In order to prevent a core meltdown, the operators started to use sea water to cool the core. I am not quite sure if they flooded our pressure cooker with it (the second containment), or if they flooded the third containment, immersing the pressure cooker. But that is not relevant for us.

The point is that the nuclear fuel has now been cooled down. Because the chain reaction has been stopped a long time ago, there is only very little residual heat being produced now. The large amount of cooling water that has been used is sufficient to take up that heat. Because it is a lot of water, the core does not produce sufficient heat any more to produce any significant pressure. Also, boric acid has been added to the seawater. Boric acid is "liquid control rod". Whatever decay is still going on, the Boron will capture the neutrons and further speed up the cooling down of the core.

The plant came close to a core meltdown. Here is the worst-case scenario that was avoided: If the seawater could not have been used for treatment, the operators would have continued to vent the water steam to avoid pressure buildup. The third containment would then have been completely sealed to allow the core meltdown to happen without releasing radioactive material. After the meltdown, there would have been a waiting period for the intermediate radioactive materials to decay inside the reactor, and all radioactive particles to settle on a surface inside the containment. The cooling system would have been restored eventually, and the molten core cooled to a manageable temperature. The containment would have been cleaned up on the inside. Then a messy job of removing the molten core from the containment would have begun, packing the (now solid again) fuel bit by bit into transportation containers to be shipped to processing plants. Depending on the damage, the block of the plant would then either be repaired or dismantled.

Now, where does that leave us? My assessment:

[Ed: Although it is not entirely clear from the editing, I think this concluding assessment is by Barry Brook of the BRAVENEWCLIMATE website]:


The plant is safe now and will stay safe.

Japan is looking at an INES Level 4 Accident: Nuclear accident with local consequences. That is bad for the company that owns the plant, but not for anyone else.

Some radiation was released when the pressure vessel was vented. All radioactive isotopes from the activated steam have gone (decayed). A very small amount of Cesium was released, as well as Iodine. If you were sitting on top of the plants' chimney when they were venting, you should probably give up smoking to return to your former life expectancy. The Cesium and Iodine isotopes were carried out to the sea and will never be seen again.

There was some limited damage to the first containment. That means that some amounts of radioactive Cesium and Iodine will also be released into the cooling water, but no Uranium or other nasty stuff (the Uranium oxide does not "dissolve" in the water). There are facilities for treating the cooling water inside the third containment. The radioactive Cesium and Iodine will be removed there and eventually stored as radioactive waste in terminal storage.

The seawater used as cooling water will be activated to some degree. Because the control rods are fully inserted, the Uranium chain reaction is not happening. That means the "main" nuclear reaction is not happening, thus not contributing to the activation. The intermediate radioactive materials (Cesium and Iodine) are also almost gone at this stage, because the Uranium decay was stopped a long time ago. This further reduces the activation. The bottom line is that there will be some low level of activation of the seawater, which will also be removed by the treatment facilities.

The seawater will then be replaced over time with the "normal" cooling water


The reactor core will then be dismantled and transported to a processing facility, just like during a regular fuel change.

Fuel rods and the entire plant will be checked for potential damage. This will take about 4-5 years.

The safety systems on all Japanese plants will be upgraded to withstand a 9.0 earthquake and tsunami (or worse)

My view - This report was posted on a useful site - BRAVENEWCLIMATE - which I am pleased to have discovered. I think it is considerably more informative than many of the press headlines, articles and TV reports, which may contain more hyperbole than expert analysis. The article above also lists other nuclear sites which should be worth investigating, if you remain interested in this subject.

David Fuller's view This report was posted on a useful site - BRAVENEWCLIMATE - which I am pleased to have discovered. I think it is considerably more informative than many of the press headlines, articles and TV reports, which may contain more hyperbole than expert analysis. The article above also lists other nuclear sites which should be worth investigating, if you remain interested in this subject.


I find Dr Josef Oehmen's article and the summary reassuring but since I have no more than an interested layman's understanding of nuclear power stations, I will remain concerned about the outlook for the Fukushima reactors until we are told by Japan's own nuclear experts on the scene that the crisis has passed.

As an enthusiastic investor in uranium shares since July 2010 - on the basis that nuclear power was an effective and clean source of energy, essential to ensure future global GDP growth - potential accidents with one or more of the world's old reactors has been my chief concern. Black Swans do not come much larger than Japan's devastating earthquake and tsunami.

We should soon find out whether this accident of nature has severely damaged the future of nuclear power, or enhanced its credibility after a major scare. Meanwhile, today's chart action by uranium miners looks climactic.

My thanks to subscribers who also sent this somewhat better link to Dr Josef Oehmen's report, posted on Business Insider, which I subsequently discovered from your emails.