Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[jlduh]

Found this doc on Nisa site, with kind of glossary of terms used in measurements at DAICHI. Don't know if this was already posted here but it may be useful:

http://www.nisa.meti.go.jp/english/files/en20110423-4-5.pdf

Note this:
Measuring instrument malfunction Measuring instrument malfunction: Down(Over)scale
/Indicator malfunction Situation as of 22:00 April 22nd

-Unit1 Spent Fuel Pool water temperature and CAMS D/W radiation monitors
-Unit2 Temperature at the Bottom Head of RPV, S/C Pressure and RPV bellows
seal temperature
-Unit3 Spent Fuel Pool water temperature and FPC Skimmer Surge Tank level
-Unit4 Spent Fuel Pool water temperature

Now the question: what is the bellows seal?

 

[|Fred]

TEPCO lied about Fukushima Dai-ni being in cold shutdown (but maybe we knew that already? we really need a timeline):
http://af.reuters.com/article/energyOilNews/idAFL3E7FL2HE20110421

May I ask what leads you to think there is a lie about Daini being Shut down ?
The linked article surely state the opposite..

 

[Dmytry]

The evacuation zones were decided based on similar plots, but not sure whether exactly these ones. These plots show the estimated exposures received so far, and the evacuation zones were, I believe, based on projections of exposures expected over the next year. (Not sure how those were calculated, whether they extrapolated from present estimated ground contamination patterns, or whether they did something fancier, such as using SPEEDI with typical wind patterns over the course of a typical year, and some assumption about ongoing emissions...)

Anyway, there have been several such maps shown, and they all have the general features of one big pseudopod going up to the North-West, and a smaller one down to the South-West, but they differ in various details after that. The people living in the northwest pseudopod (beyond the circular zone that is already under evacuation orders), in the towns of Iitatemura and surrounding areas, have been told to evacuate by the end of this month. The people in the southwest pseudopod (in the town of Iwaki) have not, if I recall correctly.

I don't think any orders to take potassium iodide have been issued, by the way, just evacuation orders.

the evacuation orders, in case we already forgot the history, were initially 20km circle, and 30km stay indoors, and remained as that for a long long while.
It really is amazing how quickly history can be altered.

 

[elektrownik]

New video from #1 unit: http://www.tepco.co.jp/en/news/110311/images/110503_1.zip

 

[jlduh]

from Dmytry

the evacuation orders, in case we already forgot the history, were initially 20km circle, and 30km stay indoors, and remained as that for a long long while

That's also my understanding.

To introduce more precision, then there has been a time in April when, while keeping these evacuation and "stay inside" statements, the government "adviced" people between 20 and 30 kms to evacuate on a "voluntarily basis".

Then there has been a recent evacuation order for some specific places outside of the 20 and even 30 kms zone, especially Litate area. That's were I'm at now.

 

[artax]

this seems to be SFP unit 4.



sorry, posted and discussed earlier! (p342)

 

[MadderDoc]

Can you please give me some links to this part of the topic?

I wish I could, but I've seen no one else mention it. However, I can offer a look at the remains of this part of the roof girder construction.

How on Earth should one go about making a steel construction look this way without using heat?

Just one more guess about the explosion of U3:
- Boom one: I think the initial explosion was a hydrogen explosion above the service floor, with minor damages on structures below the floor: this part was similar with the explosion of U4. The differences from the U1 explosion were because the upper building of U1 is steel, not concrete. At this point the pillars of the upper building were gone on the south and north wall.

- Boom two: my guess is that this part was a originated from the lower building, somewhere on the north side. Maybe because of a hydrogen release from a torus-failure, like in U2, ignited by the first explosion. (There was that PDF not so long ago about GE MK1 simulated failures). This explosion ripped the northwest corner of the building, with a strong NW and upward momentum, with a lot of debris, some of them contaminated. At this point the pillars on the west side were gone.

- Boom three: with the pillars gone the overhead crane fall down and pushed the FHM (did anybody managed to find that damned FHM of U3? It's not on the top of SFP, not on the top of equipment pool, but these parts are mostly intact, so after two weeks of pixel-hunting of every available footage and pic I see no other place for it than below the crane) through the upper concrete plug of the containment and released a lot of really hot steam, maybe with some hydrogen, maybe ignited on free air.

Any ideas, comments on this sequence?

If this boom boom boom thing is making reference to the sound of the explosion, I owe you to say, that I am one of those who do _not_ believe we have any reliable audio recording of the explosion(s).

The first frame of the explosion in the best videos indicates the initial blast is coming through the east face of the building. We see see no fire phenomenon in this frame, only the shape of black smoke over the top of the building. In the same frame we see indication of a concurrent shattering of the west face of the building. This directional arrangement is consistent with the grey 'spit out' we can see over the roof of the turbine buildings to the east, and to the west, with the grey spit out over the buildings across the road from unit 3. In the next dozen frames or so, we see the fire phenomenon, and a growing black cloud of smoke around it.

(I think it is likely that the concrete structure of the north and the south wall was shattered by the initial blast, but that is not something that can be seen from the video)

Re the FHM3, I have been looking for it too, it appears to be nowhere in sight, as you mention. It may be because it is not there (it may have been ejected and fallen far from the building) or it has sunk into the building somewhere we cannot see. Candidates for hiding ground for the FHM would be either the SFP itself, or the north west corner of the service floor (we have unexplained massive destruction of the service floor in that corner), or it could have been swallowed by the building annexed to the north wall of the reactor building, the same spot which I currently lean to could be hiding the carrying bridge for the FHM.

 

[|Fred]

Some questions from this article:
http://mdn.mainichi.jp/mdnnews/news/20110502p2a00m0na012000c.html

Well , first of all the article mix Containment Pressure Vessel and Reactor Pressure vessel , so its a bit hard to be sure of what the mean and when.. And I think you are mistaken both or they are.. If I read them right they say that they put enough watter to filled the Containment but the water remain the same level and does not fill it => Containment is leaking..

 

[jlduh]

I think this the index page of the SPEEDI data, right?

http://www.nsc.go.jp/mext_speedi/

Damn, couldn't they put an english version of this important one? They had some time in the last weeks when they were not disclosing the data...

Release 5000 data this way in one big package and you are sure that anyway only few people will be able to digest it. Transparent as concrete, yes.

 

[georgiworld]

Quite the opposite - they can be horrifying to those who DON'T understand their significance, so they were not release to not start the panic.

I am not saying that's the case, just pointing out you are jumping to conclusions.

I am more concerned about the revelation that they held back facts than I am about the the actual value of the numbers they will report. What this shows me is that their collective behavior may actually be exacerbating the disaster.

Their intellectual feudalism is hindering efforts to find a solution.

They assume they know best. It's the paternalism of their bureaucracy.

Their reluctance to accept international help is a planetary scandal. This governmental version of Colonel Saito must step aside and allow those qualified to clean up this mess.

 

[MadderDoc]

#3 RPV is 205C now, why ?<..>
Here: http://www.meti.go.jp/press/2011/05/20110503001/20110503001-3.pdf (last page)

Yes, I can see that now, thank you. I think it is a measure of the temperature somewhere in the drywell. I can see too, that it has been on the increase for several days. If it shall not be dismissed as the result of a faulty sensor (which Tepco indicates that it might be), I am not sure how to interpret it. Corium in the drywell?

 

[jlduh]

Well , first of all the article mix Containment Pressure Vessel and Reactor Pressure vessel , so its a bit hard to be sure of what the mean and when.. And I think you are mistaken both or they are.. If I read them right they say that they put enough watter to filled the Containment but the water remain the same level and does not fill it => Containment is leaking..

Well, the words are mistaking and nothing is clear, you are right. For me pressure vessel is reactor vessel, but for them i don't know...

My understanding for N°1 reactor is that Tepco is injecting water at 6m3/h inside the reactor vessel, which is leaking into the containment vessel, so the so called Dry-well which becomes in fact a wet well. My understanding was also that by doing so, and by increasing the flow to 14m3/h they were hoping to fill in the containment vessel in something like July and so bury the reactor vessel under water.

Agree?

So the question is: does the article says the increased flow test showed that the water level in the REACTOR VESSEL didn't increase (which has been the case since the very beginning, anyway) or does it says the water level inside THE CONTAINEMENT VESSEL (the dry/wet-well) did not increase as expected (which leads to the conclusion there is a leak of the containment vessel) ?

This is highly unclear to me... especially because since the very beginning Tepco is saying that the dry/wet-well is progressively filling in with water (6 m above the bottom of the reactor i even read somewhere else, which fits the 6 meters they cite in this article).

This extract though is quite coherent and precise i think:

Officials said the water level inside the reactor's pressure vessel remained almost unchanged -- at about 1.6 meters above the top of the fuel rods -- when the amount of water was temporarily increased. With water pumped into the pressure vessel leaking out, workers estimate that the water level inside the containment vessel stands at about 6 meters, but they do not know the exact level.

After almost 2 months after the accidents, i didn't see one single sketch from Tepco showing precisely what they are exactly doing, where they inject water, where they think it's leaking: from reactor to containment, from containment to basement, etc.

I don't mean that have to know everything. But at least, some self explanatory sketch for press and folks like us which explains their assumptions and the reasons of their tests! I saw none expcept some basic infography from journalists, but based on what? A sketch, or even BETTER, an actual drawing of the actual layout (!) would avoid that kind of inacurracies in words where even journalists seem to mix pressure/reactor/containment vessel wording... Instead of that, they are crying because some old drawings leaked on the internet and claim its their property? Guys we are talking about a tech design which is 40 years old, they are not going to build a lot of BWR Mark 1 reactors! Do they put in perspective of this "violation" of their so called "property" (which is not in fact) the violation of the property of the citizens living around because of their BWR Mark I reactors? The violation of their lives and happyness and probably health?

Damn, is it so difficult to explain their HYPOTHESIS and also what they are precisely doing on actual precise drawings? This pisses me off, really.

Also, could they find an even smaller police for their main page for news on their site, so it is even less readable (like a Bonzai police?)

http://www.tepco.co.jp/en/press/corp-com/release/11050208-e.html

Well, are they becoming so "transparent" that... we no more can see what they state??

 

[|Fred]

the evacuation orders, in case we already forgot the history, were initially 20km circle, and 30km stay indoors, and remained as that for a long long while.
It really is amazing how quickly history can be altered.

What is ? I would appreciate If you could refrain to make free comments like this, If you are suggesting that evacuation procedure were not done properly according to the data at hand, I'll welcome your analysis. But if it's just free bashing It's just value less I.M.O.

From what I've looked at I see a real potential concern as far as Iodine children's thyroid protection is concerned. As the accumulated dose exeded 100mSv in zone outside the evac as early as the 24/Mars

Hence my question , about order given to the population. For the rest a first approach to the document seems to indicate that evacuation was made rather appropriately..
But heck I can't check everything.

 

[~kujala~]

Did the water level of the water table under the Daichi plant moved upward with the tsunami and so there is part of the basement which is now under the water table surface?

I think so. If tsunami waters have mixed with groundwater the rise in the basement would not be seen immediately because concrete acts as a barrier between groundwater and the basement.

The expected outcome would be the levels of water inside the basement rising slowly which is what is happening.

And we don't even need tsunami waters for this: groundwater under 5 and 6 is not behaving nicely because they have had to divert it even before crisis.
http://online.wsj.com/article/SB10001424052748703922504576273930625967622.html

The radioactivity of this water is "thought to be relatively low" doesn't tell you more, right?

Well we know the radiation in the sub-drain of 5 and 6 is low-level so the expected outcome from this water infiltrating into the basement would be low-level also.

No need to make complicated theories if you have a simple one where everything behaves as it should be.

 

[MiceAndMen]

Don't underestimate them, don't overestimate yourself.

I was using the royal "we", meaning everyone here combined including people who know far more than I do. Subtract me out of the equation and "you all" would ascertain the reality in very short order. Many of you guys here have forgotten more than I ever knew about the physical sciences.

If you've looked high and low for Japanese leadership in this crisis and can't find it, that's because you haven't looked low enough yet. IMO underestimating their ability to manage this crisis is not possible.

 

[clancy688]

I don't think any orders to take potassium iodide have been issued, by the way, just evacuation orders.

I think there's a problem with potassium iodide - you only have a very short time frame which can be used for administering the medicine.

If you take it to early and nothing happens you're hazarding public health because potassium iodide can have negative influences on the human body.
But if you take it to late - after the radioactive I131 accumulated in the thyroid - the effect is exactly the opposite of what you want. The iodid is blocking the thyroid and thus sealing the I131 inside, extending the biological half life of the nuclide. If people take potassium iodide to late, they're increasing the risk of thyroid cancer!

So it would be really pointless to administer potassium iodide to the people in the extended evacuation zone now.

 

[PietKuip]

So again what are the hypothesis for this water, if we believe Tepco statement that there is no internal link from the reactor on this one (i saw some graphics on this thread which showed data that could contradict this, with level inside RPV going up and down at regular intervals, and same thing with temps. But?). A) This could be water left from the flooding of the tsunami, but it would not increase along the time; so there must be a continuous flow, right? B) Did the water level of the water table under the Daichi plant moved upward with the tsunami and so there is part of the basement which is now under the water table surface?

The elevation of the site may have moved downward because of the earthquake.

 

[MadderDoc]

Well , first of all the article mix Containment Pressure Vessel and Reactor Pressure vessel , so its a bit hard to be sure of what the mean and when.. And I think you are mistaken both or they are.. If I read them right they say that they put enough watter to filled the Containment but the water remain the same level and does not fill it => Containment is leaking..

From the outset Tepco has stated that this was an experiment to see what flow rate would be necessary to flood the containment. The experiment was planned to go eventually to a maximum of 14 m³/h, but was aborted at 10 m³/h, when the pressure in the drywell was approaching atmospheric pressure. At this point steam present in the drywell would become liable to condense, leading to suction, ingress of oxygen into the containment, and a risk it says boom. Tepco appears to have not yet flushed the containment with nitrogen enough to their satisfaction, so as to minimize the risk of a hydrogen explosion during the flooding of the containment they have planned for the future, or they could have just let the experiment go on to achieve it.

Edit: Just to add, at the time of abortion of the experiment, the increased injection to the pressure vessel had not manifested itself in an increase of the water level within the pressure vessel, which might be expected if the containment vessel through the leaks in the pressure vessel had been flooded to a level above the current level in the pressure vessel. During the experiment the level of water in the reactor vessel has stayed stubbornly at minus 1.60 meter relative to the design top of the fuel, although Tepco feels that total volume injected should have been able to increase the level in the containment above that point.I believe there is an error in the article stating that the current level of water in the pressure vessel was already 1.6 meter above the fuel, but that is not so, if it were there would be no need to flood the containment.

 

[jlduh]

To Kujala:

No need to make complicated theories if you have a simple one where everything behaves as it should be

I don't make a complicated theory out of "nothing", I'm just potentially linking this fact (water in the basement of N°6) with this post from ANTONL some time ago, based on some data that i think haven't been clearly explained so far, showing a water fluctuation of about 1m in the reactor every 10 days (rough estimate):

https://www.physicsforums.com/showpost.php?p=3267480&postcount=4940

Plot of water level and water temperature of reactor 6
Left: temp (red), Right: water level (blue)
http://www.netimago.com/image_196236.html

AntonL, did you get an explanation following your post i cite above, or some new datas?

Edit: just corrected my post for some mistakes, but here are the updated datas which show the same pattern for water level at N°6:

https://spreadsheets0.google.com/sp...ZDbX39YK-iFb0Iw&hl=ja&authkey=CP6ewJkO#gid=37

same but with a different pattern at N°5:

https://spreadsheets0.google.com/sp...ZDbX39YK-iFb0Iw&hl=ja&authkey=CP6ewJkO#gid=36

 

[jlduh]

Concerning the D/W-RPV temperature rising on n°3, that Electrownik mentionned, here is a plot showing the evolution:

https://spreadsheets.google.com/spr...ZDbX39YK-iFb0Iw&hl=ja&authkey=CP6ewJkO#gid=40

 

[MadderDoc]

The elevation of the site may have moved downward because of the earthquake.

Looking at the webcam before and after the quake it is clear that something has given in. Before the quake, the webcam could see much more of the reactor buildings. After the quake either the knoll where the webcam is sited, or the NPP, or both, must have moved downward relative to the elevation of the treetops inbetween now blocking the view. See:
http://www.gyldengrisgaard.dk/tepcowebcam/tepweb20110311.html

 

[zapperzero]

May I ask what leads you to think there is a lie about Daini being Shut down ?
The linked article surely state the opposite..

Pay a bit more attention please. I stated that TEPCO "lied" not "is lying".

The article says that the reactors are now stable, after having experienced trouble with broken cooling systems. Relevant quotes:
"Japan's Fukushima Daini nuclear plant,[...], has cleared a key milestone toward stabilising, regulators said on Thursday"
"Nuclear and Industrial Safety Agency said on Thursday it reduced the evacuation zone around the four-reactor, 4,400 megawatt Daini plant after engineers had repaired the cooling systems"

Oh. All better now, yes?

Here is a TEPCO release dated march 15:
"Restoration work in reactor cooling function that was conducted to
achieve reactor cold shutdown has been completed"
http://www.tepco.co.jp/en/press/corp-com/release/11031501-e.html

WNN reported, citing TEPCO on March 15, that
"All four units at the Fukushima Daini nuclear power plant have now achieved cold shutdown - where coolant water is at less than 100ºC - with full operation of cooling systems"
http://www.world-nuclear-news.org/IT-All_Fukushima_Daini_units_in_cold_shutdown-1503114.html

When were the cooling systems repaired, again?

 

[AntonL]

To Kujala:



I don't make a complicated theory out of "nothing", I'm just potentially linking this fact (water in the basement of N°6) with this post from ANTONL some time ago, based on some data that i think haven't been clearly explained so far, showing a water fluctuation of about 1m in the reactor every 10 days (rough estimate):

https://www.physicsforums.com/showpost.php?p=3267480&postcount=4940

Plot of water level and water temperature of reactor 6
Left: temp (red), Right: water level (blue)
http://www.netimago.com/image_196236.html

AntonL, did you get an explanation following your post i cite above, or some new datas?

Edit: just corrected my post for some mistakes, but here are the updated datas which show the same pattern for water level at N°6:

https://spreadsheets0.google.com/sp...ZDbX39YK-iFb0Iw&hl=ja&authkey=CP6ewJkO#gid=37

same but with a different pattern at N°5:

https://spreadsheets0.google.com/sp...ZDbX39YK-iFb0Iw&hl=ja&authkey=CP6ewJkO#gid=36

The fluctuating temperature is explainable, tepco only managed to get only one cooling system working and this cooling system is multiplexed between the reactor cooling and spent fuel cooling, so every time the reactor temperature rises, the cooling is used for the spent fuel pool. However that does not explain the loss of reactor water.

 

[artax]

Pay a bit more attention please. I stated that TEPCO "lied" not "is lying".

The article says that the reactors are now stable, after having experienced trouble with broken cooling systems. Relevant quotes:
"Japan's Fukushima Daini nuclear plant,[...], has cleared a key milestone toward stabilising, regulators said on Thursday"
"Nuclear and Industrial Safety Agency said on Thursday it reduced the evacuation zone around the four-reactor, 4,400 megawatt Daini plant after engineers had repaired the cooling systems"

Oh. All better now, yes?

Here is a TEPCO release dated march 15:
"Restoration work in reactor cooling function that was conducted to
achieve reactor cold shutdown has been completed"
http://www.tepco.co.jp/en/press/corp-com/release/11031501-e.html

WNN reported, citing TEPCO on March 15, that
"All four units at the Fukushima Daini nuclear power plant have now achieved cold shutdown - where coolant water is at less than 100ºC - with full operation of cooling systems"
http://www.world-nuclear-news.org/IT-All_Fukushima_Daini_units_in_cold_shutdown-1503114.html

When were the cooling systems repaired, again?

Be careful, it's very easy to get confused, there is a VERY SIMILAR nuclear plant south to the south also with FOUR reactors called FUKUSHIMA DAINI, (meaning 2)
The one with all the problems is FUKUSHIMA DAICHI (meaning 1)

 

[Rive]

I wish I could, but I've seen no one else mention it. However, I can offer a look at the remains of this part of the roof girder construction.

How on Earth should one go about making a steel construction look this way without using heat?

Well, it's an interesting picture. Where is it from? Do you have any more of this about the rest of the U3? What I have has much lesser quality.

What I see on that pic: there are at least two main release paths clearly visible, but the main beams through the pats looks more corroded than burnt, however the smaller (Al?) pieces looks melted, or at least softened. The positions of the release paths are consistent with the thermal images where some hot spots could be identified around the supposed position of reactor well.

But the image also implies that the remains of the roof structure had to be there, on the top of the heap when this release happened: so at least the west pillars had to be gone at that point (the main destruction pre-dates the release).

Also, the release had to be more corrosive than hot - hydrogen flame would cut through those beams within seconds. Steam? HOT steam?

Maybe if we can compare the RPV and D/W temperatures with the thermal images...

If this boom boom boom thing is making reference to the sound of the explosion, I owe you to say, that I am one of those who do _not_ believe we have any reliable audio recording of the explosion(s).

Quite possible but I have nothing better to work with.

The first frame of the explosion in the best videos indicates the initial blast is coming through the east face of the building...

I'm a bit skeptic with that footage. All we can see is only the closest visible objects, without clean directions.

About the FHM I've spotted something but it'll take some time to present it.

 

[Borek]

When were the cooling systems repaired, again?

Define "repaired". It can as well mean the situation was under some kind of control since March 15th, but for some reason they are now more confident it will work as expected. Say, after finishing additional inspections.

My usual disclaimer: I am not stating that's the case, I am just stating you don't have enough information to state what you stated.

 

[zapperzero]

Be careful, it's very easy to get confused, there is a VERY SIMILAR nuclear plant south to the south also with FOUR reactors called FUKUSHIMA DAINI, (meaning 2)
The one with all the problems is FUKUSHIMA DAICHI (meaning 1)

No, artax. Both have problems. I know of which I speak.

 

[jlduh]

Looking at the webcam before and after the quake it is clear that something has given in. Before the quake, the webcam could see much more of the reactor buildings. After the quake either the knoll where the webcam is sited, or the NPP, or both, must have moved downward relative to the elevation of the treetops inbetween now blocking the view. See:
http://www.gyldengrisgaard.dk/tepcowebcam/tepweb20110311.html

Well the difference between before and after is very surprising indeed... but i really doubt that the plant, but also for example the area where all the cooling water from the plant is released into the sea, could have lowered so much in comparison with the viewpoint of the webcam, this is huge difference!

I would imagine more a scenario where the webcam has moved down because of the quake (see the change is between the 14h00 and the 15h00 image).

 

[artax]

Sorry Zapper,.,... just a mistake I made early on...So what's going wrong at Daini?
Oh, seems you're using the previous releases to suggest TEPCO are capable of lies. I don't doubt that one bit. I have been suspicious of everything they have said from the beginning.

 

[zapperzero]

Define "repaired".

Ay, there's the rub. TEPCO is using two definitions at two different points in time.

This is just like Clinton's "I did not have sex with that woman" where it turned out later that he was using his own idiosyncratic version of "sex" at the time that he made the statement.

It's called lying. Some middle manager got scared, lied and forgot to tell the others. No need for you to cover for him . It's not a big deal, even, except inasmuch as it underlines the lack of good leadership.

 

[Borek]

It's called lying.

I tried to dig through the links you posted:

http://af.reuters.com/article/energyOilNews/idAFL3E7FL2HE20110421

http://www.world-nuclear-news.org/IT-All_Fukushima_Daini_units_in_cold_shutdown-1503114.html

http://www.tepco.co.jp/en/press/corp-com/release/11031501-e.html

and either I am missing something, or there is no differences between all three. WNN and TEPCO pages both state that reactors were shut down on March 15th, Reuters states

engineers had repaired the cooling systems and maintained the plant in a "cold shutdown" for several weeks.

which probably means that the systems were repaired several weeks ago and the plant was kept in cold shutdown state since. Or is my English failing me and Reuters text means cooling system was repaired just now?

 

[Jorge Stolfi]

I believe there is an error in the article stating that the current level of water in the pressure vessel was already 1.6 meter above the fuel, but that is not so, if it were there would be no need to flood the containment.

Indeed, water level in the #1 reactor has been 1.6 meters below the top of the fuel for some 40 days now. It is even lower in reactors #2 and #3.

Levels seem to have increased by a few inches when the water flow was doubled, weeks ago, only to fall again when the flow dropped back to the usual ~6 m^3/h I would guess that there are substantial leaks on the side of the RPVs (Broken pipes? Open valves? Cracks?) at those heights. However, it is not clear how the water level is measured, and, in each of #2 and #3, the two gauges give diferent levels, 30-50 cm off.

 

[zapperzero]

So what's going wrong at Daini?

Not much right now. They had trouble with the cooling systems early on, had to prepare to vent some radioactive air. Apparently, some of the plant cooling systems and possibly the containment for unit one failed to withstand a below design basis earthquake:

http://www.tepco.co.jp/en/press/corp-com/release/11031104-e.html
"For Unit 1, the emergency core cooling system automatically started up
due to increase in the reactor containment pressure assumed to be caused
by leakage of reactor coolant in the reactor containment."

then

http://www.tepco.co.jp/en/press/corp-com/release/11031209-e.html
"Injection of water into the [#1] reactor had been done by the Reactor Core
Isolation Cooling System, but at 3:48AM, injection by Make-up Water
Condensate System begun."

whew, right?

then it all goes south again, at units one and two:
http://www.tepco.co.jp/en/press/corp-com/release/11031218-e.html
"- At 5:22AM, the temperature of the suppression chamber exceeded 100
degrees. As the reactor pressure suppression function was lost, at 5:22AM,
it was determined that a specific incident stipulated in article 15,
clause 1 has occurred.
- We decided to prepare implementing measures to reduce the pressure of
the reactor containment vessel (partial discharge of air containing
radioactive materials) in order to fully secure safety."

Why do you think I keep complaining that we need a timeline?

 

[Rive]

About the FHM I've spotted something but it'll take some time to present it.

I dunno. The problem with this pixel-hunting is that anything can be something else too.

 

[jlduh]

We decided to prepare implementing measures to reduce the pressure of
the reactor containment vessel (partial discharge of air containing
radioactive materials) in order to fully secure safety. This preparation
work started at around 9:43am.

Hummm... that's new to me (and maybe others?). Wasn't aware that they were planning a venting operation also at Unit 1 on Daini site. It seems that as we were fully concentrated with some reason on th Daichi plant, the way to "cold stop" at Daini N°1 was not so straight and smooth as we heard about (but Tepco at least reported it, we just didn't hear about it).