Functional safety assessment process for MITICA safety system in the ITER neutral beam test facility

The Safety System of the ITER Neutral Beam Test Facility (NBTF) aims to deal with all risks for people and environmental safety related to SPIDER and MITICA operation. A coordinating system, called Central Safety System (CSS), was designed to supervise safety-relevant systems, implement safety actions on the different plant units to guarantee the NBTF personnel safety and provide an effective human interface of the NBTF safety. The SPIDER CSS, the part of CSS dealing with SPIDER and NBTF shared items, is in operation, while the MITICA CSS is in the detailed design phase. The MITICA CSS will have the same architecture and principles as SPIDER CSS. A safety risk analysis was carried out based on a Hazard Identification (HAZID) methodology: MITICA plant was partitioned into 46 nodes, for each node possible hazards were identified based on a list drawn up from EN ISO 12100 standard and, after that, the risk assessment process was performed. As a result, the Safety Instrumented Functions (SIF) to be implemented in the MITICA CSS were defined. Through a Layer Of Protection Analysis (LOPA) approach, in accordance with the IEC 61511 standard, the Safety Integrity Level (SIL) was allocated to each SIF. This paper will describe the MITICA risk analysis process and present the relevant functional safety results for MITICA CSS implementation.