NISA has a concise summary of the status of the reactors at Fukushima Daiichi (pdf)
Includes temperatures on reactor vessel surface where available.
They show reactor 2 as cold and unpressured, the rise in temperature in reactor 1 - so something in there is generating heat at a significant rate, but at least the rector vessel is pressurized; and reactor 3 is a mess, warm core and unpressured.
Not mentioned in those reports is the amount of salt in the reactors. A simple (low) estimate is can be made assuming that all the residual decay heat production goes to steam, which has be replenished with salt water:
((7 MW) / (2000 (J / g))) * (10 days) * .03 = 90 720 kilograms
The NYTimes gives something about half of this: http://www.nytimes.com/2011/03/24/world/asia/24nuclear.html?hpw
NaCl has a much lower thermal conductivity than the zirconium cladding at the core temperatures... it also has a much lower melting point.
One more point: I can understand (given the condition of the reactor) all of the difficulties they have been having with maintaining the reactor core stability. What I would like to know is how they lost control of the spent fuel pools.
As mentioned in the comments in a previous post, simple estimates put the timescale for depleting all the water in the spent fuel pools (for reactor 4 at least) at ~5 days. These pools required much less water replenishment than the reactors did at the beginning of the crisis. From the news reports it appears they just forgot about the pools (or these estimates are wrong and there is a leak). On the other hand, perhaps they thought it would be a lost cause if they have a reactor meltdown, and finite pumps and pressure.
The salt is worrying. Also because if they really have ongoing fission the neutron flux will lead to some nasty Cl radioisotopes.
The temperature rise in 1 suggests that the cores are still dynamic, a successful cold shutdown should imply very little residual power generation in the core by this point.
I think the spent fuel pond issue is primarily a site management problem - no one who knows that they are doing in overall charge. But, it sounds like at least one of the ponds (I think in #3) is cracked...
It is also important to remember that these aren't "just" nuclear reactors - they are large industrial facilities with high power equipment, machinery and flammable materials on site. Turning the electricity back on after, shall we say, unschedule stoppages, is going to be quite hazardous - machines coming back on turned on; electrical shorts; overloads, all kinds of fun stuff in random places.
Some of you may know about this already, but the JDF have posted IR imaging of the site.
This comes with a temperature scale and everything.
See Arms Control Wonk
Have to pay close attention to time stamps as conditions and information are now changing several times a day. Gets confusing too when you have to switch time zones.
I think the spent fuel pond issue is primarily a site management problem - no one who knows that they are doing in overall charge.
From the news reports it appears they just forgot about the pools (or these estimates are wrong and there is a leak). On the other hand, perhaps they thought it would be a lost cause if they have a reactor meltdown, and finite pumps and pressure.