Spatially resolved micro-X-ray fluorescence and micro-X-ray absorption fine structure study of a fractured granite bore core following a radiotracer experiment

Abstract

Spatially resolved X-ray absorption and fluorescence investigation with a micrometer-scale resolution on actinide-containing samples provide information necessary for safety assessment of nuclear waste disposal. In this paper one example of such an experiment is presented. This example entails neptunium speciation in a fractured granite bore core from the Swedish Äspö Hard Rock Laboratory following a radiotracer experiment using µ-XAFS and µ-XRF. In order to probe micro-volumes below the surface in the granite samples and thereby avoid potential changes in the Np speciation during cutting of the bore core, a confocal irradiation-detection geometry is employed. µ-XAFS results for a selected granite bore core cross section with~3 nmol Np/g reveal that Np, originally introduced as Np(V) in the tracer cocktail, is present in the granite in its reduced Np(IV) form. The Np(IV) is often present as particles, tens of µm in size. Elemental distribution maps show the tracer Np to be located in fissures and permeable channels not larger than 100 µm. The Np distribution appears often correlated with Zn also present in some fissures. We observe small granite fissures containing Fe (presumably Fe(II)), where we do not detect any Np. It is feasible that inflowing Np(V) has a shorter residence time in large fractures, while in the smaller fissures migration is slower, leading to longer residence times, i.e., reaction times, where it is reduced to less soluble Np(IV) and becomes thereby immobilized.

Atomic spectrometry update–X-ray fluorescence spectrometry

“…The Kb 2,5 /Kb 1,3 ratio was selected as the analytical signal and the authors claimed that in igneous rocks where FeO/Fe 2 O 3total > 0.25, the XRF determination of the FeO content could be performed at an accuracy comparable with that of wet chemical analysis. A geochemical study with a difference was undertaken by Denecke et al 184 who used m-SRXRF and m-XAFS to evaluate the speciation of neptunium in a fractured granite bore core from the Swedish Aspo Hard Rock Laboratory. A confocal irradiation-detection geometry was used to demonstrate that the Np V tracer was reduced to Np IV and was located in fissures and permeable channels often correlated with the presence of zinc.…”

Recent advances in analysis of trace elements in environmental samples by X-ray based techniques (IUPAC Technical Report)

“…[30,[152][153][154]. An example of μ-XRF and μ-XAS speciation investigation of neptunium in fractured granite follows, and is intended to demonstrate the utility of the techniques [155][156][157].…”

Systems considerations for Resonance-Ionization Mass Spectroscopy in the application of Nuclear Forensic Analysis by Ray Mariella Jr

“…µ-X-ray-fluorescence 35,36 prescreening of multi-gram samples after a detonation could identify the µm-scale spots where the device components condensed, which would enable the spatially-accurate analytical capabilities of RIMS to extract important information, such as U and Pu isotopic composition. Although rapid µ-XRF, today, employs synchrotron radiation, there is every reason to believe that the technology of table-top Xray sources 37 will continue to advance so that a fieldable system may be produced, within the next decade.…”

“…Recent examples of X-ray microprobe analysis for actinides are shown, below. e.g., 2-D elemental maps from Denecke 35 ref 38 Dahlgaard 2005 RIMS analysis of Pu, U, from Erdmann and Trautmann 39 , shows the spatial resolving power of RIMS, in their study of radioactive particles, previously mapped by others 38,40,41 , from the Thule, Greenland, nuclear incident: As a result of this accident, fissile material (enriched uranium and plutonium) contained in the bombs and depleted uranium from the casing was released and traces of this material can still be found in the environment, for example in sediment samples.…”