It was stated (and continues to be, in places) that the owner-operator of the Fukushima Daiichi site (TEPCO) and that the Japanese government have been less than forthcoming with information, and that operations on the site and effects off site have been covered up. This could not be further from the truth; simply look at all the posts on this site and all the videos on the APR YouTube Channel for this proof. To this end (that is, for the sake of transparency) a very detailed recovery timeline was developed and published widely by all concerned parties and continues to be used to this day.
The achievement of 'cold shutdown' is one of the steps on this timeline, and as such when it's reached, it's announced. This is simple enough for anyone to understand. But who made this determination? Let's look at a quote from NISA's site (Nuclear and Industrial Safety Agency) to get the facts:
December 19, 2011... NISA website. "The Nuclear Emergency Response Headquarters evaluated that the reactors at Fukushima Daiichi NPS, TEPCO, were brought to a condition equivalent to "cold shutdown" and, even if an unforeseeable event occurs, the exposure dose at the site boundaries can be kept at a sufficiently low level as a result of the evaluation of the securing of safety at nuclear reactor facility of Fukushima Daiichi NPS, TEPCO, at the completion phase of Step 2, stating that a safe condition has been achieved and the accident at the NPS itself has come to be settled."
So, the Nuclear Emergency Response Headquarters (this is a special construct of the Japanese Government) decided that the condition had been achieved, and it seems obvious to me that NISA and TEPCO would be included in this decision making simply by virtue of the complicated manner in which the Japanese nuclear industry operates. Thus, this is neither a unilateral nor simply a political announcement - it's technical. And it's mapped out on the timeline as a required step.
What does this mean? Well, "cold shutdown" is a term normally used for intact reactors in normal conditions; the term is adapted here to indicate (as I've posted before) that the reactors are cooled down sufficiently and that release of radionuclides to the atmosphere is minimal or zero. Here are some further specific facts:
-No further core damage is occurring (or has for some time.)
-No condition of explosive hydrogen accumulation exits, with nitrogen purge to the reactors and primary containments and gas handling systems operating.
-No condition of decay heat buildup in the reactors exists, with both feedwater system cooling feed and core spray ring feed in progress.
-No condition of dose above 1 mSv/yr exists outside the nuclear power station.
-No condition of wide uncontrolled atmospheric release exits with the reactors cooled down below 100C and thus no boiling occurring to disperse materials with steam.
In the final analysis, this announcement is kind of like saying "I think I have caught a cold." You already had the cold before you knew it; the symptoms accumulated until as a group you put them all together to determine you were sick. This announcement is very similar; each of the contributory factors was reached independently of the others in ways, but tied together in ways so that the actual state of "cold shutdown" has existed for weeks. Only now did the nuclear response headquarters unit, NISA and TEPCO collaboratively decide that it was time to announce without doubt that this status had been achieved. What this means is detailed above; it could not be more clear what this means and does not mean. It also could not be more clear that there is no political advantage in making this announcement for anyone - it's a matter of plant status, and that's all.
8:15 AM Eastern Tuesday December 20, 2011
ATOMIC POWER REVIEW
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UPDATE DECEMBER 21, 2011
Here are some links that readers might find to be of interest.
NRC Definition of "Cold Shutdown"
Nuclear Energy Institute's statement - December 19, 2011
IAEA welcomes news of cold shutdown at Fukushima Daiichi
Link to PDF file from TEPCO to IAEA mentioning previous "stable cooling" threshold and the later, now achieved "cold shutdown" status
NRC Chairman Jaczko's comments after a visit to Fukushima Daiichi, on the cold shutdown announcement and plant conditions
Below, a graph from Tokyo Electric Power Company showing core decay heat generation for all three Fukushima Daiichi reactors. In reality, "Fukushima Daiichi" is "Fukushima Number One" nuclear power plant site, and 1F is the TEPCO code for Fukushima Daiichi. Thus, 1F1 is Fukushima Daiichi No. 1 reactor plant, 1F2 is No. 2 and 1F3 is No. 3. Note that core power due to decay heat as calculated by ORIGEN2 analysis code as of September 2011 is already down to roughly one megawatt for No. 2 and No. 3 plants, and down to roughly 0.8 MWt for No. 1 plant.
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