This report on modular high temperature gas cooled reactors (modular HTGRs) is intended to supplement the IAEA Safety Standards Series. The publications in this series related to the present report are the Safety Requirements on Safety of Nuclear Power Plants: Design [1] and the Safety Guide on Safety Assessment and Verification for Nuclear Power Plants [2]. Clarification of the accident analysis methodology at the next level is provided by the Safety Report on Accident Analysis for Nuclear Power Plants [3], which contains a comprehensive description of the general methodology for accident analysis.

The objective is to establish a set of practical suggestions based on the best practices worldwide for performing accident analyses of nuclear power plants. These reports do not focus exclusively on a specific reactor type; however, although most recommendations are general and applicable to all types of nuclear reactor, specific recommendations and examples do apply mostly to water cooled reactors.

More specific guidance on performing accident analysis will depend on the characteristics of the nuclear power plant in question, and is usually developed for specific reactor designs or groups of reactor designs. Such design specific guidance is now being developed as separate safety reports. The reactor types covered include pressurized water reactors (PWRs) [4], boiling water reactors (BWRs), pressurized heavy water reactors (PHWRs) [5] and high power channel type reactors (a Russian design known as the RBMK) [6].

Furthermore, since several Member States are in various stages of design and deployment of modular HTGRs, and with several vendors developing HTGR systems and components, new guidance on accident analysis specific to modular HTGRs is useful. This report complements the Safety Guides in the IAEA Safety Standards Series and supports the Member States in establishing their own analysis capabilities and safety standards.