Characteristics of uranium uptake of Boda Claystone Formation as the candidate host rock of high level radioactive waste repository in Hungary

Abstract

In Hungary two geological sites of the Boda Claystone Formation (BCF) located in the W-Mecsek Mountains (South Hungary) have been selected for the study of potential host rocks for high level radioactive waste (HLW), Gorica (G) Block and W-Mecsek Anticline (WMA) Block. The aim of the study was to obtain information on the uranium uptake characteristics of both sites. Our results revealed that in the sample, taken from WMA Block, where dolomites have ankerite rims and U-bearing rings, newly formed FeOOH precipitations were observed, which partly replaced the ankerite at near neutral pH (6.8). UO 2 2+ ions were adsorbed easily due to the enhanced specific surface area and high adsorption capacity of FeOOH formed from the dissolution of ankerite. The oxidation of Fe 2+ leads to the formation of FeOOH parallel to partial reduction of U 6+ to U 4+ . 75% of uranium was taken up by clay minerals and 25% by FeOOH although the ankerite concentration is as low as 6% in WMA Block of BCF. In G Block, the argillaceous matrix was found to be mainly responsible for the UO 2 2+ uptake. The study demonstrated that the U retention capacity of different BCF locations was significantly influenced by the mineralogy of these sites.

Microscale analysis of metal uptake by argillaceous rocks using positive matrix factorization of microscopic X-ray fluorescence elemental maps

“…For D11-U, Factor 4 contained uranium at the highest concentration, 400 µg/g, accompanied with Ca, Mn and Fe as main elements. This finding is in accordance with the ring appearance and SEM/EDX measurements [40], that the mineral phase responsible for the strong uranium uptake was the ankerite rims surrounding dolomite grains. The presence of the ankerite rims could also be verified using micro-XRD (Figure 10c).…”

A modified version of Archie’s law to estimate effective diffusion coefficients of radionuclides in argillaceous rocks and its application in safety analysis studies

“…(Baeyens and Bradbury, 2004). b In addition to the tabulated data: Analcime 10 wt%; Hematite 6 wt% (Breitner et al, 2015, Table 1). c Marques , no information on uncertainty given.…”

Predicting the uptake of Cs, Co, Ni, Eu, Th and U on argillaceous rocks using sorption models for illite

“…These two areas have been selected as most appropriate for deep geological disposal. The sample used in this study was taken from the borehole Ib-4 located in the Gorica block at a depth of 540 m (Breitner et al, 2015).…”