Model testing of radioactive contamination by 90Sr, 137Cs and 239,240Pu of water and bottom sediments in the Techa River (Southern Urals, Russia)

Sediment and (137)Cs behaviors in the Ogaki Dam Reservoir during a heavy rainfall event

We performed a simulation of sediment and (137)Cs behaviors in the Ogaki Dam Reservoir, one of the main irrigation reservoirs in the Fukushima prefecture, Japan, during a heavy rainfall event occurred in 2013. The one-dimensional river and reservoir simulation scheme TODAM, Time-dependent One-dimensional Degradation and Migration, was applied for calculating the time dependent migration of sediment and (137)Cs in dissolved and sediment-sorbed forms in the reservoir. Continuous observational data achieved in the upper rivers were used as the input boundary conditions for the simulation. The simulation results were compared with the continuous data achieved in the lower river and we confirmed the predicted values of sediment and (137)Cs in sediment-sorbed form at the exit of reservoir satisfactorily reproduced the observational data. We also performed sediment and (137)Cs behavioral simulation by changing the water level of the reservoir, because such a dam operation could control the quantities of sediment and (137)Cs discharge from and/or deposition in the reservoir. The simulation clarified that the reservoir played an important role to delay and buffer the movement of radioactive cesium in heavy rainfall events and the buffer effect of the reservoir depended on particle sizes of suspended sediment and the water level. It was also understood that silt deposition was the main source of the bed contamination (except for the initial fallout impact), while clay was the main carrier of (137)Cs to the lower river at a later stage of rainfall events.

Reconstruction of the contamination of the Techa River in 1949-1951 as a result of releases from the "Mayak" Production Association

More accurate reconstruction of the radioactive contamination of the Techa River system in 1949-1951 has been made on the basis of refined data on the amounts and the rate of discharge of radionuclides into the Techa River from the Mayak Production Association; this has led to the development of a modified Techa River model that describes the transport of radionuclides through the up-river ponds and along the Techa River and deposition of radionuclides in the river-bottom sediments and flooded areas. The refined Techa River source-term data define more precisely the time-dependent rates of release and radionuclide composition of the releases that occurred during 1949-1951. The Techa River model takes into account the time-dependent characteristics of the releases and considers (a) the transport of radionuclides adsorbed on solid particles originally contained in the discharges or originating in the up-river ponds as a result of stirring up of contaminated bottom sediments and (b) the transport of radionuclides in soluble form. The output of the Techa River model provides concentrations of all source-term radionuclides in the river water, bottom sediments, and floodplain soils at different distances from the site of radioactive releases for the period of major contamination in 1950-1951. The outputs of the model show good agreement with historical measurements of water and sediment contamination. In addition, the river-model output for (90)Sr concentration in the river water is harmonized with retrospective estimates derived from the measurements of (90)Sr in the residents of the Techa Riverside villages. Modeled contamination of the floodplain soils by (137)Cs is shown to be in agreement with the values reconstructed from late measurements of this radionuclide. Reconstructed estimates of the Techa River contamination are being used for the quantification of internal and external doses received by residents of the Techa Riverside communities.

Regional-scale application of the decision support system MOIRA-PLUS: an example of assessment of the radiological impact of the Chernobyl accident on the fresh water ecosystem in Italy

The present work illustrates the customisation and application of the decision support system MOIRA-PLUS (a MOdel-based computerised system for management support to Identify optimal remedial strategies for Restoring radionuclide contaminated Aquatic ecosystems and drainage areas) to the fresh water environment in Italy. MOIRA-PLUS is aimed at evaluating the behaviour of radiocaesium and radiostrontium in fresh water ecosystems and at assessing the appropriateness of suitable strategies for the management of contaminated water bodies by the application of multi-attribute analysis techniques. MOIRA-PLUS can be applied to complex networks of lakes, rivers and tributaries and can be straightforwardly customised utilising data and information from readily accessible sources such as official websites provided by scientific or government organisations. The present work shows an application of the decision system to 10 lakes and 18 rivers in Italy contaminated with (137)Cs of Chernobyl origin. Site-specific values of some aggregated transfer parameters were estimated for the most important Italian lakes. Although high values of fish and water consumptions were hypothesised, very low doses to public from the fresh water pathway following the accident were calculated.

Distribution and accumulation of heavy metals in the water and sediments of the River Sava

The distribution and accumulation of assorted heavy metals and a long-lived radionuclide (Cu, Zn, Pb, Cd, U, Th and 137Cs) in the water and sediment of the River Sava (in Serbia) were investigated at three locations in the vicinity of industrial and urban settlements (Sabac, Obrenovac, Belgrade). The concentrations of heavy metals in the sediment were found to be in the ranges: 29.6-145.1 mg kg-1 for Cu, 53.2-253.6 mg kg-1 for Zn, 14.2- 78.6 mg kg-1 for Pb, 0.3-24.6 mg kg-1 for Cd and 4.0-12.5 Bq l-1 for 137Cs. These values correlate to the concentrations in the river water if expressed by equilibrium distribution coefficients Kd (dm3 g-1) between the solid and liquid phases. The degrees of accumulation and enrichment of tracer metals were determined.