Corium: the word taboo Tepco. Why the company responsible for the biggest nuclear disaster in the world never talk about it? Just because it’s the most dangerous substance ever created by man, a sort of magma uncontrollable and unmanageable, with immeasurable consequences.
When the corium Fukushima was formed?
The failure of the cooling system of the Fukushima Daiichi plant was held March 11, 2011, but we do not yet know the exact cause or causes (earthquake, tsunami, and possible human error in the reactor 1). Anyway, after two months of cover-ups, TEPCO has finally acknowledged that the hearts of Units 1, 2 and 3 had melted. The reactor 1 has not been cooled for 14 hours and 9 minutes, 2 for 6 hours and 29 minutes and 3 for 6 hours and 43 minutes ( link ).
According to the data known to fuel reactors Fukushima Daiichi, we know the masses of the three fuel corium:
- Corium 1: 69 tons
- corium 2: 94 tons
- corium 3: 94 tons
is a total mass of molten fuel to 257 tons.
For comparison, the corium Three Mile Island was a mass of about 20 tons and that of Chernobyl 50 to 80 tons. In Fukushima, the corium are therefore unprecedented mass, which explains, among other difficulties faced by experts to model the accident.
In reactor No. 1 of Fukushima Daiichi, the heart was composed of 400 assemblies consist of 63 fuel rods each. Reactors 2 and 3 were for their compounds, each of 548 assemblies, constituted themselves 63 fuel rods. Knowing that a pencil contains about 360 pellets, we can deduce that in the three reactors concerned, there are more than 33 million chips in play
And as each pellet is supposed deliver as much energy as one ton of coal, it is understandable why the corium develops a tremendous heat in total autonomy.
At Chernobyl, it took 6-7 months to get a "cold shutdown" of the mass of corium. But 18 years after the accident, in 2004, we still measured a temperature of 36 ° C near the molten fuel (2).
In Fukushima, the latest roadmap Tepco (3) in July – as the analysis the IRSN – announced a "cold shutdown" reactor for January 2012: the company communicates only effect on the reactors, not the corium. And for good reason, it may take a few decades before a cooling one. We must therefore see the term "cold shutdown" as a facade of communication minimizing the disaster.
As for the corium 3, it should be noted that it contains plutonium MOX fuel. The latter consisting of plutonium 6.25% , and the heart of the reactor 3 containing 32 assemblies of the 548 present, we can evaluate at least 300 kg mass of plutonium MOX fuel contained in the corium 3, excluding the plutonium from spent fuel contained in the other assemblies 516 (4).