Spatiotemporal Distribution of ~(241)Am in the Vicinity of the Waste Isolation Pilot Plant - 19543

摘要

Environmental monitoring around nuclear facilities is essential for characterizing the baseline conditions that are critical for identifying releases and quantifying their effects, should they occur, and for assessing post-closure performance. The spatiotemporal distribution and transport behavior of~(241) Am in the vicinity of a deep geologic repository for transuranic waste were assessed using data spanning the pre-operational phase to the present, including an accidental radionuclide release in 2014. The ~(241)Am background values of 0.027±0.109 μBq/m~3 (aerosols), and 0.061±0.065 Bq/kg (soil), as well as the ~(241)Am/~(239+240)Pu ratios of 0.41±0.06 (aerosols) and 0.38±0.04 (soil), are similar to global fallout values. Pre-operations concentrations of~(241) Am show a strong seasonal dependence, attributed to resuspension of soils contaminated by global fallout, with no contribution from the upwind Project Gnome site (~(241)Am/~(239+240)Pu =0.24±0.08). During the 2014 accidental release, aerosol concentrations of ~(241)Am briefly increased to 115.2 μBq/m~3 at an onsite monitoring station, and 81.4 μBq/m~3 at a station ～1 km downwind of the exhaust shaft, changing the ~(241)Am/~(239+240)Pu from ～0.37 to ～10. However, some four years later, conditions have returned to background. Almost 90% of the ~(241)Am inventory is the 0-5 cm soil layer and there is no evidence of concentrations above regulatory standards, or that can be attributed to waste disposal operations.