Long Term Diffusion (LTD) Introduction

HYRL University of Helsinki, Dept of Chemistry - Laboratory of Radiochemistry, Finland
JAEA Japan Atomic Energy Agency, Japan
NRI National Institute Rez, Czech Republic
Nagra National Cooperative for the Disposal of Radioactive Waste
AIST National Instutute of Advanced Industrial Science and Technology
(Geological Survey of Japan)

This is a long-term, large-scale experiment which aims to further examine in-situ matrix diffusion and pore space visualisation at the Grimsel Test Site.

Matrix diffusion is......
The process by which solute, flowing in distinct fractures, penetrates into the surrounding rock and is transported, through a connected system of pores or micro-fractures, into the rock matrix.

The importance of matrix diffusion in the context of a radioactive waste repository is that it provides a mechanism for greatly enlarging the area of rock surface in contact with advecting radionuclides, from that of the flow path surfaces (and infills), to a much larger portion of the bulk rock and increases the global pore volume which can retard radionuclides

This is especially crucial when considering the calculated contribution to dose from weakly- and non-sorbing radionuclides such as ¹²⁹I and ¹⁴C and offers a more realistic dose reduction scenario than many of the exotic engineering solutions currently being proposed for the engineered barrier.