In the service of current and future nuclear power, CEA conducts research on instrumentation, which is essential for the safety of power plants and the digital transformation of the French nuclear industry. For example, CEA is designing TUSHT (High Temperature Ultrasonic Translators) sensors that act as rangefinders, flowmeters, defect meters and imagers. They operate in liquid sodium at 550°C and can be used in sodium-cooled fast reactors (4th generation reactors). The CEA is also developing integrated optical sensors in components fabricated using metal additive manufacturing technology, representative of components of a nuclear power plant. This in situ instrumentation aims to carry out on-line monitoring - temperature, deformation, radioactivity dose, etc. - throughout the life of an installation, whatever the generation of reactor concerned. This monitoring is accompanied by a high level of software acquisition power and innovative visualisation technologies that demonstrate the current capacity to manage large quantities of digital data. This data will be used to feed the future digital reactor, a project led by nine French partners (EDF, CEA, Framatome, ESI Group, Corys, Aneo, Axone, Boost-Conseil and the CNRS with the CRAN automatic control laboratory in Nancy). This “digital reactor” will make it possible to virtually immerse oneself in the operation of a reactor and to access a great deal of information on the behaviour of its components in normal or incidental operating situations.