See glossary pages 33 to 36 See glossary pages 33 to 36 Fukushima, the inevitable disaster scenario The Fukushima Daiichi Nuclear Power Station (NPS) was equipped with six boiling water reactors (BWRs). An earthquake of exceptional intensity triggered a domino effect leading to the destruction of four nuclear reactors. The lessons learned from this disaster, rated level 7 – the most severe level on the International Nuclear Events Scale (INES) – contributed greatly to the improvement of the safety of nuclear facilities in France and across the world. 11 March 2011, 14:46 – The event that triggered the disaster: an exceptional earthquake Japan was hit by the most intense earthquake in its history, with a registered magnitude of 9.1 on the Richter scale. The epicentre was situated out at sea, 130 km offshore of the north-east coast. The electrical power supply of the Fukushima Daiichi NPP was damaged by the earthquake and the backup power supply took over. The three reactors in operation were immediately shut down by the automatic safety systems (reactor trip, emergency cooling), and the cooling procedure began normally. Less than one hour later, at 15:41, the tsunami caused by the earthquake reached the coast and the Fukushima site. The wave caused by the earth- quake reached up to 15 m in height, devastated 600 km of shoreline and travelled up to 10 km inland. The facility, built to withstand an earthquake of magnitude 8 and a 5.7-metre-high tsunami, was entirely flooded. The tsunami damaged the water intakes in the sea, which led to loss of the heat sink and the cooling pumps, thereby depriving the reactors and the spent fuel pools of their normal cooling sources. The water then entered the buildings housing the emergency diesel generator sets and La communication officielle n’a pas été bonne, c’est évident. Cependant, l’idée du nBWRs.s’arrête à la frontière ne vient pas du Pr. Pellerin .» THE ACCIDENT The BWR reactor The Fukushima Daiichi NPS was equipped with six BWRs. These reactors owe their name to the fact that the heat released by fission boils the water in which the fuel cladding in the reactor core is immersed. The steam produced expands in the turbines which produce electricity. At the time of the accident, only reactors 1, 2 and 3 were in operation (the others were shut down). 11 March 2011 An earthquake, whose epicentre was situated 130 km east of Sendai, followed by a tsunami, hit Japan near the Fukushima Daiichi NPP. Fukushima Tokyo Sendai Fukushima Tokyo Sendai 26 • Les cahiers Histoire de l’ASN • November 2023
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