Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[SteveElbows]

My other question is whether this shield plug has moved considerably away from the position that it is supposed to be in. Is it supposed to be so much further away from containment than the rest of the containment wall? (i.e. in photo it is much nearer to camera than the rest of wall, is it supposed to be flush to wall?)

 

[MadderDoc]

My other question is whether this shield plug has moved considerably away from the position that it is supposed to be in. Is it supposed to be so much further away from containment than the rest of the containment wall? (i.e. in photo it is much nearer to camera than the rest of wall, is it supposed to be flush to wall?)

As I understand it, the backside of the shield plug is not meant to be flush with the wall, but there is not supposed to be so much of an opening (the 'crevice') between the wall and the shield plug as there is now, so the shield plug is not in place, and appears as pushed out a bit from some impulse from inside the hatch.

BTW, if there is currently an active leak of water from somewhere in PCV flange of the hatch, as the wet floor inside the hatch could indicate, would that mean the PCV of unit 3 is water filled to that level?

 

[Rive]

BTW, if there is currently an active leak of water from somewhere in PCV flange of the hatch, as the wet floor inside the hatch could indicate, would that mean the PCV of unit 3 is water filled to that level?

IMHO not necessarily. In U2 PCV the water level is low, but everything is wet and there is heavy 'rain' inside. A small leak can catch enough water to keep wet those rails and areas even if it's not under water if the 'weather' is any similar in U3 PCV.

Ps.:

By the way I am quite impressed with the quality of the video from the robot that did the reactor 2 torus room survey, good detail & well lit.

It'll be perfect for steam hunting :-)

 

[SteveElbows]

BTW, if there is currently an active leak of water from somewhere in PCV flange of the hatch, as the wet floor inside the hatch could indicate, would that mean the PCV of unit 3 is water filled to that level?

Not sure, would need to know something about leak rate. As we saw from video inside reactor 2 containment, water injection/spraying can cause a lot of droplets of water to be dispersed quite widely inside containment. Failure to get inside torus room at reactor 3 doesn't help build a picture either.

By the way I am quite impressed with the quality of the video from the robot that did the reactor 2 torus room survey, good detail & well lit.

http://photo.tepco.co.jp/en/date/2012/201204-e/120419-01e.html

 

[SteveElbows]

As I understand it, the backside of the shield plug is not meant to be flush with the wall, but there is not supposed to be so much of an opening (the 'crevice') between the wall and the shield plug as there is now, so the shield plug is not in place, and appears as pushed out a bit from some impulse from inside the hatch.

If I take the diagrams they used literally, then its been seriously displaced. We see from both the main floor plan and the smaller diagram that either side of the outer shield plug, the wall comes out at at approx 45 degree angle, so the 'frame' around the plug sticks out compared to the rest of the wall. But the shield plug is currently well beyond this, perhaps as much as a meter or so away from the frame?

 

[MadderDoc]

Aha, very interesting.

Its not terribly surprising given that we have previously seen attention paid to high radiation levels from the rail on the floor in front of this equipment hatch.

( Last november http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111122_02-e.pdf )
<..>.

Those rails might be what the shield plug is traveling upon, cf.the floorplan of Unit2 which is showing the hatch in the open position:

The PCV hatch we are talking about would seem to be large opening seen to the right at the equator of the PCV bulb in that never-boring photo of a BWR reactor during construction before it gets dressed up in concrete:

 

[SteveElbows]

The more I look at the photo, the more I think that plug should be flush with the frame part of the wall.

This is because you can see behind the ladder the part of the wall that is at about 45 degrees, which to me means that the wall to the left of the ladder is the frame part that's supposed to be about flush with the plug.

 

[SteveElbows]

Those rails might be what the shield plug is traveling upon, cf.the floorplan of Unit2 which is showing the hatch in the open position:

Yes I think this fact was fairly well discussed at the time that the rails (& attempted cleaning of rails) was news.

 

[MadderDoc]

If I take the diagrams they used literally, then its been seriously displaced. We see from both the main floor plan and the smaller diagram that either side of the outer shield plug, the wall comes out at at approx 45 degree angle, so the 'frame' around the plug sticks out compared to the rest of the wall. But the shield plug is currently well beyond this, perhaps as much as a meter or so away from the frame?

Agreed, it seems to be displaced quite a lot more than a bit :-)

 

[SteveElbows]

The PCV hatch we are talking about would seem to be large opening seen to the right at the equator of the PCV bulb in that never-boring photo of a BWR reactor during construction before it gets dressed up in concrete:

No, I think that opening is on the opposite side to the equipment hatch we are talking about today. Look at where the personnel airlock is on that photo (equator).

Anyway I have been looking again at the photos and videos from November that showed robots cleaning the rail areas.

I am still a bit uncertain as to how everything should look under normal conditions. For example looking at images at left of page 2 of this document:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111105_02-e.pdf

It seems that the equipment hatch itself has some thin doors. Both of these doors were open in first photo, but they managed to shut the right-hand one in second photo. This is confirmed by another photo on page 4.

So now I am not sure if this entire structure has moved, or whether the plug part that moves on rails is behind these doors (and structure that sticks out is a kind of porch).

Then look at this document:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111122_02-e.pdf

First image on page 2 shows that this structure is at an angle, not 90 degrees to the floor. Can see probable hinge for the thin doors that I mention above.

Also if TEPCO diagram of radiation detection points has point very close to where equipment hatch should be at normal time, so either diagram is lying or it hasn't really moved forwards like I suggested before.

So I think its quite easy for me to make a mistake when looking at this stuff, really could do with seeing photos of how equipment hatch of this type should look under normal conditions, but equipment hatch pictures we have seen at other sites are very different so not much help.

 

[SteveElbows]

OK I have figured out my above confusion.

There is an additional white box that has doors on it, that is in front of the main shield plug that we saw in todays photo. It is further to the left, so cannot be seen much in that photo, but it is visible in the cleanup photos which I mentioned in previous post.

Check out the following video at about the 7 minute mark, and it becomes very clear, because we can see both this protruding porch that has doors on it, and the much larger shield plug that is behind it. The grey box with black wire duct that goes upwards and then left can be seen in todays photo and that video, thus making sense of the whole thing.

http://www.tepco.co.jp/en/news/libr...368209002&bclid=59370327002&bctid=59374639002

 

[MadderDoc]

<..>

There is an additional white box that has doors on it, that is in front of the main shield plug that we saw in todays photo. It is further to the left, so cannot be seen much in that photo, but it is visible in the cleanup photos which I mentioned in previous post.

Check out the following video at about the 7 minute mark, and it becomes very clear, because we can see both this protruding porch that has doors on it, and the much larger shield plug that is behind it. The grey box with black wire duct that goes upwards and then left can be seen in todays photo and that video, thus making sense of the whole thing.

http://www.tepco.co.jp/en/news/libr...368209002&bclid=59370327002&bctid=59374639002

Thanks, well done! So the plug has in fact moved considerably.

 

[SteveElbows]

Well, I don't think anything I've said or shown proves this conclusively. Maybe its supposed to stick out of the wall like that, but I have serious doubts about that.

Sadly it may be hard to learn more unless some journalists actually notice this news and ask the right questions. Or someone who knows what that hatch is supposed to look like talks.

I am somewhat amused that the websites that like to do big scary headlines and poor analysis of Fukushima disaster don't seem to have noticed this stuff, maybe there is a flashing light or some weather on a camera that is distracting them.

 

[tsutsuji]

If this big plug was moved, how ? Earthquake or explosion ?One more unit 2 thermometer is broken :

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120419_04-e.pdf We evaluated the reliability of the thermometer (RPV bottom head 135°) which was monitored for reference based on safety regulations 138 through direct current resistive measurement. We evaluated the thermometer broken down based on the increase in direct current resistance. No large swings confirmed at other thermometers, monitoring posts, and PCV gas management system indicators. We will continue monitoring PCV temperature by thermometers (RPV bottom upper head 270°and RPV upper skirt junction 135°).

http://www.tepco.co.jp/tepconews/library/movie-01j.html 19 April press conference 14:50 (Junichi Matsumoto on the robot mission into unit 2's torus room) : we recorded sounds with an IC recorder, but the "beep beep" sounds of the radiation dosimeter is mixed to it, so we could not make a good sound recording. We were thinking that water flowing sounds could be checked that way, but in retrospect the situation is that it could not be done well enough. Concerning this PCV suppression chamber torus room inspection with "Survey Runner" [the robot's name], one thing is that we confirmed that it is possible to use Survey Runner for this kind of mission, and the other thing is that at this point, although some heat insulating material covers were found to have fallen down, no major pipe or equipment deformation or damage was found in the upper part of the torus room. [...] (20:26, replying to a question by NHK's Hanada) I think it is possible that the heat insulating material's covers fell down because of the earthquake. As one year has elapsed since the earthquake and the humidity was high, corrosion can also be a possible cause. The exact cause is not known, but the heat insulating material, the wool-like material itself was not blown away, so that we think the cause is not liquids or gasses flowing out of the pipe. [...] (29:01) If no damage is found in the upper part of the torus room, we'll have to find a way to inspect underwater. [...] (29:30) Hanada : What methods can be thought to inspect the inner side of the torus room and the lower part that is not submerged by water ? Matsumoto : first we have to create a route astride the suppression chamber to get to the inner side catwalk. If we manage to take Survey Runner there, we can have it make a round trip on the inner side catwalk and inspect the vent pipes. For the area between the water surface and the catwalk, the grating is an obstacle, but I think it is possible to move the camera so that it focusses downwards. At this point we have not yet decided how or when we will do that. [about sound recording] I think perhaps we can try to record sounds again after turning off [all other] sounds. [about unit 3's equipment hatch] (...) (33:30) Yomiuri's Funakoshi: What did you want to see with this survey ? Matsumoto: One thing is that if water is oozing like that, it could be a valid water level. One other thing is that when we inspected the North-eastern area with Packbot, water was accumulated near the rail, and the radiation there was comparatively high, so we thought it was quite probable that water is leaking from the PCV (...) At this point, we don't know if it is a leak. The situation is that although it is wet like this, it was not confirmed that water is flowing. Funakoshi: Which quantity of water is accumulated on the floor ? Matsumoto: the floor is somewhat wet. At present we don't know the width and length of the wet area. Funakoshi: You don't know which percentage of the area is wet, and which percentage is dry ? Matsumoto: No we don't. We only inspected a small part with the endoscope. As the radiation is high the duration of the work was 4 minutes. Funakoshi: what is the most natural leak route that can be thought ? Matsumoto: the hatch is closed with bolts, like a manhole, and the most likely route is between bolt and packing.

http://www.tepco.co.jp/en/press/corp-com/release/2012/1202043_1870.html Report submitted to NISA concerning response to safety regulation breach during first FY2011 safety investigation at Fukushima Daiichi Nuclear Power Station

 

[jim hardy]

No, I think that opening is on the opposite side to the equipment hatch we are talking about today. Look at where the personnel airlock is on that photo (equator).

Are there two hatches?
Looking a MadderD's drawing in post 12898, the one at 2 o'clock is clearly a hatch with plug extended.
Opposite, 8 o'clock, is that another one with plug inserted?
It'd make sense to have one near each recirc pump for motor replacement.

Not a BWR guy,

old jim

 

[SteveElbows]

Are there two hatches?
Looking a MadderD's drawing in post 12898, the one at 2 o'clock is clearly a hatch with plug extended.
Opposite, 8 o'clock, is that another one with plug inserted?
It'd make sense to have one near each recirc pump for motor replacement.

Not a BWR guy,

old jim

Well the other large opening, that you describe as 8 oclick, looks a bit different on the plans we've seen. If I take the diagram literally then I get the idea that this hatch is not routinely used, does not have rails, may have been 'bricked in'. Perhaps it is was only used during reactor construction, or could be unblocked if something went wrong with opening the other one that is normally used. Been a while since I saw photos of this area, seem to think I may have seen a picture that confirms it is blocked off, but maybe I dreamt it.

There is also the personnel airlock one, which is obviously smaller, and in a part of the building that I don't think we have seen much of.

Big shame nobody at the press conference seemed to ask about whether the plug was further forwards than it should be when closed according to what Tsutsuji translated (thanks again!). Understandable that they talk about the unseen bolted hatch by the steel part of containment and possible kind of leak, but I really wanted to know whether todays discussion about the plug being forwards is true and important or not. Now I have no idea if/when we will ever find this out!

 

[MadderDoc]

Well the other large opening, that you describe as 8 oclick, looks a bit different on the plans we've seen. If I take the diagram literally then I get the idea that this hatch is not routinely used, does not have rails, may have been 'bricked in'. Perhaps it is was only used during reactor construction, or could be unblocked if something went wrong with opening the other one that is normally used. Been a while since I saw photos of this area, seem to think I may have seen a picture that confirms it is blocked off, but maybe I dreamt it.

There is also the personnel airlock one, which is obviously smaller, and in a part of the building that I don't think we have seen much of.

The area at the other large opening has been the scene of some cleaning and monitoring effort, so there is reasonable photo coverage of it. It appears as you say, to be blocked with a semipermanent plug. The plug appears to be in position, same as shown in the diagram of unit 2. That is: its outer face is at some distance from the wall, on the right hand side it has that 45 angles frame reinforcement you've pointed to, in order to meet the wall. On its left hand side it comes together with the shield walls around the personal airlock.

Best views I've found are at around 12:09 in this video:
http://photo.tepco.co.jp/en/date/2011/201106-e/110615-01e.html

Areas close to where the plug meets the wall to the right of this opening appear to be strong gamma sources:

http://photo.tepco.co.jp/en/date/2011/201106-e/110611-02e.html

and there has been quite some cleaning efforts at the site:
http://photo.tepco.co.jp/en/date/2011/201107-e/110702-01e.html

Big shame nobody at the press conference seemed to ask about whether the plug was further forwards than it should be when closed according to what Tsutsuji translated (thanks again!). Understandable that they talk about the unseen bolted hatch by the steel part of containment and possible kind of leak, but I really wanted to know whether todays discussion about the plug being forwards is true and important or not. Now I have no idea if/when we will ever find this out!

Assuming the plug was not moved by the earthquake or later events, the only possibility I can see how the plug can be in the semi-open position shown to us by the Tepco diagrams and videos would be if it had been intentionally, temporarily unplugged and I think if that were the case Tepco would have left no doubt about it. From that I deduce that the plug must have been moved by the earthquake or later events.

 

[jim hardy]

From that I deduce that the plug must have been moved by the earthquake or later events.

One can be sure the plug is restrained for seismic acceleration. When M is that large a small A generates lots of F; that ~1/2 g quake would have made the plug push against its restraints with half its considerable weight.

Presumably there's a bolted steel door on inside that could flex on overpressure and push against the plug like a piston. The available force from pressure is far greater than from earthquake but one has to consider most of it should have been opposed by door's rigidity. We need a GE guy who knows the design of that piece.

As always not quite enough data. But it is interesting to keep these observations in the back of our mind and be on lookout for relevant details.

You guys are doing an excellent job at that.

 

[MadderDoc]

If this big plug was moved, how ? Earthquake or explosion ?

I can't exclude that the earthquake moved it, I suppose it could plausibly have moved anything anywhere, however this plug appears so distinctly to have been pushed out, so I'd put my money on an explosion (some pressure wave from it).

(...) (33:30) Yomiuri's Funakoshi: What did you want to see with this survey ? Matsumoto: One thing is that if water is oozing like that, it could be a valid water level. One other thing is that when we inspected the North-eastern area with Packbot, water was accumulated near the rail, and the radiation there was comparatively high, so we thought it was quite probable that water is leaking from the PCV (...) At this point, we don't know if it is a leak. The situation is that although it is wet like this, it was not confirmed that water is flowing. Funakoshi: Which quantity of water is accumulated on the floor ? Matsumoto: the floor is somewhat wet. At present we don't know the width and length of the wet area. Funakoshi: You don't know which percentage of the area is wet, and which percentage is dry ? Matsumoto: No we don't. We only inspected a small part with the endoscope. As the radiation is high the duration of the work was 4 minutes. Funakoshi: what is the most natural leak route that can be thought ? Matsumoto: the hatch is closed with bolts, like a manhole, and the most likely route is between bolt and packing.

Thanks a lot, tsusuji, for these extra insights non-Japanese speaking users get from you.

From one of Tepco's publications, I've attached a cropped diagram, and a photo of a PCV hatch, as seen from inside the PCV. From what I've read elsewhere, the flange of a Japanese BWR would be sealed with silicone rubber seals, which should be good for at least 225 degrees C, but PCV temperatures upwards of 400 C were reported during the weeks after the explosion.

 

[SpunkyMonkey]

I can't exclude that the earthquake moved it, I suppose it could plausibly have moved anything anywhere, however this plug appears so distinctly to have been pushed out, so I'd put my money on an explosion (some pressure wave from it).

The fact that the first floor into which any impulse from the crevice would have entered was covered with dust and rubble and looked like it was hit by a hurricane further supports that the plug was pushed open by the explosion. Or maybe just that an impulse passed through the crevice whenever the plug was moved.

However, could the interior hatch still be in place and any impulse that pushed out the plug have been carried by air between the PCV steel liner and the concrete surrounding it? The reason I wonder this is that despite the disarray in the first floor, I'm not impressed that it took the full explosive force one might expect had there been a direct passage from a PCV explosion into the first floor. Or maybe the hatch was largely left in place but just enough of an impulse passed through its seams to push out the plug.

Btw, which Tepco publication has those images?

 

[MadderDoc]

<..>could the interior hatch still be in place and any impulse that pushed out the plug have been carried by air between the PCV steel liner and the concrete surrounding it?

Well, I can't see why not. Mostly anywhere on the surface of the PCV a leak might happen would blow out directly to that space.

The reason I wonder this is that despite the disarray in the first floor, I'm not impressed that it took the full explosive force one might expect had there been a direct passage from a PCV explosion into the first floor. Or maybe the hatch was largely left in place but just enough of an impulse passed through its seams to push out the plug.

Btw, which Tepco publication has those images?

Certainly it is my impression too, that this hatch hardly was at the focus point of an explosion, only it might have been affected by one.

Sorry, I wrote Tepco publication, strike that, I remembered falsely, I got those images from a METI hosted document, "Development of containment vessels repair method"

 

[westfield]

Tepco followup Video of the Fukuichi Unit 3 Equipment Hatch Shield PlugBrowns Ferry NPP
( just for reference on the mass of these things - and if I've learned nothing else today it's that BWR equipment hatch images are few and far between )

This is fukuichi Unit 1's Equipment hatch shield plug:

And finally for the hatch curious, a fuku daini personnel airlock:

Edit: I expect there will be some interesting posts over the weekend regarding Unit 3.

 

[SpunkyMonkey]

Tepco followup Video of the Fukuichi Unit 3 Equipment Hatch Shield Plug

Thanks! Hard to understand what we're seeing. The robot appears to travel down the hallway to the plug then inject a probe into the crevice @ 0:55. So it's what appears thereafter and until extraction perhaps at 3:33 that should be of interest.

Around 2:10 appears what at first I assumed to be water drops streaking across the screen. But freeze framing suggests they are something like wires or filaments of some kind

@ 2:11

@ 2:14

@2:18​

because their lengths are wriggly / irregular and sharp ended, unlike the expected paths of water droplets. What these are I have no idea.

 

[SpunkyMonkey]

What the heck are these filaments in the "www.youtube.com/watch?v=zndssc4qe7g#t=2m10s" ?​

 

[SpunkyMonkey]

There's a moment in the new Unit-3 PCV-hatch video here when the camera probe seems to climb over a little wall then finds itself in a space facing a reflective or wet wall. Is that wall metal or wet? In this space the ccd snow indicating radiation goes to its maximum intensity. A few filaments like those above also appear in this footage.

To help actualize what / where this hotspot is I posted this video that loops the entry into the hotspot. The prior link takes you to the full context of this hotspot.

 

[elektrownik]

Is this pcv hatch main plug ? There is a lot of corrosion so it can be wet if seals are damaged by temperature or plug was moved by earthquake/explosion.

 

[elektrownik]

What the heck are these filaments in the "www.youtube.com/watch?v=zndssc4qe7g#t=2m10s" ?​

I know what is this. When camera touch wall some small pices of debris/sediment are falling down.

 

[westfield]

What the heck are these filaments in the "www.youtube.com/watch?v=zndssc4qe7g#t=2m10s" ?​

I've step-framed through it a few times now - personally, I think the artifacts are paint flakes caught in the slow speed of the camera. It happens the most when the camera is against the surface with dry flaky paint on it, moving across it. Small camera "jiggles" would create the loops and shapes like that. It also happens once or twice after exiting the penetration. Contrary to what you say the artifacts don't stay around for more than a frame or two which I think they would if they were some kind of filament.


BTW, it was a person, not a robot on the end of the camera stick.

Presuming Tepco would have briefed the hapless person that shot this to get images of the inner hatch itself and the flange around it (there's really nothing else in that space to look at) and having stepped though it a few times I'm fairly convinced we are mostly seeing exactly that. (Edit : I read the handout now which confirms the hatch was the target)

Unfortunately it's not clear if the moisture is coming from through the hatch flange or from the interface between the concrete and the PCV. I guess Tepco will probably send someone else in there to stick the camera in via the other side of the plug to get another view.

It also confirms very clearly that the shield plug is slighty more than half way out.
It would be interesting to know if that shield plug had any locking mechanism on its wheels - the only reason to do that would be for seismic protection.


EDIT : I see electownik beat me with the paint flakes ;)

 

[MadderDoc]

The video, I've found, makes more easily sense if it is rotated something like 180-270 degrees.

There's a moment in the new Unit-3 PCV-hatch video here when the camera probe seems to climb over a little wall then finds itself in a space facing a reflective or wet wall. Is that wall metal or wet? In this space the ccd snow indicating radiation goes to its maximum intensity. A few filaments like those above also appear in this footage.

I think there may have been a rapid movement of the camera a this striking change of scene and pick-up of radiation, or perhaps the video could at this point have been redacted, (while it otherwise does give the impression of being a continuous recording.)

 

[westfield]

Is this pcv hatch main plug ? There is a lot of corrosion so it can be wet if seals are damaged by temperature or plug was moved by earthquake/explosion.

Overpressure combined with overheat in the PCV could also be a possible cause of hatch seal failure.

If the flange was hot and under pressure then later colder with no pressure the seal could be "baked" into a thinner profile so to speak leading to failure without having needed to melt as such.

However, another possibility is moisture running down or welling up in the gap between PCV and it's concrete shell.

So unfortunately we cannot know if the hatch seal is compromised as yet or how it has failed if it did.

 

[Rive]

However, could the interior hatch still be in place and any impulse that pushed out the plug have been carried by air between the PCV steel liner and the concrete surrounding it? The reason I wonder this is that despite the disarray in the first floor, I'm not impressed that it took the full explosive force one might expect had there been a direct passage from a PCV explosion into the first floor. Or maybe the hatch was largely left in place but just enough of an impulse passed through its seams to push out the plug.

Well spotted. Now I think it's safe to assume that U3 first floor were not directly affected by hydrogen or steam explosion. By comparing the pictures of the U3 first floor with pictures from U4 floor 4-5 (where there was a 'mild' explosion) this theory can be backed up even stronger.

U3 first floor has common air space with areas where there was explosion, so I think there was no Hydrogen on the first floor at all. So the equipment hatch seals had to be more or less intact when the explosion happened (otherwise there would be Hydrogen which likely would have been ignited).

About the shield plug: apart from the earthquake and the internal pressure there is one more possibility: after the explosion on the fifth floor there might be a short period of vacuum in the building. Maybe that was able to suck that plug outward?

 

[SpunkyMonkey]

I know what is this. When camera touch wall some small pices of debris/sediment are falling down.

That's got to be the answer.

I've step-framed through it a few times now - personally, I think the artifacts are paint flakes caught in the slow speed of the camera. It happens the most when the camera is against the surface with dry flaky paint on it, moving across it. Small camera "jiggles" would create the loops and shapes like that.

But camera jiggle doesn't explain their unique wriggly shapes. Camera jiggles would not affect just one thing in the frame leaving other immediately nearby things stable and in focus. Perhaps unique aerodynamic properties of irregular flakes plus chaotic air motion or static cause chaotic wriggly-shaped fall paths. Though the one that's a loop @ 2:16:21 is hard not to see as a multi-strand filament.

Contrary to what you say the artifacts don't stay around for more than a frame or two which I think they would if they were some kind of filament.

Where did I say anything to the contrary?

 

[westfield]

<snip>

About the shield plug: apart from the earthquake and the internal pressure there is one more possibility: after the explosion on the fifth floor there might be a short period of vacuum in the building. Maybe that was able to suck that plug outward?

If we are looking at posibilities -

Regarding any buildup of water between the concrete shell and the PCV (post explosion) - Apart from this shield plug area where else might it flow to at a reasonable rate?
Keeping in mind that normally it's quite important to the long life of the reactor to keep this void dry by keeping moisture out of it.

If water could build up in that void between the shells it would be quite a head of water potentially pushing at the back of the plug, tons. Sure it would dribble out a little around the plug but if water head in the void around PCV was large enough it could eventually push the shield plug out to where it is now - water then quite rapidly drains to the floor level of the equipment hatch where it continues to well up out of the void as it may be doing now - water entering void is reduced now because they are being a lot more accurate with where they are pumping\spraying water now compared to the initial post explosion response where tons of water was sprayed all over the place onto the exposed top floor of the RB. If the sprayed water up top goes through to where the PCV cap is and it can't enter the PCV where does it go? There is also some leakage from the U3 SFP, where does that go.

This would cover why there is water weeping out of there, why it's quite active, why the floor around there is also quite active, and how the shield plug got moved out.

Of course that's just another possibility, it will be interesting to see what Tepco can find out about it.

I guess it would also mean the U3 PCV has (edit: even more of ) an accelerated corrosion issue.

 

[westfield]

<snip>

Where did I say anything to the contrary?

My apologies. When you said "freeze frame" earlier I assumed you were saying they were present for multiple frames as you stepped though frame by frame to support your idea that they might be some sort of filament and not a radiation artifact.Re the squiggles, if they are right at the camera lens then their apparent movement and any movement of the lens itself will be appear to be much greater than for a subject that is further away from the lens even by a few inches.

To be honest, I'm over the artifacts already. I'd be much more excited if they weren't there and we could see better :)

 

[SpunkyMonkey]

Wonder what these two little objects are (one white one red) that appear to be close to the crevice entry ("www.youtube.com/watch?v=zndssc4qe7g#t=3m12s" ):

frame 3:14:24​

If a powerful impulse blasted the shield plug outward, would we find little light-weight objects like these in the hatch passageway through which a powerful impulse passed? Wouldn't be intuitive. But that of course assumes that's where they area, or that where they are should have been swept clean by an impulse. Or perhaps the objects fell off the camera. An awful lot of unknowns.