Radionuclide transport in fractured chalk under abrupt changes in salinity

Tuvia Turkeltaub; Noam Weisbrod; Mavrik Zavarin; Elliot Chang; Annie B Kersting; Nadya Teutsch; Sari Roded; Emily L Tran; Yehonatan Geller; Yarden Gerera; Ofra Klein-BenDavid

doi:10.1016/j.scitotenv.2023.168636

Radionuclide transport in fractured chalk under abrupt changes in salinity

Sci Total Environ. 2024 Feb 20:912:168636. doi: 10.1016/j.scitotenv.2023.168636. Epub 2023 Nov 18.

Authors

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. Electronic address: tuviat@bgu.ac.il.
² The Zuckerburg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research, Ben Gurion University of the Negev, Midreshet Ben Gurion 8499000, Israel.
³ Glenn T. Seaborg Institute, Lawrence Livermore National Laboratory, PO Box 808, Livermore, CA 94550, USA.
⁴ Geological Survey of Israel, 32 Yeshayahu Leibowitz St., Jerusalem 9371234, Israel.
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; Now at Shamir Research Institute, University of Haifa, Qatsrin 1290000, Israel.
⁶ Geological and Environmental Science Department, Ben Gurion University of the Negev, Beersheva 8410501, Israel.
⁷ 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.

PMID: 37981163
DOI: 10.1016/j.scitotenv.2023.168636

Abstract

Internationally, it has been agreed that geologic repositories for spent fuel and radioactive waste are considered the internationally agreed upon solution for intermediate and long-term disposal. In countries where traditional nuclear waste repository host rocks (e.g., clay, salt, granite) are not available, other low permeability lithologies must be studied. Here, chalk is considered to determine its viability for disposal. Despite chalk's low bulk permeability, it may contain fracture networks that can facilitate radionuclide transport. In arid areas, groundwater salinity may change seasonally due to the mixing between brackish groundwater and fresh meteoric water. Such salinity changes may impact the radionuclides' mobility. In this study, radioactive U(VI) and radionuclide simulant tracers (Sr, Ce and Re) were injected into a naturally fractured chalk core. The mobility of tracers was investigated under abrupt salinity variations. Two solutions were used: a low ionic strength (IS) artificial rainwater (ARW; IS ∼0.002) and a high IS artificial groundwater (AGW; IS ∼0.2). During the experiments, the tracers were added to ARW, then the carrier was changed to AGW, and vice versa. Ce was mobile only in colloidal form, while Re was transported as a conservative tracer. Both Re and Ce demonstrated no change in mobility due to salinity changes. In contrast, U and Sr showed increased mobility when AGW was introduced and decreased mobility when ARW was introduced into the core. These experimental results, supported by reactive transport modeling, suggest that saline groundwater solutions promote U and Sr release via ion-exchange and enhance their migration in fractured chalk. The study emphasizes the impact of salinity variations near spent fuel repositories and their possible impact on radionuclide mobility.

Keywords: Carbonate rocks; Cerium; Ionic strength; Radionuclides; Reactive transport; Strontium; Uranium.