It would appear that the authorities are now scrapping the bottom of the barrel for solutions to control the situation (if they were ever in control), much like the Chernobyl response. The differences at the Fukushima installation are of course much more dire than even for the Chernobyl accident.

i) There are six reactors at the Fukushima installation all with on site storage of spent hot fuel rods. The Fukushima Reactor No 4 boiled dry spent fuel pond fire has completely destroyed the reactor containment building exposing the environment to these radionuclide fission products.

ii) It would appear that all six reactors have on site spent fuel reactor ponds.

iii) I suspect that the explosion in reactor number 3 which completely destroyed the environmental containment building along with most of reactor building, was subject to a Plutonium fizzle (yellow flash) within the reactor (reported Neutron radiation was reported prior to the explosion) rather than a hydrogen explosion, which sent the stored reactor spent fuel storage pond 1500 feet into the air.

iv) Using water cannon as a method of cooling down the reactors and storage ponds is a desperate last measure.

v) A Greenpeace Nuclear consultant stated last night on the BBC has stated that about 1800 metric tonnes of reactor fuel and hot spent fuel is on site at Fukushima distributed among the 6 reactors although he did say that only a few percent of this amount will most likely become airborne aerosols, much as the case in Chernobyl.

http://www.reuters.com/article/2011/03/15/japan-quake-russia-nuclear-idUSLDE72E1TJ20110315

http://www.reuters.com/article/2011/03/15/uk-japan-nuclear-chernobyl-idUSTRE72E69P20110315

They may have to change the Nuclear Accident scale and expand it to an 8.