Interaction between spent fuel components and carbonate rocks.

Deep geological repository is considered the internationally accepted method for spent fuel (SF) disposal. In countries where salt, clay, tuff and granite are unavailable at geologically suitable area, other rock types may come into consideration. In Israel, carbonate rocks make up a significant portion of the surface and subsurface lithologies, thus, low permeability carbonates were evaluated as possible host rocks for a repository, and for an interim storage facility. Sorption and retardation capacity of SF components to low permeability carbonate rocks were evaluated using their chemical simulants. Strontium and Cs represent components that may leach during interim storage, while U and Ce (as a simulant for redox-active actinides) represent components that may leach under repository conditions. Rocks from the Upper Cretaceous Mount Scopus Group were sampled from boreholes at the Yamin Plateau, Israel. Single point batch experiments were conducted with synthetic rainwater spiked with tracers and interacted with five rock types of various particle sizes at 25 °C. Results were evaluated using the LeachXS™-ORCHESTRA geochemical speciation and data management program. Cerium removal was found to be related to the HCO3- concentration in solution, where Ce precipitated as Ce2(CO3)3·XH2O and as an amorphous carbonate phase. Removal of Cs and Sr was controlled by clays. No Sr co-precipitation as carbonate species was observed. Uranium was removed mainly by sorption onto solid organic matter, whereas clays had no significant role in U sorption. Iron-(hydr) oxides may have also played a role in U removal. Calculated partition coefficients for U, Cs, and Sr were in the order of 101-102 mL/g. Grain size had no significant effect on the retention capacity of the studied rocks due to similar effective surface area. The current study indicates that a repository or an interim storage facility within carbonate rocks, would provide only partial isolation of radionuclides from the environment, hence, additional engineered barriers may be required.

Quantitative analysis of trace element concentrations in some gem-quality diamonds.

The geochemical signature of diamond-forming fluids can be used to unravel diamond-forming processes and is of potential use in the detection of so-called 'conflict' diamonds. While fluid-rich fibrous diamonds can be analyzed by a variety of techniques, very few data have been published for fluid-poor, gem-quality diamonds because of their very low impurity levels. Here we present a new ICPMS-based (ICPMS: inductively coupled plasma mass spectrometry) method for the analysis of trace element concentrations within fluid-poor, gem-quality diamonds. The method employs a closed-system laser ablation cell. Diamonds are ablated and the products trapped for later pre-concentration into solutions that are analyzed by sector-field ICPMS. We show that our limits of quantification for a wide range of elements are at the sub-pg to low pg level. The method is applied to a suite of 10 diamonds from the Cullinan Mine (previously known as Premier), South Africa, along with other diamonds from Siberia (Mir and Udachnaya) and Venezuela. The concentrations of a wide range of elements for all the samples (expressed by weight in the solid) are very low, with rare earth elements along with Y, Nb, Cs ranging from 0.01 to 2 ppb. Large ion lithophile elements (LILE) such as Rb and Ba vary from 1 to 30 ppb. Ti ranges from ppb levels up to 2 ppm. From the combined, currently small data set we observe two kinds of diamond-forming fluids within gem diamonds. One group has enrichments in LILE over Nb, whereas a second group has normalized LILE abundances more similar to those of Nb. These two groups bear some similarity to different groups of fluid-rich diamonds, providing some supporting evidence of a link between the parental fluids for both fluid-inclusion-rich and gem diamonds.