4 1.2. THE REQUIREMENT FOR ADVANCED MODELS TO PREDICT MARINE DISTRIBUTION OF RADIONUCLIDES AFTER LAND-BASED ACCIDENTAL RELEASES Models play a major role in the cases of accidental releases of pollutants in order to obtain rapid assessments and decisions for countermeasures to minimize the potential impact on humans and the environment. The IAEA has been organizing programmes of international model testing since the 1980s. The possible benefits of carrying out model validation and testing at an international level were recognized by the Swedish Radiation Protection Institute, which sponsored the Biospheric Model Validation Study (BIOMOVS and BIOMOVS II) programmes starting in 1985 [3]. The Chornobyl accident in 1986 created a renewed need for reliable assessment tools in many countries and provided an increased impetus for work in this area. It also created new data sets that could be put to use for model testing. As a consequence, the IAEA was prompted to start a programme on the Validation of Model Predictions (VAMP) in 1988, which concluded in 1996 [4]. More recently, the Environmental Modelling for Radiation Safety (EMRAS) Programme, which ran 2003–2007, included a working group on Testing of Models for Predicting the Behaviour of Radionuclides in Fresh Water Systems and Coastal Areas [5]. Five scenarios were studied as part of this programme, including two estuaries (Dnieper-Bug in Ukraine and Huelva in Spain). However, a solely marine environment was not considered and the aquatic environment was also not included in the EMRAS II Programme2 (2009–2011) which followed on from EMRAS. In this context, a number of marine models have been used to evaluate the transport and dispersion of oil, radionuclides and other pollutants both for short term predictions and also for long term assessments of the impact to humans by the consumption of marine food, as well as for the impact to the environment and biota. In relation to radionuclide dispersion modelling, major international exercises on modelling of transport and transfer of radionuclides in the marine environment were related to deep-sea dumping [6], disposal of intermediate and high- level waste in Arctic coastal seas [7] and nuclear weapons testing in the South Pacific [8]. During the recent decade several significant developments indicate that a new international modelling exercise is warranted. Recent developments include: advances in modelling (complex three dimensional (3-D) hydrodynamic models, optimized coding allowing implementation of complex models, techniques involving various scales and deterministic/statistical approaches, ecological modelling, dynamic transfer models, etc.), improved knowledge of oceanographic and atmospheric drivers, increased database of generic and specific parameters, new knowledge of chemical form specific biogeochemistry and the e?ect of environmental change (e.g. ocean acidification) on the fate of radionuclides in the marine environment. The Fukushima Daiichi NPP accident in Japan, March 2011, resulted in significant releases to the marine environment, which prompted a large interest from modellers worldwide. Tracking contaminated seawater of defined origin can be used as a tool to validate oceanographic models 2 For more information on EMRAS II programme, see http://www-ns.iaea.org/projects/emras/emras2/