Fukushima reactor #4 heating very fast

There has been a drip of very worrying news yesterday and today on reactor number 4 of the ill-fated Fukushima Daiichi NPP.

You may remember that it was first said that reactor number 4 only had a pool of spent nuclear fuel stored when the accident happened (which was in itself very worrisome), but it has been known recently (thanks to worker tweets) that this was false and the reactor was in fact operative in March 2011 when the earthquake and tsunami destroyed the site. So there are at least five uncontrolled reactors in coastal Fukushima prefecture: four in Fukushima Daiichi and one in Fukushima Daini further south (I say at least because there's a lot of information that is being held and the situation could be even worse than that - if worse is a word that still makes any sense in this context of Hell unleashed).

The reactor is heating very very fast: 27ºC in three days, plus 3ºC in just three hours earlier today. At this rhythm it will hit 100ºC (water boiling point) in a matter of hours if it has not already (it was 72ºC at 4pm JST).

More: TEPCO has admitted also that:

• Water injections can't stop the heating anymore. 
• They have been injecting massive amounts boric acid (neutron absorber, used to slow down nuclear reactions) and water into this reactor in what seems a last ditch attempt that probably failed anyhow.   

Also steam has been growing over reactor 4 tonight (Japanese time, today for Europe and North America).

So expect something big happening in that reactor in a matter of hours probably.

Regularly updated information sources on the disaster: Fukushima Diary, Energy News.

Update: helicopters are surveying the area. 

Update (Feb 7): thick smoke at reactor 4.