Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[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.

 

[MadderDoc]

<.>
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.

I'd like first to see some honest curiosity to understand what happened at that plant, without which I can't see how one can conceptualise it and produce a proper model. Once there, implementing a good simulation of the model ought to be the trivial part. I couldn't care less about the fiddling with parameters and assumed events to get existing models to produce output with some semblance to actual data and that's all I've seen so far.

 

[jim hardy]

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

well more exactly , ... sufficient to heat HALF the water in a 'typical' pool BY 140 deg...

Boiling away 1760 lbs/hr would be around 20 tons a day, which is hardly a dent in that 1500 ton inventory.

So if the pool was not pretty low on water it got more heat from someplace.

Conversely if it got no more heat, it musta been pretty low?

i don't know which is the truth, but assumed at the time it was low on water.
Again, that was an assumption but it did fit with the 'gamma backscatter' idea as cause of high radiation readings around building, and with high radiation readings from helicopters..loss of water = loss of shielding above spent fuel.

But i wasn't there. And there's surely other possibilities.
That one could unravel.

What's your thoughts?

 

[Rive]

So if the pool was not pretty low on water it got more heat from someplace.

We know that there were leaks around the reactor cavity on the side of the EQ pool. Maybe there were leaks on the other side too?

For the first times, when the internal pressure of the reactor were high that would mean steam condensing in the pool, raising it's temperature: later on as the pressure drops water would flow in and cool the containment cap.



Slightly connected: the water in the pool were filtered for cesium and other radioactive elements, but this filtering stopped after some time. Do we have any data about the pool water contamination after the filtering stopped?

I think if there is fuel with damaged cladding in the pool then the cesium level would rise after the filtering stopped. If the fuel cladding is intact, the Cs level would be steady.

If the fuel cladding is intact then there must have been other source for that Cesium.
Maybe from steam coming from the reactor, condensed in the pool?

 

[MadderDoc]

well more exactly , ... sufficient to heat HALF the water in a 'typical' pool BY 140 deg...

Boiling away 1760 lbs/hr would be around 20 tons a day, which is hardly a dent in that 1500 ton inventory.

So if the pool was not pretty low on water it got more heat from someplace.

Conversely if it got no more heat, it musta been pretty low?

i don't know which is the truth, but assumed at the time it was low on water.
Again, that was an assumption but it did fit with the 'gamma backscatter' idea as cause of high radiation readings around building, and with high radiation readings from helicopters..loss of water = loss of shielding above spent fuel.

But i wasn't there. And there's surely other possibilities.
That one could unravel.

What's your thoughts?

Well. First, look at the facts: There's a 1400 m³ pool of water with 0.5 MW of decay heat from spent fuel in it and its cooling has failed. 5 days later the operator informs its safety regulatory agency that due to the failed cooling, steam plumes are being emitted from the pool. The safety agency informs the public that this is the operator's estimate of the situation.

Next, there's the impeccable assumption: The laws of physics were not suspended in the pool.

Then follows the inescapable conclusion: What passed in this case as information from the operator to the agency, and from the agency to the public, was not information, not even false information. It was nonsense. Had it only been false information, that would be understandable. But no, for a statement to be possibly false, it must be implied that it can be possibly a true description of reality. Otherwise the statement is just so much nonsense -- and as your math has shown you, what was reported by the operator and sent on to the public by the agency was postulating a physical impossibility had occurred. All such statements are alike, they express nothing, they are all nonsense.

Imagine the operator had reported some other physical impossibility, e.g 'that gravity had reversed over the plant and was emptying the pool', and the safety agency reported this on to the public, the nonsensical nature of it all would have been clear to many people. It takes more knowledge to realize that a 1400 cubic meter pool of water cannot possibly be steaming plumes due to failed cooling after having been heated with 0.5 MW for a couple of days. The unsuspecting and ill-informed public would be excused in not 'getting it'. For Tepco the operator, and for NISA the agency, there is no excuse, and only a few credible explanations, none of which are flattering, and this is not the place to express them.

The fact remains, that what we were told about the situation in the pool did not make sense.

OK, so back to your considerations. If I get it, you meant to be able to extract as a fact that the pool was boiling from the nonsense "White smoke was seen rising from the vicinity of Unit-3 <..>TEPCO estimates that failing to cool the SFP has resulted in evaporation of pool water, generating steam.", then you added the assumptions that either the pool had lost a lot of water for unknown reasons, or it had an unknown heat source, then you coupled it to the observation of high doserate measured above the building, and got a plausible case of exposed fuel in the pool. But that seems to me to have been assumption upon assumption upon nonsense, and no surprise then that it was all wrong.

 

[MadderDoc]

We know that there were leaks around the reactor cavity on the side of the EQ pool. Maybe there were leaks on the other side too?

For the first times, when the internal pressure of the reactor were high that would mean steam condensing in the pool, raising it's temperature: later on as the pressure drops water would flow in and cool the containment cap.

The pool interface is of a different construction than that of the equipment pool, it is a double layered gate, held tight by the hydraulic pressure of the pool water. From what can be discerned in published video footage, the gates are in place, and a major steam route from inside the reactor seems to have passed close by, but on the side of the reactor, not that of the pool. While of course it cannot be held that the gates must be completely tight, there is no indication of any significant leak between the pool and the space over the reactor cavity, no indication that the pool has lost water to that space, or that steam from that space has added heat to the pool water. The added assumption of such a leak would seem to me superfluous, it doesn't appear to explain anything.

Pass on the Cesium thing. IRC the plan has been, using mobile units, with first reverse osmosis, then ion exchangers, to desalinate the water in the pools in turn, starting with unit 4. I do not know where SFP3 would be in the process.

 

[wizwom]

Well. First, look at the facts: There's a 1400 m3 pool of water with 0.5 MW of decay heat from spent fuel in it and its cooling has failed. 5 days later the operator informs its safety regulatory agency that due to the failed cooling, steam plumes are being emitted from the pool. The safety agency informs the public that this is the operator's estimate of the situation.

Next, there's the impeccable assumption: The laws of physics were not suspended in the pool.

Then follows the inescapable conclusion: What passed in this case as information from the operator to the agency, and from the agency to the public, was not information, not even false information. It was nonsense. Had it only been false information, that would be understandable. But no, for a statement to be possibly false, it must be implied that it can be possibly a true description of reality. Otherwise the statement is just so much nonsense -- and as your math has shown you, what was reported by the operator and sent on to the public by the agency was postulating a physical impossibility had occurred. All such statements are alike, they express nothing, they are all nonsense.

Imagine the operator had reported some other physical impossibility, e.g 'that gravity had reversed over the plant and was emptying the pool', and the safety agency reported this on to the public, the nonsensical nature of it all would have been clear to many people. It takes more knowledge to realize that a 1400 cubic meter pool of water cannot possibly be steaming plumes due to failed cooling after having been heated with 0.5 MW for a couple of days. The unsuspecting and ill-informed public would be excused in not 'getting it'. For Tepco the operator, and for NISA the agency, there is no excuse, and only a few credible explanations, none of which are flattering, and this is not the place to express them.

The fact remains, that what we were told about the situation in the pool did not make sense.

There could very well have been localized boiling.
However, steam plumes occur in air very commonly far below the boiling temperature. The air above the surface just has to get a saturation above the prevailing dew point.
It is fairly rare in pool applications, but any fisherman can tell you about a misty lake, which is exactly the same effect, but with the lake microclimate as the cool side.

 

[Rive]

The pool interface is of a different construction than that of the equipment pool...

Yes, you are right. Even if the FHM wreck damaged it the effect would be different. Thanks.

 

[MadderDoc]

There could very well have been localized boiling.
However, steam plumes occur in air very commonly far below the boiling temperature. The air above the surface just has to get a saturation above the prevailing dew point.
It is fairly rare in pool applications, but any fisherman can tell you about a misty lake, which is exactly the same effect, but with the lake microclimate as the cool side.

Yes, wizwom, but this is the steam plume from 'the vicinity of Unit 3' which Tepco is talking about on March 16th:
http://gyldengrisgaard.dk/fuk/20110316_0935%20satellite/20110316_0935_Digitalglobe_zoom_thumb.jpg

Edit: See also the March 16th hourly webcam images

 

[jim hardy]

If I get it, you meant to be able to extract as a fact that the pool was boiling from the nonsense "White smoke was seen rising from the vicinity of Unit-3 <..>TEPCO estimates that failing to cool the SFP has resulted in evaporation of pool water, generating steam.", then you added the assumptions that either the pool had lost a lot of water for unknown reasons, or it had an unknown heat source, then you coupled it to the observation of high doserate measured above the building, and got a plausible case of [nearly_jh] exposed fuel in the pool.

you got it.
IF that steam indeed came from the pool, there had to be a cause for pool being so hot.
With the modest heat input that pool had, either its thermal capacity was less than expected for that much water
or the heat input was more than expected.If neither of those is so then the steam came from someplace else.

why is that "nonsense" ?

EDIT
I think one of us misunderstands something the other is saying and our difference lies in semantics not thermodynamics. It is sooooo difficult to make communication precise.

old jim

 

[MadderDoc]

you got it.
IF that steam indeed came from the pool, there had to be a cause for pool being so hot.
With the modest heat input that pool had, either its thermal capacity was less than expected for that much water or the heat input was more than expected.
If neither of those is so then the steam came from someplace else.
why is that "nonsense" ?

I apologize if I have given you the impression that seems implied by your question, I really thought I had clearly identified the target of that description to be the estimate by Tepco, that the pool was steaming plumes due to failed cooling, indeed I think you just quoted me to that effect.

What you have written there is just the sort of mental model one makes of possibilities and logical implications when one is trying to get a foothold in regards of some problem. I wouldn't call any of it nonsense. Otoh, I can't see where you are coming from with it, nor where you are going, also I think the option 'someplace else' might be specifiable both as to its whereabouts, and its logical implications. Better to chalk up the whole playing field, before deciding how to tackle the problem.

EDIT
I think one of us misunderstands something the other is saying and our difference lies in semantics not thermodynamics. It is sooooo difficult to make communication precise.

old jim

Yes surely, but I think we will get by.

 

[MadderDoc]

If neither of those is so then the steam came from someplace else.

Yes,seeing we can't assume there was no steam, that steam had to be coming from somewhere,
so evidently if steam was _not_ coming from the spent fuel pool, it had to come from someplace else.

However, looking at the published bits and pieces of Tepco's videos from March the 16th,
whether or not we would conclude that steam was coming from the spent fuel pool,
we would still have to accept that steam was (also) coming from someplace else,
since there is clearly a steam plume to be seen originating from the equipment pool in those videos.

In this poor video shot, we see from left to right (north to south) across the building, the contour of the equipment pool with a steam plume coming out of it,
the fallen girders across the reactor top area, and to the right of the girders, another plume, the origin of which is, shall we say, ambiguous.
The green splotch below that plume is the spent fuel pool.

 

[jim hardy]

I really thought I had clearly identified the target of that description to be the estimate by Tepco,

now i see clearly that you did. But i somehow missed it earlier. So my apology is extended.

Better to chalk up the whole playing field, before deciding how to tackle the problem.

i often try to rule things out.
When the "three minutes after" satellite photo came out showing what looks like that same plume,

i set out looking for what could have heated pool that quickly.

That path seemed implausible. I don't even know if they actually were the same plume.
So i decided to wait it out. That the plume came from someplace other than spent fuel pool is certainly not ruled out.

old jim

 

[MadderDoc]

<..>
i often try to rule things out.
When the "three minutes after" satellite photo came out showing what looks like that same plume,

i set out looking for what could have heated pool that quickly.

That path seemed implausible. I don't even know if they actually were the same plume.
So i decided to wait it out.

Trying to put myself in your situation at the time you saw this photo, I imagine you'd have a possible case of nearly exposed fuel on March 16th in your mind. The satellite photo would have seemed to you to have possible repercussions to that, indicating a possible case of nearly exposed fuel already shortly after the explosion on March 14th, and then, a possible case of pool involvement in the Unit 3 explosion, the explanation of which 'hydrogen explosion' you felt was in miss of something.

As I recall, I came out from the curious incident of the pool on March 16th with no clear conception of what it was about, except for an intuitive feeling of bait and switch. I had that feeling arranged to reinforce a possible case of the presence of an unwillingness to admit PCV involvement in the Unit 3 explosion. Pool involvement, I believe, was not something I really thought of until it occurred to me that other people did. But then it just became a case for me of accommodating that possibility. To me that seemed pretty straightforward, seeing the energetics of flashing large quantities of water into steam in a short instant it left pool involvement with only a tiny probability of a case of criticality, bordering to the impossible according to experts, which I have to trust in such matters.

That the plume came from someplace other than spent fuel pool is certainly not ruled out.

In respect to the never-ending circle of expanding knowledge along with language to express it ..

I suggest we can say less conservatively, that the plume from the building, at least for a part of that plume, did in fact come from someplace else, i.e. the PCV. Evidence, also evidence from a very early stage indicates this to be the case, no evidence appears to contradict it. The only inconsistency it produces is with Tepco's estimate on March 16th, which appeared to be, that the plume in its entirety was caused by evaporation of water from the pool.

 

[jim hardy]

Thanks for 'walking in my shoes'. I find it helpful in my troubleshooting to ask myself "What would make a rational person say that? Just what was the picture in his mind right then ?"

...pool involvement with only a tiny probability of a case of criticality, bordering to the impossible according to experts

I watched the TV news video that morning and thought it had to be the SFP. I even emailed Arnie Gundersen to ask if those racks had boraflex and could go fast critical on loss of moderator.. i think i set him off on a tangent.
But as i learned more about their pools and about fast fission cross sections i too decided it wan't the pool.
Photos have since confirmed.

part of that plume, did in fact come from someplace else, i.e. the PCV.

So next i looked into recriticality on reflood as described in ORNL and European BWR studies.
But Morbius made a pretty strong case against thermal recrificality and his credentials are awesome.
So next i looked into low enrichment Pu with U reflector.
And into Hafnium cross section at high energy(~10mev)
And what i found out is i don't know enough about fast reactor physics to make meaningful calculations. So i can't put a number on it. I admit defeat.
You could be right.
But for me that train of thought is too speculative to make any strong assertions.

As i said on another forum i'll have to wait for photographs of reactor head.

What's that "evidence from a very early stage " you mention ?
Probably i looked at it (i was obsessive back then) and tucked away in the 'unresolved observations' basket , and would like to know what facet it was that has retained your attention.

That was a very clearly communicated post, by the way . With my Asperger's i had to study it but it parsed quite well. Thanks !old jim

 

[mheslep]

...
But Morbius made a pretty strong case against thermal recrificality and his credentials are awesome.

Sorry, do you recall roughly when and in what thread was that part posted? This thread?

 

[zapperzero]

Sorry, do you recall roughly when and in what thread was that part posted? This thread?

That would be the explosion thread, now lost to time and incompetence. Sorry. Some people here may have copies of the Google cache before it expired or other such things - there is a discussion earlier in this thread wrt the demise of that thread. It was closed for moderation and never reopened. There is no backup at PF.

Morbius (aka Gregory Greenman iirc) was arguing, based on his extensive experience designing nukes and on some calculations he did, that unmoderated recriticality is impossible in reactor fuel, in any configuration, that moderated criticality is only possible in a 50/50 "matrix" configuration of fuel/(light)water, that there is no way that such a configuration could have been achieved with melted fuel.

He also stated that there is no way that the neutron-reflecting properties of either water surrounding fuel or reactor steel and other metals could have changed this.

At the time, I was obsessing over the possibility of pulsating criticality in reactor 3, which I saw as a way to explain some of the readings we saw in the first few weeks.

The issue of spent fuel in the pools was only marginally touched upon, I believe.

I present this along with pre-emptive apologies for any inexact info, both to you and to Morbius. It has been a rather long time and my memory is not getting better.

 

[jim hardy]

Sorry, do you recall roughly when and in what thread was that part posted? This thread?

It was in the 'Unit 3 explosion' thread which is no longer with us.
Would have been within a very few days of June 12 2011.

He ran a Monte Carlo program and said , to best of my recollection, 'corium' couldn't go if it has less than 10% enrichment because it lost the optimal geometry of an assembled core.
Monte Carlo is outside my experience base. All i know is it's a sophisticated neutronics program used by genuine experts.
I accepted his opinion as a solid data point. for uranium.old jim

zz posted while i was typing. He has a better memory for detail than i do.

we don't disagree, thanks zz i worry about anything i do from memory.

 

[zapperzero]

we don't disagree, thanks zz i worry about anything i do from memory.

De nada, I do too.

 

[MadderDoc]

It was in the 'Unit 3 explosion' thread which is no longer with us.
Would have been within a very few days of June 12 2011.

He ran a Monte Carlo program and said , to best of my recollection, 'corium' couldn't go if it has less than 10% enrichment because it lost the optimal geometry of an assembled core.
Monte Carlo is outside my experience base. All i know is it's a sophisticated neutronics program used by genuine experts.
I accepted his opinion as a solid data point. for uranium

IIRC, his challenge to criticality theoreticists is to postulate a credible mechanism for getting the fuel arranged as it is in the core and with no control rods between them, and submerged in water.

As regards the fuel in the SFP, that leaves afaics only the possibility of some disturbance overturning racks causing fuel to rearrange and come back to rest in the right positions for the criticality to happen. While not impossible, the probability of such occurrence is too low to take a theory about it seriously until one can say that one has examined and exhausted all other options for explanation.

As regards the fuel in the core, jim hardy did bring up a mechanism involving control rod melt-away in a degrading core during a LOCA. Criticality could then happen on subsequent reflooding of portions of un-melted fuel assembly parts being still in their original positions however now devoid of control rod material between them.
This would seem to me a much more likely contender for a criticality theory.

But, however much a theory of a criticality event makes a lot of exciting energy available for destruction -- the Unit 3 reactor, it must be assumed, at the time of the explosion was already shock full of hydrogen and accumulated energy in hot water, the system had already in it plenty enough of energy available for its own destruction. An assumption of criticality then becomes just one of many possible triggering factors, for its particular quality: energy, there is no need.

 

[MadderDoc]

What's that "evidence from a very early stage " you mention ?

I was thinking of the visual evidence from Tepco's intensive helicopter surveys on March 16th. Although in written sources Tepco comes over as saying that the plume in its entirety was due to water evaporated from the SFP , even this lousy video shot taken during the mission leaves no doubt that the reality of the situation was, shall we say, a bit more complex. Note the clear visibility of the steam plume out of the equipment pool. Surely Tepco would have noticed the presence of that plume, which certainly is not steam produced by water evaporated from the SFP many meters away. In fact, views like this would have suggested to me that the plume in its entirety might have very little to do with the spent fuel pool. Tepco, alas, curiously appears to have reported to NISA the opposite judgement, that it was all coming out from there.

 

[jim hardy]

this one looking opposite direction also has appearance of steam coming out nearer reactor.

this one it's hard to say. Reactor would be centered on fourth column.

not sure where i got this one. Top one is from Cryptome, [EDIT: add] http://cryptome.org/eyeball/daiichi-npp3/daiichi-photos3.htm , twenty-third one down. It's worth loading the zipped full resolution ones from link at top of that page..[end edit]



Thanks, it had not occurred to me to localize the sources of the steam. Guess I'm intimidated by not knowing the piping there.

............

BTW - that control rod meltaway and recriticality scenario is not my creation. It's the subject of NUREG CR-5653.
which has this great line: "... the operations staff may be very surprised..."
It's bad science to go looking for things that support one's preconceived notions.
Mea culpa. The enormity of that explosion set me off looking for reasons to believe it got a fission boost.

old jim

 

[jim hardy]

challenge to

...postulate a credible mechanism for getting the fuel arranged as it is in the core and with no control rods between them, and submerged in water...

Experiments to investigate the phenomena of core melt progression in prototypical BWR core geometries have been carried out in the Annular Core Research Reactor (ACRR) at Sandia National Laboratories (one BWR test) and at the CORA out-of-pile facility9 at the Kernforschungszentrum Karlsruhe (KfK) in the former Federal Republic of Germany (six BWR tests). The first of these was the DF-4 experiment,"° conducted within the ACRR in November 1986. The test apparatus, placed within the cylindrical region surrounded by the ACRR annulus, included a control blade arm, channel box walls, and 14 fresh fuel rods. The apparatus was dry, but the 20inch (50-cm) long test section was supplied from below with a steam flow representative of BWR boiloff conditions.
When the DF-4 fuel rod cladding was heated beyond the runaway zirconium oxidation temperature, the energy release associated with oxidation accelerated the temperature escalation. Much of the clad melted at 2125 K (3365°F) and relocated downward; the remainder was converted to and remained in place as ZrO2, which has a much higher melting point ([4900'F]2978 K).
The control blade in the DF-4 experiment melted earlier than expected and progressively and rapidly relocated downward. Subsequently, the reactor was shutdown to terminate power generation within the test assembly fuel rods before fuel melting could begin. In a post-test crosssection, the relocated control blade material was found in the form of an ingot at the very bottom of the test section, which was below the bottom of active fuel. Both the control blade and the channel box wall portions of the DF-4 test section were more than 90% destroyed due to melting and relocation during the experiment, but the fuel pellet stacks were predominantly still standing. Relocated cladding blocked the base of the fuel rod regions of the experiment.

Figure 3.7-15 illustrates the results of the DF-4 experiment, extrapolated to the same portion of the core that is represented in Figure 3.7-14. (Here the water rods, which were not included in the DF-4 experiment, have been assumed to relocate in the same time frame as the channel box walls.) The ramifications of these standing fuel pellet stacks in the absence of control blades with respect to the potential for criticality if water were to be introduced at this point in an actual accident sequence should be obvious.

Figure 3.7-15 You'll have to look at the document for i don't know how to copy the figure here. Its descriptor says it all, though. _jh
Relocation of control blades and channel box walls leaves on U02pellets encased in thin Zr02sheaths sic

http://pbadupws.nrc.gov/docs/ML0210/ML021080117.pdf

so i could niether prove nor disprove it happened, only that it's deemed possible by credible sources..

old jim

 

[jim hardy]

ps

Nureg CR-5653 was hard to find but it seems available here:

http://www.findthatfile.com/download.php?i=84077748&t=hPDF

12 meg , takes a while .

 

[rmattila]

There's also one report by the Nordic nuclear safety group on the issue of BWR recriticality:

http://www.nks.org/scripts/getdocument.php?file=111010111119589

 

[zapperzero]

Fwiw, i had proposed a mechanism where there is thermal inversion in the melt (ceramic ends up on the bottom) then the melt breaches in the bottom head and is blown down into the water which was supposed to exist on the PCV's bottom, as in the report you provided.

This would result in a steam explosion, of course, and would also create a bed of small ceramic fragments which when re-flooded might (I thought) go critical and provide the fluctuating radiation and heat levels we were seeing at the time as well as the periodic spikes of Iodine in the water.

Morbius chewed me over for thinking that it's even remotely possible for a debris bed to self-arrange into a favorable geometry.