IRSN’s report "Fukushima, one year later" illustrates both the vast amount of data that are now available on the accident’s sequences, and the limited understanding achieved so far of a particularly complex accident, beyond its obvious initiating events.
Detailed understanding of how nuclear accidents unfold, of their consequences of all kinds, and of the related decision-making and response processes is a major source of short- and long-term progress in nuclear safety, radiation protection and emergency response management.
The earthquake of March 11, 2011 deprived the Fukushima Daiichi plant of all external power sources, and the subsequent tsunami completely disabled the reactors cooling systems. However, in order to be able to understand exactly how the accident unfolded, a more precise understanding is needed of the ensuing sequence of the other malfunctions that eventually led to the repeated releases of radioactivity. This understanding is facilitated by new pieces of evidence that are gradually being uncovered, but several years will be necessary to explore in detail the still highly radioactive reactor buildings. So far, the severity of the accident and the magnitude of the releases have been assessed through environmental measurements rather than through a precise understanding of the accident's phenomenology. The latter will take all the more time in that the reactors involved are not identical, did not contain equivalent fuel cores, and did not react to the events in the same way.
Committed to enhancing nuclear safety in France and abroad, IRSN is deeply involved in developing knowledge of the circumstances and consequences of the Fukushima Daiichi accident in order to be able to gradually draw lessons from it and adapt doctrines and scientific risk assessment tools. Doing so will take time and a lasting commitment to working closely with international scientific partners, particularly within the NEA and IAEA frameworks.
Download the report : Fukushima, one year later - Initial analyses of the accident and its consequences (pdf file)