A parte il fatto che la radioattività nel mare stranamente non cala sembra adesso che cede il cemento della vasca di raffreddamento sopra il reattore n°4, quello dell’esplosione di idrogeno. Pompa guasta, tecnici arrivati per elicottero.
Tre le cause per il fenomeno della radioattività costante nel oceano: i fiumi che portano il fallout, la rovina stessa che emette ancora radioattività nella misura di 300 gigabecquerel/mese, la sedimentazione di plankton ecc.
Most of that radioactivity dispersed across the Pacific Ocean, where it became diluted to extremely low levels. But in the region of the ocean near the plant, levels of caesium-137 have remained fixed at around 1,000 becquerels, a relatively high level compared to the natural background. Similarly, levels of radioactive caesium in bottom-dwelling fish remain pretty much unchanged more than 18 months after the accident.
In fact, a fresh analysis by oceanographer Jota Kanda at the Tokyo University of Marine Science and Technology suggests that not one source, but three, are responsible. First, radioactivity from the land is being washed by rainfall into rivers, which carry it to the sea. Second, the plant itself is leaking around 0.3 terabecquerels (1012 becquerels) per month, he estimates.
“We can’t answer the basic question of when these fisheries will be able to open.”
But Kanda thinks that the third source, marine sediment, is the main cause of the contamination. Around 95 terabecquerels of radioactive caesium has found its way to the sandy ocean floor near the plant. How it got there, Kanda says, no one is sure. It may have been absorbed directly by the sand itself, or it may be that tiny marine organisms such as plankton consumed the radioactive caesium and then deposited it on the sea floor through their excretions.