The source and reference inventory of 239+240 Pu in the soil of China

Abstract

This study used the large existing database on 137Cs reference inventories, according to the radioactivity ratio of 137Cs/239+240Pu (32.5,137Cs radioactivity is corrected to 2005) in the Northern Hemisphere, and converted 137Cs reference inventories to the corresponding values for 239+240Pu. The 137Cs Reference Inventory Model for Mainland China (137Cs-RI MCM) had been used to establish an analogous, by using Kriging/Cokriging interpolation to simulate the spatial distribution of the Pu-RI in the soils across China. At present, the measured deposition inventories for 239+240Pu range from 7.3 to 546Bq/m2 and Pu-RI simulated values range from 3 to 812Bq/m2. Maxima in the deposition inventory correlated well with those of the Pu-RI simulation, which suggested the 137Cs-RI MCM has potential for the simulation of the Pu-RI in the soils of the mainland of China. In-homogeneity in the atmospheric deposition of 137Cs and 239+240Pu however lead to deviations between the local Pu-RI simulation values and the measured 137Cs/239+240Pu radioactivity ratios present in Chinese soil cores. In order to better illustrate the feasibility of the 137Cs-RI MCM, this study compared theoretical wet deposition inventories of 239+240Pu with the corresponding Pu-RIs in 62 cities of China between latitudes 30~40°N, this showed that the theoretical calculations of Pu-RI or total deposition inventories and wet deposition inventories were reasonable.