The nuclear event in Fukushima started with the Tohuku earthquake and the subsequent tsunami in 2011. It was interesting to notice that employing a probabilistic risk assessment (PRA) would have resulted in a decent chance for station backout due to tsunami (5%) and should have been factored into the decision-making process. Now let’s look at the technical details of what happened.
What happened?
The tsunami of 2011 resulted in the flooding of the low-lying blocks of the reactor buildings, and that caused system backout (main and electrical power and the Emergency diesel generators). This contributed to a lack of cooling and, thereby, the reactor melting. The cladding material of the fule rode is made of Zirconium (Zr), and at elevated temperatures, Zr reacted with water leading to the production of hydrogen and explosions. The end result was damage to the fuel core and a release of fission products, including the radioactive I and Cs.
