Paper short abstract:

This talk re-examines the use of the Rasmussen Report and the probabilistic methods in France during the 1970s. The engineers received the report with enthusiasm but some reserves. I link this appreciation of the Report to underpinning scientific, and political contexts.

Paper long abstract:

This talk aims to highlight the nexus between the representations of scientists about what is a "severe accident" and the way "nuclear safety" is assessed in the very specific French context of nuclearity [Hecht 1998]. I will focus on the discussions started in France after the publication of the Rasmussen Report in 1974 about the use of probabilistic methods of risk assessment and their articulation with the traditional deterministic "methods of barriers". At this time severe accidents were understood as accidents with unacceptable releases of radionuclides outside the power plant. These scenarios were considered highly hypothetical by the scientists and engineers even if they started to study these. The first large scale probabilistic nuclear safety assessment, the Rasmussen report (1974-1975), suggested that a nuclear core meltdown was not as « hypothetical » as expected in the early 1970. This point caught the attention of the Institut de Protection Nucléaire (IPSN) that took more in consideration these scenarios for enhancing safety. Some Rasmussen conclusions were counter-intuitive, like the fact that a core meltdown is more likely to occur after a small break in the primary circuit than after a large one. I show that the choice of using or not the probabilistic methods of risk assessment was very different for each institution and could be determined by the economic and political circumstances.