Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[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 That's why I think the videos of the press kit are of poorer quality than the original, and that there is unpublished video footage.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.

 

[MadderDoc]

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.

I did not mean to explain the high temperature reading of the bellows air as failure of that particular sensor as due to heat or whatever: exactly seeing several sensors in different places got unreliable at about the same time, that rather pointed me to a common failure somewhere outside the sensor -- and then you come with a junction box which fits the pattern perfectly. :-o

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.

Yes, Tepco also indicates this to be the case. They observed the 'phenomenon' in 'parts such as the bellows air'. The near-by RPV flange lower part displays the same phenomenon, and temperature readings from there are also generally high, indeed at times higher than the bellows air. Before the spraying apparently whacked the junction box for a while, high temperatures there at the top of the reactor matched well up with the temperature at the bottom, from where the fuel is supposedly heating the system. Seeing the upper sensors cannot be assumed to be close to a heat source, yet are hot, it suggest to me they are close to a gas exhaust from the reactor.

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.

Now, you never know what an idea does when left to sizzle. The DS pit does not in fact seem to be able to hold water except for a shallow layer at the bottom of it, but I don't think Tepco would necessarily have known that at the time. Attempting to fill the DS pit would seem to be a weirdly indirect way of dealing with the situation, though. Otoh, Tepco would likely have known that there was a steam source associated with the gate to the DS pit, quenching that source too could theoretically have been an objective.

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.

Surely it would have been suspected in any circle in the know from right after the explosion that the containment might be compromised. And surely Tepco would have observed steam plumes from the building in the days following the explosion and wondered what they were about, and whether they might indicate PCV failure.

However Tepco appears to have been actively stepping back from that possibility, indeed giving NISA the impression it had found evidence to contradict it, and this happened in close timely connection with the Tepco+Gov decision to initiate the spraying to the top of the building, at some time during the afternoon of March 16th.

NISA Relase March 16 12:30:
-"White smoke was seen rising from the vicinity of Unit-3 at around 8:30, Mar. 16. Damage to the containment vessel of the unit is suspected."

NISA Release March 16 19:00:
-"White smoke was seen rising from the vicinity of Unit-3 at around 8:30, Mar. 16. TEPCO estimates that failing to cool the SFP has resulted in evaporation of pool water,
generating steam."

Edit: Just to add, whether or not we believe the excessive sprayings to the top of the building during those days served the purpose of filling the PCV with water, at the same time the amounts of water directly injected strongly suggest the presence of that objective: On March 20th pump capacity was doubled and over the five next days of March 20, 21, 22, 23, and 24 Tepco estimates to have injected a sum total of 7500 m³ into the reactor, more than enough to fill the reactor pressure vessel and the PCV to the top.

 

[jim hardy]

You fellows have remarkable recall and ability to find old information. I envy you your filing systems. I plod, and am days behind your thoughts here.


Convection is pretty effective at heat transport particularly where there's a phase change as with steam. That's how 'heat pipes' work.
So a warm wet pool of water at bottom of RPV near boiling, underneath a cool bellows at top of RPV would condense steam on underside of bellows by natural circulation. Steam being lighter than air it would work well , keeping bellows around saturation temperature of RPV. Hydrogen being lighter than steam could stop the process though.
(M_olecularW_eight of air = 29. MW of steam = 18, MW hydrogen of course =2.)

NISA Release March 16 19:00:
-"White smoke was seen rising from the vicinity of Unit-3 at around 8:30, Mar. 16. TEPCO estimates that failing to cool the SFP has resulted in evaporation of pool water,
generating steam."

that was five days after earthquake..?
given decay heat of that pool's spent fuel inventory it should be easy to calculate what mass of water would be raised to almost 212F in five days. if we know whare it started - That should provide one estimate of SFP water inventory... if that estimate turns out unreasonable then the heat balance around pool can be questioned, and more head scratching. will tinker with that later on.

nuceng - i think i found some instrument racks on page 5 of your drawing?
Are those RPV sensors located in same racks as level sensors?

old jim

 

[jim hardy]

Edit: Just to add, whether or not we believe the excessive sprayings to the top of the building during those days served the purpose of filling the PCV with water, at the same time the amounts of water directly injected strongly suggest the presence of that objective:

that is part of the BWR severe accident mitigation strategy, reason is to provide external cooling to the pressure vessel delaying melt-through. There's a modification to cut holes in the support shroud so it can't trap air. I should have saved that link if anyone is interested will lok for it.

Of course they also worried about the extra mass of a flooded containment should another quake come while it's flooded.
Those poor guys.

 

[Rive]

that is part of the BWR severe accident mitigation strategy, reason is to provide external cooling to the pressure vessel delaying melt-through.

I've seen papers about similar strategies for PWRs too.

 

[MadderDoc]

<..> a warm wet pool of water at bottom of RPV near boiling, underneath a cool bellows at top of RPV would condense steam on underside of bellows by natural circulation. Steam being lighter than air it would work well , keeping bellows around saturation temperature of RPV. <..>

Yes, but they were measuring temperatures in the 2-300s deg. C range at the top of the depressurised vessel. It would be physically impossible to heat anything to that kind of temperature by condensation of saturated steam inside the vessel.

that was five days after earthquake..?
given decay heat of that pool's spent fuel inventory it should be easy to calculate<..>

Oh yes, and certainly an agency like NISA had people who could do it. Even a BOE would indicate the madness of the matter. Tepco's proposition that the pool was steaming due to failed cooling postulated the occurrence of a plain physical impossibility -- yet NISA didn't bark, just placated it down as the operator's estimate of the situation.

 

[jim hardy]

Tepco's proposition that the pool was steaming due to failed cooling postulated the occurrence of a plain physical impossibility

hmm i hadnt actually tried the arithmetic out. Real rough back-of-envelope::

half megawatt of decay heat (post 13115) = 500kw X 3412.7 BTU/kwh = 1.706E6 BTU/hr
for 5 days = 120 hours X 1.706E6 BTU/hr = 2.05E8 BTU
to raise water from (let's guess) 72F to 212F is about 140 BTU/lb
so 2.05E8 / 140 = 1.46E6 pounds of water could be warmed that much by the fuel
that's 731 US tons of water
or 664 metric tons of water

i think the pool holds considerably more so i figured it had leaked some.
But that was just an assumption.
This reference gives 1.5 million liters as typical BWR SFP water inventory
http://books.google.com/books?id=lt...page&q=bwr spent fuel capacity water&f=false

which would be 1.5 million KG , 1500 metric tons, 2.25 X my estimate above.

So if it's 'typical' per that book it would have to have lost ~half its water.

Dont know if this is of any use at all
it's just the kind of rough sanity checks i do on myself to keep that "excess of imagination" from getting me in trouble.
please check my arithmetic....

old jim

 

[MadderDoc]

please check my arithmetic....

old jim

Do check your physics, there's a thing called latent heat of evaporation which you appear to have neglected.

 

[NUCENG]

You fellows have remarkable recall and ability to find old information. I envy you your filing systems. I plod, and am days behind your thoughts here.


Convection is pretty effective at heat transport particularly where there's a phase change as with steam. That's how 'heat pipes' work.
So a warm wet pool of water at bottom of RPV near boiling, underneath a cool bellows at top of RPV would condense steam on underside of bellows by natural circulation. Steam being lighter than air it would work well , keeping bellows around saturation temperature of RPV. Hydrogen being lighter than steam could stop the process though.
(M_olecularW_eight of air = 29. MW of steam = 18, MW hydrogen of course =2.)

that was five days after earthquake..?
given decay heat of that pool's spent fuel inventory it should be easy to calculate what mass of water would be raised to almost 212F in five days. if we know whare it started - That should provide one estimate of SFP water inventory... if that estimate turns out unreasonable then the heat balance around pool can be questioned, and more head scratching. will tinker with that later on.

nuceng - i think i found some instrument racks on page 5 of your drawing?
Are those RPV sensors located in same racks as level sensors?

old jim

Caveat: the following applies to a US BWR. Japanese mileage may vary.

If I remember correctly instrument racks contain the pressure and level transmitters/ analog sensors and those racks are located on the first floor outside of the drywell. The inside drywell piping is routed out to these instruments so there are no wires or junctions inside the containment. No guarantee, but I think 1C55 and 1C56 were the numbers on those racks.

Temperature elements are inside containment and thermocouple and RTD cabling is routed out of the drywell and there are junction boxes in the systems inside and outside containment. The Environmental Qualification program qualifies cabling for design basis conditions of pressure, temperature, humidity, spray, submergence, seismic loads, and radiation. However, it is clear that the conditions at the Fukushima plants exceeded design basis conditions. Further the period these instruments are qualified for is not unlimited. I have previously shared the possibility that the post-accident chemistry and radiation are likely attacking the electrical wiring as well. Nuclear plant instrumentation tends to use redundancy, diversity, and independent routing to prevent local failures from being single points of failure.

I have been reluctant to weigh in on some of these discussions because they seem too speculative and I am not sure we will gain anything by trying to answer why instruments failed until they can actually retrieve them and do post mortems. I am not suggesting that this discussion isn't valid or interesting. I will try to provide answers on my experience where I can. I am reading these posts and appreciate the effort being made to understand what happened.

One of the most important things is to get good simulations of the conditions inside the drywell and torus during the accidents that match the information we actually have. This is likely to be available to develop new qualification requirements well before they can actually start retrieving failed cables or sensors.

 

[jim hardy]

latent heat of evaporation...

i just figured the heat to raise the pool temperature to boiling, absent evaporation

steaming carries away copious heat thereafter
a half megawatt should evaporate 1760 lbs/hr, or 29 lbs/minute (latent heat 970 BTU/lb)
making 785 cubic ft/minute of steam, less than a ten foot cube

of course approach to that would be asymptotic as evaporation rate increases.

 

[MadderDoc]

i just figured the heat to raise the pool temperature to boiling, absent evaporation

Yes, you found the decay heat to be sufficient only to heat the water of the pool to about 140^oF (60^oC), not even warm enough to make instant coffee of, and with na'r a BTU left for evaporating any of it.

steaming carries away copious heat thereafter
a half megawatt should evaporate 1760 lbs/hr, or 29 lbs/minute (latent heat 970 BTU/lb)
making 785 cubic ft/minute of steam, less than a ten foot cube
of course approach to that would be asymptotic as evaporation rate increases.

Right, so even assuming every BTU of decay heat in miraculous contradiction of the laws of thermodynamics could have been channelled into evaporation, the pool could have had lost only an insignificant fraction of its water by March 16th.