Challenges and R and D program for improving inspection of sodium cooled fast reactors and systems

Improvement of In Service Inspection and Repair (ISI and R) capabilities has been identified as a major item of future SFR since ISI and R is strongly involved in safety analysis (number 1 defence line: verification of material and equipment state during reactor life), in economy reliability, and in investment protection (repair). Based on the feedback experience of sodium cooled reactors, a pluri-annual R and D program was defined for the development of sodium fast reactors ISI and R capabilities. This specific R and D program is parted in four : - Conceptual design improvement of the primary circuit, in order to limit the structures and components to be surveyed, to locate the sensible zones in accessible areas from outside or from inside (welded junctions) and to reduce the welds. - Development of the measurements and inspection techniques. Two axes are investigated : continuous monitoring during operation (instrumentation), and periodic inspection tools (NDE during maintenance period). - Providing the necessary accessibility and development of remote control (robotics) with adapted carriers. - Identification, development and validation of repair processes and techniques for repair interventions. ISI and R objectives for sodium fast reactor primary circuits have been specified with respect to the preliminary specifications issued by the French utilities (EDF) for the future nuclear plants (GENIV). Taking into account of the feed back knowledge, and the updated specifications, the main actions of ISI and R R and D program are : - Design : SFR conceptual design looks for improvement and innovative solutions (pool, loop, hybrid...) as regards ISI and R capabilities and accessibility. - ISI and R techniques : - Measurements and diagnosis during operation often require in sodium sensors able to support high temperature conditions (550 deg. C). Interest was identified for telemetric measurement as used on Phenix Plant. - Direct examinations of the material state remain necessary and Non Destructive Techniques for periodic inspections are studied. UltraSonic (US) technique seems to be the basis, but EMAT is also investigated specifically to provide global diagnosis of the reactor vessel with few locations of a multi-array transducer. Possibilities for inspection from outside based on guided waves (through several internal structures) are also examined according to the Phenix experience (inspection of the core support shell). Transducers for these periodic inspections (under sodium at 180oC) are studied. Ultrasonic coupling at relatively low temperature has also to be optimized. - Examination of immersed structure surface, under sodium condition, seems possible and could be used also for remote intervention (under sodium viewing). - Simulation codes and experimental facilities : Corresponding to these numerous techniques, experimental tests are planned in water and then in sodium, meanwhile simulation codes (e. g. CIVA) must be developed / adapted to evaluate and compare the promising designs. The main milestones of this R and D program are : - Transducers validation (US telemetry, and NDT sensors) under sodium conditions in 2012, - Definition of key elements of robotic equipment for under sodium intervention and first validation of repair intervention processes and techniques (cleaning, machining, welding) in 2012. (author)