Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[frangin]

Seawater Levels of Iodine at unit 2 Iodine-131: 24,000 becquerels/liter on may 28 (was only 5,200 becquerels/liter at the same place the day before) : is this rising significant and can be related to RVP/corium state ?

 

[jim hardy]

Mr Charisma

maybe i can put it in real basic terms here for a non engineer.

in the spent fuel pool , as you know normal heat removal is via a pump and heat exchanger.

If that path is lost the pool will heat up until evaporation is carrying away all the heat that's being added. That heatup is somewhat slow because the pool is so big that it can absorb a lot of heat.

I'm an old guy , still use English units . One BTU heats a pound of water one degreeF, and one BTU per second is within 5% of a kilowatt which is convenient for in-your-head calculating... So a ton of water can absorb one kilowatt for an hour and only get heated 3600 btu/2000lb = about 1.8 degreeF. well that's a ~5% approximation. But it gives you a feel.

Now the heat carried away by evaporation goes up with temperature of course, for as you know warm water evaporates quicker.

If it takes 212 degrees to carry away the heat that's where the pool will settle. It can't get hotter than that at sea level. But at 212 we stop calling it evaporation and start calling it boiling. It could be a benign quiet 212 or a vigorous roiling boil, whatever is required to carry away the heat.

Boiling would be no big deal for the fuel , remember it is accustomed to making steam at around around 547 degreesF.. but it makes the area uncomfortable for people and wets all the equipment that's nearby. And the rapid evaporation carries contamination into the air in the room. So they try to keep the pool at a comfortable temperature not so much to protect the fuel but for convenience and safety of the workers. Somebody could fall in... It's just good sense to keep it comfortable.

An excursion up to boiling is not a big deal but it temperature cycles the stainless steel pool liner plate which will tend to expand and maybe buckle a little bit, so should be avoided.

just an aside - water is a really neat substance for moving heat. To change a pound of it from 212F water to 212F steam takes about 900 BTU's . Compare that to the measly 180BTU's to go from icewater to boiling it's 5X as much...
So as evaporation speeds up due to temperature climbing so does heat removal and by a lot. and that's why the old watched pot never boils...

i hope this helps you form a good mental picture in your head..

 

[mscharisma]

Mr Charisma

maybe i can put it in real basic terms here for a non engineer.

in the spent fuel pool , as you know normal heat removal is via a pump and heat exchanger.

If that path is lost the pool will heat up until evaporation is carrying away all the heat that's being added. That heatup is somewhat slow because the pool is so big that it can absorb a lot of heat.

I'm an old guy , still use English units . One BTU heats a pound of water one degreeF, and one BTU per second is within 5% of a kilowatt which is convenient for in-your-head calculating... So a ton of water can absorb one kilowatt for an hour and only get heated 3600 btu/2000lb = about 1.8 degreeF. well that's a ~5% approximation. But it gives you a feel.

Now the heat carried away by evaporation goes up with temperature of course, for as you know warm water evaporates quicker.

If it takes 212 degrees to carry away the heat that's where the pool will settle. It can't get hotter than that at sea level. But at 212 we stop calling it evaporation and start calling it boiling. It could be a benign quiet 212 or a vigorous roiling boil, whatever is required to carry away the heat.

Boiling would be no big deal for the fuel , remember it is accustomed to making steam at around around 547 degreesF.. but it makes the area uncomfortable for people and wets all the equipment that's nearby. And the rapid evaporation carries contamination into the air in the room. So they try to keep the pool at a comfortable temperature not so much to protect the fuel but for convenience and safety of the workers. Somebody could fall in... It's just good sense to keep it comfortable.

An excursion up to boiling is not a big deal but it temperature cycles the stainless steel pool liner plate which will tend to expand and maybe buckle a little bit, so should be avoided.

just an aside - water is a really neat substance for moving heat. To change a pound of it from 212F water to 212F steam takes about 900 BTU's . Compare that to the measly 180BTU's to go from icewater to boiling it's 5X as much...
So as evaporation speeds up due to temperature climbing so does heat removal and by a lot. and that's why the old watched pot never boils...

i hope this helps you form a good mental picture in your head..

Thank you for your efforts. I really appreciate it. However, I was not talking about the SFP, but rather the water temperature in the pressure vessel. It was my understanding that it should be kept from boiling when in a cold-shutdown state. Apparently, TEPCO wasn't that concerned with it getting close to boiling temperature, even though they could have used the emergency water injection system. That's what I don't understand.

As Kyodo writes here: http://english.kyodonews.jp/news/2011/05/94090.html
"If the unit had been left unattended with the temperature surpassing 100 C, the water containing nuclear fuel inside the reactor could have boiled and evaporated, thereby exposing the fuel and damaging it."

Or, in other words: how close to boiling does it have to come before the emergency water injection system should be used? Shouldn't it have been used immediately, just to not take any chances?

 

[Gary7]

I think this is a question that none of us can answer; "Why didn't Tepco act sooner?" It is a question that only Tepco can answer, and we can only speculate on. Obviously the reactor core is made to handle boiling water and steam (it being a "boiling water reactor"), and so the temperature of 94c isn't particularly worrisome if the RPV is undamaged. Since the reactor has been in stable shutdown for some two months now, I think they can assume there is no critical structural damage to the RPV. Given the many erroneous readings in the past, perhaps it is an assumption that we should not easily make. Be that as it may, there certainly seems to be no catastrophic damage to #5. Was there a danger of the water level becoming so low as to expose the fuel? I suppose so - eventually - but before this would happen I believe there were other systems available to pump water into the RPV. Regarding whether or not Tepco should have taken measures sooner than they did, it is probably a question for the "more political thread".

 

[jim hardy]

Well the laugh is on me! Sorry for the misunderstanding, it was at my end..

Or, in other words: how close to boiling does it have to come before the emergency water injection system should be used? Shouldn't it have been used immediately, just to not take any chances?

Just as in the pool you have some time before enough water evaporates to lower the level very much.

i haven't followed status of unit five - is the vessel open and pool flooded up to refueling level? if so the vessel and pool are one body of water with deep end at vessel and there's lots of water.

if they are separated, same logic applies - get some pump cooling before it gets warm enough to make things uncomfortable. One assumes they made a decision to fix the failed pump rather than manipulate the valves to align another one, and that may have been actually faster. They know how much effort is involved in each operation, i don't. if it was heating slowly they knew how much time they had.

In that industry things are very proceduralized and "by the book".
Physics and common sense may say you're fine, but if cold shutdown is let's say defined as 95.0 degrees and you get to 95.06 degrees it's a violation of the rules. It gets treated administratively no different than a truly serious one.
I would bet they did what they felt was the safest...and they were probably right. conditions are bad there and if they had to send men into a dangerous area to manipulate the valves, well, it weighed in their decision.

but to your question of what conditions dictate start of emergency equipment - that'll be in their written procedures and probably involves a time factor too.. i simply don't know their operation.

sorry to dodge your question - that's best i can do. A BWR operations guy could answer it better.

i still have faith in the plant guys. They are doing the impossible over there and i pray for them.old jim

edit gary answered while i was typing... thanks G!

 

[Astronuc]

Thank you for your efforts. I really appreciate it. However, I was not talking about the SFP, but rather the water temperature in the pressure vessel. It was my understanding that it should be kept from boiling when in a cold-shutdown state. Apparently, TEPCO wasn't that concerned with it getting close to boiling temperature, even though they could have used the emergency water injection system. That's what I don't understand.

As Kyodo writes here: http://english.kyodonews.jp/news/2011/05/94090.html
"If the unit had been left unattended with the temperature surpassing 100 C, the water containing nuclear fuel inside the reactor could have boiled and evaporated, thereby exposing the fuel and damaging it."

Or, in other words: how close to boiling does it have to come before the emergency water injection system should be used? Shouldn't it have been used immediately, just to not take any chances?

Ideally, the reactor is made as cold as possible, or below boiling so there is not increase in pressure that would allow fission products, particularly volative fission products to be more mobile.

Ideally, fission products are enclosed in the fuel rod cladding tubes. When there is a fuel breach, the gaseous and volatile fission products like I and Cs, can get into the coolant, and steam if there is any steam. In order to mitigate transport of fission products from breached fuel, one wants to get the reactor (and spent fuel) as cool as possible. It is also an issue for the workers. They cannot work around scalding steam unless they have heat resistant suits.

 

[SteveElbows]

Sounds like they are already starting to admit that the roadmap timescale is unrealistic:

http://english.kyodonews.jp/news/2011/05/94111.html

Bit cheeky blaming this on the analysis of meltdowns and containment damage though, considering they should have been able to form those conclusions long before they even wrote the roadmap.

 

[mscharisma]

I think this is a question that none of us can answer; "Why didn't Tepco act sooner?" It is a question that only Tepco can answer, and we can only speculate on. Obviously the reactor core is made to handle boiling water and steam (it being a "boiling water reactor"), and so the temperature of 94c isn't particularly worrisome if the RPV is undamaged. Since the reactor has been in stable shutdown for some two months now, I think they can assume there is no critical structural damage to the RPV. Given the many erroneous readings in the past, perhaps it is an assumption that we should not easily make. Be that as it may, there certainly seems to be no catastrophic damage to #5. Was there a danger of the water level becoming so low as to expose the fuel? I suppose so - eventually - but before this would happen I believe there were other systems available to pump water into the RPV. Regarding whether or not Tepco should have taken measures sooner than they did, it is probably a question for the "more political thread".

My question is not so much "why didn't TEPCO act sooner" or in any way political. I'm merely interested in whether or not it is safe from a technical standpoint to let the water come so close to boiling while installing a new pump instead of using already in place emergency systems. Of course, if it's not safe and/or not "by the book", then my question would certainly become "why didn't they act sooner."
Maybe in my lay(wo)man's mind, I just assumed (yes, I know the saying about "assume") that it's pretty much an automatic process: if one cooling system fails or part of it fails, no questions asked, the next one is put in operation. It takes me by surprise that it's apparently up to the ... hm, who? ... to decide when emergency cooling is activated and when not?

 

[MathMajor3_14]

New at this, first post. Thinking; so far weather patterns have saved the situation. Weather is changing, any comments for the next few months? Seasonal patterns?

See this link for excellent WX in the area:

> http://www.yr.no/place/Japan/Other/Fukushima_I_Nuclear_Power_Plant/ <

 

[MiceAndMen]

Sounds like they are already starting to admit that the roadmap timescale is unrealistic:

http://english.kyodonews.jp/news/2011/05/94111.html

Bit cheeky blaming this on the analysis of meltdowns and containment damage though, considering they should have been able to form those conclusions long before they even wrote the roadmap.

Without veering too much into the political realm, that assumes the roadmap plan was not merely a Public Relations device. For those of us who believe that, it's not surprising at all.

Wait and see what happens now with the rainy season approaching. I think their water pumping strategy will not work as soon as the runoff and leakage through cracks quickly overwhelms their ability to deal with it.

 

[westfield]

However, the twisted metal structure we see here in the foreground appears to be made of steel sheet-ware of an extension which we do not see in any of the structural elements of the roof.

I looked at the video some more and while it does have a funky shape if you "un-origami" it in your head it becomes evident it's just a plain "T" section bent over on itself - the crud collected in the "pocket" at the main bend makes it look like something more complex.

Such are the perils of trying to figure out this stuff, even forgiving the photography limitations, once something is bent and\or burnt even everyday shapes can become difficult to recognise.

 

[GJBRKS]

My question is not so much "why didn't TEPCO act sooner" or in any way political. I'm merely interested in whether or not it is safe from a technical standpoint to let the water come so close to boiling while installing a new pump instead of using already in place emergency systems. Of course, if it's not safe and/or not "by the book", then my question would certainly become "why didn't they act sooner."
Maybe in my lay(wo)man's mind, I just assumed (yes, I know the saying about "assume") that it's pretty much an automatic process: if one cooling system fails or part of it fails, no questions asked, the next one is put in operation. It takes me by surprise that it's apparently up to the ... hm, who? ... to decide when emergency cooling is activated and when not?

To have an amount of liquid water at 99.9 Celsius boil at 100 Celsius ,
it needs an equivalent energy input of around 540x times the energy to raise it 1 degree below boiling point.
And a 1000x times to raise it one degree when it is steam

So to make it boil from 100 degrees ,
you would have to add the same energy as to raise its temperature from -400 to 100 degrees ( roughly speaking as the heat energy changes at lower temperatures) , -400 Celsius however is impossible of course.

Or vice versa : the amount of energy released when condensing is equal to the absorbed heat energy of steam at a temperature of 1100 degrees celsius

So you see that it takes a lot more energy to make it all boil than to make it raise in temperature , thereby making the chance it would drop the waterlevel rather small in such a timeperiod

 

[MadderDoc]

I looked at the video some more and while it does have a funky shape if you "un-origami" it in your head it becomes evident it's just a plain "T" section bent over on itself - the crud collected in the "pocket" at the main bend makes it look like something more complex.

Such are the perils of trying to figure out this stuff, even forgiving the photography limitations, once something is bent and\or burnt even everyday shapes can become difficult to recognise.

I have attached no particular significance to the peculiar hook shape, nor inferred it to indicate anything of a complex shape. Certainly there can be no argument that what we are looking at has been bent severely out of its original shape. I can't see from you markup how you imagine the original shape of such a 'plain "T" section', which you indicate to clearly recognise this piece to have been originally. Also, have you formed an opinion from where it could have originated?

 

[htf]

To have an amount of liquid water at 99.9 Celsius boil at 100 Celsius ,
it needs an equivalent energy input of around 540x times the energy to raise it 1 degree below boiling point.
And a 1000x times to raise it one degree when it is steam

...

Sorry, but this is a rather confusing explanation.

Things are quite simple: when not cooled, some water will evaporate and the pressure will raise and the water temperature will consequently raise beyond 100°C. The normal operation temperature of a BWR is ~280°C at a pressure of ~70 bar. This means that in an intact PRV the temperature and pressure can go up to that values without danger. So a lot of decay energy can easily be absorbed even without cooling for some time: energy for evaporating some water + energy for heating up the water beyond 100°C. This gives a lager buffer. Remember, it took hours to raise the water temperature by ~20°C.

So, there was no immediate danger from that point of view. To aspects are more alarming to me:

1. It seens that unit #5 and #6 are less stable than Tepco claims.

2. There seems to be no working automatic monitoring system in place. To my understanding the pump failure has not been detected for hours.

 

[MiceAndMen]

I have attached no particular significance to the peculiar hook shape, nor inferred it to indicate anything of a complex shape. Certainly there can be no argument that what we are looking at has been bent severely out of its original shape. I can't see from you markup how you imagine the original shape of such a 'plain "T" section', which you indicate to clearly recognise this piece to have been originally. Also, have you formed an opinion from where it could have originated?

I wondered about that thing since the video first came out. The embedded "teardrop" - or "airfoil" - shaped void is very odd. I have not a clue nor a guess as to where it came from. To me, it doesn't look like an "L" or a "T" piece at all. It resembles most of all a metal pastry stuffed with concrete rubble or stone pebbles. It doesn't look like anything has folded over, because then how would the rocky stuffing get inside? It almost looks like whatever it was originally, it was already filled with concrete/rocks/grout/whatever and has been broken off of a larger thing. (Sorry for the extreme non-technical descriptions, but I have no better way to describe the thing.)

Does anyone have a good size estimate for it?

 

[intric8]

New at this, first post. Thinking; so far weather patterns have saved the situation. Weather is changing, any comments for the next few months? Seasonal patterns?

Everyone is concerned about how the typhoon would detrimentally effect operations at the plants, well it seems to have obliterated in-air readings around Iitate. Much lower, for now.

http://www.falloutphilippines.blogspot.com/

On seasonal Japan wind changes and precipitation, just basic info -

http://falloutphilippines.blogspot.com/2011/04/japan-summer-weather-is-nigh-and-heres.html

 

[Jorge Stolfi]

That reminds me. How many floors does reactor 3 building have? And how many were destroyed? Is building four the same design?

http://giappopazzie.blogspot.com/2011/05/post-tecnico-4-approfondimento-sulla.html

 

[tsutsuji]

Two nuclear power plant operators may have exceeded the 250 mSv limit : http://www.euronews.net/newswires/947269-two-fukushima-workers-may-have-exceeded-radiation-limit/

 

[swl]

Seawater Levels of Iodine at unit 2 Iodine-131: 24,000 becquerels/liter on may 28 (was only 5,200 becquerels/liter at the same place the day before) : is this rising significant and can be related to RVP/corium state ?

What is the source far that data? Do you know if there was an equal increase in the Cesium levels?

If ONLY the Iodine-131 increased, I would wonder about criticality. If not, I wonder if it is just a matter of the rainwater runoff.

 

[elektrownik]

Reactor 5 temperature increase again ??
90.5
92.2
93.7
83.0
76.5 <-pump replaced and on
70.0
64.9
60.8
56.5
52.8
50.5
50.0
50.9 <-temperature start increasing again
53.1
55.3
57.5
59.6
61.5
64.0
66.0
68.1

 

[swl]

At some time on May 28th somebody or something has removed several treetops south of the plant: Tepco's webcam facing the south wall of unit 4 now has a considerably better view to it:

It has been quite windy, so I wonder if the trees are not simply bowing from the wind. It's still quite windy now, but we should know in a day or two if the view of the unit 4 building is once again obscured.

On another point, while I'm usually bothered by the rain, I'm glad for the rinsing we've had over that past could days; there was this grey dust coating everything and I'm glad it's gone for now. Wish I had access to a GM counter.

According to the news here, the rainy season has officially started. If I remember the news correctly, the start is 17 days earlier than usual and one of the earliest starts ever. But to be honest, from what I can tell, the meteorologists have no clue about the rain beyond a week or two into the future.

 

[rowmag]

I wondered about that thing since the video first came out. The embedded "teardrop" - or "airfoil" - shaped void is very odd. I have not a clue nor a guess as to where it came from. To me, it doesn't look like an "L" or a "T" piece at all. It resembles most of all a metal pastry stuffed with concrete rubble or stone pebbles. It doesn't look like anything has folded over, because then how would the rocky stuffing get inside? It almost looks like whatever it was originally, it was already filled with concrete/rocks/grout/whatever and has been broken off of a larger thing. (Sorry for the extreme non-technical descriptions, but I have no better way to describe the thing.)

Does anyone have a good size estimate for it?

The red and white Thermo Label attached to the sampling tube is, I believe, about 3 cm long, so that gives a scale. The twisted metal thing is probably about the size of one's hand, or maybe a bit smaller, barring some trick of perspective.

 

[Bandit127]

Two nuclear power plant operators may have exceeded the 250 mSv limit : http://www.euronews.net/newswires/947269-two-fukushima-workers-may-have-exceeded-radiation-limit/

Looks like they ingested some iodine 131 somehow.

Regarding the two TEPCO male employees, we were informed that levels of
internal radioactivity (iodine 131) present in their thyroids is higher
than normal according to the Japan Atomic Energy Agency (Independent
Administrative Corporation), which is cooperating with us in the
conducting of the examinations and evaluations.

From: http://www.tepco.co.jp/en/press/corp-com/release/11053003-e.html"

 

[Jorge Stolfi]

I have began to update my plots of main variables (temperature, pressure, water leve, water input and CAMS) for Fukushima Daiichi units #1-#3:

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/Main.html

The previous version stopped at NISA press release 128. The new version includes NISA releases 145--152. Releases 129--144 will be entered next time.

The new version also adds many data points of pressure, water level, and CAMS for the earlier days, from consolidated and supposedly revised tables posted by TEPCO:

http://www.tepco.co.jp/nu/fukushima-np/f1/images/syusei_level_pr_data_1u.pdf
http://www.tepco.co.jp/nu/fukushima-np/f1/images/syusei_level_pr_data_2u.pdf
http://www.tepco.co.jp/nu/fukushima-np/f1/images/syusei_level_pr_data_3u.pdf

Other data sources out there may be merged later if time allows.

In light of this new data, several data points were corrected or removed from the plots. However this process may have added many new errors, watch out.

TEPCO is now posting a dozen or so temperature readings from each reactor. Since other eople have been plotting this data, I have no plans to include it in my plots.

The latest NISA releases show two numbers for the water pumping in #3. Presumably one is the fire extinguishing line, the other the main water inflow line. Which is which?

All the best, --stolfi

 

[tsutsuji]

Reactor 5 temperature increase again ??
90.5
92.2
93.7
83.0
76.5 <-pump replaced and on
70.0
64.9
60.8
56.5
52.8
50.5
50.0
50.9 <-temperature start increasing again
53.1
55.3
57.5
59.6
61.5
64.0
66.0
68.1

If you look at the plot at the top of http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/11053006_temp_data_56u-e.pdf you can see that it is a regular pattern everyday. Apparently the cooling system doesn't start until the temperature rises above 70°C or so. It seems that they can't cool the reactor and the pool at the same time. While the pool is cooling, the reactor is heating up, and vice-versa.

 

[westfield]

I have attached no particular significance to the peculiar hook shape, nor inferred it to indicate anything of a complex shape. Certainly there can be no argument that what we are looking at has been bent severely out of its original shape. I can't see from you markup how you imagine the original shape of such a 'plain "T" section', which you indicate to clearly recognise this piece to have been originally. Also, have you formed an opinion from where it could have originated?

yes the markup on the still frame is not helping really is it - I stepped through the video frames. then I folded a bit of paper into an angle shape and "bent" it to visualise how it might fold. I think the crud is hiding the edges continuing from the teardrop bending point.

But if it's not a "T" it won't be the last time I'm wrong;)



And are you kidding? It might have come from R4 for all anyone knows.

 

[DSamsom]

Temperatures in RPV reactor 3 are on the rise again after they lowered the rate of cooling water. That decission was most likely taken to limit the amount of radioactive waste water (problems with full tanks and/or leaking tank). Wonder whether they can afford to pump more water in the reactor again, given the fact that most tanks are full.

http://www.tepco.co.jp/nu/fukushima-np/f1/images/11053013_temp_data_3u-j.pdf

 

[SteveElbows]

The latest NISA releases show two numbers for the water pumping in #3. Presumably one is the fire extinguishing line, the other the main water inflow line. Which is which?

What release are you reading? The ones I've looked at have tended to state which is which, and for reactor 3 the fire line rate has been 0 for a few days now. But the same thing is being done at reactor 2 now, so you should see 2 readings for that one at the moment.

 

[SteveElbows]

Looks like we are going to get a new live video feed from the site starting on Tuesday:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110530_02-e.pdf

 

[joewein]

The latest NISA releases show two numbers for the water pumping in #3. Presumably one is the fire extinguishing line, the other the main water inflow line. Which is which?

All the best, --stolfi

Feeding via the fire extinguishing line was completely stopped on May 28 at 20:54. 13.5 m3/h is being fed via the feedwater pipe alone now.

 

[NUCENG]

"That just doesn't happen" under normal circumstance when the pool is cooled,
and H2 and O in solution quickly recombine, but
[PLAIN]http://k.min.us/invwtS.JPG

https://www.physicsforums.com/attachment.php?attachmentid=35318&d=1304876672" Light Water Reactor Hydrogen Manual by Allen L Camp

In https://www.physicsforums.com/showpost.php?p=3287847&postcount=6068" , using above paper I worked out that some 120 to 150kg of Hydrogen could have been developed in SFP-4



Conspiracy believers would quickly prove that the http://en.wikipedia.org/wiki/High_Frequency_Active_Auroral_Research_Program"

I have followed up on the potential for radiolysis and believe it is a plausible explanation for the Unit 4 explosion and damage. I am still looking at the possible scenario of Hydrogen gas from unit 3 through the SBGT system ducting.

1. I calculated decay heat for Unit 4 based on a full core offload 102 days before 3/11/2011 using rated thermal power of 2381 MWt and three batches of spent fuel aged 1 year (204 bundles), 2 years (204 bundles) and 3 years (171 bundles). I used the methodology of ANSI/ANS-5.1-1979. This calculation estimated decay heat in the Unit 4 SFP as 3.05 MW.
2. Using the various plant drawings posted on the forum I estimated spent fuel pool water volume of 1170 m^3 or 1.17E6 kg.
3. Assuming adiabatic heating and an initial temperature of 25 degC at the time of Loss of Spent Fuel Pool Cooling (15:45 3/11/2011) the estimated time to boiling was 33.5 hours or 3/13/2011 13:12 hr.
4. Using the ORIGEN2 analysis I have referenced before and the same core/batch assumptions used in #1 above I estimated total ionizing radiation in the spent fuel pool as 6.18E24 eV/sec. I determined that alpha and neutrons interactions are several orders of magnitude less than Beta and Gamma so these were ignored. The total used includes Bremsstrahlung radiation and x-rays.
5. Then assuming a production rate of 44 molecules of H2 per 1E4 eV of radiation from the Hydrogen Manual AntonL has referenced, I come up with a production rate of .0903 g of H2/sec. The method used in the Hydrogen Manual indicated it was probably a significant over-estimate of hydrogen generation and this calculation is about one tenth of that estimate. One note in the calculation used by AntonL is that the rates in the table he used are average rates over the entire production time, and need to be converted to instantaneous production reates which will also lower the production rate. I assumed that once pool boiling starts the H2 gas will be released from the pool at the production rate.
6. TEPCO does not know exactly when the damage to Unit 4 occurred, but damage was observed about 3/15/2011 at 06:00. This gives a maximum duration of boiling and hydrogen production.
7. Again using the calculated decay heat rate and latent heat of vaporization of water I calculated a boil-off rate of 1.35 kg/sec from the pool. It would have taken until 3/18/2011 to boil off half the pool volume. Therefore there was no fuel uncovered.
8. Using the discovery time of the Unit 4 building damage, a maximum of 16.9% of the pool volume could have boiled off.
9. In this same time a maximum hydrogen production of 13.25 kg was possible.
10. If we ignore steaming rate and other contributions that could have caused dilution of hydrogen in the refueling floor, a simple linear first order differential equation model would result in a LEL of Hydrogen (4% by volume) in about 15.8 hr or 3/14/2011 05:00. By the time damage was discovered the concentration could have been as high as 65%. This ignores significant dilution due to approximately 20 m^3 of steam entering the refueling floor every second. That steam could have explained why the blowout panels were open on Unit 4 since they would relieve at a low (inches of water) pressure. There was no ventilation assumed due to lass of power, however there could have been some airflow through the blowout panels due to steaming, condensation and buoyancy driven flow.
11. Assuming that all of the generated hydrogen remained in the building, I used an spreadsheet (Estimating Pressure Increase and Explosive Energy Release Associated with Explosions, Version 1805.0), from the NRC website to estimate the explosive power of the hydrogen. This spreadsheet calculated an equivalent TNT weight of 385 kg. Using the perimeter of damage calculation method from US NRC RG 1.91 the radius for overpressure of 1 psi where structural damage could occur is about 130 m.

The intent of these calculations was to determine if the times and sources of heat and radiation would permit explosive concentrations of hydrogen to exist with only radiolysis and fuel pool boiling. More detailed modeling of the interplay between air flow, steam, and hydrogen or use of thermal-hydraulic analysis codes could refine this picture. , but as of now it looks like this scenario is plausible. Thanks AntonL.

 

[elektrownik]

@NUCENG but if fuel wasnt uncovered then what could be source of ignition ? There was no power supply.
I have another question about fuel damage in #4 sfp, after tepco report about unit 1 core melt I think that damage to fuel should start not in upper part of fuel racks in sfp, but in center (inside rack), so maybe fuel upper part looks good, but it is damaged where we can't see...

 

[NUCENG]

One followup on my last post. Based on the calculations and the fact that Unit #4 fuel pool heat sources aere so much larger than at units 1, 2, and 3. Only significant leakage from the spent fuel pools could have produced enough inventory loss to uncover fuel in those pools.

 

[etudiant]

I have followed up on the potential for radiolysis and believe it is a plausible explanation for the Unit 4 explosion and damage. I am still looking at the possible scenario of Hydrogen gas from unit 3 through the SBGT system ducting.

1. I calculated decay heat for Unit 4 based on a full core offload 102 days before 3/11/2011 using rated thermal power of 2381 MWt and three batches of spent fuel aged 1 year (204 bundles), 2 years (204 bundles) and 3 years (171 bundles). I used the methodology of ANSI/ANS-5.1-1979. This calculation estimated decay heat in the Unit 4 SFP as 3.05 MW.
2. Using the various plant drawings posted on the forum I estimated spent fuel pool water volume of 1170 m^3 or 1.17E6 kg.
3. Assuming adiabatic heating and an initial temperature of 25 degC at the time of Loss of Spent Fuel Pool Cooling (15:45 3/11/2011) the estimated time to boiling was 33.5 hours or 3/13/2011 13:12 hr.
4. Using the ORIGEN2 analysis I have referenced before and the same core/batch assumptions used in #1 above I estimated total ionizing radiation in the spent fuel pool as 6.18E24 eV/sec. I determined that alpha and neutrons interactions are several orders of magnitude less than Beta and Gamma so these were ignored. The total used includes Bremsstrahlung radiation and x-rays.
5. Then assuming a production rate of 44 molecules of H2 per 1E4 eV of radiation from the Hydrogen Manual AntonL has referenced, I come up with a production rate of .0903 g of H2/sec. The method used in the Hydrogen Manual indicated it was probably a significant over-estimate of hydrogen generation and this calculation is about one tenth of that estimate. One note in the calculation used by AntonL is that the rates in the table he used are average rates over the entire production time, and need to be converted to instantaneous production reates which will also lower the production rate. I assumed that once pool boiling starts the H2 gas will be released from the pool at the production rate.
6. TEPCO does not know exactly when the damage to Unit 4 occurred, but damage was observed about 3/15/2011 at 06:00. This gives a maximum duration of boiling and hydrogen production.
7. Again using the calculated decay heat rate and latent heat of vaporization of water I calculated a boil-off rate of 1.35 kg/sec from the pool. It would have taken until 3/18/2011 to boil off half the pool volume. Therefore there was no fuel uncovered.
8. Using the discovery time of the Unit 4 building damage, a maximum of 16.9% of the pool volume could have boiled off.
9. In this same time a maximum hydrogen production of 13.25 kg was possible.
10. If we ignore steaming rate and other contributions that could have caused dilution of hydrogen in the refueling floor, a simple linear first order differential equation model would result in a LEL of Hydrogen (4% by volume) in about 15.8 hr or 3/14/2011 05:00. By the time damage was discovered the concentration could have been as high as 65%. This ignores significant dilution due to approximately 20 m^3 of steam entering the refueling floor every second. That steam could have explained why the blowout panels were open on Unit 4 since they would relieve at a low (inches of water) pressure. There was no ventilation assumed due to lass of power, however there could have been some airflow through the blowout panels due to steaming, condensation and buoyancy driven flow.
11. Assuming that all of the generated hydrogen remained in the building, I used an spreadsheet (Estimating Pressure Increase and Explosive Energy Release Associated with Explosions, Version 1805.0), from the NRC website to estimate the explosive power of the hydrogen. This spreadsheet calculated an equivalent TNT weight of 385 kg. Using the perimeter of damage calculation method from US NRC RG 1.91 the radius for overpressure of 1 psi where structural damage could occur is about 130 m.

The intent of these calculations was to determine if the times and sources of heat and radiation would permit explosive concentrations of hydrogen to exist with only radiolysis and fuel pool boiling. More detailed modeling of the interplay between air flow, steam, and hydrogen or use of thermal-hydraulic analysis codes could refine this picture. , but as of now it looks like this scenario is plausible. Thanks AntonL.

Thank you for this lucid evaluation and analysis.
It indicates that the hydrogen made the inside of building 4 into a fuel/air explosive package of stunning efficiency. I am amazed that less than 15kg of hydrogen could do so much damage, particularly as some of the hydrogen would have escaped through the open blow out panels. But unless there was another source of hydrogen, such as the postulated leakage from reactor 3, this is what we have.

 

[elektrownik]

I also don't understand why unit 4 sfp water temperature is always 84C and 62C for unit 3 sfp, this is not possible that there is no change... also why water level in unit 2 is so low, it looks like they can't fill it with water like in unit 4... it is ~4000 max, but usualy 2000-3000 and unit 4 is 6500 after injection

 

[Astronuc]

I also don't understand why unit 4 sfp water temperature is always 84C and 62C for unit 3 sfp, this is not possible that there is no change... also why water level in unit 2 is so low, it looks like they can't fill it with water like in unit 4... it is ~4000 max, but usualy 2000-3000 and unit 4 is 6500 after injection

Unit 4 SFP had a full core offload, so there was some fuel with a fair amount of decay heat. Unit 4 also had 1331 assemblies in it. Unit 3 SFP had fewer assemblies, and they were only discharged assemblies from last year and previous cycles with 1, 2, 3, . . . years of cooling. The number of assemblies in the SFPs is posted early in this thread.

There could also be structural damage in any of the SPFs, including cracks in the stainless steel liner and concrete structure.

 

[jlduh]

Looks like they ingested some iodine 131 somehow.


From: http://www.tepco.co.jp/en/press/corp-com/release/11053003-e.html"

Again, and as was already discussed it in other threads, this raises the question of the accuracy and the meaning of the measurements in mS/h by dosimeters. In this case again, the difference seems to come from ingested particulates (so this is internal contamination and not external irradiation).

 

[NUCENG]

@NUCENG but if fuel wasnt uncovered then what could be source of ignition ? There was no power supply.
I have another question about fuel damage in #4 sfp, after tepco report about unit 1 core melt I think that damage to fuel should start not in upper part of fuel racks in sfp, but in center (inside rack), so maybe fuel upper part looks good, but it is damaged where we can't see...

Let's just list a couple ignition sources that might have been present:

• Emergency lighting batteries giving out,
• Sparks due to metal on metal shifting in rubble in aftershocks
• Static Electrical Discharge

In the fuel racks in the spent fuel pool cooling is done by buoyancy driven natural circulation. As water heats around the fuel rods it rises and is replaced by cooler water from below. Thus the hotest temperatures are at the tops of fuel assemblies, even if in a spent fuel pool.

In addition, remember that control rods are pulled from the top down out the bottom of the vessel. This is pretty simplistic, but in general the fuel is burned out from the top down and that results in higher decay heat at the top of fuel. Fuel loading in rods is adjusted and rod patterns are used to try to even the heat generation rate over the length of the rod during normal operation, but in general the simple picture works as an adequate approximation.

 

[elektrownik]

Thanks for explanations, in case of ignition
Emergency lighting batteries giving out - I think that we can exclude this because batteries die 8 hours after blackout (if I remember correct from reports)


@Astronuc yes I understand there is more fuel (and not so old) in 4 than in others, but for example they were able to fill unit 1 sfp more than 2, and also no change in temperature in sfp 3 and 4 suggest sensor failure

 

[NUCENG]

Thank you for this lucid evaluation and analysis.
It indicates that the hydrogen made the inside of building 4 into a fuel/air explosive package of stunning efficiency. I am amazed that less than 15kg of hydrogen could do so much damage, particularly as some of the hydrogen would have escaped through the open blow out panels. But unless there was another source of hydrogen, such as the postulated leakage from reactor 3, this is what we have.

Yes, I was surprised at the number until I watched a newreel of the Hindenberg fire. I had previouslt done some TNT equivalencies based on gasoline, fuel oil and propane, but was shocked by the number for hydrogen. I;m not so sure I like the ideas of automobiles running around banging into each other and powered by hydrogen.

 

[SteveElbows]

I also don't understand why unit 4 sfp water temperature is always 84C and 62C for unit 3 sfp, this is not possible that there is no change... also why water level in unit 2 is so low, it looks like they can't fill it with water like in unit 4... it is ~4000 max, but usualy 2000-3000 and unit 4 is 6500 after injection

Just look at the dates - they take temperature of 3 & 4 via sensor attached to concrete pump, and they don't do it very often at all. The 84c is from may 7th and 62c for reactor 3 was measured on may 8th.

As for the water levels, these are the water levels of the skimmer surge pool, not the fuel pool itself. Same with temperature readings for reactor 2, its the skimmer water, which is why temp goes up when they inject water. When pool gets near top, water can move from pool to skimmer surge tank(s), and so we see skimmer level go back up and temperature also rises as hot pool water moves into skimmer tank.

Now its certainly true that when pool 2 is filled, skimmer level does not go as high as it used to. It goes up to about 4000mm these days, but when they used to fill it in april it went as high as 5000 or 6000mm, even higher than that at times. I can't tell you why, but there are likely a few explanations which are nothing to worry about.

 

[AntonL]

Staring soon -
this should be interesting if they zoom in
as a static view it will be boring

We can start the first discussion - is the nearest exhaust stack leaning or not?
I think the camera is not mounted horizontal [PLAIN]http://k.min.us/icHSBk.JPG

 

[tonio]

I have followed up on the potential for radiolysis and believe it is a plausible explanation for the Unit 4 explosion and damage. I am still looking at the possible scenario of Hydrogen gas from unit 3 through the SBGT system ducting.

1. I calculated decay heat for Unit 4 based on a full core offload 102 days before 3/11/2011 using rated thermal power of 2381 MWt and three batches of spent fuel aged 1 year (204 bundles), 2 years (204 bundles) and 3 years (171 bundles). I used the methodology of ANSI/ANS-5.1-1979. This calculation estimated decay heat in the Unit 4 SFP as 3.05 MW.
2. Using the various plant drawings posted on the forum I estimated spent fuel pool water volume of 1170 m^3 or 1.17E6 kg.
3. Assuming adiabatic heating and an initial temperature of 25 degC at the time of Loss of Spent Fuel Pool Cooling (15:45 3/11/2011) the estimated time to boiling was 33.5 hours or 3/13/2011 13:12 hr.
4. Using the ORIGEN2 analysis I have referenced before and the same core/batch assumptions used in #1 above I estimated total ionizing radiation in the spent fuel pool as 6.18E24 eV/sec. I determined that alpha and neutrons interactions are several orders of magnitude less than Beta and Gamma so these were ignored. The total used includes Bremsstrahlung radiation and x-rays.
5. Then assuming a production rate of 44 molecules of H2 per 1E4 eV of radiation from the Hydrogen Manual AntonL has referenced, I come up with a production rate of .0903 g of H2/sec. The method used in the Hydrogen Manual indicated it was probably a significant over-estimate of hydrogen generation and this calculation is about one tenth of that estimate. One note in the calculation used by AntonL is that the rates in the table he used are average rates over the entire production time, and need to be converted to instantaneous production reates which will also lower the production rate. I assumed that once pool boiling starts the H2 gas will be released from the pool at the production rate.
6. TEPCO does not know exactly when the damage to Unit 4 occurred, but damage was observed about 3/15/2011 at 06:00. This gives a maximum duration of boiling and hydrogen production.
7. Again using the calculated decay heat rate and latent heat of vaporization of water I calculated a boil-off rate of 1.35 kg/sec from the pool. It would have taken until 3/18/2011 to boil off half the pool volume. Therefore there was no fuel uncovered.
8. Using the discovery time of the Unit 4 building damage, a maximum of 16.9% of the pool volume could have boiled off.
9. In this same time a maximum hydrogen production of 13.25 kg was possible.
10. If we ignore steaming rate and other contributions that could have caused dilution of hydrogen in the refueling floor, a simple linear first order differential equation model would result in a LEL of Hydrogen (4% by volume) in about 15.8 hr or 3/14/2011 05:00. By the time damage was discovered the concentration could have been as high as 65%. This ignores significant dilution due to approximately 20 m^3 of steam entering the refueling floor every second. That steam could have explained why the blowout panels were open on Unit 4 since they would relieve at a low (inches of water) pressure. There was no ventilation assumed due to lass of power, however there could have been some airflow through the blowout panels due to steaming, condensation and buoyancy driven flow.
11. Assuming that all of the generated hydrogen remained in the building, I used an spreadsheet (Estimating Pressure Increase and Explosive Energy Release Associated with Explosions, Version 1805.0), from the NRC website to estimate the explosive power of the hydrogen. This spreadsheet calculated an equivalent TNT weight of 385 kg. Using the perimeter of damage calculation method from US NRC RG 1.91 the radius for overpressure of 1 psi where structural damage could occur is about 130 m.

The intent of these calculations was to determine if the times and sources of heat and radiation would permit explosive concentrations of hydrogen to exist with only radiolysis and fuel pool boiling. More detailed modeling of the interplay between air flow, steam, and hydrogen or use of thermal-hydraulic analysis codes could refine this picture. , but as of now it looks like this scenario is plausible. Thanks AntonL.

Is this realistic? You calculate a steam production of 20 m^3 per second. You state that this steam production explains why the blowout panels were open on unit 4. It seams to me that in a space that is open to the outer world and that is flushed with 20 cubic meters of steam per second (I assume that this means that the upper floor of the reactor is "refreshed" with steam every few minutes or so) any accumulation of hydrogen is very unlikely. It seems more likely to me that the hydrogen concentration in this upper floor will more or less equal the hydrogen/steam production rate coefficient.

 

[Astronuc]

Thanks for explanations, in case of ignition
Emergency lighting batteries giving out - I think that we can exclude this because batteries die 8 hours after blackout (if I remember correct from reports)


@Astronuc yes I understand there is more fuel (and not so old) in 4 than in others, but for example they were able to fill unit 1 sfp more than 2, and also no change in temperature in sfp 3 and 4 suggest sensor failure

Yes - it is quite possible that various sensors have lost calibration. It may be the case that the core level readings were faulty, and that the cores went dry even though the level indicators showed some level of coolant. Similarly for the SFPs.

 

[NUCENG]

Is this realistic? You calculate a steam production of 20 m^3 per second. You state that this steam production explains why the blowout panels were open on unit 4. It seams to me that in a space that is open to the outer world and that is flushed with 20 cubic meters of steam per second (I assume that this means that the upper floor of the reactor is "refreshed" with steam every few minutes or so) any accumulation of hydrogen is very unlikely. It seems more likely to me that the hydrogen concentration in this upper floor will more or less equal the hydrogen/steam production rate coefficient.

The secondary containment (reactor building) is designed for minimal leakage so it can be maintained at a negative pressure with normal ventilation during plant operation and with the SBGT system during accidents. Any significant heatup or energy release can raise building pressure and cause the blowout panels to open. Once they are open some ventilation flow due to wind or steam or hydrogen may occur but the flow rates will be fairly small due to no mechanical ventilation. If anyone can suggest approaches to refine the modeling of steam and hydrogen and airflow in the refueling floor, I can take another stab at it.

I calculated a boiloff rate based on adiabatic heating and came up with 20 m^3/sec. That would be saturated steam at 100 deg C entering the air on the refueling floor. Some of it will heat up the air space and condense. More will condense on surfaces that are below 100 decg C. Some will indeed slip out through the open blowout panels, but without a lot more time and work all I can say is that my numbers are conservative. That 20 m^3/sec will not result in a flow out the openings of 20 m^3/sec. The approximate volume of the refuel floor is about 2E5 m^3. It will be hot and humid and there will be some steam dilution and mixing of hydrogen. However over time the hydrogen concentration has 24 hours from the minimum time I calculated to accumulate to the Lower Explosive Limit in the top of the bulding. If even a few kg of hydrogen reach an explosive concentration there is enough energy to perform significant damage to the building as we see.

My purpose was not to say what happened. I don't know that for certain, but to use the tools I have to see if I could find anything that would rule out the theory of radiolysis as the source for building 4 damage. What I found is that the theory is plausible, not proven, but it may be what happened. It further supports previous evidence that the fuel in unit #4 was not significantly damaged. (Low concentrations of radioctivity in SFP #4, and visual evidence).

 

[tonio]

The secondary containment (reactor building) is designed for minimal leakage so it can be maintained at a negative pressure with normal ventilation during plant operation and with the SBGT system during accidents. Any significant heatup or energy release can raise building pressure and cause the blowout panels to open. Once they are open some ventilation flow due to wind or steam or hydrogen may occur but the flow rates will be fairly small due to no mechanical ventilation. If anyone can suggest approaches to refine the modeling of steam and hydrogen and airflow in the refueling floor, I can take another stab at it.

I calculated a boiloff rate based on adiabatic heating and came up with 20 m^3/sec. That would be saturated steam at 100 deg C entering the air on the refueling floor. Some of it will heat up the air space and condense. More will condense on surfaces that are below 100 decg C. Some will indeed slip out through the open blowout panels, but without a lot more time and work all I can say is that my numbers are conservative. That 20 m^3/sec will not result in a flow out the openings of 20 m^3/sec. The approximate volume of the refuel floor is about 2E5 m^3. It will be hot and humid and there will be some steam dilution and mixing of hydrogen. However over time the hydrogen concentration has 24 hours from the minimum time I calculated to accumulate to the Lower Explosive Limit in the top of the bulding. If even a few kg of hydrogen reach an explosive concentration there is enough energy to perform significant damage to the building as we see.

My purpose was not to say what happened. I don't know that for certain, but to use the tools I have to see if I could find anything that would rule out the theory of radiolysis as the source for building 4 damage. What I found is that the theory is plausible, not proven, but it may be what happened. It further supports previous evidence that the fuel in unit #4 was not significantly damaged. (Low concentrations of radioctivity in SFP #4, and visual evidence).

OK. Some remarks. If I am correct, the size of R4 building is 35 x 45 m. Assuming that the height of the refuelling floor is close to 15 m, it;'s volume is about 20.000 m^3, about a tenth of what you specify. This space, which I assume is well isolated (apart from the open blowout panels) and is not mechanically ventilated anymore, is heated by a large SPF, which generates about 3 MW of heat. I am not a physicist, but I assume that such a powerfull heat source, dumping an amount of steam in this space which is enough to fill it completely in just 1,5 minutes, will heat it to a temperature close to 100 degrees and will effectively refresh it's (steamy) atmosphere every few minutes.

 

[thehammer2]

I just want to bring up a point regarding NUCENG's calculations. When you consider the steam rate and the hydrogen production rate coming off of the pool, the ratio of steam to hydrogen in the space above the pool based on those production rates is only valid right at the surface of the pool. As the gas mixture leaves the pool, the hydrogen is MUCH less dense than the gases around it, so due to buoyancy alone, it will rise to the top and accumulate. The result is stratification, like oil floating on top of water.

Now, to picture what would tend to happen consider this analogy. Let's imagine we have an upside down glass sitting on a table. This glass is the containment building, and the surface of the table is the surface of the SFP. We begin filling the glass somehow from the surface of the table (How is unimportant in this analogy. It's just coming from the surface of the table) with a mixture of water (representing steam) and oil (representing hydrogen). If the glass is filled slowly relative to its volume, the water (steam) and oil (hydrogen) separate with the oil rising to the top. Once the glass (containment building) is full, let's further imagine the water and oil keeps trying to enter the glass from the table surface (more steam and hydrogen leaving the SFP) and it springs a leak (analagous to the blowout panels popping) below the oil-water interface.

Now, what's newly entering the glass from the surface of the table is still a mixture, but what's leaving the glass because the exit points are below the water/oil interface is largely water. Sure, some oil will leave through the holes, but the oil that was above the holes before they opened up will remain, as there's no real way for them to get to the holes. Further, as the water and oil are still entering at the same rate they were before, but the liquid leaving the glass is largely water, the concentration of the oil in the glass begins to rise since the water is preferentially leaving the glass due to the location of the holes. The oil further collecting in the glass is still rising due to buoyancy and increasing the size of the pocket of oil trapped at the top.

I think this analogy can pretty well illustrate the behavior of the gases. Sure, there would be a gradient of concentrations versus a hard interface, and some of the behaviors of the materials would be different due to the differences between gases and liquids, but the point is to illustrate the mechanism by which buoyancy of the gases and the location of the entrance and exit points of the gases can set up a method by which a small hydrogen rate compared to the steam rate can result in stratification and buildup of explosive gases.

 

[Borek]

I am not so sure about stratification. Bubbles of pure hydrogen will go up, no doubt about it. But if the gases are well mixed, from what I remember stratification due to masses of molecules is negligible, as mixing due to thermal motion is way too strong. For reasonably good results you need very high towers and very low temperatures (cryogenic distillation) - neither were present.

 

[elektrownik]

http://jen.jiji.com/jc/eng?g=eco&k=2011053000813"

 

[Bandit127]

http://jen.jiji.com/jc/eng?g=eco&k=2011053000813"

To provide a sense of scale, the 2.9 million becquerels (MBq/ccm) of Cs 137 quoted in the article is very close to the 3.0 MBq/ccm that was reported in water from Unit 2's basement on 19th April. Tepco said that was "extremely high".

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110419e2.pdf"