Diffusion of ions in compacted bentonite

Book · Fri Dec 31 04:00:00 EST 1993

OSTI ID:100796

Madsen, F T; Kahr, G ^[1]

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1. Swiss Federal Inst. of Tech., Zurich (Switzerland)

In Switzerland compacted bentonite is proposed to surround special steel containers holding high-level nuclear fuel waste in a repository 500 to 1,500 meters below ground level. The diffusion coefficients of K{sup +}, Cs{sup +}, Sr{sup 2+}, Fe{sup 2+}, Fe{sup 3+}, Cl{sup {minus}}, and I{sup {minus}} were determined as non-stationary, apparent diffusion coefficients under dynamic conditions in free-standing compacted specimens of Na-bentonite MX-80 and Ca-bentonite Montigel at ambient temperature. For dry densities between 1,300 kg/m{sup 3} and 2,100 kg/m{sup 3} the apparent diffusion coefficients depend primarily on the water content of the bentonite specimens. An increase in water content from 7% to 25% is followed by an increase of the coefficient by a factor of about 100. For water contents between 20 and 25% the following apparent diffusion coefficients were determined: K{sup +}=5{times}10{sup {minus}11} m{sup 2}/s, Cs{sup +}=6{times}10{sup {minus}12}, Sr{sup 2+}=3{times}10{sup {minus}11}, Fe{sup 2+}, Fe{sup 3+}=4{times}10{sup {minus}11}, Cl{sup {minus}}=1{times}10{sup {minus}10}, and I{sup {minus}}=1{times}10{sup {minus}10} m{sup 2}/s. The diffusion coefficients of Fe{sup 2+}- and I{sup {minus}}-ions were also determined using a diffusion apparatus. For dry densities of ca. 1,600 kg/m{sup 3} and a water content of 25% the apparent diffusion coefficients of Fe{sup 2+} at ambient temperature are about 8{times}10{sup {minus}13} to 7{times}10{sup {minus}12} m{sup 2}/s. An exchange of free cations in the bentonites had no effect on the apparent diffusion coefficients of the Fe{sup 2+}-ions. For dry densities of around 1,700 kg/m{sup 3} and water contents of around 20% the apparent diffusion coefficients of iodide-ions measured in the diffusion apparatus are 2--4{times}10{sup {minus}11} m{sup 2}/s at ambient temperature. At 150 C the apparent diffusion coefficients of iodide ions measured in the diffusion apparatus are 3--5{times}10{sup {minus}11} m{sup 2}/s.

• OSTI ID: 100796
• Report Number(s): CONF-930906--; ISBN 0-7918-0691-X
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
BENTONITE
CESIUM COMPOUNDS
CHLORIDES
DIFFUSION
EXPERIMENTAL DATA
HIGH-LEVEL RADIOACTIVE WASTES
IODIDES
ION EXCHANGE
IRON COMPOUNDS
PERMEABILITY
POTASSIUM COMPOUNDS
RADIOACTIVE WASTE DISPOSAL
STRONTIUM COMPOUNDS
SWITZERLAND
UNDERGROUND DISPOSAL
WATER SATURATION