### Abstract

This report contains an experimental study of diffusion
in the water filled pores of rock samples. The samples
studied are rapakivi granite from Loviisa, southern
Finland. The drill-core sample was sectioned
perpendicularly with diamond saw and three cylinder
formed samples were obtained. The nominal thicknesses
(heights of the cylinders) are 2, 4 and 6 cm. For the
diffusion measurement the sample holders were pressed
between two chambers. One of the chambers was filled with
0.0044 molar sodium chloride solution spiked with
tracers. Another chamber was filled with inactive
solution. Tritium (HTO) considered to be water equivalent
tracer and anionic 36Cl were used as tracers.
The data has been modelled by assuming that the porosity
can be divided in two categories: through-transport and
dead-end porosity. The rock-capacity factor a is also
divided in the same ratio in those two categories.
The numeric computation software MATLAB was used to
perform the fittings. Simplex-algorithm was used to
minimize the sum of squares of the difference between the
measured and calculated values.
The effective diffusion coefficient De is the strongest
fitting parameter and a decreasing tendency is seen, when
the thickness of the sample increases. The values for
36Cl are smaller than for tritium both in the case of De
and a. The results suggest that a+ is decreasing as a
function of thickness. As to the length of the dead-ended
pores lde, no clear tendency is seen. Neither the
fraction nor the length of the dead-ended pores show
clear differences between 3H and 36Cl.

Original language | English |
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Place of Publication | Espoo |

Publisher | VTT Technical Research Centre of Finland |

Number of pages | 34 |

ISBN (Print) | 951-38-4490-0 |

Publication status | Published - 1994 |

MoE publication type | Not Eligible |

### Publication series

Series | VTT Tiedotteita - Meddelanden - Research Notes |
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Number | 1556 |

ISSN | 1235-0605 |

### Keywords

- porous materials
- granites
- rock-fluid interactions
- diffusion
- radionuclide migration
- solutions
- modelling

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## Cite this

Lehikoinen, J., Uusheimo, K., & Valkiainen, M. (1994).

*The effect of thickness in the through-diffusion experiment*. VTT Technical Research Centre of Finland. VTT Tiedotteita - Meddelanden - Research Notes, No. 1556