Conceptual Designs Of Complementary Safety Devices For Astrid: From Selection Method To Selected Options

International audience– To comply with the GEN IV objectives set for it, the 600 MWe Advanced Sodium Technological Reactor for Industrial Demonstration (ASTRID) promises enhanced safety. The ability to shut the reactor down in any condition is one of the most important safety aspects. At the end of ASTRID preconceptual design phase (end of 2012), the need for additional safety devices that would complement ASTRID low void fraction (CFV) design core natural behavior in case of unprotected loss of flow (ULOF) and loss of heat sink (ULOHS) transients emerged from the transient studies in order to meet temperature criteria on coolant, core and primary circuit structures. The process from the selection method, on the basis of ASTRID functional specifications and safety requirements, to the selected options/designs, on the basis of itemization of these specifications/requirements and value engineering, of ASTRID Complementary Safety Devices (DCS) is presented. In this paper, only DCS dedicated to core melting Prevention (DCS-P) that would passively shutdown the reactor, i.e. whose actuation would be triggered by the sole physical effects induced by the transient, are dealt with regardless of whether they would depend on ASTRID first two distinct and independent fast-acting reactor shutdown systems (RBC and RBD) or not. Several concepts of such DCS-P were considered among which SEPIA (abbreviation for SEntinal for Passive Insertion of Antireactivity) concept of absorber subassembly specifically designed by CEA, (DCS-P)-H concept of hydraulically suspended absorber rod subassembly and (DCS-P)-RBD_Curie concept based on the exploitation of the Curie point of the RBD electromagnetic delatch system; they are listed and discussed with regard to whether and how they could effectively match each type of ULOF and ULOHS transient (some concepts that were abandoned are discussed as well). Concepts which are the most promising in ASTRID framework, resulting from the best way their combination could deal with all considered transients, are finally described; these will be further investigated and developed in the near future