Migration Of Radiocesium Research Articles

Changes with time in the migration of radiocesium in the soil, as observed near Chernobyl and in Germany, 1986–1994

At a near-field grassland site at the Chernobyl nuclear power plant (ChNPP) and at a grassland site in Germany the mean residence half-times of Chernobyl-derived 137Cs were determined for various soil layers as a function of time. For that purpose, the annually observed vertical distributions of this radionuclide in the soil were evaluated with a compartment model. The main difference between these two sites with respect to the migration of radiocesium was apparent in the top soil layer, where the residence half-time increased at the German site between 1987 and 1994 from about 0.7 to 2 years, while it decreased at the ChNPP site from about 9 to 3 years. In the deeper soil layers the residence half-times increased at both sites with increasing time and decreased with depth in a rather similar way. The opposite behavior of the residence half-time in the top soil layer at the two sites results from the fact that 137Cs was deposited at the ChNPP site predominantly in the form of rather insoluble fuel particles, while at the German site this radionuclide was attached in a more available form to natural aerosols. The increase of the 137Cs residence half-times with time at both sites in the deeper layers can be explained by the progressive fixation of radiocesium by clay minerals of the soil.

Studies of the rate of migration of radiocesium in some types of soils of Eastern Poland

The activity of Cs-137 and Cs-134 in some types of soils of Eastern Poland was studied. The contribution of Cs-137 from post-Chernobyl fall-out as a function of depth in the soil profiles was calculated from the Cs-134:Cs-137 activity ratio taken from the literature just after the Chernobyl accident. Such information makes it possible to calculate the rate of vertical migration of radiocesium in various types of soils. The rate of the post-Chernobyl Cs-137 migration was found to exceed the rate of migration of Cs-137 from experimental nuclear explosions in the atmosphere. Cs-137 from the Chernobyl accident was found in a layer of soil a few cms thick in most of the soils which were examined. The contribution of post-Chernobyl radiocesium to the total contamination of the surface layer (0–5 cm) with cesium was ≈77%.

Radiotracer method in the study of environmental speciation and migration of contaminants.

Principles, advantages, and limitations of the use of radiotracer method for the analysis of speciation and migration of contaminants in the environment are briefly discussed. Several recent examples of use in the author's laboratory are given: development of the separation method for methylmercury and inorganic mercury in hair, analysis of the speciation of cadmium in soil solutions, study of the interaction of 137Cs and 58Co with suspended sediments in river water, and determination of input data for mathematical modeling of radiocesium migration in a small river.

Migration of radiocesium in two forest soils as obtained from field and column investigations

Depth profiles of radiocesium were measured in a podsolic parabrown earth of a spruce stand and in a podsol of a pine stand up to 3 years after the Chernobyl accident. At the same sites undisturbed soil columns of 20 cm diameter and 40 cm length were taken, transferred to the laboratory and irrigated intermittently with synthetic rainwater containing initially a known amount of radiocesium. The resulting migration of radiocesium in the columns under unsaturated conditions was determined as a function of time up to 3 years with a scanner technique. The depth profiles of radiocesium observed in the field and in the columns were evaluated with a compartment model to obtain the residence half-times of this radionuclide in the various soil horizons. The field observations yielded a residence half-time in the organic layer of both soils of ∼4–6 years for Chernobyl-derived cesium, and of 10–15 years for cesium from the global fallout of weapons testing. In the mineral soil (0–5 cm), under spruce, the residence time of Chernobyl-derived cesium was 15 years, that of cesium from the global fallout (present in the soil since ∼30 years) was 50 years. Under pine, the residence time in the mineral soil was 4 years for Chernobyl-derived cesium, and 11 years for global fallout cesium. Obviously, in each layer of both soils cesium becomes less available for migration with time. The residence times of radiocesium evaluated from the column experiments were in good agreement with those obtained from the field observations. Due to the comparatively short duration of the column experiments, however, the long-term increase of the residence time of radiocesium in soil was not yet unambiguously observable.

Effects of acid irrigation and liming on the migration of radiocesium in a forest soil as observed by field measurements

The effect of normal irrigation, acid irrigation, and liming on the vertical migration of radiocesium from Chernobyl and global fallout was investigated by determining the activity of 134Cs and 137Cs in the upper horizons (LOfl, Of2, Oh, Aeh, Alh, Al) of six experimental plots of a forest soil (spruce stand) as a function of time. For the Of2 and Oh horizons (but not for the LOfl horizon) of the control plots during our period of observation (600 days from 30 April 1986), we found a significant increase in the mean residence half-time (τ) of Chernobyl-derived cesium from ∼ 70 to 500 days, indicating that Cs is sorbed more strongly with time. The different types of soil management showed an effect only in the Of2 horizon. Irrigation, especially when acid, prevents the increase of τ with time. Liming reduces the rate of migration of Cs significantly, even if the plots are irrigated with normal or acid water. Cesium-137 from global fallout was present mainly in the Oh and Aeh horizons, but was less mobile than Chernobyl-derived Cs by one order of magnitude.

Factors affecting interaction of radiocesium with freshwater solids

The paper aims at the analysis of principal factors affecting the interaction of radiocesium with freshwater solids, important for the migration of radiocesium in rivers. Uptake of radiocesium by bottom sediments and suspended solids from small streams was studied as a function of pH and composition of aqueous phase, of the concentration of cesium in water and of the composition of freshwater solids, using laboratory model experiments. pH had negligible effect on the uptake in the pH range 5–9, the uptake decreased at pH values less than 3–5 depending on the nature and concentration of the solids. Addition of cations suppressed the uptake in the order K+>Na+>Ca2+, the suppression began at 0.001, 0.01 and 0.1 mol.dm−3 concentration, respectively. Increase in cesium concentration in water caused a decrease of radiocesium uptake, but at very low concentrations of cesium combined with higher concentration of sediment (2g·dm−3) the uptake was independent of cesium concentration. Removal of carbonates, oxidic coatings and organic matter from a sediment did not affect the sorption properties of the sediment. The nature of the effects found confirms that cesium is sorbed mainly by clay components of freshwater solids. Results obtained are compared with literature data and conclusions are drawn on the importance of the factors studied for modelling of radiocesium migration in rivers.

The migration of fallout 134Cs, 137Cs and 106Ru from Chernobyl and of 137Cs from weapons testing in a forest soil

AbstractTo estimate the accumulation and vertical migration of radiocesium and radioruthenium, the activity concentrations of Chernobyl‐derived 134Cs, 137Cs and 106Ru as well as of 137Cs from the global fallout of weapons testing observed in the upper horizons of a forest soil (Hapludult, spruce stand) were evaluated with a compartment model. The resulting residence half‐times were used to estimate the mean rates of transport of these radionuclides. For Chernobyl‐derived 134Cs and 137Cs within the time period of 200–600 days after the beginning of the fallout the rates were between 4 cm/yr (Of1‐horizon) and 2 cm/yr (Oh‐horizon), and for 106Ru between 4 cm/yr (Of1‐horizon) and 7 cm/yr (Oh‐horizon). These rates, though considerably slower than observed in the same soil during the initial infiltration of these radionuclides with a rain shower, are (depending on the soil horizon) still higher by a factor of 3–6, when compared to the rates of transport of 137Cs from the global fallout of weapons testing in the same soil. Because global fallout 137Cs is in the soil since about 20 years, these results suggest that the fixation of radiocesium in the forest soil is a rather slow process.

Migration of radiocesium in a zeolite-solution system

Some properties of natural zeolite from Zaloska gorica, Slovenia, Yugoslavia were investigated to establish its applicability in solidification and for storage purposes of radioactive waste. It was found that this material is a rather good sorber for cesium, with a capacity of about 0.6 meq g−1. The migration rate of Cs+ in a system ion exchanger-aqueous solution was investigated and correlated with the sorption behaviour of cesium in a system. The leaching rate of cesium from concrete containing zeolite was measured.