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International audience; For some years now, CEA, namely the French Alternative Energies and Atomic Energy Commission, leads researches and developments to improve safety and availability of the GEN-IV Sodium-cooled Fast Reactors (SFR). One of these items of development concerns the core control and monitoring of the SFR Instrumentation and control system (IandC system). The Core Control and Monitoring System (CCMS) must be able to operate in all core conditions. The CCMS involves measurements, estimations and tracking of core control and monitoring parameters. It also commands the core control actions performed by the neutron absorber rods and primary system pumps. In this way, the CCMS uses all the means available to keep the operator informed of the state of the core components and core operation, while being able to detect events that could lead to the deterioration of core components. The measurements system of the CCMS comprises five main sub-systems devoted to take continuous measurements to insure a high level of both nuclear safety and power plant availability. Those five measurements sub-systems are the Neutronic Measurement System (NMS), the Thermal Measurement System (TMS), the Hydraulic Measurement System (HMS), the cladding Leaktightness Measurement System (LMS) and the core Geometry Measurement System (GMS). The five measurements sub-systems following features can be distinguished-NMS provides neutronic indications such as neutronic power and reactivity and relies on in-vessel high-temperature fission chambers. -TMS provides thermal indications such as inlet core or outlet subassembies coolant temperatures and relies on short response time thermal devices. -HMS provides hydraulic indications such as inlet core or outlet subassembies coolant flow rate and relies on miniaturized eddy current flowmeters. -LMS provides fuel cladding leaktightness defect indications (cladding rupture) and fuel cladding leaktightness defect location indications (ruptured sub-assembly). -GMS provides dynamic core geometry deformation indications (abnormal movements or vibrations of a fuel sub-assembly) and relies on high temperature ultrasonic transducers, high temperature strain gauges and accelerometer.This paper describes the definition and design of three of these five measurements sub-systems (TMS, HMS and GMS) which has been conducted in accordance to the methodology of systems engineering for the basic design of an innovative GEN-IV nuclear-fission power demonstrator called ASTRID. Moreover, in order to comply with their key operational requirements, the measurement sub-systems must be reliable and maintainable, that means capable respectively of achieving a continuous service and undergoing modifications and repairs. These dependability requirements completed with other operating safety requirements such as the inability of leading to damages to other vessel components (called innocuity in systems engineering). Then furthermore, this paper highlights how the measurements system development fulfils all the key GEN IV SFR requirements.