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Processes Related to the Water Uptake by EUROBITUM Bituminised Radioactive Waste: Theoretical Considerations and First Experimental Results

Published online by Cambridge University Press:  01 February 2011

An Mariën ,
Steven Smets ,
Xiangling Li  and
Elie Valcke
An Mariën
Affiliation:
W&D Expert Group, SCK•CEN, Boeretang 200, 2400 Mol, Belgium
Steven Smets
Affiliation:
W&D Expert Group, SCK•CEN, Boeretang 200, 2400 Mol, Belgium
Xiangling Li
Affiliation:
Euridice Eig, SCK•CEN, Boeretang 200, 2400 Mol, Belgium
Elie Valcke
Affiliation:
W&D Expert Group, SCK•CEN, Boeretang 200, 2400 Mol, Belgium
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Abstract

According to the present Belgian radioactive waste management program, Eurobitum bituminised radioactive waste will be disposed of in a geologically stable underground clay formation. The Boom Clay is studied as a potential host formation because of its low diffusion and high retention properties towards radionuclides. The presence of the radioactive waste should not disturb these properties. Due to the presence of hygroscopic salts (25 to 30 weight% NaNO3), Eurobitum will take up pore water which will result in a swelling and possibly in a very high swelling pressure. First scoping calculations suggest that the swelling pressure exerted to Boom Clay should remain below 7 to 8 MPa to avoid the formation of fractures. If the bitumen in EUROBITUM behaved like a perfect semi-permeable membrane and if no swelling were allowed after the dissolution of NaNO3 into a saturated solution of 10.8 M, osmotic pressures of ∼50 MPa could be attained. To better understand the interaction between the swelling Eurobitum and the host formation, coupled hydro-chemical-mechanical constitutive laws for Eurobitum have to be developed. To this purpose, water uptake tests under constant volume (‘confined’) and constant stress (‘semi-confined’) conditions are being performed. After ∼2 years of hydration of small inactive Eurobitum samples in constant volume conditions, the swelling pressure has raised to ∼12 MPa. The volume of samples that can swell against counter pressures of 2.2, 3.3, or 4.4 MPa (constant stress tests) increased with ∼5 to 11 volume%, independently of the applied counter pressure. Approximately 10 weight% of the initial NaNO3 content has been leached.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1107: Scientific Basis for Nuclear Waste Management XXXI , 2008 , 151
Copyright
Copyright © Materials Research Society 2008

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