Vertical migration of radionuclides in the vicinity of the chernobyl confinement shelter

Investigation of Radionuclide Migration at Sites Adjacent to the 30-km Exclusion Zone of the Chernobyl Nuclear Power Plant

ABSTRACT

This paper reports the study of the vertical migration of radionuclides in soils at test sites adjacent to the 30-km Chernobyl Exclusion Zone. The results of this effort demonstrate that the migration processes for studied pollution occur similarly to the fuel fallout behavior at the vicinity of the Chernobyl Nuclear Power Plant (ChNPP) Unit 4. It was also observed that the main fallout component, 137Cs, originated from aerosol fallout and was bound in the surface layer. The authors determined a significant increase of 60Co, 94Nb, and 241Am radionuclide concentrations in soils near the ChNPP Unit 4 and suggested their appearance due to the installation of the New Safe Confinement. Niobium-94 activity is proposed as a marker for monitoring the "fresh" fallout in the Chernobyl Exclusion Zone.

Current ionising radiation doses in the Chernobyl Exclusion Zone do not directly impact on soil biological activity

Although soil organisms are essential for ecosystem function, the impacts of radiation on soil biological activity at highly contaminated sites has been relatively poorly studied. In April-May 2016, we conducted the first largescale deployment of bait lamina to estimate soil organism (largely soil invertebrate) feeding activity in situ at study plots in the Chernobyl Exclusion Zone (CEZ). Across our 53 study plots, estimated weighted absorbed dose rates to soil organisms ranged from 0.7 μGy h^-1 to 1753 μGy h^-1. There was no significant relationship between soil organism feeding activity and estimated weighted absorbed dose rate. Soil biological activity did show significant relationships with soil moisture content, bulk density (used as a proxy for soil organic matter) and pH. At plots in the Red Forest (an area of coniferous plantation where trees died because of high radiation exposure in 1986) soil biological activity was low compared to plots elsewhere in the CEZ. It is possible that the lower biological activity observed in the Red Forest is a residual consequence of what was in effect an acute high exposure to radiation in 1986.

The study of the combined effect of soil properties on the rate of diffusion of 60Co

The direct estimation of the value of the diffusion component of mass transfer of pollutants in arable soil horizons is an important task of scientific and applied importance. The values of effective diffusion coefficients of ⁶⁰Co radionuclide (D_eff) in water-saturated samples of different soils with disturbed structure and the same initial bulk density were obtained during the laboratory experiment. Of particular interest is the assessment of the contribution of individual specific characteristics of soils that have undergone the gleying process to the regulation of D_eff⁶⁰Co.There was noted a significant variability of D_eff⁶⁰Co for investigated soils due to different soil characteristics. To assess this, influence a statistical approach has been used, where edaphic factors representing the most important characteristics of the soils acted as independent variables (predictors), and the dependent (resulting) variable was D_eff⁶⁰Co. The contributions of each of the selected indicators of soils state (independent variables) in varying of D_eff⁶⁰Co were also identified. During the experiments, there was revealed a particularly strong increase in the D_eff⁶⁰Co for soils with a high Eh, ΣFr._<0.01 mm and decrease in the absolute value of the dependent variable with two predictors: pH_H2O and P₂O_5mobile in conditions of excessive moisture. Based on the study of the dependence between the main physicochemical soil properties and the magnitude of effective diffusion coefficients (D_eff⁶⁰Co), the selected physicochemical characteristics of soils were ranked by the degree of influence on the value of the dependent variable: pH_H2O > Eh > ΣFr._<0.01 mm > P₂O_5mobile > C_org.At the same time, the multiple linear regression analysis of the obtained data showed statistical significance for two independent predictors of the model (pH_H2O and ΣFr._<0.01 mm). As a result, semi-partial determination coefficients responsible for the share of the total variation of the dependent variable due to the statistically significant corresponding independent variables (pH_H2O and ΣFr._<0.01 mm) were calculated based on the data presented.