Further to my guess in post 576 that there was some nuclear fuel exposed and leaking fom the core of reactor 3 has unfortunately been correct, or so it would seem according to NISA who said, "3.9 million becquerels of radiation was detected from 1 cubic centimeter of water sampled from the floor of the building. The radiation level was about 10,000 times higher than the water inside a normally operating nuclear reactor."
The agency said, "The water sample indicated it is highly likely the leak comes from the reactor itself, not from the pool storing spent nuclear fuel."
Meanwhile, preperations are underway to begin pumping fresh purified water into the reactors once again. This will not aid cooling, which seems to be relatively stable at the present time, but it will help prevent corrosion inside the reactor. Sea-water is doing the job, but officials are concerned that corrosion will fur up the water channels making cooling harder.
The corrosive effects of hot salty water could also accelerate the dissolution of nuclear fuel rods, pellets and casings. The casings are zirconium which is strong, but reactive. It is used as it is virtually transparent to neutrons and thus does not slow the reactor down.
Every day that passes, the decay heat in the reactors grows less and less. Normally, irradiated rods are left to cool in water for a couple of months before being transferred to the common pool where most of the spent rods are kept. The longer they can cool down without any further melting, the higher the chances that no more melting will take place.
It will likely be some time before we find out where the breach is, if ever, but the good news is that some of the instrumentation will be recovered due to the access to mains power.
http://www3.nhk.or.jp/daily/english/25_29.html
