STATE OF THE ART OF THE CONCEPTUAL DESIGNS FOR ASTRID CONTROL AND SHUTDOWN RODS

Itemising ASTRID SPECIFICATIONS  ENHANCED SAFETY  lessons learned from previous fast reactors operations  structural materials and guidance surface coatings/hard-facings  COST SAVINGS  reduce absorber subassembly length  extend residence time to match the residence cycle and, if possible, life span of the absorber elements with those for the fuel cycles (4 runs of 360 or 400 EFPD each)  reduce the total number of absorber subassemblies  keep the enriched absorber material requirement as low as possible  2 distinct and independent fast-acting reactor shutdown systems  Additional core safety features/systems as potential options based on passive insertion of negative reactivity in the core  Designed absorber subassemblies:  RBC subassembly (power regulation/compensation for reactivity change during lifetime/normal or emergency shutdown)  RBS subassembly (emergency shutdown)  SEPIA* subassembly (*abbreviation for SEntinal for Passive Insertion of Antireactivity) { RD common thread: use the most durable materials possible  for RBC and RBS subassembly RD high refractoriness  the most capable of meeting the operating requirements for SEPIA  Hf metal (robust/durable alternative to boron materials + mitigation potential)  IRRADIATION outlook:  hard-facing materials for guidance parts exposed to neutron flux  absorber elements with representative design FOCUS on SEPIA preliminary thermohydraulic/hydraulic analysis RBC & RBS absorber element-CONCEPTS & DESIGN  Two coupled domains…  Fuel SA pin bundle + outside and central wrappers  Spherical absorber elements + capsule  … treated using two project codes  CADET  LICOS/Pleiades  Thermohydraulic feasibility OK  B 4 C is thus far no suitable material solution  Reference option: vented pin + B 4 C pellets + tubular shroud  Alternative (materials & design) options: HfB2/TiB2/Hf; splitted double shroud; single or double-donut shaped absorber column  Thermomechanical calculations  using LICOS/Pleiades project code  to check matching of criteria* * (no absorber or shroud melting; no ACMI; cladding integrity)  to assess the accessibility of higher performances 