An approach for the introduction of passive system unavailability in an accident sequence

The objective of the present study is the development of a consistent approach for the introduction of passive safety systems into an accident sequence, usually defined by fault tree and event tree models, in the fashion of and in combination with an active system or a human action. With reference to the thermal-hydraulic passive systems (e.g. natural circulation systems), in addition to the component failures (i.e. mechanical and electrical faults), the impairment of the physical principle upon which the system relies, deserves special consideration. Additional research and investigations with focus for instance on the development of the dynamic event tree which should fit properly the issue, are required to add credit to the methodology and to reach a final assessment.