Generation IV SFR Nuclear Reactors: Under Sodium Robotics for ASTRID

For non-removable components of the future ASTRID prototype, repair operations will be performed in a gas environment. If the faulty area is located under the sodium free level, the gas-tight system will have to contain the inspection and repair tools and to protect them from the surrounding liquid sodium. Concerning repair tools, the unique laser tool has been selected for future SFRs: the repair scenario for in-sodium structures will first involve removing the sodium (after bulk draining), then machining and finally welding. Concerning conventional tools (brush or gas blower for sodium removal, milling machine for machining and TIG for welding for which its feasibility was demonstrated in the 1990's) are still considered as a back-up solution. The maintenance of future ASTRID nuclear reactor prototype (inspection, repair) will be performed during shut down periods with some robotic carriers which have to be introduced within the main vessel, in primary 200 deg. C sodium coolant with argon gas cover. Inspection campaigns will be 20 days long. These robots (or carriers) will allow bringing inspection and repairing tools up to concerned components and structures. The needed degrees of freedom associated to these operations will be assumed either directly by the carrier itself or by specifics lower end carrier device for accurate local positioning. Several carriers will be designed, well adapted to specific needs: type of maintenance operation and location of inspection and repair sites. Feedback experience was gained during Superphenix SFR operation with the MIR robot which allowed to successfully make the Non Destructive Examination of main vessel welding joints, the carrier being outside bulk sodium. Operating conditions for the ASTRID robots will be harder from those of the MIR robot: temperature ranging from 180 deg. C to 200 deg. C, radiation dose ranging from 105 to 106 Gy, but mainly direct immersion within liquid sodium coolant. At the design phase of these robots, three main configurations have been considered, depending on the adopted solution for robot component seclusion: Zone 1: Tight surrounding shell cooled by argon gas flow. Constraints: irradiation and 70 deg. C temperature, Zone 2: Tight surrounding shell (not cooled). Constraints: irradiation and 180 deg. C-200 deg. C temperature, Zone 3: No tight surrounding shell. Constraints: irradiation and 180 deg. C-200 deg. C temperature and immersion within liquid sodium. It appears that some technical solutions do exist for future in sodium carriers, using available trade components. Qualification tests will be necessary in order to confirm some specific components (such as polymers, greases, sensors, reducers, motors, bearings). For bearings, a specific test program has to be performed in order to check their capability for static and dynamic loadings during in sodium operation (without lubricant). Electrical motor development for 200 deg. C operation seems possible and R and D work is being done in 2013 with already available components. (authors)