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

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Abstract

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.

Section snippets

Introduction and background

Two major areas of emphasis in the International Atomic Energy Agency's recent BIOMASS (Biosphere Modelling and Assessment Methods) programme were the improvement of the accuracy of model predictions and the improvement of modelling procedures within the general area of environmental assessment. The BIOMASS programme had three major themes, including Radioactive Waste Disposal, Environmental Releases, and Biosphere Processes. Theme 2 of BIOMASS, Environmental Releases, focused specifically on

Description of the test exercise

The accident at the Chernobyl Nuclear Power Plant on 26 April 1986 led to the contamination of vast areas of Europe across a range of climatic and socioeconomic regions. The agricultural area in the Iput River catchment basin, located about 200 km to the northeast of Chernobyl, was one of the most highly contaminated areas in Russia, with an average contamination density of 137Cs of 800,000 Bq m−2 and localized contamination up to 1,500,000 Bq m−2. A number of countermeasures were imposed in the

Participating modellers

Eight individuals or groups participated in the test exercise (Table 1), in addition to the scenario authors, who made their own set of calculations based on the input information. Modelling approaches to selected parts of the assessment are summarized in Table 2. Most of the models had been developed for situations other than this specific test exercise, and in several cases modifications had to be made for this exercise. In particular, modification at some level (e.g., modification of the

Results

Comparisons of predicted and measured 137Cs activity concentrations are shown for selected agricultural (Fig. 1, Fig. 2, Fig. 3) and natural products (Fig. 4, Fig. 5). For agricultural plants (crops and pasture) and animal products, the highest levels of 137Cs activity were observed in 1986 (Fig. 1, Fig. 2, Fig. 3). After several years, activity concentrations in most products dropped by an order of magnitude or more due to the decrease in 137Cs availability and the imposition of

Discussion

In general, final model predictions from many participants were within a factor of two or three of the observed means for many endpoints, although this was not always the case. For some models and endpoints, predictions and observations differed by an order of magnitude or more, at least for some time periods. In several cases, the predictions agreed generally with the observations but did not reproduce the dynamics of the radionuclide concentrations very well. In particular, the initial (1986)

Summary and conclusions

The Iput River test exercise provided an opportunity to compare modelling approaches and model predictions for assessment of the long-term radioecological situation for an area highly contaminated with a long-lived radionuclide that is important both for its contribution to environmental contamination from fission products and for its contribution to human doses from such contamination. The use of 137Cs data provided a unique opportunity to study the contribution of different transfer routes

Acknowledgements

The Iput River model testing exercise represents the combined efforts of a number of persons and organizations, without whom this manuscript would not have been possible. Preparation of the test scenario, the BIOMASS final report, and this manuscript were supported in part by the U.S. Centers for Disease Control and Prevention under Grant #R32/CCR416742 and Orders #0009869061, #0000063925, #0000163231, and #0000262994.

References (10)

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