This paper present the risk assessment performed for an irradiator of category IV panoramic. The probabilistic safety assessment (PSA) was developed by the Mexican Nuclear Regulatory Authority (CNSNS). The assessment was performed under a Research Contract signed with the International Atomic Energy Agency (IAEA), as part of the Coordinated Research Program (CRP) to Investigate Appropriate Methods and Procedures to Apply PSA Techniques of Large Radiation Sources A thorough review of the incidents that have taken place in such facilities around the world has been performed to identify potential initiating events. The risk measures or end states associated with the irradiator facility have also been defined. A failure mode effect analysis (FMEA) has been carried out to define the possible events that give rise to disturbances in the plant and have the potential to lead to consequences of concern. As a result, a complete list of initiating events has been set up. The analysis of the response of the plant due to the occurrence of disturbances that required a plant shutdown by means of event trees have also been performed. Fault trees have been developed for safety and operational systems. Coordinated efforts between CNSNS and MDS Nordion staff have been carried out to analyze specific function of safety equipment and understand their safety features for the development of accident sequences and fault trees. The operator response to an accident sequence was analyzed by means of the THERP methodology. In order to identify the potential benefits obtained with the application of a second HRA generation methodology, the ATHEANA methodology was applied at selected scenarios and their results are presented as sensitivity analysis. Finally, the quantification of accident sequences was completed using the SAPHIRE computer code.
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