Il Giappone ha 55 reattori in 17 località, e ne trae un terzo della propria elettricità. Se i tentativi di raffreddamento dei reattori fallissero, il risultato sarebbero esplosioni e contaminazione radioattiva.
La fusione avviene quando la reazione nucleare delle barre di zirconio che contengono il combustibile di uranio non è più controllata, il nocciolo radioattivo arriva a migliaia di gradi e inizia a liquefarsi. Una fusione completa può rompere la struttura di contenimento e altre barriere protettive diffondendo prodotti radioattivi. Tuttavia, un reattore non esplode come una bomba atomica. Per prevenire la fusione il primo passo fondamentale è la riduzione della temperatura in all the reactor vessel. The reactor core is surrounded by a heavy sarcophagus of steel and this in turn comperto by a cage of concrete and steel containment.
In a reactor in Fukushima, in operation since 1971, are ongoing attempts to prevent the meltdown. The work is complicated by the fact that the need to release pressure in the reactor vessel has led to an explosion that brought down the roof and walls of the containment building. According to official sources, the building is intact, but concerns persist about the fissile fuel overheated. In a desperate move, have pumped large amounts of sea water in the reactor vessel to try to cool the hot core, which, according to experts, means that the Japanese are trying a desperate move because the sea water - combined with boric acid, which absorbs neutrons of nuclear fission - is corrosive which means the loss of the plant. Not dramatic, since the reactor would have turned 40 a few days and was destined soon to be divested. Official sources say that Japanese units 1, 2 and 4 Fukushima have increased the pressure in the containment buildings and equipment failure. As a result, was given a steam vent in each unit and considered to release more to reduce the pressure. The central Onagawa, with three reactors, is in a state of emergency. The Japanese Nuclear Safety Agency said Saturday that a small amount of radioactive cesium release of a reactor in Fukushima container building before the explosion. According to official sources, the presence of cesium does not mean there is necessarily a partial melting, because it could result from a mechanical failure. Of the more than 180 000 people evacuated, about 160 have been exposed. The authorities reported that radiation absorbed in one hour is equal to that absorbed in one year for the natural radioactivity. Exposure to radioactive iodine released in an accident can cause thyroid cancer.
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