Uranyl binding to humic acid under conditions relevant to cementitious geological disposal of radioactive wastes

A. Stockdale, N. D. Bryan
  • Mineralogical Magazine, December 2012, Mineralogical Society
  • DOI: 10.1180/minmag.2012.076.8.52

Effect of organic carbon on mobility of uranium in a geological disposal facility: preliminary study

What is it about?

It is likely that radioactive wastes will be placed in an underground geological disposal facility. Such a facility will be dry during its operational phase but will likely become saturated with groundwater after closure. Extensive use of concrete will form part of the engineering of the facility. Once re-saturated with groundwater this will create a highly alkali (high pH) environment. Dissolved organic carbon is the brown discolouration you see in streams draining peat moorland and is the product of the decay of once living plants and organisms (the tannic acid that makes your black tea is another example). This organic carbon is present in all groundwaters and is an important chemical in the mobility of dissolved metals - including radioactive elements. This study reports experimental results showing the interactions of an oxidised uranium form with organic matter.

Why is it important?

Once closed a geological disposal facility will be saturated with groundwater and the interaction with concrete will create a high pH environment. We therefore need to have robust data on the interaction between waste forms and the surrounding water. This study reveals that the higher the pH the lower the interaction of organic carbon with oxidised uranium. This mean that the conditions created by groundwater flowing through concrete will not significantly increase the changing of uranium waste from solid to dissolved (and mobile) forms.

Perspectives

Anthony Stockdale (Author)

This study also showed that the presence of other dissolved metals may not have the expected effect of decreasing the amount that can be bound to organic carbon. With this in mind, it may be better to take a cautious approach when doing model predictions for Safety Cases by assuming no effects from other metal ions.

The following have contributed to this page: Anthony Stockdale