Deformation measurement sensor operating in a hostile environment and including an optical movement measurement module, and measurement system using said sensor.The sensor includes: an enclosure comprising an opening; a movable element having a first surface that is brought into contact with an object (4) that can deform, for example a nuclear fuel rod, and a second surface that is reflective and extends into the enclosure through the opening; a sealed, resilient connecting component performing a return function between the element and the enclosure; and, inside the enclosure, a module for creating an interference light using a light reflected by the second surface of the element. Deformation of the object results in a modification to the interference light that is representative of the deformation.