Scholar
11. Scheetz, B.E., Freeborn, W.P., Anderson, C., Zolensky, M. and White, W.B.(1985), The Role of Boron in Monitoring the Leaching of Borosilicate Glass Forms. In Scientific Basis for Nuclear Waste Management VIII. Mat. Res. Soc. Symp. Proc. 44, 129–134.Google Scholar
12. Gin, S., Ribet, I. and Couillaud, M. (2000), Role and Properties of the Gel Formed during Nuclear Glass Alteration: Importance of Gel Formation Conditions. In International Workshop on Glass in its Disposal Environment, Bruges, April 2000. To be published in J. Nucl. Mat.Google Scholar
13. Bourcier, W.L., Pfeiffer, D.W., Knauss, K.G., McKeegan, K.D. and Smith, D.K. (1990), A Kinetic Model for Borosilicate Glass Dissolution Affinity of a Surface Alteration Layer. In Scientific Basis for Nuclear Waste Management, Mat. Res. Soc. Symp. Proc. vol. 176, 209–216.Google Scholar
14. Vernaz, E. and Gin, S. (2000), The Apparent Solubility Limit of Nuclear Waste Glass (In these proceedings).Google Scholar
15. Linard, Y. (2000), Thermochimie des verres borosilicatés: Contribution à l'étude de l'altération des verres de confinement de déchets radioactifs. Ph.D. thesis. Université Paris VII, France.Google Scholar
16. Jégou, C., Gin, S. and Larché, F. (2000) Alteration Kinetics of a Simplified Nuclear Glass in an Aqueous Medium: Effects of Solution Chemistry and of Protective Gel Properties on Diminishing the Alteration Rate. (accepted for publication in J. Nucl. Mat.).Google Scholar
17. Gin, S., Jégou, C. and Vernaz, E.Y. (2000), Use of Orthophosphate Complexing Agents to Investigate Mechanisms Limiting the Alteration Kinetics of French SON 68 Nuclear Glass, (accepted for publication in Applied Geochemistry).Google Scholar
18. Gin, S., Jollivet, P., Mestre, J.P. Jullien, M. and Pozo, C. (2000), French SON 68 Nuclear Glass Alteration Mechanisms on Contact With Clay Media, (accepted for publication in Applied Geochemistry).Google Scholar