Local and global trace plutonium contributions in fast breeder legacy soils

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 Pu-240/Pu-239 ratio is anomalously low, as per the reduced Pu-240 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 Pu-239 contributions on-site are estimated at (341)% 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 Pu-240/Pu-239 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. This study proposes a method to differentiate between local plutonium-based contamination in soils versus trace plutonium stemming from global dispersion in the past, such as fallout from detonation and atmospheric testing of nuclear weapons.

Automated summary

Trace-level plutonium in the environment is often a combination of local and global contributions, typically originating from human activities. Isotopic ratio anomalies in plutonium can provide forensic insights into specific activities, aiding in the development of clean-up strategies.