Abstract
Current research on radionuclide disposal is mostly conducted in granite, clay, saltstone, or volcanic tuff formations. These rock types are not always available to host a geological repository in every nuclear waste-generating country, but carbonate rocks may serve as a potential alternative. To assess their feasibility, a forced gradient cross-borehole tracer experiment was conducted in a saturated fractured chalk formation. The mobility of stable Sr and Cs (as analogs for their radioactive counterparts), Ce (an actinide analog), Re (a Tc analog), bentonite particles, and fluorescent dye tracers through the flow path was analyzed. The migration of each of these radionuclide analogs (RAs) was shown to be dependent upon their chemical speciation in solution, their interactions with bentonite, and their sorption potential to the chalk rock matrix. The brackish groundwater resulted in flocculation and immobilization of most particulate RAs. Nevertheless, the high permeability of the fracture system allowed for fast overall transport times of all aqueous RAs investigated. This study suggests that the geochemical properties of carbonate rocks may provide suitable conditions for certain types of radionuclide storage (in particular, brackish, high-porosity, and low-permeability chalks). Nevertheless, careful consideration should be given to high-permeability fracture networks that may result in high radionuclide mobility.
Highlights
Despite continued reliance on nuclear energy worldwide, a permanent disposal solution for most spent nuclear fuel produced globally has yet to be determined
The present study investigates the potential mobility of the radionuclide analogs (RAs) Ce, Re, Sr, and Cs through a chalk rock fracture network by use of a forced-gradient field-scale tracer experiment
In the presence of dissolved carbonates, mixed hydroxycarbonate solids analogous to those of Ce may form through the precipitation of actinides in the (III) and (IV) redox states as An(OH)(CO3)(s) and An(OH)2m(CO3)n(s), respectively.[7]
Summary
Despite continued reliance on nuclear energy worldwide, a permanent disposal solution for most spent nuclear fuel produced globally has yet to be determined. Groundwater rich in dissolved bicarbonate, found within carbonate rocks, has been shown to influence the speciation and mobility of soluble radionuclides such as U5,6 and other actinides, resulting in stable aqueous complexes such as the triscarbonato species AnO2(CO3)3m−6.7 Groundwater of high ionic strength and dissolved carbonate concentrations, provides unfavorable sorption conditions,[8,9] leading to greater potential mobility of dissolved radionuclides. Field-scale transport studies such as this provide the basis for the safety assessment of geological nuclear repositories intended to house spent fuel
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
