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Modeling of an in-situ diffusion experiment in granite at the Grimsel Test Site

Published online by Cambridge University Press:  30 June 2014

Josep M. Soler ,
Jiri Landa ,
Vaclava Havlova ,
Yukio Tachi ,
Takanori Ebina ,
Paul Sardini ,
Marja Siitari-Kauppi  and
Andrew J. Martin
Josep M. Soler
Affiliation:
IDAEA-CSIC, Barcelona, Catalonia, Spain.
Jiri Landa
Affiliation:
UJV-Rez, Husinec-Rez, Czech Republic.
Vaclava Havlova
Affiliation:
UJV-Rez, Husinec-Rez, Czech Republic.
Yukio Tachi
Affiliation:
JAEA, Tokai, Japan.
Takanori Ebina
Affiliation:
JAEA, Tokai, Japan.
Paul Sardini
Affiliation:
University of Poitiers, France.
Marja Siitari-Kauppi
Affiliation:
University of Helsinki, Finland.
Andrew J. Martin
Affiliation:
NAGRA, Wettingen, Switzerland.
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Abstract

Matrix diffusion is a key process for radionuclide retention in crystalline rocks. Within the LTD project (Long-Term Diffusion), an in-situ diffusion experiment in unaltered non-fractured granite was performed at the Grimsel Test Site (www.grimsel.com, Switzerland). The tracers included 3H as HTO, 22Na+, 134Cs+ and 131I- with stable I- as carrier.

The dataset (except for 131I- because of complete decay) was analyzed with different diffusion-sorption models by different teams (NAGRA / IDAEA-CSIC, UJV-Rez, JAEA, Univ. Poitiers) using different codes, with the goal of obtaining effective diffusion coefficients (De) and porosity (ϕ) or rock capacity (α) values. A Borehole Disturbed Zone (BDZ), which was observed in the rock profile data for 22Na+ and 134Cs+, had to be taken into account to fit the experimental observations. The extension of the BDZ (1-2 mm) was about the same magnitude as the mean grain size of the quartz and feldspar grains.

De and α values for the different tracers in the BDZ are larger than the respective values in the bulk rock. Capacity factors in the bulk rock are largest for Cs+ (strong sorption) and smallest for 3H (no sorption). However, 3H seems to display large α values in the BDZ. This phenomenon will be investigated in more detail in a second test starting in 2013.

Keywords

diffusiongeologictransportation
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1665: Symposium NW – Scientific Basis for Nuclear Waste Management XXXVII , 2014 , pp. 85 - 91
Copyright
Copyright © Materials Research Society 2014 

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References

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