[Radiological Aspects of Transition of Russian Areas Affected by the Chernobyl Accident to Normal Activities].

Dynamics of radiation situation in settlements, agriculture and forestry on the Russian Federation areas af- fected by the Chernobyl accident is presented. A set of challenging problems on public radiation protection and rehabilitation of territories was determined. The main objective at a long-term period after the accident is a stage-wise return of the affected areas to normal activity without any radiological criteria restrictions. For practical realization of this process it is necessary to change the national statutes and regulations consid- ering the contemporary international approaches, to pass to the current exposure situation and to establish reference levels, to define criteria of transition of the areas affected after the Chernobyl accident to normal activity. The change of conceptual approaches will allow one to revise the boundaries of settlement zoning and to develop the regulatory framework on procedures of changing their status from radioactively contami- nated zone to normal activity zone; to develop the regulatory framework on the procedures of transition of agricultural and forest lands classified as radioactively contaminated zones to territories where the traditional husbandry is possible. The Russian Federation has positive experience of transition of areas contaminated as a result of the Chernobyl accident to normal activity.

[Revision of parameters of radionuclide migration in agroecosystems].

Results of the project IAEA "Environmental Modelling for Radiation Safety" (EMRAS) on revision of parameters of radionuclide migration in agroecosystems are presented. Methodical approaches to a grouping of the initial information are stated. The databases on parameters of radionuclide transfer in agricultural plants for various climatic zones, and also in system a diet--an organism of an agricultural animal are described. The examples of an estimation of parameters are resulted.

Effects of non-human species irradiation after the Chernobyl NPP accident.

The area affected by the Chernobyl Nuclear Power Plant accident in 1986 has become a unique test site where long-term ecological and biological consequences of a drastic change in a range of environmental factors as well as trends and intensity of selection are studied in natural settings. The consequences of the Chernobyl accident for biota varied from an enhanced rate of mutagenesis to damage at the ecosystem level. The review comprehensively brings together key data of the long-term studies of biological effects in plants and animals inhabiting over 20 years the Chernobyl NPP zone. The severity of radiation effects was strongly dependent on the dose received in the early period after the accident. The most exposed phytocenoses and soil animals' communities exhibited dose dependent alterations in the species composition and reduction in biological diversity. On the other hand, no decrease in numbers or taxonomic diversity of small mammals even in the most radioactive habitat was shown. In a majority of the studies, in both plant and animal populations from the Chernobyl zone, in the first years after the accident high increases in mutation rates were documented. In most cases the dose-effect relationships were nonlinear and the mutation rates per unit dose were higher at low doses and dose rates. In subsequent years a decline in the radiation background rate occurred faster than reduction in the mutation rate. Plant and animal populations have shown signs of adaptation to chronic exposure. In adaptation to the enhanced level of exposure an essential role of epigenetic mechanisms of gene expression regulation was shown. Based on the Chernobyl NPP accident studies, in the present review attempts were made to assess minimum doses at which ecological and biological effects were observed.

[The dose estimation of woody plants in the long-term after the Chernobyl NPP accident].

Dosimetric models have been developed to estimate the exposure doses of woody plants growing in the area contaminated by long-lived radionuclides. The models are parameterized based on the data obtained from the experimental plots in the south-west districts of the Bryansk region affected by radioactive fallout of the Chernobyl NPP accident. Doses are estimated to generative organs of pine trees from these plots. The contribution from various sources and types of ionizing radiation to the absorbed dose formation for these objects is determined.

Chernobyl radionuclide distribution, migration, and environmental and agricultural impacts.

The distribution and migration of radionuclides released into the environment following the Chernobyl accident in 1986 are described. The Chernobyl disaster resulted in the consumption of farm products containing radionuclides as a source of irradiation of the population due to the prevalence of a rural type of human nutrition in the affected region. Economic and radiologic importance of countermeasures for reducing the impacts of the accident are described. The basic radioecological problem is described in which the area where direct radiation contamination of biota was observed is considerably smaller than the zone where concentrations of radionuclides through the food chain exceeded the permissible standards. The radiation-induced effects in biota in the affected area are described. In the long-term post-accident period, the radionuclide distribution between components of ecosystems (including humans) and doses are considered in comparison to a technologically normal situation of nuclear power plant operation. This analysis demonstrates that if radiation standards protect humans, then biota are also adequately protected against ionizing radiation.

[Chernobyl and the environment].

Analyzed information which describes a wide spectrum of the consequences of radioactive contamination of natural ecosystems by the Chernobyl accident. The main regularities of radionuclide migration in the environment was been considered and scales of radiation damage to biota assessed. The area where signs of direct damage to biota are visible is shown to be noticeably smaller in size that the area where radionuclide concentration in environmental objects is above the permissible levels. The importance of the impact of radioactive contamination of natural ecosystems is assessed in terms of formation of exposure doses to the population. The conclusion was made that the detriment from all the factors is larger for humans (direct irradiation, limitation of the economic activity, etc.) than for biota.

[Radiological assessment of protective countermeasures in the private sector of rural settlements in the Chernobyl nuclear power plant accident area].

The effectiveness of countermeasures on private farms in rural settlements of the Russian Federation affected by the Chernobyl accident for the period of 1986-2005 was assessed. The averted collective doses to the residents of these settlements and the contribution of restrictive and agricultural countermeasures to dose reduction in the rural population have been estimated.

[The radioecological situation in the agricultural sphere in the contaminated regions of russia during the long-term after the Chernobyl accident].

The results of the contamination monitoring of the agricultural land and products in 2000-2005 in the regions of Russia affected by the Chernobyl accident are presented. The contribution is assessed of foodstuffs to the formation of internal exposure doses to the population during the long-term after the accident. Prediction is made of the change in the radioecological situation in radioactively contaminated areas.

[The effects of non-human species irradiation after the Chernobyl nuclear accident].

Data are presented on the effects of irradiation of different biota species after the Chernobyl accident.

[The effects of the agricultural countermeasures on the irradiation of the population in the areas affected by the Chernobyl nuclear accident].

Radiological results were evaluated from the introduction of protective agricultural measures in the collective sector of the agroindustrial complex in the Chernobyl affected areas for the period of 1987-2005. The averted collective doses due to the reduction of 137Cs concentration in farm products were estimated, including the contribution to the averted collective dose of different food stuffs consumption.

Decision making framework for application of forest countermeasures in the long term after the Chernobyl accident.

After the ChNPP accident a very large part of the territories covered by natural and artificial forests are contaminated with long-lived radionuclides, especially 137Cs. To protect people against exposure associated with forest contamination in the most affected regions of the NIS countries, countermeasures have been developed and recommended for the forest management. The paper presents a decision making framework to optimise forest countermeasures in the long term after the ChNPP accident. The approach presented is based on the analysis of the main exposure pathways and application of radiological, socio-economical and ecological criteria for the selection of optimal countermeasures strategies. Because of the diversity of these criteria modern decision support technologies based on multi-attributive analysis were applied. The results of the application of this approach are presented in a selected study area (Novozybkov district, Bryansk region, Russian Federation). The results prove and emphasize the need for a flexible technique to provide the optimised forest countermeasures taking into account radioecological, social and economic features of contaminated forests.

Comparative radiation impact on biota and man in the area affected by the accident at the Chernobyl nuclear power plant.

A methodological approach for a comparative assessment of ionising radiation effects on man and non-human species, based on the use of Radiation Impact Factor (RIF) - ratios of actual exposure doses to biota species and man to critical dose is described. As such doses, radiation safety standards limiting radiation exposure of man and doses at which radiobiological effects in non-human species were not observed after the Chernobyl accident, were employed. For the study area within the 30km ChNPP zone dose burdens to 10 reference biota groups and the population (with and without evacuation) and the corresponding RIFs were calculated. It has been found that in 1986 (early period after the accident) the emergency radiation standards for man do not guarantee adequate protection of the environment, some species of which could be affected more than man. In 1991 RIFs for man were considerably (by factor of 20.0-1.1 x 10(5)) higher compared with those for selected non-human species. Thus, for the long term after the accident radiation safety standards for man are shown to ensure radiation safety for biota as well.

Model testing using data on 137Cs from Chernobyl fallout in the Iput River catchment area of Russia.

Data collected for 10 years following the Chernobyl accident in 1986 have provided a unique opportunity to test the reliability of computer models for contamination of terrestrial and aquatic environments. The Iput River scenario was used by the Dose Reconstruction Working Group of the BIOMASS (Biosphere Modelling and Assessment Methods) programme. The test area was one of the most highly contaminated areas in Russia following the accident, with an average contamination density of 137Cs of 800,000 Bq m-2 and localized contamination up to 1,500,000 Bq m-2, and a variety of countermeasures that were implemented in the test area had to be considered in the modelling exercise. Difficulties encountered during the exercise included averaging of data to account for uneven contamination of the test area, simulating the downward migration and changes in bioavailability of 137Cs in soil, and modelling the effectiveness of countermeasures. The accuracy of model predictions is dependent at least in part on the experience and judgment of the participant in interpretation of input information, selection of parameter values, and treatment of uncertainties.

[The use of computer system in the introduction of countermeasures in agriculture after the Chernobyl accident].

In the development of strategies for countermeasures aimed at the rehabilitation of contaminated areas, essential is to identify criteria for assessing their effectiveness and factors influencing the priority of the criteria chosen. A method is suggested for assessing effectiveness of countermeasures in agriculture based on a multicriterium analysis of radiologic, economic, regulatory and socio-psychological indicators characterizing the use of countermeasures. Rating of countermeasures strategies is presented depending on financing of works on the rehabilitation of the Chernobyl affected areas.

[Prediction of 137Cs behaviour in the soil-plant system in the territory of Semipalatinsk test site].

A mathematical model of 137Cs behaviour in the soil-plant system is presented. The model has been parameterized for the area adjacent to the testing area Ground Zero of the Semipalatinsk Test Site. The model describes the main processes responsible for the changes in 137Cs content in the soil solution and, thereby, dynamics of the radionuclide uptake by vegetation. The results are taken from predictive and retrospective calculations that reflect the dynamics of 137Cs distribution by species in soil after nuclear explosions. The importance of factors governing 137Cs accumulation in plants within the STS area is assessed. The analysis of sensitivity of the output model variable to changes in its parameters revealed that the key soil properties significantly influence the results of prediction of 137Cs content in plants.

[Prediction of 137Cs accumulation in animal products in the territory of Semipalatinsk test site].

The paper describes mathematical models for 137Cs behavior in the organism of horses and sheep pasturing on the bording area to the testing area "Ground Zero" of the Semipalatinsk Test Site. The models are parameterized on the base of the data from an experiment with the breeds of animals now commonly encountered within the Semipalatinsk Test Site. The predictive calculations with the models devised have shown that 137Cs concentrations in milk of horses and sheep pasturingon the testing area to "Ground Zero" can exceed the adopted standards during a long period of time.

137Cs availability for soil to understory transfer in different types of forest ecosystems.

A quantitative analysis of 137Cs bioavailability in forest soils in the long term after the Chernobyl NPP accident based on a 3-year (1996-1998) investigation is presented. Five forest sites with different trees, composition and properties of soil were studied to identify factors determining radiocaesium transfer to different understory species. The following parameters were investigated: 137Cs activity concentrations and its speciation in various horizons of forest soil, accumulation of this radionuclide by different species of understory vegetation and distribution of root biomass in the soil profile. It has been shown that one decade after the deposition maximum 137Cs activity in soil of the experimental sites considered is located in different soil layers dependent on moisture regime, characteristics of litter and soil properties. A linear dependence between aggregated transfer factors for different species and groups of species of understory vegetation and exchangeable and available fractions of radiocaesium in soil was found. The vertical distribution of 137Cs activity, percentage of exchangeable radiocaesium in each horizon of litter and soil, as well as distribution of root systems (mycelia) over the soil profile are key factors governing variations in the availability of 137Cs for transfer to all forest understory components.

137Cs distribution among annual rings of different tree species contaminated after the Chernobyl accident.

The distributions of 137Cs among annual rings of Pinus sylvestris and Betula pendula at four experimental sites located in the most contaminated areas in the Russian territory after the Chernobyl accident in 1986 were studied. Trees of different ages were sampled from four forest sites with different tree compositions and soil properties. The data analysis shows that 137Cs is very mobile in wood and the 1986 rings do not show the highest contamination. The difference between pine and birch in the pattern of radial 137Cs distribution can be satisfactorily explained by the difference in radial ray composition. 137Cs radial distribution in the wood can be described as the sum of two exponential functions for both species. The function parameters are height, age and species dependent. The distribution of 137Cs in birch wood reveals much more pronounced dependence on site characteristics and/or the age of trees than pines. The data obtained can be used to assess 137Cs content in wood.

[Modelling of 137Cs migration in agroecosystems under safety and rehabilitation measures]. / Modelirovanie migratsii 137 CS v agroékosistemakh v usloviiakh provedeniia zashchitnykh i reabilitatsionnykh meropriiatii.

Mathematical model describing dynamics of 137Cs transfer in agroecosystems under rehubilitation measures on arable, haylands, pastures and natural meadow ecosystems is presented. Possibilities of the model application for prediction of the radionuclide content in agricultural production and estimation of efficiency of countermeasures in region of the ChNPP accident are shown.

[Comparative analysis of the effectiveness of countermeasures in rural settlements in the long-term period after the accident at the Chernobyl AES]. / Sravnitel'nyi analiz strategii primeneniia zashchitnykh meropriiatii v sel'skikh naselennykh punktakh v otdalennyi period posle avarii na Chernobyl'skoi AES.

A comparative analysis of the strategy of countermeasures aimed at reducing exposure doses to the rural population is presented. The effectiveness of the proposed system of countermeasures assessed by criteria such as reduction factor of exposure doses and cost of averted doses. Costs of countermeasures in the rural settlements located in the affected zone are calculated for a long term after the Chernobyl NPP accident.