On March 11, 2011 after a 9.0 magnitude earthquake, a 15-metre tsunami disabled the power supply and cooling of three Fukushima Daiichi reactors and within the first three days all three cores largely melted (World Nuclear Association 2016). The tsunami flooded the Daiichi plant which disabled 12 out of the 13 back-up generators on site, disabled the heat exchangers for dumping reactor waste heat and decay heat to the sea which eventually caused the three units to lose the ability to sustain proper reactor cooling and water circulation functions (World Nuclear Association 2016). After two weeks, the three reactors (units 1-3) were stabilized with water addition and by July they were being cooled with recycled water from the new treatment plant. It was only declared an official 'cold shutdown condition ' in mid-December 2011. The FDNPP accident was rated 7 on the INES scale, due to high radioactive releases over days 4 to 6, eventually a total of about 940 PBq (World Nuclear Association …show more content…
Restrictions for tap water were canceled by April 1, 2011. 131-I levels dropped faster than expected suggesting a shorter effective half-life in tap water than 8 days and did not indicate any exceedances of the early regulatory limit for 134Cs + 137Cs of 200 Bq/kg (Merz, et al, 2015). Later monitoring did not show any detectable 134Cs + 137Cs in tap