APR: your source for nuclear news and analysis since April 16, 2010

Friday, March 11, 2011

Japan situation stabilizing

Finally, at 9:35 PM Eastern on Friday we have some good solid reporting about all the plants operated by TEPCO at both Fukushima sites.

First, an evacuation zone ordered originally at Fukushima Daiichi (Site 1) was expanded on order of the visiting Prime Minister, not on order of the operators, so that a situation more serious than previously occurring is now NOT suspected. A standard evacuation of the inner ring zone at Fukushima Daini has also now been ordered, as a standard precaution.

Next, it appears that emergency generators are in place at both sites covering the bulk of the cooling and I&C needs for the time being.

Third, it looks as if all affected plants are admitting coolant on their steam driven standby injection pumps and are either allowing reliefs to pop or else are manually lifting them occasionally to control primary plant temperature and pressure. This situation seems the same for all plants with differing rates of success, Fukushima Daiichi Plant 1 being the most serious at the moment.

Radiation levels outside the plant limits are tolerable.

Release of steam appears to have been from the secondary containments; wind is directly off shore at last check, and any radioactive gases are dispersed at sea.

Below, you will find a reference picture of a typical GE BWR containment and will see the reactor at center in its pressure vessel. Around this is the drywell, meant to contain any primary leakage or worse should the primary rupture. The large and heavy secondary containment is also clearly labeled. This illustration blows up very large if clicked. From WASH-1250 Final Draft.

More as the situation evolves, but right now the story seems about as one would expect. However, aftershocks are occurring.

UPDATE 10:45 PM FRIDAY: We have confirmed that the plants affected have been using their condensate water as make-up for the primary plant water inventories. Also, the apparent intermittent primary relieving by the normal methods is causing high pressures in the containments, which is what is being relieved and covered by the news so inaccurately. Wind still out to sea.


  1. I'm a little puzzled. If control rods are in place and if primary cooling circulation is operating, how come secondary cooling is maxed out?

    Is it that core temperatures were so high that protracted cooling is necessary?

    If so could such high temperatures cause structural problems in the core?

    Or is primary cooling compromised?

  2. Yes, the plants were shut down apparently from full load immediately and it appears that at least in the case of the Daiichi plants, although the diesels started immediately they then shut down at about the scram +1 hour time. It was then that the serious chain of events began, with no pump power and a great deal of decay heat remaining. There are no structural problems at present so far as we can ascertain.