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The Influence of Thermal Gradients on the Long-Term Evolution of the Near-Field Environment of High-Level Nuclear Wastes Disposal

Published online by Cambridge University Press:  10 February 2011

C. Poinssot ,
P. Toulhoat  and
B. Goffé
C. Poinssot
Affiliation:
Commissariat à l'Energie A tomique, DCC/DESD/Service for Nuclear waste storage and disposal studies, CEA de Saclay, F-91191 Gif sur Yvette - France Ecole Normale Supérieure, Laboratory for Geology, 24 rue Lhomond, F-75005 Paris, France
P. Toulhoat
Affiliation:
Commissariat à l'Energie A tomique, DCC/DESD/Service for Nuclear waste storage and disposal studies, CEA de Saclay, F-91191 Gif sur Yvette - France
B. Goffé
Affiliation:
Ecole Normale Supérieure, Laboratory for Geology, 24 rue Lhomond, F-75005 Paris, France
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Abstract

The initial stage of some HLW disposal systems will be characterised by a large thermal pulse in the near-field environment, due to the heat of the radioactivity decay. This will lead to the development of a transient spatial thermal gradient between the hot canister and the cold geological medium, which could significantly affect the composition and the elemental distribution within the near-field environment. A coupled experimental and modelling work is presented in order to determine the influence of a thermal gradient on water-rock interaction processes. First experiments with a simulated nuclear glass evidenced mass transfer processes leading to chemical differentiation in the solid phases between the hot and the cold end of the system. The relevance of these experimental results to the case of a HLW disposal is strongly supported by in-situ experiments at Stripa, in which a realistic EBS under thermal gradient developed exactly the same mass transfers.

In order to understand the driving force of these processes, we tried to model simplified experiments by using a mixing cell geochemical model built upon the geochemical code EQ3/EQ6. The discrepancies between modelling and experiments indicate the existence of coupled processes involving irreversible precipitation.

Finally, thermal gradients were applied in nuclear glass-clay interaction experiments to enhance elemental migrations. The main results are: (i) a re-crystallisation of the initial clay toward a more silicic one through incorporation of elements released by the glass, (ii) a strong influence of clay chemistry on the nuclear glass secondary phases.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 506: Symposium – Scientific Basis for Nuclear Waste Management XXI , 1997 , 431
Copyright
Copyright © Materials Research Society 1998

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References

REFERENCES

[1] Buscheck, T. A. and Nitao, J. J., “the importance of thermal loading conditions to waste package performance at Yucca Mountain,” in Scientific basis for nuclear waste management XVIII (Elsevier Science Publishers, 1995).Google Scholar
[2] P.A.G.I.S, “Performance Assessment of Geological Isolation System for Radioactive Waste,” Commission of the European Community, EUR 1175 EN, 1988.Google Scholar
[3] Carnahan, C. L., “Thermodynamic coupling of heat and matter flows in near-field regions of nuclear waste repositories,” in Scientific basis for Nuclear Waste Management VII, edited by McVay, G.L. (Elsevier Science Publishers, 1984) pp. 1023–1030.Google Scholar
[4] Carnahan, C. L., “Thermodynamically coupled mass transport processes in a saturated clay,” in Scientific basis for Nuclear Waste Management VIII, edited by Jantzen, C.M., Stone, J.A., and Ewing, R.C. (Elsevier Science publishers, 1985) pp. 491–498.Google Scholar
[5] Jamet, P., Fargue, D., and Marsily, G. de, “Coupled processes in the near-field,” SKB, Stockholm, technical report 91-59 - Proceedings from the technical workshop on near-field performance assessment for high-level waste, 1991.Google Scholar
[6] Marsily, G. de, Fargue, D., and Goblet, P., “How much do we know about coupled transport processes in the geosphere and their relevance to performance assessment?,” GEOVAL 87 internat. symp. Proc., 2, pp.475–491, 1987.Google Scholar
[7] Caquineau, S., “An improved procedure for the X-ray diffraction analysis of low-mass atmospheric dust samples,” European Journal of Mineralogy, 9, pp. 157–166, 1997.Google Scholar
[8] Poinssot, C., Goffr, B., Magonthier, M. C. M., and Toulhoat, P., “hydrothermal alteration of a simulated nuclear waste glass: induced effect of a thermal gradient and of a chemical barrier,” European Journal of Mineralogy, vol. 8, pp. 533–548, 1996.Google Scholar
[9] Trotignon, L., “La corrosion aqueuse des verres borosilicatés; nature et propriétés des couches d'altération,”. PhD thesis, Université Sabatier, P., Toulouse, 1990, pp. 161.Google Scholar
[10] Poinssot, C., Goffé, B., and Pozo, C., “Hydrothermal interaction between a simulated nuclear waste glass and a clayey barrier under thermal gradient,” V1 international symposium on Experimental Mineralogy Petrology and Geochemistry, Bayreuth, pp.51, 1996.Google Scholar
[11] Vernaz, E. Y. and Dussossoy, J. L., “Current state of knowledge of nuclear waste glasses corrosion mechanisms: the case of R7T7,” Applied Geochemistry, vol. Suppl. Issue 1, pp. 13–22, 1992.Google Scholar
[12] Push, R., Kamland, O., Lajudie, A., Lechelle, J., and Bouchet, A., “Hydrothermal field test with French candidate clay embedding steel heater in the Stripa mine,” SKB, SKB report 93.02, 1992.Google Scholar
[13] Pozo, C., Jullien, C., and Poinssot, C., “evolution of an engineered barrier under thermal gradient during the Stripa experiments : influence of the clay texture on the element transfers,” presented at 21st MRS symposium, Davos, 1997.Google Scholar
[14] Wolery, T. J. and Daveler, S. A., “EQ6 - a computer program for reaction path modeling of aqueous geochemical systems: User's guide and documentation,” Lawrence Livermore National Laboratory, Livermore, California UC-70, 30/03/89 1989.Google Scholar
[15] Helgeson, H.C., “Thermodynamics of hydrothermal systems at elevated temperatures and pressures,” American Journal of Science, vol.267, pp.729–804, 1969.Google Scholar
[16] Poinssot, C., Toulhoat, P., and Goffd, B., “Interaction between a nuclear glass and clayey backfill materials under thermal gradient.,” Applied Geochemistry, accepted for publication.. Google Scholar
[17] Grambow, B., “A general rate equation for nuclear waste glass corrosion in Scientific basis for Nuclear Waste Management VIII, edited by Jantzen, C.M., Stone, J.A., and Ewing, R.C. (Elsevier Science Publishers, 1985) pp. 15–28.Google Scholar