I've repeatedly noted that we may experience a "China syndrome" type of accident at Fukushima.
For example, I pointed out in September:
Mainichi Dailly News notes:
As a radiation meteorology and nuclear safety expert at Kyoto University's Research Reactor Institute, Hiroaki Koide [says]:
The nuclear disaster is ongoing.
At present, I believe that there is a possibility that massive amounts of radioactive materials will be released into the environment again.
At the No. 1 reactor, there's a chance that melted fuel has burned through the bottom of the pressure vessel, the containment vessel and the floor of the reactor building, and has sunk into the ground. From there, radioactive materials may be seeping into the ocean and groundwater.
The government and plant operator TEPCO are trumpeting the operation of the circulation cooling system, as if it marks a successful resolution to the disaster. However, radiation continues to leak from the reactors. The longer the circulation cooling system keeps running, the more radioactive waste it will accumulate. It isn't really leading us in the direction we need to go.
It's doubtful that there's even a need to keep pouring water into the No.1 reactor, where nuclear fuel is suspected to have burned through the pressure vessel. Meanwhile, it is necessary to keep cooling the No. 2 and 3 reactors, which are believed to still contain some fuel, but the cooling system itself is unstable. If the fuel were to become overheated again and melt, coming into contact with water and trigger a steam explosion, more radioactive materials will be released.
We are now head to head with a situation that mankind has never faced before.
Mainichi also reports:
The Ground Self-Defense Force (GSDF) and residents of the zone between 20 and 30 kilometers from the stricken Fukushima No. 1 nuclear plant held an emergency evacuation drill on Sept. 12 ... in preparation for any further large-scale emission of radioactive materials from the plant.
The scenario for the drill presupposed further meltdown of the Fukushima plant’s No. 3 reactor core, and a local accumulation of radioactive materials emitting 20 millisieverts of radiation within the next four days. ...
And nuclear expert Paul Gunter says that we face a "China Syndrome", where the fuel from the reactor cores at Fukushima have melted through the container vessels, into the ground, and are hitting groundwater and creating highly-radioactive steam:
Nuclear expert Arnie Gundersen said recently that a new built up of hydrogen may cause the reactors to explode again:
Nuclear expert Dr. Ian Fairlie - former scientific secretary to the United Kingdom government’s Committee Examining Radiation Risks from Internal Emitters, who advises the European Parliament as well as local and national authorities in several countries - told Dr. Helen Caldicott:
Really it’s just a matter of time before it [the corium] goes through and into the bottom of the actual station itself. And if it ever hits ground, well… there’s a lot of water sloshing around there, if molten fuel gets into that water it will immediately flash to steam and you will have huge steam explosions going on.
I’m not ruling out a nuclear bomb-type explosion”.
And the architect who actually designed Fukushima Reactor No. 3 - Uehara Haruo, former president of Saga University - told popular Japanese news source Live Door on November 17th that (translation courtesy of Fukushima Diary):
In this interview, [Haruo] admitted Tepco’s explanation does not make sense, and that the China syndrome is inevitable.
He stated that considering 8 months have passed since [the March 11th earthquake] without any improvement, it is inevitable that melted fuel went out of the container vessel and sank underground, which is called China syndrome.
He added, if fuel has reaches a underground water vein, it will cause contamination of underground water, soil contamination and sea contamination. Moreover, if the underground water vein keeps being heated for long time, a massive hydrovolcanic explosion will be caused.