The BIOMOSA (BIOsphere MOdels for Safety Assessment of radioactive waste disposal) project was part of the EC fifth framework research programme. The main goal of this project was to improve the scientific basis for the application of biosphere models in the framework of long-term safety studies of radioactive waste disposal facilities and to enhance the confidence in using biosphere models for performance assessments. The study focused on the development and application of a generic biosphere tool BIOGEM (BIOsphere GEneric Model) using the IAEA BIOMASS reference biosphere methodology, and the comparison between BIOGEM and five site-specific biosphere models. The site-specific models and the generic model were applied to five typical locations in Europe, resulting in estimates of the annual effective individual doses to the critical groups and the ranking of the importance of the exposure pathways for each of the sites. Uncertainty in the results was also estimated by means of stochastic calculations based on variation of the site-specific parameter values. This paper describes the generic model and the deterministic and stochastic results obtained when it was applied to the five sites. Details of the site-specific models and the corresponding results are described in two companion papers. This paper also presents a comparison of the results between the generic model and site-specific models. In general, there was an acceptable agreement of the BIOGEM for both the deterministic and stochastic results with the results from the site-specific models.

This paper describes the development and application of site-specific biosphere models that might be used for assessment of potential exposures in the framework of performance assessment studies of nuclear waste disposals. Model development follows the Reference Biosphere Methodology that has been set up in the framework of the BIOMASS study. In this paper, the application is to real sites at five European locations for which environmental and agricultural conditions have been described and characterised. For each of the sites a biosphere model has been developed specifically assuming a release of radionuclides to waters that are used by humans, for example as drinking water for humans and cattle and as irrigation water. Among the ingestion pathways, the intakes of drinking water, cereals, leafy vegetables, potatoes, milk, beef and freshwater fish are included in all models. Annual individual doses were calculated, and uncertainties in the results were estimated by means of stochastic calculations. To enable a comparison, all results were normalised to an activity concentration in groundwater of 1 Bq m(-3) for each of the radionuclides considered ((36)Cl, (79)Se, (99)Tc, (129)I, (135)Cs, (226)Ra, (231)Pa, (230)Th, (237)Np, (239)Pu, and (238)U), i.e. those that are usually most relevant in performance assessment studies of nuclear waste disposals. Although the results do not give answers in absolute terms on potential future exposures, they indicate the spectrum of exposures that might occur in different environments and specify the interaction of environmental conditions, human habits and potential exposure.

In the framework of the BioMoSA project for the development of biosphere assessment models for radioactive waste disposal the Reference Biosphere Methodology developed in the IAEA programme BIOMASS was applied to five locations, situated in different European countries. Specific biosphere models were applied to assess the hypothetical contamination of a range of agricultural and environmental pathways and the dose to individuals, following contamination of well water. The results of these site-specific models developed by the different BioMoSA partners, and the individual normalised dose to the exposure groups were compared against each other. Ingestion of drinking water, fruit and vegetables were found to be among the most important pathways for almost all radionuclides. Stochastic calculations revealed that consumption habits, transfer factors, irrigation rates and distribution coefficients (Kd(s)) were the most important parameters that influence the end results. Variations in the confidence intervals were found to be higher for sorbing elements (e.g. (36)Cl, (237)Np, (99)Tc, (238)U, (129)I) than for mobile elements (e.g. (226)Ra, (79)Se, (135)Cs, (231)Pa, (239)Pu). The influence of daughter products, for which the distribution into the biosphere was calculated individually, was also shown to be important. This paper gives a brief overview of the deterministic and stochastic modelling results and the parameter sensitivity. A screening methodology was introduced to identify the most important pathways, simplify a generic biosphere tool and refine the existing models.

The BioMoSA (Biosphere Models for Safety Assessment of Radioactive Waste Disposal) project was part of the EC fifth framework research program. The main goal of this project was the improvement of the scientific basis for the application of biosphere models in the framework of long-term safety studies of radioactive waste disposal facilities. Another aim of the project was to provide operators and regulatory bodies with guidelines for performance assessments of repository systems. The study focused on the development and application of site-specific models and a generic biosphere tool BIOGEM (BIOsphere GEneric Model), using the experience from National programs and the IAEA BIOMASS reference biosphere methodology. The models were applied to 5 typical locations in Europe, resulting in estimates of the annual individual doses to the critical groups and the ranking of the importance of the pathways for each of the sites. The results of the site-specific and generic models were then compared. Uncertainty in the results was estimated by means of stochastic calculations which allowed a comparison of the overall model uncertainty with the variability across the different sites considered.

Analysis of sensitivity and uncertainty of assessment models for external costs, which is monetarization of environmental impacts, of a commercial fusion plant were performed. The assessments covered the plant's entire life cycle, and adopted the ExternE methodology, which had been used to calculate external costs from other energy sources. Based on the SEAFP study, three different power plant designs were considered. The method developed in ExternE to estimate uncertainty gave very large ranges. A statistical error propagation method was employed for this study. Rather than as a single value, model input parameter values were given as distributions, from which random input sets of data were constructed. The models were then run with these sets, and the ensemble of output results was analysed statistically, yielding estimates of the uncertainty due to variation of the model parameteres. More information of parameter variation is needed for a more realistic estimation of model uncertainty, though. Sensitivity analyses were performed by varying all input parameters in a similar fashion. All model parameters were assumed to have a gaussian distribution with standard deviations of 10% of the mean value. The results pointed out the most essential parameters of the models. The sensitivity analyses are also useful for estimating the most effective ways to reduce the model computed external costs.

Carbon-14 was added to the epilimnion of a small Canadian Shield lake to investigate primary production and carbon dynamics. The nature of the spike and subsequent monitoring allowed the investigation of both short-term and longer-term processes relevant to evaluating impacts of accidental and routine releases and of solid waste disposal. Data from this experiment were used in the BIOMOVS II program as a validation test for modelling the fate of the 14C added to the lake. Four models were used: (1) a simple probabilistic mass balance model of a lake; (2) a relatively complex deterministic model; (3) a complex deterministic model; and (4) a more complex probabilistic model. Endpoints were 14C concentrations in water, sediment and lake whitefish over a thirteen year period. Each model produced reasonable predictions when compared to the range of the observed data and when uncertainty in model predictions is taken into consideration. The simple lake model did not account for internal recycling of 14C and, in this respect, its predictions were not as realistic as those of the more complex models for concentrations in water. However, the simple model predictions for the 14C inventory remaining in lake sediment were closest to the observed values. Overall, the more complex probabilistic model was the most accurate in simulating 14C concentrations in water and in whitefish but it overestimated 14C retention in the lake sediments, as did the other complex models. Choice of parameter values for transfer rate to sediment and gaseous evasion are important in influencing model predictions. Although predicted concentrations of 14C in fish of dynamic models were more accurate than those using equilibrium bioconcentration factors typically used in assessments, large variability in observed 14C concentrations in whitefish emphasizes the need for a better understanding of the important processes that influence these contaminant concentrations.

Already as a result of the highly successful first phase of the international BIOsphere MOdel Validation Study (BIOMOVS) considerable progress had been made in representing features, events and processes (FEPs) relevant to many aspects of biosphere modelling. Nevertheless, at the start of BIOMOVS II, it was recognised that there was a need to further investigate and develop available tools for representing the biosphere in long-term assessments of radioactive waste disposal. At a practical level, the Complementary Studies working group looked at the way contemporary models were able to perform calculations for a real site given the type of data available in real performance assessments.The use of a well-defined database allowed detailed comparisons of FEPs for transport as well as for the calculation of exposure pathways. Results have indicated not only the common basis in many model descriptions but also where further development and consolidation are required. This paper summarises some of the key findings from the study.The title Complementary Studies was chosen for the working group to indicate that work would complement waste disposal related scenarios from the first phase of BIOMOVS. Within BIOMOVS II the work of the group also complemented the Reference Biospheres working group. (C) 1998 Elsevier Science Ltd. All rights reserved.

The purpose of this study was to design a generic model for long-term predictions of the Cs-137 concentration in lakes, emphasizing the secondary load of radiocaesium to the waterbody from lake sediments and drainage area. If the concentration of Cs-137 in lake waters can be accurately predicted, estimates of concentration in fish will be more reliable. The inflow from the drainage area is estimated from the fraction of outflow areas, whereas resuspension from lake sediments is estimated from the maximum depth and surface area. The model is based on compartment theory. Modelling results for six lakes are presented. There was very good agreement between model results and observed values, for both water and lake sediments, although there were minor discrepancies for sediments in the deepest lakes. Analyses of the model results showed that, for deep lakes, the main contribution maintaining the concentration in lake waters is inflows from the drainage area, whereas for shallow lakes, the main factor is resuspension for caesium rich sediments.

The migration of radionuclides through catchment basins, by run-offer wash-off waters and rivers, the resuspension from sediments and the subsequent transport are important phenomena involving long-term contamination of water bodies. The main aim of the CEC Project "Analysis and modelling of the migration of radionuclides deposited in catchment basins of fresh water systems" is to investigate the various aspects of these phenomena in order to develop models assessing the behaviour of radionuclides in drainage areas of fresh water systems. In the present paper preliminary results of the research will be described:(a) The migration from catchment basins to water body may be quantified by using the so called "transfer functions" ("T.F." = amount of radionuclide (Bq s(-1)) flowing, per unit time, from the catchment to the water body following a pulse deposition on the catchment). A variety of such functions were evaluated using experimental data collected in various European rivers following the Chernobyl accident;(b) A literature survey of models predicting radionuclide migration from catchment to water bodies was carried out. The model review was intended to highlight the dominant processes involved in radionuclide migration from catchment areas to surface water bodies and to investigate the various possible approaches to drainage area modelling;(c) The long-term exchange of radionuclides between sediment and water was investigated.

In the present paper, the principles of Empirically Based Uncertainty Analysis (EBUA) are described. EBUA is based on the evaluation of ‘performance indices’ that express the level of agreement between the model and sets of empirical independent data collected in different experimental circumstances. Some of these indices may be used to evaluate the confidence limits of the model output. The method is based on the statistical analysis of the distribution of the index values and on the quantitative relationship of these values with the ratio ‘experimental data/model output’. Some performance indices are described in the present paper. Among these, the so called ‘functional distance’ (d) between the logarithm of model output and the logarithm of the experimental data, defined as d2 = Σn1(ln Mi − ln Oi)2n where Mi is the ith experimental value, Oi the corresponding model evaluation and n the number of the couplets ‘experimental value, predicted value’, is an important tool for the EBUA method. From the statistical distribution of this performance index, it is possible to infer the characteristics of the distribution of the ratio ‘experimental data/model output’ and, consequently to evaluate the confidence limits for the model predictions. This method was applied to calculate the uncertainty level of a model developed to predict the migration of radiocaesium in lacustrine systems. Unfortunately performance indices are affected by the uncertainty of the experimental data used in validation. Indeed, measurement results of environmental levels of contamination are generally associated with large uncertainty due to the measurement and sampling techniques and to the large variability in space and time of the measured quantities. It is demonstrated that this non-desired effect, in some circumstances, may be corrected by means of simple formulae.

A given fallout of radiocesium (e.g. after the Chernobyl accident) will be distributed and taken up by biota very differently in various types of lakes. Thus, lakes have different “sensitivities” to radiocesium. Important environmental factors regulating the biouptake of 137Cs are the lake water retention time and the K concentration of the water. Several practically useful and ecologically relevant methods exist to remediate lakes contaminated by radiocesium, e.g. liming, potash treatment and fertilization of low-productive lakes. The basic aim of this paper is to use a validated, state-of-the-art model for radiocesium in lakes, the VAMP model, first to illustrate the fact that different lakes have different ‘sensitivities’, and then to simulate the effects of alternative remedial methods. Target variables in these tests are Cs concentrations in lake water and in predatory fish. These results emanate from IAEAs VAMP project. The lakes included in this work cover a wide range of lake and catchment characteristics.