Abstract
Trace-level plutonium in the environment often comprises local and global contributions, and is usually anthropogenic in origin. Here, we report estimates of local and global contributions to trace-level plutonium in soil from a former, fast-breeder reactor site. The measured 240Pu/239Pu ratio is anomalously low, as per the reduced 240Pu yield expected in plutonium bred with fast neutrons. Anomalies in plutonium concentration and isotopic ratio suggest forensic insight into specific activities on site, such as clean-up or structural change. Local and global 239Pu contributions on-site are estimated at (34 ± 1)% and (66 ± 3)%, respectively, with mass concentrations of (183 ± 6) fg g−1 and (362 ± 13) fg g−1. The latter is consistent with levels at undisturbed and distant sites, (384 ± 44) fg g−1, where no local contribution is expected. The 240Pu/239Pu ratio for site-derived material is estimated at 0.05 ± 0.04. Our study demonstrates the multi-faceted potential of trace plutonium assay to inform clean-up strategies of fast breeder legacies.
Highlights
Trace-level plutonium in the environment often comprises local and global contributions, and is usually anthropogenic in origin
The motivation for this study is to determine whether the local contribution to trace plutonium abundance on a fast breeder site might be discerned from the global contribution, to inform the extent to which cleanup of the local component might be necessary
The novelty in our study is that we apply accelerator mass spectrometry (AMS) to soil samples from a fast breeder site, we separate local and global contributions, where the isotopic inventory of the local component is consistent with that derived from a fast breeder, we identify the potential for forensic analysis of two-specific, inventory-based anomalies on-site and we estimate the 240Pu/239Pu ratio for local material, self consistently, which is observed to be consistent with material of breeder origin
Summary
Trace-level plutonium in the environment often comprises local and global contributions, and is usually anthropogenic in origin. We report estimates of local and global contributions to trace-level plutonium in soil from a former, fast-breeder reactor site. The depth-resolved assessment of plutonium residues in Lake Ontario sediments followed, yielding a 240Pu/239Pu ratio[5,6] consistent with Krey et al Subsequently, Buesseler et al.[7] reported measurements of a dated coral record from the North Pacific of 239Pu mass (~55 fg g−1) and 240/239Pu ratio (>0.2), the latter reflecting the predominance of fallout in this environment, in agreement with the prior art[3]. Given this context, the motivation for this study is to determine whether the local contribution to trace plutonium abundance on a fast breeder site might be discerned from the global contribution, to inform the extent to which cleanup of the local component might be necessary
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