The 2011 accident at the Fukushima Daiichi nuclear power plant has released huge amounts of radioactive substances into the Pacific Ocean. These radionuclides are being dispersed and transferred through the ocean, and numerous studies of these processes have been carried out using three-dimensional hydrodynamic circulation models, dispersion models and compartmental models on different space- and time-scales to predict the behaviour of the radionuclides and, further on, to estimate doses to biota and human populations. Similar studies, focusing mainly on short-term and short- to medium-range predictions, can be applied to other coastal nuclear facilities and various emergency scenarios. The objective of this CRP is to compare available ocean models, adapt operational models to radionuclide modelling, work out connections to real-time data streams and assist Member States in the development of expert systems for emergency preparedness. The Fukushima discharges will be used as a benchmark study for the Pacific Ocean. The simulated data will be compared with actual measurement results from that region. Measurement data can be used from the Asia–Pacific Marine Radioactivity Database (ASPAMARD), which is currently being updated under the IAEA regional technical cooperation project RAS/7/021, “Marine Benchmark Study on the Possible Impact of the Fukushima Radioactive Releases in the Asia–Pacific Region”. The CRP will also compare predictions obtained from different models and further develop models for dispersion and transfer of radionuclides in the marine environment, which can be used for radiological and environmental impact assessments in support of decision-making in case of accidental releases of radionuclides to the marine environment. The CRP will develop the scientific basis of marine modelling during nuclear and radiological emergencies and will be coordinated with relevant activities under the IAEA’s Modelling and Data for Radiological Impact Assessments (MODARIA) programme in order to improve capabilities in the field of environmental radiation dose assessment.