"The Fukushima Dai-ichi Nuclear Power Plant Accident (FDNPPA) derived 134Cs, 137Cs and 110mAg in blue sharks captured in the Northwest Pacific during 2011-2018 were assessed for the first time in the aspects of radioactive contamination, temporal variation, maternal-to-fetus transfer, tissue distribution and radiation dose, to demonstrate the impacts of the FDNPPA on blue sharks.
The contribution of the FDNPPA derived radiocesium in blue sharks (>52%) was estimated based on 134Cs/137Csactivity ratios. The effective and ecological half-lives of the FDNPPA derived 134Cs (270 d, 410 d), and 137Cs (430 d, 450 d) were calculated.
These contaminations decreased with time and returned to the level before the FDNPPA during the period of Sep. 2017-Sep. 2018.134Cs and 137Cs tended to distribute in muscles, while 110mAg mainly distribute in their guts. 134Cs and 137Cs were also transferred to fetuses and the activities were up to ~30% of the maternal activities.
Dose assessment demonstrated that the highest FDNPPA derived dose rate in blue sharks (~0.42 nGy/h) was far below the ERICA ecosystem screening benchmark of 10 μGy/h and the committed effective dose in humans from ingesting blue shark meat (0.06-0.90 μSv) was far less than that from annual consumption of food and water.
It was far from causing radiation harm to blue sharks and humans, suggesting that the impacts of the FDNPPA on blue sharks were not significant." This is what the researchers who published the study on Chemosphere said: Radioactive impacts of the Fukushima Dai-ichi Nuclear Power Plant Accident on blue sharks in the Northwest Pacific.
The triggering cause of the accident was the Tōhoku earthquake and tsunami of 11 March 2011. At the moment of the quake, the plant's anti-seismic safety system instantly shut down all reactors with an automatically activated SCRAM procedure.
After shutdown, the reactors still required cooling to continue, to dissipate the heat generated by the residual nuclear reactions, which normally persist for a period of a few days. In the absence of the electricity supplied by the reactors, the emergency electric generators, powered by diesel and present for this purpose in the building of each reactor, were immediately activated, which provided the energy necessary to allow the normal operation of the cooling systems.
The interruption of the cooling systems and of every source of electrical power, as well as a malfunction of the passive emergency cooling system of reactor 1, caused in the following hours the loss of control of reactors 1, 2 and 3, which were active at moment of the earthquake.
All three reactors underwent complete meltdown, albeit at different times, on dates between 12 and 15 March. Over the next few hours and days, four distinct explosions occurred in the reactor buildings, caused by leaking hydrogen, some of which destroyed the upper structures of two reactor buildings.