Update 17th March 07:41 Tokyo
So we have potentially damaged containment vessels and significant fuel melt that will lead to radiological discharges are likely.
In Tokyo, the risk from radiation remains low. Beyond Japan, it remains unbelievably low!
If you are not near the plant, you are still OK.
Update 15th March 18:14 Tokyo
All the info above remains correct according to the available data. The lack of hard data (which I mentioned) has not improved and is what was making even me a little nervous: My current feelings on the situation. <-- This has turned out to be sadly prescient. The best info summary currently available is Gakunman’s Live Report.
Original post, no longer current.
The good news: As I understand it, both units 1 and 3 have been flooded with seawater and are now safe. They will never produce power again, but public safety is more important than economic return. 4 has had a fire, which I understand to be under control now, but was not fuelled – it is bad for raising temperature in the area and could throw up tiny amounts of materials in the smoke but this is not our biggest problem.
Unit 2, after suffering much the same problems as the other ones, has also reached the flood-with-seawater level to cool the core down.
The pumps which are supposed to keep the fuel rods covered with sea water have a problem so the level was not high enough and it appears that up to about 80 cm of fuel rod were exposed for some time. This probably means that some of it will have melted (see What the Media Doesn’t Get About Meltdowns for info on melted fuel). Some radioactive materials are likely to have escaped.
If I understand correctly, this is not dis-similar to the Three Mile Island accident which (as noted in the previous post) was much less bad than the popular perception of it.
The water level is rising again according to Chief Cabinet Secretary Edano which is good because if it cools down, no more melts. It is also very important to note that by “some radioactive materials” this should still only affect the very local area (within 3 km to cause any potential health problem at all and 20 km for an increased risk from atmospheric discharge).
So, where does the melted stuff end up? In the containment vessel which was intact up until this morning. This morning, when I was kind of expecting to wake up to all three being totally under control, we’ve had further bad news. The torus at the bottom of the containment vessel (a key part of the cooling mechanism) and the containment vessel itself are damaged.
For those who have been worrying about how bad it could get, this is about as bad as it could get. The loss of more radioactive material into the surrounding environment and atmosphere is inevitable. This still does not mean the end of the world. The danger outside the 20km exclusion zone remains low. The radiation levels at the plant are very high, but these drop off with distance squared (ie very quickly) and dosages must be kept in perspective.
We need more information on how bad the damage to the containment vessel is to make any further insights. This is the most serious accident of recent years but we are still all basically safe!