Currently, at least 3 reactors are having melt out.
Even Mr.Koide from Kyoyo University, who has been the most insightful advisory of us says, there is no major risk of explosion as long as the fuel rods are underground.
Tepco announced they started building the impermeable wall on the sea side of reactor 1~4 on 10/28/2011. They say it takes 2 years to build.
However, in Chernobyl, the biggest concern was the explosion underground after melt out.
They put tons of human robots to settle it down.
They assumed if melted fuel touches the underground water vein, it would cause hydrovolcanic explosion so the entire area of Europe would be uninhabited.
Soviet union was also afraid of the contamination of river.
They ended up putting 800,000 people to settle it down and they suffer from severe health damage.
In Japan, everything is concealed and nobody seems concerned about hydrovolcanic explosion and water contamination though it is likely to be going on already.
Though Fukushima had container vessel, now that all of them were destroyed,the situation is similar to Chernobyl.
Roughly estimating,Chernobyl needed 800,000 people.
In Fukushima, reactors 1~6 are in crisis, which means 800,000×6=4,800,000 people are needed to dedicate their lives.
The video below is very insightful.
It explains what Soviet did to avoid hydrovolcanic explosion.
600 pilots died.
10,000 coal miners were put (all in 20s or 30s) into digging the hole under the reactor, and at least 2500 of them died before 40s.
In short, we must pay 6 times more price for Fukushima.
Yes, nuclear is cheap, and environmentally friendly.