Les cahiers de l'ASN #03 - 10 years after Fukushima

A sequence of natural phenomena of an exceptional scale creating a domino effect: all the ingredients were there for a major accident at the Fukushima Daiichi NPP. In four days, one of the world’s largest nuclear power plants was destroyed. A major earthquake, followed by an exceptional tsunami, led to the failure or loss of all the emergency systems. 14h46 15h41 Disaster scenario for a major nuclear accident THE FUKUSHIMA NUCLEAR ACCIDENT 12 march 2011 EXPLOSION IN REACTOR 1 BUILDING The building which housed this reactor collapsed following a hydrogen explosion. 11 march 2011 EARTHQUAKE Japan recorded the strongest earthquake in its history. Its magnitude was 9.1 on the Richter scale, with an epicentre at sea, 130 km off the North-East coast. The electrical power supply was damaged by the earthquake but the emergency supply took over. The three reactors in operation were immediately shut down by the automatic safety systems, and the cooling procedure began normally. TSUNAMI The wave caused by the earthquake, which was up to 30 m high, devastated 600 km of shoreline and penetrated up to 10 km inland. The emergency electricity source was flooded by the tsunami and the water supply pumps were thus disabled. At the same time, the seawater intakes were clogged with detritus created by the tsunami. The reactor cores were then only cooled by a single system, the failure of which would inevitably lead to core melt. 1 * See glossary page 24 2 • Les cahiers de l’ASN • March 2021