Title:
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An investigation into the heterogeneity of vein type uranium ore deposits : implications for nuclear forensic analysis
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THE International Atomic Energy Agency (IAEA) has recorded 2734
incidents of illegally trafficked nuclear materials since 1995. Questions
including What is the material? Where were the materials
sourced? and Why is the material being trafficked? need to be answered
in order to close trafficking routes and stop these materials falling into the
wrong hands. To do this, the material is analysed by a suite of analytical
techniques in order to form a characteristic nuclear forensic fingerprint. This
can then be compared to a nuclear forensic database containing representative
samples of known origin to find a match.
One of the key limitations of these databases is within mine heterogeneity.
Representative sample databases only contain few and often small physical
samples which are assumed to accurately represent a large geographical
area. An increasing number of studies have determined significant within
mine variation in signatures, this in some cases is larger than the variation
between two different sites.
This study aims to test the heterogeneity of a set of nuclear forensic signatures
within vein type uranium deposits at a selection of different geographical
scales. Sample sets from South West England and the Berias region
of Portugal are analysed to deduce if small database samples are actually
representative of large mining areas. It is also tested if these signatures are
modified by the first stage of the uranium processing route; acid leaching.
The nuclear forensic tools focussed on in this study are uranium and gangue
mineralogy, major and minor elemental analysis, REE patterns and uranium
isotope ratios.
In summary, significant heterogeneity was found at all geographical scales
tested. This indicates that databases need to be regularly updated as a
deposit is extracted, and should include a moving average and range in signatures
per site rather than a single physical sample. Although significant
heterogeneity was found, in most cases, by using a selection of signatures, individual
mines could be separated. It was concluded that much of the within
mine variation observed in the ore sampled could be transferred through acid
leaching during processing. In most cases elemental impurity patterns were
not significantly effected by acid leaching, but uranium isotope signatures
were variably affected and could not be traced back to their parent ore.
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