RAMI analysis for EAST upper full tungsten divertor water cooling system

Highlights: • The functional analysis of EAST upper full tungsten divertor cooling system was performed. • A failure modes, effects and criticality analysis of EAST upper full tungsten divertor cooling system was performed. • The reliability and availability of EAST upper full tungsten divertor cooling system and its main functions were calculated. • RAMI analysis approach was applied to EAST upper full tungsten divertor cooling system for its technical risk evaluation. - Abstract: EAST (Experimental Advanced Superconducting Tokamak) device is a D-shaped full superconducting tokamak with actively water cooled plasma facing components. As the EAST project technical risk control and possible failure mitigation approach, RAMI (Reliability, Availability, Maintainability and Inspectability) analysis was required for the upper full tungsten divertor water cooling system, which insures the system to cool the PFCs with high efficient and safety without leakage. At the same time the cooling water could be at suitable pressure, temperature and velocity, water parameters of cooling circuit also could be monitored. A functional breakdown was prepared and all functions are described using the IDEFØ (Integration DEfinition Function – language Ø) method. FMECA (Failure Mode, Effects and Criticality Analysis) was performed to the system initial risk. There are 31 risks for the initial state, including 7 major risks. No major risk remains after taking into account all the actions. RBDs (Reliability Block Diagrams) were prepared to calculate the reliability and availability of each function. The initial availability of upper divertor cooling water system was 93.63%, after optimization the expected availability was 98.56% over 11,520 h. It was assessed that the upper full tungsten divertor water cooling system RAMI analysis results meet the EAST project requirement during this design phase and the results will be qualified further when the system design is updated.