In-service inspection and instrumentation for ITER vacuum vessel

In-service inspection (ISI) is required according to the French Order for Nuclear Pressure Equipment and also to protect plant investment and to ensure machine availability. The ITER VV maintenance and monitoring program includes Inservice Monitoring, Periodic Test and Periodic Inspection. Inservice Monitoring includes commissioning tests, continuous vacuum and water leakage monitoring and load follow-on monitoring. Periodic Test includes regular pressure tests and leak tests. For the outer shell welds of the main vessel, the equatorial region of “port #7” and lower penetrations are selected for Periodic Inspection. R&D for ISI is underway and tools and maintenance systems are being developed. Mock-ups were constructed to demonstrate its feasibility. In addition, a study of acoustic emission monitoring has started using a mock-up. The VV instrumentation is a system to monitor the VV status in normal and off-normal conditions. The VV instrumentation system includes approximately 1600 sensors, mounting devices, cables, cable holders, vacuum feed-throughs for the vessel and the cryostat, control cubicles and interrogating systems. Approximately 850 thermocouples are installed to monitor temperatures on plasma-side and cryostat-side surfaces of the vessel. Resistive and FBG strain gauges are also mounted on the vessel surfaces. Displacement sensors and accelerometers are installed to obtain data of VV movements during plasma disruptions or VDEs. These data are utilized to calculate forces on the VV. This calculation is essential to categorize plasma disruption or VDE events during the ITER operational phase.