Assessing nuclear energy transition scenarios requires appropriate modelling tools. The IAEA tool Model for Energy Supply System Alternatives and their General Environmental Impacts (MESSAGE) is described in this publication. The tool simulates the development of a complete energy system and provides a convenient platform for modelling and analysing nuclear energy systems (NES), as it can efficiently model nuclear technologies with their specific features. Among other things, the tool can help produce a description of an entire NES with time dependent parameters for long-term planning; confirm the feasibility of a NES through correlation and consistency of all NES components, taking into account all constraints and boundary conditions imposed on the system; balance fissile material in a close fuel cycle and determine fuel cycle requirements. In addition, it assists the user in the choice of alternatives by comparison of different options relating to fuel requirements and volume and toxicity of waste. The publication provides a detailed guidance on how to build mathematical models representing complex nuclear energy systems within the framework of the MESSAGE tool.

Member States have recognized the increasing need to model future nuclear power scenarios in order to develop strategies for sustainable nuclear energy systems. The IAEA model for energy supply strategy alternatives and their general environmental impacts (MESSAGE) code is a tool that supports energy analysis and planning in Member States. This publication documents the experience gained on modelling and scenario analysis of nuclear energy systems (NES) using the MESSAGE code through various case studies performed by the participating Member States on evaluation and planning for nuclear energy sustainability at the regional or national level. The publication also elaborates on experience gained in modelling of global nuclear energy systems with a focus on specific aspects of collaboration among technology holder and technology user countries and the introduction of innovative nuclear technologies. It presents country case studies covering a variety of nuclear energy systems based on a once-through fuel cycle and a closed fuel cycle for thermal reactors, fast reactors and advanced systems. The feedback from case studies proves the analytical capabilities of the MESSAGE model and highlight the path forward for further advancements in the MESSAGE code and NES modelling.

This publication assists existing and potential stakeholders in the definition of competitive approaches regarding design and deployment of small and medium sized reactors (SMR). It provides a framework for assessment of the investment attractiveness of nuclear power plant projects that adopts small reactor to be deployed in multi-modules and incorporate modularization construction technology. Main chapters detail past experience and future plans in several IAEA Member States and present the suite of models to assist designers and guide potential users on the economic performance and investment attractiveness of SMRs. A framework for the consolidated application of such models is also suggested. The annexes, contributed by Member States, provide in depth descriptions of different assessment models and give examples of their application.

This publication describes the purpose and scope of the INPRO service Analysis Support for Enhanced Nuclear Energy Sustainability (ASENES) and its potential benefits to Member States. The publication highlights the links between this service and overall technical support to Member States for the planning and development of nuclear energy, and explains how it integrates with other IAEA services supporting knowledgeable decision making on nuclear power. An overview of analytical tools developed by INPRO for this purpose is also provided.

The Nuclear Fuel Cycle Simulation System (VISTA) is a simulation system which estimates long term nuclear fuel cycle material and service requirements as well as the material arising from the operation of nuclear fuel cycle facilities and nuclear power reactors. It is a scenario based simulation tool which can model several nuclear fuel cycle options including existing nuclear power reactor types and future possible reactor types. The past operations of the power reactors and fuel cycle facilities can be modelled in the system, in order to estimate the current amount of spent fuel stored or total Pu in stored spent fuel. It can also accept future projections for nuclear power and other scenario parameters in order to predict future fuel cycle material requirements.The model has been designed to be an optimum mixture of simplicity, speed and accuracy. It does not require too many input parameters if the purpose is just to compare the requirements for selected scenarios. Furthermore, the accuracy of the system can be improved by introducing more detailed and correct sets of input parameters.