This thesis studies the design and evolution of the risk regulation regime of nuclear safety in France between 1945 and 2017. Based on the concept of “risk regulation regimes” (Hood et al, 2001), we propose a model that identifies three periods, corresponding to three types of "philosophies". During the first period (1945-1969), an embryonic regulatory regime developed within CEA is characterized by "experimentation and autocontrol". The second period of "reasonable flexibility" (1969-1986) is marked by an institutional reorganization but leaves many room for maneuver to experts and operators, in a context of intensive industrial development. Finally, during the third period (1986-2017), a
regime "in search of auditability" is the product of hybridization between the regime of "reasonable flexibility" and a standardized regime responding to international good practice (openness, transparency, and regulator’s and expert’s independence). To explain the evolution of the regime, we focus on one of its components, the rules, which we analyze as regulatory instruments, and we describe as "regulatory work" all activities and interactions of a group of agents who act to design, transform and implement these instruments (for our case, flooding rules and guides). We argue that regulatory work is at the same time cognitive, political, social and organizational, and, beyond producing an instrument, it results in exploring evolutions of the regulation regime, while building both the knowledge mobilized in regulatory instruments and interorganizational collective that shares them. This process would explain the relative slowness of the ongoing hybridization process.