A new study by the Ministry of Energy announced that the RPV of Reactor 1 has failed, and over between 85% and 90% of unit 1′s fuel fell down into the primary containment vessel and is embedding itself in the concrete containment floor. The institute used a computer program to estimate the damage to the fuel rods, and calculate the damaged state of the fuel.
In all three units, core-concrete reaction took place according to Tepco.
At unit 1, a maximum 65 cm depth of concrete was eroded, which, in the worse case, leaves only a 37 cm thick layer of concrete between melted fuel and the PCV’s steel bottom.
The results are very serious, according to their estimate, fuel cladding tubes were damaged 5 hours 31 minutes after emergency shutdown, and the RPV bottom was damaged 7 hours 21 minutes after emergency shutdown.
In another study, Tepco says that “considerable amount” of fuel fell down into PCV at unit 1, without saying exactly how much, and that at units 2 and 3, “some of the fuel” fell down into PCV.
The new calculations also show that about 70% of the fuel in Unit 2 is also fallen into the containment, and what fuel remains in Reactor 3 is likely in the same state.
Experts are worried about the effects of corium on the concrete floor of the containment vessel, which varies in thickness. There is evidence of new activity in the corium as it escapes into the containment and begins eroding the concrete.
The contaminated water is believed to leak through, for example, interstices in pipes. A 12 cm depth of concrete was eroded at unit 2, and 20 cm at unit 3.
Tepco’s handouts on this topic (Japanese) :Estimate of fuel damage
Fuel damage workshop :
Condition of fuel
Plant behaviour after accident
Improvement and assessment of JAEA model based on real conditions
List of approaches to grasp fuel condition
MAAP analysis and core-concrete reaction study
Source: NHK News
Source: Yahoo Japan
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