Fukushima Fukushima: Unit 2 Discharge - Why Differs from Units 1 & 3?

[SteveElbows]

I am following up on some of the things I said in recent days with a bit more clarity.

I tried to learn more about the MELCOR system which they used to do the analysis of the accident. I mentioned that analysis graphs for reactor 2 showed contamination in additional areas compared to the ones for reactors 1 & 3.

I have learned that the FHB (Fuel handling Building) does indeed seem to simply mean the upper refuelling floors of the building. The reactor building label on these charts does not include these refuelling floors.

I have also seen, by looking at an old study of Peach Bottom, that MELCOR is based on treating the different parts of the reactor & buildings as nodes, and defining the possible pathways that substances can take through the network of nodes. In that particular old study, I note with interest that their node map didn't actually have a pathway for the suppression chamber to emit stuff directly to the environment, instead it goes via the drywell, which then goes to the torus room, then to the various rooms in the reactor building. Once it reaches reactor building rooms it can then travel to other rooms, to the environment, or to the refuelling floor. From the refuelling floor it can then go to the environment, and looking at the graph we can see that their analysis gave them results where about half of the environmental release came via the refuelling floors, and the other half escaped at some earlier stage of the pathway that cannot be determined from that graph.

Note that this is of course a model rather than how things actually work out in reality, but as its the model they used to come up with one of the very few sets of figures we have to work with for this thread about reactor 2, its worth understanding. Also note that as far as I know we don't actually know what the node map for Fukushima looks like, we don't know exactly what they put into the analysis. For example their version may have a node map that allows for direct release from suppression chamber to environment, rather than the via drywell path that I just mentioned, I have no way to know.

Anyway for the reactor 2 analysis I've decided that it can be easier to refer to the following NISA document rather than the government report to the IAEA, the file is more manageable and on a few pages presents the sequence of events in a more understandable way. Its the same analysis as we saw in the other versions, and in some areas it is worse, but for the stuff I am talking about right now its pretty handy.

http://www.nisa.meti.go.jp/english/press/2011/06/en20110615-5.pdf

For example on page labelled as 7 it reminds us that according to this analysis:

in terms of how events developed, it is surmised that the RPV was damaged at the time when there was a substantially elevation of containment pressure as recorded around 0:00 on the 15th, hence a large elevation in the containment pressure and temperature.

The release of radioactive materials from Unit 2 is considered mainly due to leakage caused by rise in containment pressure as melted fuel is believed to have moved beginning at 21:00 on March 14, as well as the PCV vent, and release due to leakage from the suppression chamber and other factors assumed in relation to the large impact noise in the vicinity of the suppression chamber

And there is quite a nice chart showing the timing of various things along with data from that period. Its on what would be labelled page 11, but is probably actually page 12 of the document as the first page is an additional coversheet. I will come back to these timings later as they will help clarify some of the stuff that has been mentioned before in this thread.

 

[SteveElbows]

The other really important thing the document reminded me of was something that was mentioned in this thread many months ago, but that I had forgotten about when I was going on about drywell pressure the other day. In order to make their analysis spit out drywell pressure estimates that are close to the real data that was actually measured, they had to assume some sort of containment leak starting within a day of the earthquake & tsunami hitting, days earlier than the 'main event' at reactor 2.

This is shown very clearly in the graphs that are on pages labelled 2-15 and 2-16. Case 1 is where they assume no leak. Case 2 assumes a leak in PCV of 50 cm² and case 3 assumes a leak in S/C of 300cm². Case 2 fits most closely with the observed data.

Anyway the new twist I wanted to put on this old detail, is whether it is possible that the blow-out panel at reactor 2 was actually blown out by containment leak quite early on, rather than the explosion at reactor 1 building. I don't think it will be very easy to draw any conclusions on this seeing as we only have limited detail about the containment leak estimation used in the analysis, but it doesn't take too much pressure for one of these panels to blow out does it? So perhaps this possibility deserves a little more attention?

 

[SteveElbows]

I will have to return to the timing of reactor 2 events another day, sent all my time this evening looking at a document that is quite handy for getting a sense of how MELCOR works. There are other documents too but this one has a better node diagram of the different parts of the Peach Bottom MELCOR model than the one I saw the other day.

http://prod.sandia.gov/techlib/access-control.cgi/2007/077697.pdf

The diagrams are really great, and can be found on pages 93-96. There is plenty else in this document that's of interest but I shall not go on about that now. How I wish I had these diagrams handy during many discussions over the last year.

 

[NUCENG]

Nope, most definitely not.

That's only a "containment vent", not a reactor vent. Moreover, it doesn't vent high pressure. It only ensures, that, at high pressure, the pressure doesn't get any higher. And that only goes for the containment.
So when pressure inside the containment reaches a certain value (I think it was twice the normal pressure), the containment cap lifts and pressure escapes. The pressure falls slightly and then the cap closes again. So the pressure can't go over twice the normal pressure, but it also can't go below twice the normal pressure.
But that still doesn't vent the reactor pressure vessel. And the unfiltered release ("dry venting") can't happen that way. Because for reactor pressure to escape via a lifting containment cap, the gases have to travel through the wetwell (torus). Which they obviously didn't, that's why we have such a dirty release for Unit 2.
So there must've been an other path.

The vessel has pressure relief valves that go to the torus (wetwell). If the coolant piping or vessel are breached the vessel releases pressure to the drywell and through the Drywell to Torus Vent pipes. If the pressure in the drywell is below the pressure in the torus the Torus to Drywell Vacuum breakers will mjnjmjze pressure differences between the torus and drywell. There are also vacuum breakers from atmosphere to the torus to prevent containment from being below atmospheric pressure.

Containment can be filtered and vented to the stack from either the drywell or the wetwell through the SBGT system if power is available. The hardened wetwell vent system is intended to vent from the torus to the stack. In this case the vented effluent is scrubbed through the water in the wetwell to retain soluble and particulate products. At least some plants can also use a dry vent path from the drywell through the hardened vent path without the scrubbing of the wetwell path.

The design uses a pressure suppression mode of operation. The water volume in the suppression pool absorbs the energy and condensessteam. As s it heats up there are cooling systems (sprays and heat exchangers) to keep the suppression pool below saturation temperatures. At Fukushima the cooling systemslost power to the pumps and eventually the suppression pools were no longer available to keep the containment pressure low.

Unit 1 IC systems were lost due to possible human error and there were no low pressure ECCS systems due to loss of AC power. Units 2 and 3 also had no low pressure ECCS systems available due to loss of AC power. In units 2 and 3 the heatup of the Pool also resulted in loss of the steam exhaust path for the RCIC and HPCI systems (battery backed High Pressure ECCS systems). In all three plants, the heatup also meant that vessel relief valve discharge to the torus could no longer be condensed.

Bottom line, they couldn't reduce the pressure so they could use the fire trucks and lower pressure pumps to cool the reactor fuel. That was unrecoverable.

In the specific case of Unit 2 the containment failure was apparently in the torus providing a vent pathdirectly to the building. This would have resulted in direct release of non-condensibles and probably further releases due to rapid boiling in the suppression pool due to the pressure release. If the unit 1 and Unit 3 failures were initially throughthe stretching of the drywell caps they would have eventually reseated as you described. The assumed torus failure in Unit 2 would have remained open allowing a larger release path.

In all three units there were also probably failures of the containment penetrations for cables and piping systems due to high temperatures and pressures. The potential that the torus failure in Unit 2 remains open even today is my best guess for why Unit 2 releases are assumed to be greater than the other units.

 

[NUCENG]

There has been speculation on EX-SKF that the rupture disk did rupture, but that debris from within the RPV clogged the piping for the vent. Given the violence of the events, this does seem plausible.

The Hardened vent path does not connect directly to the RPV. It is connected to the airspace in the top of torus (above the suppression pool). If the drywell vent path is used it is from the drywell above the level where blockage is likely.

 

[NUCENG]

It seems to me that successful venting through the designated path is almost impossible under accident conditions and without electricity, at least for the Mark I containment (don't know if it would work out better for other containment designs).

Is the "blow out panel" opened at unit 2 actually an improvisation or a feature?
Because units 1 and 3 explosions showed us that trying to contain gases and Hydrogen (which must be released anyway) within the secondary containment might not be the right approach in an emergency.

Blowout panels on the reactor building are a design feature initially designed to relieve from pipe breaks or ruptures in the secondary contaiment or possibly during low pressures from a tornado.

The reactor safety design basis is to prevent the fuel temperatures that can result in fuel damage and hydrogen generation. Blowout panels were never designed for hydrogen control.

 

[SteveElbows]

Im trying to come up with a simple set of factors that could be involved in making the reactor 2 release so substantial.

Im thinking along the lines of one or more of the following, some of which are related to lack of venting or the amount of time that water was not pumped into the reactor:

The state of the suppression chamber at the time of core melt (pressure, temp, amount of water).
The pressure that the primary containment was under at the moment of containment failure.
The pressure that the primary containment was under at the time the core left the reactor.
The pressure of the reactor vessel at the time the core left the vessel.
The location or nature of the containment failure. (Including possibilities such as the blowdown of core material into the torus room).
Brief dry venting.
The pathway that the radioactive material was able to travel through the reactor building and perhaps refuelling floor, and/or turbine building before reaching the environment.

When considering the above it would be rather helpful to know the status of a variety of other blowout panels. I understand that some other nuclear reactors of similar design have panels or other stuff that will fail under pressure in various other places, such as between lower main reactor building and the refuelling floors, between the reactor building and the turbine building, etc. Not sure what Fukushima had but knowing more about these would give further clues about any release pathways, at least ones that may have happened quite dramatically under pressure.

 

[etudiant]

The Hardened vent path does not connect directly to the RPV. It is connected to the airspace in the top of torus (above the suppression pool). If the drywell vent path is used it is from the drywell above the level where blockage is likely.

The speculation was based on the idea that lagging material dislodged by the earthquakes and subsequent reactor excursions, which would have created much stronger than nominal steam bursts, was the culprit in blocking the vents. The pipe is not very big apparently, about 6 inches in diameter.

 

[NUCENG]

Im trying to come up with a simple set of factors that could be involved in making the reactor 2 release so substantial.

Im thinking along the lines of one or more of the following, some of which are related to lack of venting or the amount of time that water was not pumped into the reactor:

The state of the suppression chamber at the time of core melt (pressure, temp, amount of water).
The pressure that the primary containment was under at the moment of containment failure.
The pressure that the primary containment was under at the time the core left the reactor.
The pressure of the reactor vessel at the time the core left the vessel.
The location or nature of the containment failure. (Including possibilities such as the blowdown of core material into the torus room).
Brief dry venting.
The pathway that the radioactive material was able to travel through the reactor building and perhaps refuelling floor, and/or turbine building before reaching the environment.

When considering the above it would be rather helpful to know the status of a variety of other blowout panels. I understand that some other nuclear reactors of similar design have panels or other stuff that will fail under pressure in various other places, such as between lower main reactor building and the refuelling floors, between the reactor building and the turbine building, etc. Not sure what Fukushima had but knowing more about these would give further clues about any release pathways, at least ones that may have happened quite dramatically under pressure.

Good list/

I don't know of other blowout panels in the Reactor Building proper. There is a series of hatches from the first floor to the refueling floor for movement of spent fuel casks and other heavy loads. These hatches are not designed to be air tight. Many US plants have open web cargo nets on these hatches as fall protection. Neither are there airtight doors on stairwells. Finally the elevator shaft is not airtight. The SBGT system (emergencies) and reactor building ventilation system (normal operation) are designed to keep the reator building at a negative pressure compared to the atmosphere. This ensures the leakage in the building and the exhaust is through monitored paths to detect possible radioactivity releases.

 

[NUCENG]

The speculation was based on the idea that lagging material dislodged by the earthquakes and subsequent reactor excursions, which would have created much stronger than nominal steam bursts, was the culprit in blocking the vents. The pipe is not very big apparently, about 6 inches in diameter.

There have been significant regulatory requirements to address the potential for lagging and debris to clog PWR sump strainers and BWR ECCS system strainers in the torus suppression pool. The debris would have to defy gravity to clog the vent pipes. Remember there was no attempt to start venting until well after the earthquake.

It is possible that debris could have been generated by blowdown after the RPVs were breached. And it is possible some made its way into the torus. But unless there was some significant wave action and simultaneous vent flow to hold the debris in the vent pipe penetration, it would have no reason to plug the opening. I think that is unlikely.

 

[SteveElbows]

Good list/

I don't know of other blowout panels in the Reactor Building proper. There is a series of hatches from the first floor to the refueling floor for movement of spent fuel casks and other heavy loads. These hatches are not designed to be air tight. Many US plants have open web cargo nets on these hatches as fall protection. Neither are there airtight doors on stairwells. Finally the elevator shaft is not airtight. The SBGT system (emergencies) and reactor building ventilation system (normal operation) are designed to keep the reator building at a negative pressure compared to the atmosphere. This ensures the leakage in the building and the exhaust is through monitored paths to detect possible radioactivity releases.

Thanks very much for the detail. Certainly I agree that we know of many non-airtight pathways from one part of the building to another, after all we have seen robots climbing the stairs without meeting doors that are hard to open. My talk of other blowout panels was based on a long reportI read recently, though I can't lay my hands on it right now as I've looked at too many different docs recently. I will post about this again when I find it.

How about between the reactor & turbine buildings? Overall when looking at all the post-disaster talk on the internet, I sometimes feel that the turbine buildings have not received enough attention, although that's not surprising considering that only a few times have we gotten any info, surveys etc from the turbine buildings. We saw blowout panels open on at least a few of the turbine buildings west-facing walls in the footage from days/weeks after the disaster struck, not sure that we ever heard whether these were opened by humans, by explosions, or by pressure.

 

[NUCENG]

Thanks very much for the detail. Certainly I agree that we know of many non-airtight pathways from one part of the building to another, after all we have seen robots climbing the stairs without meeting doors that are hard to open. My talk of other blowout panels was based on a long reportI read recently, though I can't lay my hands on it right now as I've looked at too many different docs recently. I will post about this again when I find it.

How about between the reactor & turbine buildings? Overall when looking at all the post-disaster talk on the internet, I sometimes feel that the turbine buildings have not received enough attention, although that's not surprising considering that only a few times have we gotten any info, surveys etc from the turbine buildings. We saw blowout panels open on at least a few of the turbine buildings west-facing walls in the footage from days/weeks after the disaster struck, not sure that we ever heard whether these were opened by humans, by explosions, or by pressure.

The turbine building has a separate ventilation system, that also uses a monitored exhaust path. However, according to discussions about Fukushima, there may have been cable paths and or drains that permitted leakage to move from the Reactor Buidling to thr Turbine Building. There is also a steam tunnel for the feedwater and main steam piping. Finally there are airlocks between the buildings to allow access, even though there may be pressure differences between buildings.

 

[r-j]

Forgive me, but how does anyone know how much radioactivity came from each building?

 

[clancy688]

Excellent question. I was asking myself the same thing. But apparently, TEPCO knows. Or they think they know. There's a detailed listing of how much radiation every building spew:

http://www.kantei.go.jp/foreign/kan/topics/201106/pdf/attach_04_2.pdf

Check out page seven.

(Though it's probably outdated by now... recent publications give much higher numbers for the total released quantity of Cs)

 

[tsutsuji]

Jun16-11, 05:37 PM:

Hm, okay. Let's see, "TEPCO reports that Unit 2 is probably responsible for nearly all of the contamination."

I think that's better than my previous claim. Of course I'd be interested in how TEPCO decided that Unit 2 released that much radioactivity.

Did they actually measure what was coming out of Units 1, 2 and 3? (I can't really imagine how that would be possible without dozens of sensors in and on the reactor buildings). Did they make that statement based on the course of events? (Big radioactivity spike after the explosion sound in Unit 2 -> Unit 2 is entirely at fault)
Or do they perhaps know more than us? But you're probably right. Before we can discuss why Unit 2 popped out so much radioactivity, we need to evaluate first if and/or why the report about that is justified.

Please note that in its report of 12 March 2012 http://www.irsn.fr/FR/expertise/rap.../IRSN_Rapport_Fukushima-1-an-apres_032012.pdf page 46/189, the French IRSN expresses the view that unit 3 released more radiations than unit 2:

(in PBq)

                  Xe-133     I-131    Cs-137
unit 1           1530           13          1
unit 2           2180           57          6
unit 3           2240          126        14

They comment, page 47/189 : the distribution among the reactors estimated by IRSN is uncertain (...) most [other] experts agree with each other on the view that reactor No. 2 produced a majority of releases, because of the PCV damage that occurred during the hydrogen explosion. Moreover, after the main release period (up to 17 March) attributing the releases to each reactor is very uncertain.

Surprisingly, on page 29/189, they ignore Tepco's view that there was no hydrogen explosion at unit 2 (and that the sound heard and the seismic measurement recorded around 6 AM on 15 March was produced by an explosion at unit 4).

Surprisingly, on page 36/189 Figure 5-16 they attribute the MP8 radiation peak in the night of 12 March to "unit 2 PCV venting" ? Wasn't unit 2's venting started on 14 March ?

 

[SteveElbows]

Well sadly that report does not go into much detail about how they did calculations etc.

Certainly we should still be careful when comparing the reactors, because nobody really knows and there are a number of factors which can have a very large impact on estimates:

The assumption that reactor 2 suppression chamber sustained damage can make a big difference to release estimates, and although TEPCO said explosion wasn't there, damage cannot be ruled out yet. Probably safe to assume that most release estimates still involve assumption of s/c damage at reactor 2.

Possible very brief factor 2 drywell vent that we don't know whether actually happened or not (at 0:02 on 15th).

The wind was blowing out to sea during key big events for reactor 3, so it would be easier to underestimate this reactors releases.

Later events at reactor 3 might be hard to distinguish from events at reactor 2, and we hear little of events that happened after the 16th.So with this in mind, it is probably safer to say the following, as opposed to saying that reactor 2 released more in total. Reactor 2 was responsible for the majority of the contamination on land, because of timing of wind and rain. And because of the highly contaminated water int he basement and the leaking of some of this to the ocean, we can blame reactor 2 for a lot of the ocean contamination too. But reactor 3 could have released a lot into the air over the sea, and may have contributed to some of the march 15th-16th and 20th land contamination that's mostly blamed on reactor 2.

While the French report is lacking in some areas, I think it is very very good for looking at the detail of what the weather was doing at key moments, and the land contamination data.

As to why it labels an event of a graph as being caused by reactor 2 venting at approx 9pm on the 12th, this looks like a simple mistake to me but I shall go and check other sources to remind myself what event actually happened at that time.

 

[MadderDoc]

<..>
What I find especially annoying is that we don't even know exactly when steam was first noticed to be coming from the blowout panel hole in the side of reactor 2. We certainly know that plenty of steam etc came out of this hole later, as we have footage, but not knowing when it began is frustrating. Assuming it was from the reactor rather than the fuel pool, which is a reasonable bet given much later footage showing steam from the reactor arena and the robot-measured radiation readings showing high levels by one side of the floor above the reactor well, we may well imagine that this started on March 15th. But it would be good to know for sure, especially as events at reactor 4 building on the 15th also got in the way of really clear explanations of radiation data on that day.

http://www.tepco.co.jp/en/news/110311/images/110412_1f_tsunami_6.jpg (This is the earliest dated photo I know of showing steam coming from Unit 2.)

 

[SteveElbows]

http://www.tepco.co.jp/en/news/110311/images/110412_1f_tsunami_6.jpg (This is the earliest dated photo I know of showing steam coming from Unit 2.)

Wow! I had missed that one when it was originally released as Tepco published it last April in reference to tsunami water levels, I had not considered the possibility that the photo was taken on a crucial day of the unfolding disaster.

If the timestamp is accurate then this photo was taken during the period when the reactor 2 drywell pressure was falling substantially, and a time when large number of people had been evacuated from the site. Hardly the time that you would choose to send people to take photos relating to the tsunami, but certainly a time where you may want photo of what's happening at reactor 2.

I didn't find other photos taken with the same camera, so its hard to find evidence that the time & date were correct. I note that the photos taken from the ground that show reactor 4 damage were taken with a different camera approximately one hour earlier (if this other cameras timestamp is accurate).

 

[MadderDoc]

Wow! I had missed that one when it was originally released as Tepco published it last April in reference to tsunami water levels, I had not considered the possibility that the photo was taken on a crucial day of the unfolding disaster.

If the timestamp is accurate then this photo was taken during the period when the reactor 2 drywell pressure was falling substantially, and a time when large number of people had been evacuated from the site. Hardly the time that you would choose to send people to take photos relating to the tsunami, but certainly a time where you may want photo of what's happening at reactor 2.

I didn't find other photos taken with the same camera, so its hard to find evidence that the time & date were correct. I note that the photos taken from the ground that show reactor 4 damage were taken with a different camera approximately one hour earlier (if this other cameras timestamp is accurate).

A _third_ camera was according to exif data involved in the taking of the photo at
http://www.tepco.co.jp/en/news/110311/images/110412_1f_tsunami_5.jpg.

According to its exif data this photo was taken about 10 minutes before the photo showing steam from unit 2, and the camera was pointed west, from 100 m down the road between units 2 and 3, i.e. pointed towards the position from which the steam photo according to its exif data was taken a few minutes later.

Judging from details shown in this photo (e.g the presence of particular pieces of debris, that were later removed, and the absence of hoses laid out later,) this photo must have been taken quite soon after the explosion in unit 3, so I am rather confident that the exif date of this photo is correct.

And albeit indirectly, this would support that the Unit 2 steam photo was in fact taken on the morning of March 15, along with other photos, apparently by a 2+ camera/man expedition.

 

[Gary7]

From today's Tokyo Shinbun

Large Release From Unit 2 - "From the upper part of the containment vessel"
Tepco Announcement on Fukushima Accident

On March 19th Tepco announced that the sudden increase in radiation readings measured around the power plant on March 15th last year was possibly caused by leaks coming from between the containment vessel and its lid, as well as from pipe connections. Previously it was thought that the most likely source of the radiation was damage to the suppression chamber.


The article goes on to say that the suppression chamber was initially suspected because of the large explosion heard just as pressure readings from the suppression chamber dropped, but that it was later determined that the explosion was from #4 (this based on seismic readings from around the plant on the morning of the 15th of March, 2011).

 

[tsutsuji]

From today's Tokyo Shinbun

Link : http://www.tokyo-np.co.jp/article/national/news/CK2012032002000020.html

The announcement was made at the Japan Atomic Energy Society meeting in Fukui.

The explosive sound was heard at 06:10 on 15 March 2011.

Almost at the same time, unit 2's suppression chamber pressure reading declined to 0 Pa, which is below atmospheric pressure.

The radiation rose to 15 mSv/hour at the main gate at 9 AM on 15 March 2011.

Tepco's nuclear safety group manager Koichi Miyada said that unit 2's PCV pressure declined from 730 kPa at 7 AM on 15 March 2011 to 150 kPa at 11 AM, and "it is inferred that at this stage, large quantities of radioactive substances were released". "(as the S/C pressure reading below atmospheric pressure is hard to believe) there is a high probability that the measuring instrument is broken".

 

[SteveElbows]

Thanks for the detail on this story, good timing! I assume this possibility is discussed now because they did not see massive damage when they looked inside the torus room.

Here is my attempt at an explanation for large reactor 2 environmental release even if the suppression chamber did not sustain much damage:

Its because there was no opportunity to wet-vent some of nastiest substances that were generated during the core melt. At reactors 1 & 3 they were able to wet vent after the really bad problems started, trapping a lot of these substances in the suppression chamber water. But at reactor 2 there was no such vent, so far more of these substances were mostly still in the drywell. Then the drywell failed whilst it was under high pressure, allowing these substances to be released to the environment in quite a vigorous manner.

There are other possible factors too, but I think the above is basically all we need to explain reactor 2 release being greater than the other reactors.

Other factors could include things such as the timing of the drywell failure in relation to any possible core-concrete reaction. A lot of stuff is generated by the core-concrete reaction, and at reactors 1 & 3 we could assume that wet-venting was performed after such a core-concrete reaction happened, providing some scrubbing. This didn't happen at reactor 2, where direct drywell->environment release occurred without any significant prior wet vent.

As mentioned in previous posts we should also consider that wind direction & rain/snow gave reactor 2 emission far greater chance of being detected.

Anyway I notice that on TEPCO press releases from the 19th March 2012 they mention changes to the nitrogen injection to reactor 2 in preparation for the 2nd endoscope mission, so I don't think we have to wait long to discover more about water level etc, unless this mission fails even worse than the first try.

 

[MadderDoc]

So, would the chunks of debris slumped across the reactor well (along the red fence) represent fragments of the concrete plug(s) produced by some violent impulse from below?

 

[clancy688]

What's the radiation up there? There are a lot of white dots on the picture...

 

[zapperzero]

What's the radiation up there? There are a lot of white dots on the picture...

In the tens of mSv/h iirc. The survey results were posted along with the pictures.

 

[SteveElbows]

So, would the chunks of debris slumped across the reactor well (along the red fence) represent fragments of the concrete plug(s) produced by some violent impulse from below?

I wouldn't say that, the debris doesn't really look like that to me.

To be honest I don't think we should necessarily be looking for signs of violent concrete plug action, I think it is quite possible for sizeable quantities of stuff to leak out in a far less spectacular way, e.g. via degraded gaskets, seals etc. Likewise even if the containment cap moves, it doesn't mean the concrete plugs have to.

 

[SteveElbows]

In the tens of mSv/h iirc. The survey results were posted along with the pictures.

Yeah, but in the range of hundreds of mSv/h either side of the reactor well top concrete containment caps.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120228_04-e.pdf

 

[SteveElbows]

A _third_ camera was according to exif data involved in the taking of the photo at
http://www.tepco.co.jp/en/news/110311/images/110412_1f_tsunami_5.jpg.

According to its exif data this photo was taken about 10 minutes before the photo showing steam from unit 2, and the camera was pointed west, from 100 m down the road between units 2 and 3, i.e. pointed towards the position from which the steam photo according to its exif data was taken a few minutes later.

My EXIF viewing tool says that one was from a day later, the 16th.

 

[MadderDoc]

I wouldn't say that, the debris doesn't really look like that to me.

To be honest I don't think we should necessarily be looking for signs of violent concrete plug action, I think it is quite possible for sizeable quantities of stuff to leak out in a far less spectacular way, e.g. via degraded gaskets, seals etc. Likewise even if the containment cap moves, it doesn't mean the concrete plugs have to.

True enough, but the debris is still there crying for an explanation.

 

[MadderDoc]

My EXIF viewing tool says that one was from a day later, the 16th.

You are right, thanks for the correction.