In this paper, we define, design and test a radiation tolerant full autonomous monitoring tool for Nuclear embedded applications. The goal of the instrumentation system was to record the values of some parameters such as dose, temperature or vibrations appearing inside the containment building of nuclear power plants (NPPs) during periods of electricity generation. The analysis of these data will be done to later define with confidence the ageing management policy useful for life-time extension of NPPs. For the design of the modules, we rely on commercial-off-theshelf (COTS) low power electronic components to use battery-supplied power. When the degradation of these components induced by irradiated environments is expected, tolerance is to be considered by components selection, by characterisation as near as possible to nominal environments to assess parameters drifts with working conditions and, finally, by rules and adapted design rules to reach the goals of the applications. A large amount of components starting from discrete transistors or logic units to memories and microcontrollers was associated to define and design a prototype. We then confirm the environment conditions tolerance estimated to up to 2 kGy of total dose and 80°C (176°F) by on-line irradiation experiments for individual components and functions and prototypes. Two different sets of about 60 systems were realised as industrial products and then installed on EDF facilities. They were exploited during NPPs activities of about eighteen months. This large scale experiment was concluded with the inspection of some withdrawn systems. No major degradations were observed showing the efficiency of the hardening method allowing regular use of COTS. Recorded data were thoroughly analysed with the goal to later decide to extend the instrument to a larger number of sites.