Characterisation of HTO diffusion properties by an in situ tracer experiment in Opalinus clay at Mont Terri

Exploring diffusion and sorption processes at the Mont Terri rock laboratory (Switzerland): lessons learned from 20 years of field research

“…The general concept of most field diffusion experiments at the Mont Terri rock laboratory is based on the layout used in the first DI experiment (Palut et al 2003), which was a variation of the decreasing source concentration method used in laboratory column experiments (Rowe et al 1988;Shackelford 1991). The same general principle was followed in earlier in situ large-scale experiments in the Boom Clay Formation in Belgium (Put et al 1993;De Cannière et al 1996;Aertsens et al 2013).…”

“…Conceptually, the models for the earlier experiments considered single tracer diffusion only (e.g. Palut et al 2003;Tevissen et al 2004;Van Loon et al 2004b;Yllera et al 2004;Wersin et al 2004;Soler et al 2008;Wersin et al 2008). That is, transport of a tracer (neutral, anion and/or cation) was assumed to be independent of that of any other solute.…”

“…Palut et al 2003;Van Loon et al 2004b;Wersin et al 2004;Yllera et al Editorial handling: P. Bossart and A. G. Milnes. This is paper #20 of the Mont Terri Special Issue of the Swiss Journal of Geosciences (see Bossart et al 2017, Wersin et al 2008;Gimmi et al 2014). A main interest was the comparison of results with those from laboratory experiments performed on small samples (in the order of a few cm) of the same material.…”

“…Representativeness was also an issue for the in situ tests. One of the field studies (Palut et al 2003) suggested the existence of a borehole disturbed zone (BdZ), but all the other studies (Van Loon et al 2004b;Wersin et al 2004;Soler et al 2008;Wersin et al 2008;Gimmi et al 2014) did not report such an effect. Even though some differences in transport and retention properties were observed, the laboratory values obtained in smaller-scale diffusion experiments could generally be confirmed.…”

“…6 in Bossart et al 2017) for tritiated water HTO, I -and 22 Na ? (Palut et al 2003;Gómez-Hernández and Guardiola-Albert 2004;Tevissen et al 2004;Van Loon et al 2004b;Wersin et al 2008;Soler et al 2008). Most of the field experiments in Opalinus Clay used relatively long injection intervals (*1 m) and were thus dominated by diffusion parallel to the bedding plane of the clay formation.…”