Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[MadderDoc]

Actually that's the one example of footage where it always looked to me like they were trying to spray the right part of the building (but mostly falling short).

I haven't seen the fireman footage of spraying the NE part of the building for ages, anyone got a link to that?

I know only of a short sequence from past noon on March 19th which I have previously interpreted as the fire engine's spraying to the NE corner, but on later reconsideration I've come to think I was fooled by the perspective, and that the direction of that spraying too was to about center of the building. The short sequence is at the very end of the video here.

The initial water cannon truck attempts 17-18 March were made from about position A, then from the night 18-19 March and on, the spraying was done from a stationed fire engine at position B, the thin red line indicates the route of the hose that was laid by the fire fighters to feed the fire engine. The spent fuel pool is marked at position C. The photo is from about noon on March 19th.

 

[MadderDoc]

Funny how something can elude you completely then suddenly flip to become obvious. I'd figured vaguely last time I saw the firefighter video, this could be a doorway of unit 3 with something written on it, but of course it is not. The correct interpretation also explains why swift walking is subsequently heard.

 

[SpunkyMonkey]

Here are some thoughts on the Unit 3 1st floor PVC shield plug being moved from Genn Saji, former Secretariat of Nuclear Safety Commission, Japan:

II. First photo inside of an equipment hatch of 1F3 PCV

In order to check the situation of water leakage from the equipment hatch of PCV at the northeast on the first floor, an image scope inspection at the floor of the equipment hatch was performed on April 19. A gap opening between the shield plug and the reactor building has been confirmed in the past video. This motivated TEPCO towards inspection of the situation of water leakage from the flange of the equipment hatch, by inserting an image scope into the gap opening between the shield plug and the reactor building. A short summary was released by: http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120419_03-e.pdf

Since the leak tightness of the PCV is tested each time before reactor startup, the existence of the gap-opening should indicate an overpressure event inside of the PCV beyond the design pressure. As a matter of fact, there are at least four peak pressure recorded above 0.4 MPa inside of the dry-well between March 12 to 15, ranging from 0,4 to 0.65 MPa (design pressure is 3.92 kg/cm2). However, it is strange that the PCV did not have a safety margin of withstanding to this level of over pressure. In some model PCV test, a safety margin as high as a factor of 3 was shown, if I remember correctly in a PWR containment vessel model test. There is a high possibility that the over-pressure event is related with the "spontaneous venting." Since the pressure surges events were showing peaks, I suspect an occurrence of a series of hydrogen ignition (slow burning) events. Let me attach a previous TEPCO's graph (DoseRate-PressD-W1.jpg), showing variation of the dry well pressure and dose rates measure by radiation monitoring cars and a survey meter.

 

[SpunkyMonkey]

Actually that's the one example of footage where it always looked to me like they were trying to spray the right part of the building (but mostly falling short).

Possibly the high-dose rate on the south side (imo prob caused by the stack-vent bursting on the south side and releasing lots of cesium-vapor residue) which should have been detectable by the first Geiger counter in the scene made them opt to try to reach the pool from the NW corner.

 

[SpunkyMonkey]

I am not sure how I would go on about informing the fire department -- called in an emergency to stop a spent fuel pool from boiling dry -- that they should direct their attention to a part of the building which was not steaming.

At the time, it may not have been clear from the helicopter footage that the pool wasn't largely empty. It's only with the data gained over the following weeks that we could thereafter determine that there were roof girders / materials in the pool that were obscured by water on the 16th. But on the 16th they didn't have that information about debris in the pool.

Although U3 pool didn't seem to be steaming at that time, whereas U4 pool was steaming vigorously. Perhaps that invoked fear that U3 pool was a deep dark hole with no water left to boil.

Thanks for the overview of the valve analysis!

 

[MadderDoc]

At the time, it may not have been clear <..>

That is simply not credible. Tepco shot more video footage than we've been shown, and of better quality, and they had an employee on board the helicopters sent there with the specific assignment by combined Tepco and Japanese Government order to assess the water levels of the pools.

 

[MadderDoc]

Here are some thoughts on the Unit 3 1st floor PVC shield plug being moved from Genn Saji, former Secretariat of Nuclear Safety Commission, Japan:

I would like to see it in context. "Spontaneous venting" ?

 

[MadderDoc]

<..>
Although U3 pool didn't seem to be steaming at that time, whereas U4 pool was steaming vigorously. Perhaps that invoked fear that U3 pool was a deep dark hole with no water left to boil.

Iffy. Tepco said on the press conference that day that the steam from the Unit 3 building had been found to be coming from the pool, not the reactor.

 

[SpunkyMonkey]

I would like to see it in context. "Spontaneous venting" ?

He's also taken the view that there was a PCV overpressure event(s) accounting for the ajar hatch plug. As much as that happily fits with my theory, how do we explain the small lightweight objects in the hatch passageway? I'd expect they should have been blown out of the passage had a huge impulse blasted through it. Or maybe they were dropped during an earlier but recent inspection of the passageway. We probably shouldn't expect to find them in the passageway anyway if when the plug is closed it fits with perfect tightness.

But something certainly made the first floor a mess, exactly matching a hurricane-like wind blowing through it. So everything fits for an overpressure blowing through, minus those two tiny objects in the purported blow path.

ADD: I think by "spontaneous venting" he means caused by a series of small explosions(?) in the PCV. It seems a bit of a stretch to correlate the radiation readings on campus to these hypothetical events in Unit 3, but it also seems like an interesting idea.

Tepco shot more video footage than we've been shown, and of better quality,

Is that known or assumed? I'd suspect so myself, but I don't know so. We're taking about around April 16, 2011 of course.

What is it that you're getting at, if anything, with this line of inquiry? Are their plausible motives to mislead the public that they were worried about pool 3 being dry?

 

[LabratSR]

I didnt see this posted yet. Sorry if it has been already.


April 23 Fukushima Unit 4 Walkthrough
http://youtu.be/qZOqyEzhGGQ

 

[MadderDoc]

<..>
Is that known or assumed? I'd suspect so myself, but I don't know so. We're taking about around April 16, 2011 of course.

I assume you meant to write March. The press kit from March 16 included a reasonable quality still from a non-published video sequence.

What is it that you're getting at, if anything, with this line of inquiry? Are their plausible motives to mislead the public that they were worried about pool 3 being dry?

The latter question would seem to be OT. My inquiry is directed at finding Tepco's technical rationale for letting people risk their lives to splash some water onto unit 3.

 

[jim hardy]

Tepco said on the press conference that day that the steam from the Unit 3 building had been found to be coming from the pool, not the reactor.

which led me to assume pool was low on water. If full it should have considerable thermal capacity and be not steaming yet ?
Per m'doc's post 13115 two pages back its decay heat load was only ~half megawatt.


Cross section, probably a generic drawing, looking toward ocean and pool appears on right

drawing looking West (toward land), pool appears on left side as in helicopter video

Cracks in the pool wall on reactor side (from PCV flexing ? ) would leak pool water into basement ?
That's the pool that got 4800 tons of water.
Almost 4X as much as unit 4 got(1278). But 4's pool has 5X the heat load of 3's.

As you said - i should look for something that destroys that hypothesis not supports it.

old jim

 

[MadderDoc]

Cracks in the pool wall on reactor side (from PCV flexing ? ) would leak pool water into basement ?
That's the pool that got 4800 tons of water.
Almost 4X as much as unit 4 got(1278). But 4's pool has 5X the heat load of 3's.

As you said - i should look for something that destroys that hypothesis not supports it.

old jim

On SFPs, tsutsuji posted a while back, a translation of a part, and a link to the original document:
https://www.physicsforums.com/showpost.php?p=3813126&postcount=12587

I did a quick BOE reality check of the data given there of the refill demand rate of SFP3 during concrete pump injection, and fwiw found it to be consistent with the decay heat of the pool.

 

[SpunkyMonkey]

I assume you meant to write March. The press kit from March 16 included a reasonable quality still from a non-published video sequence.

Right, I meant March. Could it be a photo (not video frame) you refer to? I think for safety the helicopter avoided a direct flyover, so I'm not sure they got much closer than we've seen.

The latter question would seem to be OT. My inquiry is directed at finding Tepco's technical rationale for letting people risk their lives to splash some water onto unit 3.

But you seem to be arguing that they had to know the pool wasn't dried out or close thereto, and yet to the contrary were saying that's what they thought. Btw, I'm not against considering if Tepco's been less than honest. There's a well-known history of coverups and evasion in Japanese nuclear industry that includes Tepco. The level of public scrutiny they're under now is probably the best deterrent, but we shouldn't assume it's an ironclad safeguard.

 

[jim hardy]

As the full water level was reached when half the predicted quantity of water had been used, it was confirmed that the predictions of evaporated quantities made until then had been conservative, and that more water had been injected than the needed quantities. Among the quantities that were injected until then, it is thought that the surplus overflowed. After the water injections that were inferred as having generated overflows, although the causal relationship is unclear, a phenomenon where the temperature in parts such as the bellows seal, rises and declines within a short time was observed.

Thanks doc i had missed that one.

 

[MadderDoc]

<..>you seem to be arguing that they had to know the pool wasn't dried out or close thereto, and yet to the contrary were saying that's what they thought.

Then I may not have expressed myself clearly.

I have been arguing that from the evidence Tepco has shown me, there would seem to have been no basis for the thought that the pool was dried out or close thereto, and that Tepco in consistence with this also never said that's what they thought.

 

[MadderDoc]

Could it be a photo (not video frame) you refer to? I think for safety the helicopter avoided a direct flyover, so I'm not sure they got much closer than we've seen.

While not having an assumed source video I cannot definitely say that an image is a frame from it. However, in the press kit, one image is an exact replica of a frame from one of the published videos, only the image is of more than double the pixel resolution as that of the frame from that video. The other images included in the press kit are of the same higher pixel resolution, but they do not match any frames of the published videos, while otoh, they do show signs of compression artefacts of a type I would expect to find in a video, but not in a jpeg compressed image produced by a camera. That's why I think the videos of the press kit are of poorer quality than the original, and that there is unpublished video footage.

 

[MadderDoc]

Thanks doc i had missed that one.

I'll send that straight on to tsutsuji who made the translation, who drew our attention to the existence of the document. Thanks tsutsuji!

Interesting observation there, btw, would like to know more about this possible 'high tide' communion between the pool and the reactor internals:
"After the water injections that were inferred as having generated overflows, although the causal relationship is unclear, a phenomenon where the temperature in parts such as the bellows seal, rises and declines within a short time was observed. "

 

[westfield]

<snip>
So if the pressure tap were near top of vessel and the sensor lower than that,
when sensing line dried out,
reported pressure would be low by the height of fluid lost.

but i don't know physical arrangement in a BWR. Mine i knew pretty well.

old jim

I'm a little late re the SRV & Instumentation posts.

This document may be a useful reference, I had been searching for Duane Arnold Energy Centre drawings for some time as it seems to be one of the closest USA BWR types to fukuichi U2 & U3.
Very similar RB & TB layout. It took quite some time to find any drawings at all.
Of course there will be differences between the plants but these are the closest I've found so far.

Some of the drawings that may be of interest to you Jim are:
(They don't really help you out with the physical relationship of tap and sensor locations though)

Page 10 - P & ID - Nuclear Boiler System
Page 11 - P & ID - Reactor Vessel Instrumentation
Page 67 & 68 - P & ID - Main Steam

 

[westfield]

They weren't expecting that water to make it into the PCV, no? So what else is left? A fire (for which there is no evidence whatsoever) or a pool that is _believed_ to be emptying fast.

In general reply to the question of what the fire dept might have been attempting to do.

This is a little out there...but so is trying to spray the pool from the NW corner of U3 with a fire truck.
The D\S pool has no watertight gate between it and the reactor void, water could flow through the concrete shield segments from the D\S pool down into the upper part of the void and onto the PCV head. Could Tepco have been trying to cool or cover the top of the PCV not the SFP?

 

[jim hardy]

"After the water injections that were inferred as having generated overflows, although the causal relationship is unclear, a phenomenon where the temperature in parts such as the bellows seal, rises and declines within a short time was observed. "

that kinda sticks out, doesn't it?

Did they not inject some concrete into that pool? One wonders where.

Sure sounds like water running over the wall down onto flange-bellows area.
Pure guess though.

Thanks Westfield for the links to DAEC
will look at them this evening
small world - my former employer bought that plant.

And if Tsutsuji needs anything i could send, pm me a mailing address.


old jim

 

[jim hardy]

Think i found 'em page 11
PT 4599A and PT 4599B?
From vessel penetrations N12A and N12B ?

Most informative drawings. Instrumentation is a lot different than my PWR.

Thanks will peruse further.

old jim

 

[MadderDoc]

"After the water injections that were inferred as having generated overflows, although the causal relationship is unclear, a phenomenon where the temperature in parts such as the bellows seal, rises and declines within a short time was observed. "

that kinda sticks out, doesn't it?

Yes, but caveat: it sticks out as would a red herring, and it leaves painfully much untold.
I may get back to some of that in another post.

Another interesting tidbit from the document:
"The records of water temperature measurements consist of only one measurement of around 60°C. "

While at least two such measurements would seem to be required for Tepco's stated technical rationale for initiating the water splashing to Unit 3:

"As the temperature of water in the spent fuel pool rose, spraying water
by helicopters with the support of the Self Defense Force was considered,
however the works today have been cancelled. " (Press release March 16th)

 

[SteveElbows]

In general reply to the question of what the fire dept might have been attempting to do.

This is a little out there...but so is trying to spray the pool from the NW corner of U3 with a fire truck.
The D\S pool has no watertight gate between it and the reactor void, water could flow through the concrete shield segments from the D\S pool down into the upper part of the void and onto the PCV head. Could Tepco have been trying to cool or cover the top of the PCV not the SFP?

I think its fair enough to consider this question, although I don't think there is very much to support this line of enquiry. We now know that prior to reactor 3 melting, they did use internal spraying systems inside containment at some points. This is of course a rather different thing, and spraying externally is not really comparable. But we could look at the pressure data (and later temperature data) to see if there is any obvious reason why they would try this stuff over the tie period they used firefighters etc. We know that they struggled for months with reactor 3 and there were a number of events that happened long after the explosion that are of interest but received very little in the way of official explanation. But again I don't think any of this stuff clearly points to an alternative reason for spraying reactor 3, or at least it hasn't in the past when I've thought about this, but maybe I missed something.

Having now watched a press conference with some tokyo hyper rescue people after their initial mission, I stick with my suggestion that one reason to attempt this mission was so that something publicly visible was being seen to be done, at a time when the authorities had otherwise been giving the impression of continually being on the back foot. One of the people in the press conference, according to one translation, even mentions bringing peace of mind to citizens.

I also have no problem believing that the radiation levels and debris in the area between reactors 3 & 4 would have large implications for where they positioned themselves, even though being on the 'wrong side' of the building made their mission far less likely to succeed.

 

[MadderDoc]

I think its fair enough to consider this question, although I don't think there is very much to support this line of enquiry. We now know that prior to reactor 3 melting, they did use internal spraying systems inside containment at some points. This is of course a rather different thing, and spraying externally is not really comparable. But we could look at the pressure data (and later temperature data) to see if there is any obvious reason why they would try this stuff over the tie period they used firefighters etc. We know that they struggled for months with reactor 3 and there were a number of events that happened long after the explosion that are of interest but received very little in the way of official explanation. But again I don't think any of this stuff clearly points to an alternative reason for spraying reactor 3, or at least it hasn't in the past when I've thought about this, but maybe I missed something.

I too would think whatever it was that reasoned the spraying would have reasoned to spray to the pool, however the area above the PCV -- cf. the adopted spraying positions -- then naturally would come in the firing line. Also, it seems during the operation that steam evolution was seen as a sign of successfully hitting the target. ( And I bet, if steam evolution had stopped, that too would have been interpreted as sucessfully hitting the target :-)

Having now watched a press conference with some tokyo hyper rescue people after their initial mission, I stick with my suggestion that one reason to attempt this mission was so that something publicly visible was being seen to be done, at a time when the authorities had otherwise been giving the impression of continually being on the back foot. One of the people in the press conference, according to one translation, even mentions bringing peace of mind to citizens.

That would seem to me more like a post event observation and part of the natural pride of his job. It can hardly have reasoned the mission in the first place. Ref your suggestion as to the nature of the reasoning behind the mission, it should be noted that it came based on a decision by Tepco and the Japanese Government in unity. So that's where we'd have to look for the rationales, whatever they might be. I am mostly interested in which technical rationale Tepco brought to the table, as you will know.

I also have no problem believing that the radiation levels and debris in the area between reactors 3 & 4 would have large implications for where they positioned themselves, even though being on the 'wrong side' of the building made their mission far less likely to succeed.

Yes, something 'trivial' as that is also where I'd put my money. Once the mission was decided, there would be safety and logistics concerns restricting their choices on how to implement it.

 

[MadderDoc]

Thermometer reliability trends

May 1st Reliability Evaluation of the Thermometers Used in the Reactor and the Primary Containment Vessel at Fukushima Daiichi Nuclear Power Station Unit 1-3

 

[NUCENG]

Think i found 'em page 11
PT 4599A and PT 4599B?
From vessel penetrations N12A and N12B ?

Most informative drawings. Instrumentation is a lot different than my PWR.

Thanks will peruse further.

old jim

Looks like we've got common ground. DAEC is a BWR4 Mk1 and I have worked there. I thought NRC had deleted this kind of drawing from ADAMs after 9/11, but it is good to have that set of drawings for discussion.

 

[MadderDoc]

@jim, I promised to get back to you on this one, albeit in this post only commenting more generally on:

"After the water injections that were inferred as having generated overflows, although the causal relationship is unclear, a phenomenon where the temperature in parts such as the bellows seal, rises and declines within a short time was observed. "

Whether due to the structure, or varieties in the use of the Japanese language, or something else or a combination, time and again I've found myself with to me unusually vague official expressions on Fukushima-related issues of my interest. Often times after some parsing, statements still leave more than one interpretation, which must then be assigned probabilities, and implicit reference to subject matter important for the understanding of it must be researched. In the end I may sit back with a statement that now makes some sense, but also with a feeling that it ought not have been so laborious, and that something more than an educated guess of what the statement is meant to express ought to result from it. Explicit in my world is always better than implicit, and more precision of language always better than less. So why on Earth can these people not write e.g. : 'At times A and B, temperature of parts X, Y and Z was seen to increase and decrease over a period of W minutes, coincident with the times when we have inferred that overflow of the pool occurred. Whether there is a causal relationship remains unclear' Why this apparent sensitivity to putting solid content into the expression?

The most serious problem with the statement above is that it makes reference to non-explicated inferences. The reader has no way of knowing which water injections the author is referring to. The reader might be able to look at available data himself, make his own inferences as to which injections could have generated overflow. He may then assume, but cannot know whether the author made similar inferences.

From the context, he would need to be looking at water injections, from the pool spraying spree started on March 17th, and until the 62 m concrete pump with a camera replaced the 52 m concrete pump on April 12th. He would need to make inferences about when overflows were generated. He would need to look at the temperature record of the bellows seal, and perhaps other parts he'd imagine could be 'such as' the bellows seal, to see if there might be patterns of rises and declines coincident with those periods of inferred overflows. Then he might know so and so, what the statement more precisely, likely, is talking about.

Of course the type of science this statement is from, science to serve company relations to the government and the public, is not generally meant to be reported in such a way that its results can be reproduced from information given in the report, it is meant only to give the reader an impression of the work that has been done, and to suggest some possible conclusions. One could say, its usefulness as a source of information rests on the a priori trust of the reader, that the reported work has been done properly, and that suggested conclusions are sound. And worse, seeing that if that trust should be broken, there would be no alternative source of information, we are led to not care about, or to accept to trust whatever wobbly that is thrown at us as better than nothing.

Perhaps I'll get back to you, seeing there is some availability of the data, when I think I know so and so, what the statement more precisely, likely, is talking about :-)

 

[westfield]

Think i found 'em page 11
PT 4599A and PT 4599B?
From vessel penetrations N12A and N12B ?

Most informative drawings. Instrumentation is a lot different than my PWR.

Thanks will peruse further.

old jim

More (This is a generic table for BWR's, not DAEC specific.)

Additionally, an example of a PT4599 is an ITT Barton Model 763

Edit @ Jim - Any idea what is the "heated leg" and what would penetrations N16A & N16B role be in that pressure sensing system?

Edit: Some of the charted values and charting parameters in a GE BWR similar to Units 2 & 3 (DAEC in this case)

 

[MadderDoc]

@jim, now I think I know so and so, what the statement more precisely, likely, is talking about :-)

"After the water injections that were inferred as having generated overflows, although the causal relationship is unclear, a phenomenon where the temperature in parts such as the bellows seal, rises and declines within a short time was observed. "

On April 12th, Tepco replaced the 52 m concrete pump at SFP3 with a 62 m concrete pump equipped with a camera, and it became obvious that the pool had been overfilled up to this point in time, the injected amounts of water were henceforth reduced. The previous spraying, on April 10th, then became the last injection that produced overflow..

Looking at the temperature at the RPV bellows air, true enough its temperature increased and declined over a short period after that injection. This assumedly is the phenomenon Tepco is talking about. Slide 1:

The red line indicates the time of the water injections, the red figures are m³ injected, and the 'phenomenon' is encircled. The same phenomenon can be seen coincident with the series of water injections leading up to that time, Slide 2, Slide 3, Slide 4, and Slide 5.

Going further back in time, we see the effect of the fire-fighter spraying on the temperature indicators. I don't know if you'll love this as an instrumentation guy, or hate it, but here goes. During the sprayings on March 19th-March 20th, the building was douched with water enough to fill the pool twice, and after that on March 20th-March 21st it was douched with enough to to fill the pool once more over. These efforts appear to have effected in the end, if nothing else, gross unreliability of many of the temperature sensors, including sensors far removed from the sensor at the RPV bellows seal: Slide 6, and Slide 7.
Edit: and Slide 8.

 

[westfield]

@jim, now I think I know so and so, what the statement more precisely, likely, is talking about :-)

"After the water injections that were inferred as having generated overflows, although the causal relationship is unclear, a phenomenon where the temperature in parts such as the bellows seal, rises and declines within a short time was observed. "

On April 12th, Tepco replaced the 52 m concrete pump at SFP3 with a 62 m concrete pump equipped with a camera, and it became obvious that the pool had been overfilled up to this point in time, the injected amounts of water were henceforth reduced. The previous spraying, on April 10th, then became the last injection that produced overflow..

.

What does the "RPV Bellows Air" column actually indicate? If it's temperature I wonder why is it consistantly so much higher than any other parts of the system in the chart?

Edit : Nevermind, I found the answer or lack of an answer for the odd temperatures in previous posts.
I was also a little confused by the label "bellows seal air", I've gathered it's the upper drywell air temperature. Nothing to do with the bellows seal as such, just that it's in the upper drywell area below the refuelling bellows.

Edit: Sorry to be just catching up - So the idea is perhaps the overflowing SFP water has penetrated the PCV & the refuelling bellows and has influenced either the actual temperature in the upper drywell area or the instrumentation?

If it's any help - In the DAEC drawings there's a TC junction box in the drywell that appears to be the termination point for ALL the drywell and RPV thermocouples at that plant.

 

[MadderDoc]

What does the "RPV Bellows Air" column actually indicate? If it's temperature I wonder why is it consistantly so much higher than any other parts of the system in the chart?

Yes it is the temperature reading of the RPV bellows air sensor.

Assuming the readings are meaningful after the obvious potential deleterious effect of the earlier spraying spree, the higher temperature suggests to me that this sensor is measuring somewhere close to a hot gas exhaust route at the top of the reactor.

Cf. the steam plumes that were seen being emitted with gusto from the top of the building at that time, the observation of which also strongly suggested the presence of a hot gas exhaust route from the reactor.

 

[westfield]

Yes it is the temperature reading of the RPV bellows air sensor.

Assuming the readings are meaningful after the obvious potential deleterious effect of the earlier spraying spree, the higher temperature suggests to me that this sensor is measuring somewhere close to a hot gas exhaust route at the top of the reactor.

Cf. the steam plumes that were seen being emitted with gusto from the top of the building at that time, the observation of which also strongly suggested the presence of a hot gas exhaust route from the reactor.

Ok, and possibly the rises in temp coincide with steam created with SFP overflow water.
That just makes me wonder again if spraying water into the DS pit from the northwest corner of U3 was deliberate and not a futile attempt to top up the SFP. Such a deadend.

 

[MadderDoc]

<..>
If it's any help - In the DAEC drawings there's a TC junction box in the drywell that appears to be the termination point for ALL the drywell and RPV thermocouples at that plant.

Ah, so that junction box got wet or something during all that early spraying.

Ok, and possibly the rises in temp coincide with steam created with SFP overflow water.
That just makes me wonder again if spraying water into the DS pit from the northwest corner of U3 was deliberate and not a futile attempt to top up the SFP. Such a deadend.

We do not know that there was spraying into the DS pit, but whether the spraying was a deliberate attempt to do something other than to top up the SFP is a valid question seeing there is that puzzling turnabout of Tepco on March 16th: from the observation of the steam plumes in the morning to have suspected PCV damage, to in the afternoon come to estimate there was no PCV damage after all but the pool might need some water, because 'the water temperature rose'. And then came a lot of spraying but with no significant fraction of the water hitting the pool?? 体どうなっているんだ

Edit: I find that if I am only willing to let go of the assumption that the Integrated Headquarter (Tepco+Gov) would have been straight with the public about the problem with unit 3 as they perceived it, I effortlessly get that they were trying to fill the PCV with water.

 

[westfield]

Ah, so that junction box got wet or something during all that early spraying.

.

The TC junction box that is located in the drywell being compromised was something I brought up because apparently multiple temperature readings appeared to be going out of whack, not just the "bellows air" temperature. The terminations in the junction box would be a good candidate for that sort of behaviour and I'm sure Jim would have some stories to tell about thermocouple terminations. I wasn't necessarily thinking about a direct effect from the water ingress, an indirect effect from excess steam\heat\salt could also compromise the junction box and it's TC terminations.

However, as already suggested, a hotspot created by steam generation in the upper drywell raising the actual temperature in the upper drywell ("bellows air") is plausable also. That would not explain any other possible thermocouple instrumentation problems in itself though.

That must be quite a localised "hotspot" though as none of the other themocouples show anything like the "bellows air"\upper drywell temperature.

Do any of the other drywell temps track the temperature variations in the "bellows air" temp at all? I havn't yet looked in detail to see if there was a trend amongst drywell temps.

We do not know that there was spraying into the DS pit, but whether the spraying was a deliberate attempt to do something other than to top up the SFP is a valid question seeing there is that puzzling turnabout of Tepco on March 16th: from the observation of the steam plumes in the morning to have suspected PCV damage, to in the afternoon come to estimate there was no PCV damage after all but the pool might need some water, because 'the water temperature rose'. And then came a lot of spraying but with no significant fraction of the water hitting the pool?? 体どうなっているんだ

Edit: I find that if I am only willing to let go of the assumption that the Integrated Headquarter (Tepco+Gov) would have been straight with the public about the problem with unit 3 as they perceived it, I effortlessly get that they were trying to fill the PCV with water.

Yes, when I said "such a deadend" I was meaning the line of discussion was such a dead end. I only hinted at the DS pit because it would have been a practical target to "gather" sprayed water in. Nowhere to go with that idea though.

As you hint at above, in those early days I also tend to think that even if Tepco knew U3 containment was compromised they didn't appear ready to publically admit it. Telling the world they were aiming to spray water into the reactor via top of the PCV would have let that cat out of the bag somewhat.