Are older nuclear reactors less safe? Evidence from incident data in the French fleet

This paper studies the impact of age and reactor technology on safety in the French nuclear fleet between 1997 and 2015. We use a novel dataset encompassing over 19,000 nuclear safety events declared by plant managers to the French regulatory agency. A major problem for evaluating the effects of age and technology is that declarations of safety events are influenced by the plant managers' level of transparency. We deal with this problem by restricting the analysis to the occurrences of particular types of events, such as automatic shut-downs. These events, due to their technical specifics, exhibit perfect detection and declaration rates. We obtain the following results. First, technology has a strong impact on reactor safety. Second, age has a significant and technology-specific effect on reactor safety. For instance, while in 1997 one additional year of age led to a 15% increase in the expected number of automatic shut-downs among the 900 MW reactors, this number was reduced to only 6% in 2014. In comparison, the 1450 MW reactors undergo a significantly larger number of automatic shut-downs, but age has a smaller effect on their rate of occurrence. Finally, we find that local transparency, defined as both detection abilities, reporting behaviours and declaration guidelines, plays a significant role in the explanation of the observed variations of declarations of events.