Japan Earthquake and Nuclear Situation and Information

15 03 2011

The following was sent to me from a friend in the nuclear business in Japan.

I don’t want to make light of the situation but CNN and others can sometimes put only the worse on the air and often don’t check out their sources. Fear sells news just like last night on Indian TV they showed the images of a mushroom cloud when they reported on the story. Nuclear reactors need to be handled an operated very carefully….radiation is not something to fool around with but they are not nuclear bombs!

A little background:

There are 2 reactor sites that are involved both belonging to and operated by Tokyo Electric (TEPCO). They are Fukushima Daiichi (meaning Fukushima #1,) and Fukushima Daini (meaning Fukushima #2). Fukushima #1 has 6 reactors and Fukushima #2 has 4 reactors. The oldest Fukushima #1 Unit 1 (F1-1) started in 1971. The newest is Fukushima #2 Unit 4 which started in 1987. They are all Boiling Water (BWR) type reactors which are in operation throughput the world. The were supplied by a combination of GE, Toshiba and Hitachi. These sites are about 250KM (~150 miles) northeast of Tokyo.

At the time of the earthquake 7 of the 10 reactors were operating; 3 were already shutdown for annual maintenance and inspection. All the operating reactors shutdown automatically as a result of the earthquake. However even though the reactors are shut down i.e there is no more nuclear reaction taking place, there is tremendous heat still being generated by the nuclear core so called “decay heat” you may hear referred to in the press reports. Because of this heat the core needs to be continuously cooled which requires water but also pumps which in turn requires power (electricity). Power for these cooling systems is generally provided by off-site sources when the reactor is not running but in an event like an earthquake this “Off-site” power may not be available which is the case for the F1 plant. The F2 plant does have offsite power so cooling has been OK. In case there is no power like at F1 there are emergency diesel generators which are suppose to start and provide that power. These did not start for as yet an unexplained reason. So without power the cooling systems didn’t work. Without cooling the temperature in the core rises and so does the temperature inside the primary (reactor) containment. The containment is a concrete structure that surrounds the reactor and core to protect it and isolate it from the surroundings. It is one of the many barriers to prevent radiation release. I’ve attached diagram that may help you understand the configuration. Two things happen when the core temperature rises; the temperature inside the reactor containment also rises causing the pressure inside to increase and the water that covers the core may boil away exposing the nuclear fuel. The containment has certain pressure limits so if the the preasure gets too high the containment must be “vented” which is what they did. This releases very small amounts of radiation to the atmosphere. If the nuclear core gets uncovered the temperature will quickly rise and the fuel could be damaged or even melt. This releases much more radiation into the primary containment. As long as the containment is OK the radiation will be contained.

So the situation as best I know from all the emails I have received is the following:

F1 Unit 1 did not have cooling for a long period of time and the core was most likely uncovered to some extent. They have now been able to inject sea water into the core and the water level has been restored. There was an explosion (not nuclear) on this unit that damaged the outer building….not the primary containment. This was most likely from Hydrogen gas that was generated when the core was uncovered. The attached diagram shows the portion of the buildng that was damaged. An 20KM area around the plant has been evacuated.

F1 Unit 3. This unit also had cooling problems and there may have been some core unvovered. Sea water has also been injected and water level has been restored.

As far as I know the other 8 units are OK with adequate cooling.

The most important thing that needs to be maintained is cooling and the primary containment integrity. Cooling will keep the core intact and minimize any radiation release and the containment is needed to keep the releases inside and away from the environment. From the latest reports it looks like things have stabilized for the moment.

Obviously this is not a good situation. However these plants are designed to provide many levels of safety systems in case there are multiple failures which looks like the case here and emergency plans are in place to protect the public. One such measure was to evacuate within the 20KM radius. While I can’t predict what will happned next I do feel confident that this will eventually be controlled and the threat to the public eliminated.

Hope this wasn’t too technical and helps you better understand the situation. I’d be happy to try to answer any questions you have. Feel free to pass this on to others.




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