SKB GWFTS task force; Predictive modeling of a matrix diffusion experiment in gneiss at ONKALO (Finland)

Soler, J. M.*; Lfgren, M.*; Nilsson, K.*; Lanyon, G. W.*; Gylling, B.*; Vidstrand, P.*; Neretnieks, I.*; Moreno, L.*; Liu, L.*; Meng, S.*; Svensson, U.*; Trinchero, P.*; Iraola, A.*; Ebrahimi, K.*; Deissmann, G.*; ha, J.*; Hokr, M.*; Vetenk, A.*; Voplka, D.*; Gvodik, L.*; Polk, M.*; Trpkoov, D.*; Havlov, V.*; Park, D.-K.*; Ji, S.-H.*; Tachi, Yukio  ; Ito, Tsuyoshi

The GWFTS Task Force is an international forum in the area of modeling of groundwater flow and solute transport in fractured rock. The WPDE experiments are matrix diffusion experiments in gneiss performed at the ONKALO underground facility in Finland. Synthetic groundwater containing several conservative and sorbing radiotracers was injected along a borehole interval. The objective of Task 9A of Task Force was the predictive modeling of the tracer breakthrough curves from the WPDE experiments. Several teams, using different modeling approaches, participated in this exercise. An important conclusion from this exercise is that the modeling results were very sensitive to the magnitude of dispersion in the borehole opening, which is related to the flow of water. Focusing on the tails of the breakthrough curves, which are more directly related to matrix diffusion and sorption, the results from the different teams were more comparable.