PLUTONIUM INVENTORIES IN 2 OLD-FIELD ECOSYSTEMS IN THE VICINITY OF A NUCLEAR-FUEL REPROCESSING FACILITY

Plutonium inventories were determined in two old-field ecosystems. Fields 1 and 2, located near a nuclear-fuel reprocessing facility that had released approximately 640 mCi (24 GBq) 238Pu and 570 mCi (21 GBq) 239,240Pu to the atmosphere in the 20 yr preceding sampling. Field 1 was 230 m from the point of release (a 62-m stack) and contained 57 nCi (2.1 kBq) 238Pu/m2 and 255 nCi (9.4 kBq) 239,240Pu/m2. Field 2 was 420 m from the stack and contained 15 nCi (0.56 kBq) 238Pu/m2 and 79 nCi (2.9 kBq) 239,240Pu/m2. The distribution of Pu between soil and vegetation components was similar in the two fields with only 1.3% of the 238Pu and 0.2% of the 239,240Pu occurring in pines, herbaceous vegetation and litter. More of the Pu could be suspended from the soil into the atmosphere by a 6 m/s wind on Field 1 than on Field 2 due to the lower biomass of herbaceous vegetation and litter on Field 1. Approximately 2% of the 238Pu and 0.5% of the 239,240Pu could be resuspended on Field 1, whereas only 0.5% of the 238Pu and 0.1% of the 239,240Pu could be resuspended on Field 2. Plutonium contamination of the vegetation occurred primarily by (1) direct deposition of recently released Pu onto vegetation, and (2) resuspension of Pu from the soil to vegetation surfaces. Root uptake apparently made negligible contributions to the Pu contents of the above-ground vegetation.