This guide details the techniques and numerical procedures required for numerical modelling of radioactivity dispersion in marine environments. The book goes beyond the basics of hydrodynamic modeling to analyze the latest trends in modeling.

This publication describes and summarizes the work of the MODARIA (modelling and data for radiological impact assessments) Programme Working Group 10. MODARIA was set up to continue the IAEA's activities in the field of testing, comparing and developing guidance on the application of models to assess radiation exposures to humans and radiological impacts on the environment. Different aspects of the MODARIA programme were addressed by ten working groups. The current publication presents the work undertaken by Working Group 10 on the modelling of marine dispersion and transfer of radionuclides accidentally released from land-based facilities. Two marine dispersion scenarios were studied. These scenarios simulated dispersion of radionuclides in the Baltic Sea following the Chernobyl accident, and dispersion in the Pacific Ocean following the Fukushima Daiichi nuclear power plant accident. The publication details some general conclusions and presents a comparison of model performance when applied to the above scenarios. The difficulties of developing operative modelling systems for supporting decision making in cases of emergencies in highly dynamic environments are highlighted.

This book is a practical guide to the subject of numerical modelling of radioactivity dispersion in the marine environment. Thus, the techniques and numerical procedures required are explained in detail, with the aim of enabling the reader to build a real mathematical model. The book covers basic concepts and techniques, such as solving the advection-diffusion equation in a simple 1D form, as well as the most recent developments (full 3D models for non-conservative radionuclides including chemical reactions and speciation). A chapter is dedicated to the basic hydrodynamic modelling that is always required to simulate the dispersion of tracers in the sea; Eulerian and Lagrangian modelling techniques are also described. A chapter describes sensitivity and uncertainty analysis, the final stage in modelling works. A review on some published radionuclide dispersion models is also included. The book also includes a CD-ROM with a Lagrangian dispersion model of the Strait of Gibraltar and several Fortran codes developed by the author which can be used to reproduce some of the cases described in the book.

Just as an environmental model typically will be composed of a number of linked sub-models, representing physical, chemical or biological processes understood to varying degrees, this volume includes a series of linked chapters exemplifying the fundamental nature of environmental radioactivity models in all compartments of the environment. Why is a book on modelling environmental radioactivity necessary? There are many reasons why such a boook is necessary, perhaps the most important that: - modelling is an often misunderstood and maligned activity and this book can provide, to a broad audience, a greater understanding of modelling power but also some of the limitations. - modellers and experimentalists often do not understand and mistrust each other's work yet they are mutually dependent, in the sense that good experimental science can direct good modelling work and vice-versa; we hope that this book can dispel mistrust and engender improved understanding. - there is an increasing reliance on model results in environmental management, yet there is also often misuse and misrepresentation of these results. This book can help to bridge the gap between unrealistic expectations of model power and the realisation of what is possible, practicable and feasible in modelling of environmental radioactivity; and finally, - modelling tools, capacity and power have increased many-fold in a relatively short period of time. Much of this is due to the much-heralded computer revolution, but much is also due to better science. It is useful to consider what gap if any still remains between what is possible and what is necessary.