Radionuclide transport in brackish water through chalk fractures

Emily L Tran; Nadya Teutsch; Ofra Klein-BenDavid; Annie B Kersting; Mavrik Zavrin; Noam Weisbrod

doi:10.1016/j.watres.2019.114886

Radionuclide transport in brackish water through chalk fractures

Water Res. 2019 Oct 15:163:114886. doi: 10.1016/j.watres.2019.114886. Epub 2019 Jul 18.

Authors

Emily L Tran¹, Nadya Teutsch², Ofra Klein-BenDavid³, Annie B Kersting⁴, Mavrik Zavrin⁴, Noam Weisbrod⁵

Affiliations

¹ The Zuckerburg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research, Ben Gurion University of the Negev, Midreshet Ben Gurion, 8499000, Israel.
² Geological Survey of Israel, 32 Yeshayahu Leibowitz St., Jerusalem, 9371234, Israel.
³ Nuclear Research Center of the Negev, Negev, P.O. Box 9001, Beersheva, 8419001, Israel; Geological and Environmental Science Department, Ben Gurion University of the Negev, Beersheva, 8410501, Israel.
⁴ Lawrence Livermore National Laboratory, Livermore, CA, 94550, USA.
⁵ The Zuckerburg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research, Ben Gurion University of the Negev, Midreshet Ben Gurion, 8499000, Israel. Electronic address: weisbrod@bgu.ac.il.

PMID: 31357014
DOI: 10.1016/j.watres.2019.114886

Abstract

Mobility of radionuclides originating from geological repositories in the subsurface has been shown to be facilitated by clay colloids. In brackish water, however, colloids may flocculate and act to immobilize radionuclides associated with them. Furthermore, little research has been conducted on radionuclide interactions with carbonate rocks. Here, the impact of bentonite colloid presence on the transport of a cocktail of U(VI), Cs, Ce and Re through fractured chalk was investigated. Flow-through experiments were conducted with and without bentonite colloids, present as a mixture of bentonite and Ni-altered montmorillonite colloids. Ce was used as an analogue for reactive actinides in the (III) and (VI) redox states, and Re was considered an analogue for Tc. Filtered brackish groundwater (ionic strength = 170 mM) pumped from a fractured chalk aquitard in the northern Negev Desert of Israel, was used as a solution matrix. Rhenium transport was identical to that of the conservative tracer, uranine. The sorption coefficient (K_d) of U(VI), Cs and Re, calculated from batch experiments with crushed chalk, proved to be a good predictor of mass recovery in transport experiments conducted without bentonite colloids. A meaningful K_d value for Ce could not be calculated due to its precipitation as a Ce-carbonate colloids. Transport of both U(VI) and Cs was indifferent to the presence of bentonite colloids. However, the addition of bentonite in the injection solution effectively immobilized Ce, decreasing its recovery from 17-41% to 0.8-1.4%. This indicates that radionuclides which interact with clay colloids that undergo flocculation and deposition may effectively be immobilized in brackish aquifers. The results of this study have implications for the prediction of potential mobility of radionuclides in safety assessments for future geological repositories to be located in fractured carbonate rocks in general and in brackish groundwater in particular.

Keywords: Bentonite colloids; Carbonate rock; Fracture flow; Ionic strength; Radionuclides.

MeSH terms

Calcium Carbonate*
Colloids
Israel
Radioisotopes
Saline Waters
Water Pollutants, Radioactive*

Substances

Colloids
Radioisotopes
Water Pollutants, Radioactive
Calcium Carbonate