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-Hydrological Dispersion Module (HDM) of JRODOS includes the chain of the models describing the washing out of the accidental deposition from the watersheds to rivernet and radionuclide transport in rivers and reservoirs. This modelling chain of HDM was renewed by the integration of two models. One-dimensional model RIVTOX_SV provides possibilities for the computing radionuclide transport in the branched river networks. Twodimensional model for shallow reservoirs and river floodplains COASTOX_UN used algorithms of the parallel computing on the unstructured mesh of the finite volume method. The renewed modelling chain was tested for the subwatersheds of the Danube river and the Dnieper river.

Abstract. The need of less conservative but reliable risk assessment for accidental tritium release was recognized in the frame of present debate on nuclear energy future. While the fusion reactor is only in research phase and risk assessment are not extremely stringent, Romania faces a debate on near future of nuclear energy with heavy water reactors, known to have a large load and release of tritium. Both tritium and 14 C are key radionuclide for CANDU and are also directly involved in the life cycle of plants and animals. An interdisciplinary approach is proposed in order to better handle the environmental transfer of tritium under accidental conditions and preparatory steps are presented.

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The paper presents several aspects believed to be relevant for the integration in the decision support systems for the management of radiological emergencies, of assessment tools addressing surface water contamination. Three exemplary cases are discussed in the context-the CONVEX 2005 international alert exercise, AXIOPOLIS 09, a national drill targeting a CANDU reactor at Cernavoda nuclear power plant in Romania, and Oltenia 07-a nation-wide drill around a scenario, involving trans-border effects of a virtual accident at a VVER reactor at Kozloduy, Bulgaria. The capability of different analytic tools were tested, including public deliverables like real-time, online decision support system's HDM module and model-based computerised system for management support to identify optimal remedial strategies for restoring radionuclide-contaminated aquatic ecosystems and drainage areas, as well as research-grade, home-made facilities, in order to identify and sort out merits and issues of interest in steering their effective utilisation.