Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[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"

 

[Bandit127]

There is a bit more detail on the two workers who exceeded 250mSv here:
http://jen.jiji.com/jc/eng?g=eco&k=2011053000517"

External exposure stood at 73.71 millisieverts for the worker in his 30s and at 88.7 millisieverts for the one in his 40s.

Does this mean that the internal exposure has been normalised to an annual or lifetime dose?

 

[MiceAndMen]

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.

Not a huge difference from your estimate, but the height of the refuelling floor is 15.8 m according to the drawings we've seen (for Unit 3), so volume is closer to 25,000 m3.

I would not assume the space is well isolated, however. Various diagrams and descriptions give me the impression that there are a multitude of open hatchways that connect the airspace of every floor to every other floor. If that is true then the atmosphere inside the building as a whole is communicable subject to drafts, convection, and buoyancy factors. There are probably rooms and spaces sealed off due to containment considerations.

But even then the entire volume of the building would be somewhat less than 71,000 m3 (35 x 45 x 45) because the primary containment vessel - which shuold be completely isolated - occupies some fraction of the total volume.

 

[elektrownik]

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201105300291"
http://ajw.asahi.com/article//0311disaster/fukushima/AJ201105300298" interesting !

 

[MiceAndMen]

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201105300291"
http://ajw.asahi.com/article//0311disaster/fukushima/AJ201105300298" interesting !

Ah yes, Megafloat to the rescue. Again. It holds 10,000 tons of water and it has been obvious for quite a while that it's not going to be very useful. A drop in the proverbial bucket.

And hoses. TEPCO has secured hoses for Plan B. Or is it Plan C, D, E or F?

 

[~kujala~]

I don't know where the news reporter got this info but he seems to confirm that groundwater level is quite high:

It has not been confirmed that contaminated water has leaked into the groundwater from the basements in large quantities, but the levels of contaminated water in the basements are currently only a few meters lower than that of the groundwater.

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201105300291

By the way, did you notice that he copied what jlduh said a couple of days ago (May 27th):

So what I foresee is the possibility that when the basements where almost empty (with regular pumps ejecting out the inflows from the watertable, which was probably routine operation to keep these basements dry), then of course the direction of flow was from outside to inside (because of hydrostatic differential). When the basements are filling in with water, the differential is reducing and eventually, this differential can be inverted if water level inside basement becomes higher than water table level outside. Then the flow will invert also, and so leakage from basement towards watertable can happen (with contamination).

https://www.physicsforums.com/showpost.php?p=3325027&postcount=8356

Asahi Shimbun May 30th:

As long as water is flowing from the surrounding groundwater into the contaminated water, because the level of the groundwater is higher than that in the basements, the threat of substantial leaks is not considered acute. But if the level of the contaminated water rises above that of the groundwater, water would begin flowing in the other direction and is likely to spread contamination.