Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[fledermaus]

I too have been curious about the strength of the second explosion.

I have done some online research and would like to share.

These two links provide information on experiments that were performed using molten corium. It was dropped into a pressure vessel partially filled with water. What results is a sudden expansion of steam and pressure.

http://www.osti.gov/bridge/purl.cover.jsp?purl=/5580609-RLgLFl/

http://www.osti.gov/bridge/purl.cover.jsp?purl=/6504026-RyrkV7/

In addition, here are some links about steam explosion in reactor vessels. The stem explosions were triggered by criticality events. However, the end result was the control rods being spat out along with some of the fuel.

http://www.inl.gov/proving-the-principle/chapter_15.pdf

neutron.kth.se/courses/reactor_physics/LectureNotes/BORAX1.pdf

I don’t know what happened at the Unit 3 explosion, but it may be possible that some of the molten fuel dropped into the lower portion of the pressure vessel during an aftershock.

 

[Astronuc]

under normal operating temperatures you don't get hydrogen produced (<300C)

One gets very little - but one does get hydrogen. Some of the hydrogen produced diffuses into the Zircaloy cladding. At < 300 C, the reaction is very slow. One can do a calculation of how much hydrogen is produced from a reaction of Zr => ZrO2 of thickness ~20-100 microns over the area of the fuel or 400 or 548 assemblies.

Also, if the fuel ruptures, then there is a Zr-linear of 75 microns thickness (which could produce about 200 microns oxide) that can react with water/steam to produce hydrgoen. How much hydrogen generated depends on how many of the cladding tubes and channels oxidized on the outer surface, and how many cladding tubes ruptured in which the liner heavily corroded/oxidized.

 

[Atomfritz]

Hi all! Great forum+thread, completely technical and no hysteric radiation fearmogery. This my first post after reading back some 100 posts.

Regarding identification of the items lying around in picture in post #3068:

My "hallucinations" are those:
1. Some tubes, maybe hydraulic, maybe fallen off the green machine.
3. Some part of-red-color-coded plumbery.
4. Impact-broken-off parts of removable pool boundary tubes.
5. Some I-beams from the wall/ceiling girder.

Regarding possibly imminent reactor explosions:

Astronuc in post #3072 mentions the risk of a violent H-Cl-reaction.
Remember back 1979, when all were trembling in hope that the hydrogen bubble in TMI would dissolve before going kaboom.

There seems to be all the needed stuff in the reactors to produce hydrogen in quantities. And there was no venting a long time. Nothing is being reported about the gases composition in the containment.
Just the in-reactor pressure readings are confusing to me. Wasn't there some underpressure? Maybe due to water levels flowing off through cracks etc? However, if I really interpreted the measurements correctly this would mean that air gets sucked into the containment and bringing oxygen in.

As a layman I cannot reject the possibility of an in-containment-explosion and this worries me.

So my question to the experts:
Can you please explain if there is still a risk of reactors exploding and burping out their contents? Or is such just impossible?

I really hope I got something wrong.

 

[Jorge Stolfi]

Chlorine gas (Cl₂) mixed with H₂ makes for a pretty good explosion.

That may hold for #1--#3, but in #4 (IIRC) they only started spraying the SPF with seawater AFTER the explosion.

 

[Astronuc]

Re: AntonL #3051, NUCENG #3053 BOREK #3054


As promised. I looked at the TEPCO sequence of events and JAIF Plant Status reports.

Explosions were reported on 3/12, 3/14, and 3/15, Unit 4 was damaged about the 15th or 16th.

Seawater had been injected into RPVs on Units 1 and 3.

Seawater injection into containment was still being planned/considered on 3/16.

TEPCO is still reporting no coolant leakage into containment on all units. ?

Conclusion: Sea water injection into contaiment followed explosions and therefor oxygen dissolved in seawater could not have been responsible for creating an explosive mixture inside containment. The only remaining possibility would have been containment failures from the earthquake, but since there was a high pressure in containment, it would be tough to get air inleakage. Unless I missed something about the mixture of steam, oxygen, hydrogen, and nitrogen in containment, I just don't see an condition that could lead to an explosion inside containment.

Time line based on TEPCO/NISA and Der Spiegel reports.

http://www.nisa.meti.go.jp/english/files/en20110327-2-1.pdf
http://www.spiegel.de/images/image-193266-galleryV9-quxr.jpg

16:36 March 11 - Loss of cooling (EDGs) at Unit 1 (about 1 hour, 50 min after earthquake, which is just after the tsunami hit the site)

15:36 March 12 - Explosion of Unit 1 (Upper containment heavily damaged)

20:20 March 12 - Seawater injection into Unit 1 RPV (via fire extinguisher line)

20:41 March 12 - Venting of Unit 3
08:41 March 13 - Venting of Unit 3

09:20 March 13 - Steam release from Unit 3
11:55 March 13 - Fresh water started to be injected to RPV via the Fire Extinguish Line.
13:12 March 13 - Seawater started to be injected to RPV via the Fire Extinguish Line.

01:10 March 14 - Seawater injection for Units 1 and 3 was interrupted due to the lack of seawater in pit.
03:20 March 14 - Seawater injection to RPV for Unit 3 was restarted.
05:20 March 14 - Operation of Vent
07:44 March 14 - The pressure in Primary Containment Vessel (PCV) of Unit 3 rose unusually.
07:52 March 14 - TEPCO reported to NISA on the event falling under the Article 15 of the Act on Special Measures Concerning Nuclear Emergency Preparedness.

11:01 March 14 - Explosion of Unit 3

19:20 March 14 - Seawater injection into Unit 2 RPV (via fire extinguisher line)

06:10 March 15 - Sound of Explosion in Unit 2 - explosion seems to be in containment.

06:14 March 15 - It was confirmed that a part of wall in the operation area of Unit 4 was damaged.
11:00 March 15 - The fire (hydrogen deflagration?) at Unit 4 occurred. (09:38 March 15th) TEPCO reported that the fire was extinguished spontaneously.

It would be useful to review the progression of damage to Unit 4 after the explosion of Unit 3, because immediately after the explosion of U3, the upper containment of Unit 4 seemed to be more or less intact.

 

[Astronuc]

That may hold for #1--#3, but in #4 (IIRC) they only started spraying the SPF with seawater AFTER the explosion.

Unit 4 is different from the other units because it's core was empty and in the SFP. The RPV would have been open, so there is no concern about hydrogen from the RPV. Units 1, 2 and 3 would be at risk.

On the othe hand, the explosion in Unit 1 occurred BEFORE seawater, but the explosion of Unit 3 (and possible explosion in Unit 2) occurred AFTER seawater injection, was introduced according to the timeline.

The SFP at Unit 4 had a greater thermal burden than the other pools - more assemblies, and particularly the fuel to be reinserted into the reactor. That fuel had only cooled about 110 days. The older fuel would have cooled for more than one year - ~ 400-500 days, and older fuel even more.

The NYTimes report of the confidential assessment cites that fuel fragments and/or particles were discharged between units, but it doesn't say which units. That would be key in terms of determining which SFP might have been the source.

 

[Jorge Stolfi]

Thanks Astronuc and others for the patient clarifications.

Another question: in a TEPCO slide set circulated weeks ago (on long term plans for spent-fuel storage) it said that assembies cool enough for dry-cask storage are individually surrounded by a boron-doped aluminum sleeve to avoid any risk of criticality.

While in the SPF, the assemblies presumably are separated by neutron-absorbing baffles or sleeves, for the same purpose. Are those neutron absorbers also made of boron-doped aluminum (MP ~660C)?

 

[artax]

yes there was a reported explosion in unit 4, but it was never videod, looking at the high res drone images, the explosion seems to have been centred lower down in the building.
The roof has bowed upwards though as can be seen from the way the top of the wall are pulled inwards.
This explosion analysis from images/deformations/debris, is by far the most interesting part of problem to me.
Probably because they've just said hydrogen explosion... and then nothing else!
It just fuels suspicion.

 

[Jorge Stolfi]

And yet another dumb question: was the #4 fuel all in one layer at the bottom of the SFP? Any chance that they might have placed some of it in a second layer? (That would still leave 5-6 meters of water above the second layer, right?)

 

[artax]

hope you don't mind if I post this link again?

http://cryptome.org/eyeball/daiichi-npp/daiichi-photos.htm

 

[Atomfritz]

...reported explosion in unit 4, but it was never videod...

It happened in dark night.
Beware: the timeline of the "Der Spiegel" is in german time, not in local time! Don't get confused!

And yet another dumb question: was the #4 fuel all in one layer at the bottom of the SFP? Any chance that they might have placed some of it in a second layer? (That would still leave 5-6 meters of water above the second layer, right?)

Some 100 posts ago somebody explained in detail, and concluded that most of the fuel will probably be in the lower (the second) pool, but some fuel might have been temporarily stored at the instruments (higher) pool together with the activated neutron flux meters etc.

 

[|Fred]

I have not seen one evidence suggesting that the BWR used at fukushima hast two pool depth. All the document seen so far indicate other wise.
That been said I don't know about stacking

 

[Astronuc]

Thanks Astronuc and others for the patient clarifications.

Another question: in a TEPCO slide set circulated weeks ago (on long term plans for spent-fuel storage) it said that assembies cool enough for dry-cask storage are individually surrounded by a boron-doped aluminum sleeve to avoid any risk of criticality.

While in the SPF, the assemblies presumably are separated by neutron-absorbing baffles or sleeves, for the same purpose. Are those neutron absorbers also made of boron-doped aluminum (MP ~660C)?

The spent fuel racks have either boraflex or boral plates. I'm not sure of the exact construction, but I do know that degradation and loss of boron is a concern, particularly if the pool heats up.

What happened at Fukushima was hypothetical - until it actually happened.

 

[jensjakob]

It happened in dark night.
Beware: the timeline of the "Der Spiegel" is in german time, not in local time! Don't get confused!



Some 100 posts ago somebody explained in detail, and concluded that most of the fuel will probably be in the lower (the second) pool, but some fuel might have been temporarily stored at the instruments (higher) pool together with the activated neutron flux meters etc.

You are right. I have been searching for that post - can remember that someone mentioned that Fukushima engineers had begun storing fuel rods at the equipment pool, due to overcapacity of spent fuel pool.

But I haven't found the post yet. But I do know that is has been stated (benefit of a visual memory)

 

[Astronuc]

You are right. I have been searching for that post - can remember that someone mentioned that Fukushima engineers had begun storing fuel rods at the equipment pool, due to overcapacity of spent fuel pool.

I find that hard to believe. There was sufficient capacity at Units 1, 2 and 3. Is this a reference to SFP in Unit 4?

They would have had to put a rack in the equipment pool. As far as I know, that pool is not cooled. The water is for shielding of any radiation on the steam separators which normally sit just above core and do get some irradation during operation.

 

[ceebs]

And yet another dumb question: was the #4 fuel all in one layer at the bottom of the SFP? Any chance that they might have placed some of it in a second layer? (That would still leave 5-6 meters of water above the second layer, right?)

In here http://www.google.co.uk/url?sa=t&so...g=AFQjCNHvmvjzUQY_apDXEqIqcmenR6gKzA&cad=rja"

It says that the spent fuel pools are at about half capacity, however, that is only after "Re-racking", whether re-racking involves more than one layer, or just assemblies beeing placed closer together would be something for people with more expertise.

looking at dates though that does appear to be before number 4 was emptied.

 

[georgiworld]

Are they finally getting their s**t together?

http://www.globalnews.ca/sports/Japan+focuses+hydrogen+buildup+after+nuclear+leak/4567696/story.html

 

[TCups]

I find that hard to believe. There was sufficient capacity at Units 1, 2 and 3. Is this a reference to SFP in Unit 4?

They would have had to put a rack in the equipment pool. As far as I know, that pool is not cooled. The water is for shielding of any radiation on the steam separators which normally sit just above core and do get some irradation during operation.

I don't think the fuel handling machine even goes past the reactor containment to the equipment pool, does it? And that being the case, then the overhead crane would be needed to transfer fuel rods, but than only happens after fuel rods have been put in casks. So, even if they wanted to get the fuel rods into the equipment pool, I can't see how they would do it.

 

[TCups]

Are they finally getting their s**t together?

http://www.globalnews.ca/sports/Japan+focuses+hydrogen+buildup+after+nuclear+leak/4567696/story.html

Very interesting! and to quote in part the referenced article:

"The possibility of another hydrogen explosion like those that ripped through reactors 1 and 3 early in the crisis, spreading high levels of radiation into the air, was "extremely low," he said.

But TEPCO suspected that the outside casing of the reactor vessel was damaged, said the official.

"Under these conditions, if we continue cooling the reactors with water, the hydrogen leaking from the reactor vessel to the containment vessel could accumulate and could reach a point where it could explode," he added."

and I again refer to my analysis at post #2936
https://www.physicsforums.com/showpost.php?p=3230713&postcount=2936

and my opinion of where damage to the reactor pressure vessel damage from lateral acceleration exceeding design parameters might be likely to occur (X marks the spot)

http://i306.photobucket.com/albums/nn270/tcups/Screenshot2011-04-05at100427AM.png

just saying . . .

 

[Jorge Stolfi]

The spent fuel racks have either boraflex or boral plates.

Google tells me that
* boraflex is some silicone polymer with boron carbide particles
* boral is a layer of boron carbide dispersed in aluminum, sanwiched between aluminum plates.

Is that correct? So
* (H2 was generated in the SFP #4), implies
* (zirconium was exposed to steam at >300C), implies
* (part of the fuel was uncovered for some time), implies
* (temperature may have reached 700C), implies
* (neutron-absorbing baffles between assemblies melted or burned out), implies
* ...?

 

[|Fred]

some one mentioned looking to see if other group of reflexion came up with different ideas..
I found this one http://forum.atominfo.ru/index.php?showtopic=575 It's in Russian.. could not make much of it .. but I don't think they conjectured anything like aou Fuel Handling Machine bullet. (speaking of witch we can identify above SFP roof debrit on the ground between unit 3 and 4.

Now my small visit to the Russian board concurred that the blueprint I found on a patent site match Fukushima plant .. as they were able to get the file.. 69Megapixel ... I'll just link you to the scaled down version 2mo 17Mega pixel
http://min.us/mvbsHCv

 

[Jorge Stolfi]

In here http://www.google.co.uk/url?sa=t&so...g=AFQjCNHvmvjzUQY_apDXEqIqcmenR6gKzA&cad=rja"

It says that the spent fuel pools are at about half capacity, however, that is only after "Re-racking" looking at dates though that does appear to be before number 4 was emptied.

Thanks, that is it. I understand that spent fuel was unevenly distributed through the 6 reactors; IIRC #4 had the largest stock. Moreover (IIRC) reactor #4, besides the fuel load removed from the RPV, also had a shipment of fresh fuel.

 

[tadjik]

One gets very little - but one does get hydrogen. Some of the hydrogen produced diffuses into the Zircaloy cladding. At < 300 C, the reaction is very slow. One can do a calculation of how much hydrogen is produced from a reaction of Zr => ZrO2 of thickness ~20-100 microns over the area of the fuel or 400 or 548 assemblies.

Also, if the fuel ruptures, then there is a Zr-linear of 75 microns thickness (which could produce about 200 microns oxide) that can react with water/steam to produce hydrgoen. How much hydrogen generated depends on how many of the cladding tubes and channels oxidized on the outer surface, and how many cladding tubes ruptured in which the liner heavily corroded/oxidized.

Apparently, whatever phenomena increases pressure in reactor 1, it seems progressive.
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/v6/plot-un1-full.png
Any hope this could just be some H2O vapor ?

And (if the question has not been raised yet) : 7 atm is a very high pressure, I thought the desin was for 4 atm ... why inject nitrogen under such circumstances ?

 

[georgiworld]

Very interesting! and to quote in part the referenced article:

"The possibility of another hydrogen explosion like those that ripped through reactors 1 and 3 early in the crisis, spreading high levels of radiation into the air, was "extremely low," he said.

But TEPCO suspected that the outside casing of the reactor vessel was damaged, said the official.

"Under these conditions, if we continue cooling the reactors with water, the hydrogen leaking from the reactor vessel to the containment vessel could accumulate and could reach a point where it could explode," he added."

and I again refer to my analysis at post #2936
https://www.physicsforums.com/showpost.php?p=3230713&postcount=2936

and my opinion of where damage to the reactor pressure vessel damage from lateral acceleration exceeding design parameters might be likely to occur (X marks the spot)

http://i306.photobucket.com/albums/nn270/tcups/Screenshot2011-04-05at100427AM.png

just saying . . .

And here is further confirmation of your hypothesis. Nice job.
http://english.kyodonews.jp/news/2011/04/83613.html

 

[Astronuc]

Apparently, whatever phenomena increases pressure in reactor 1, it seems progressive.
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/v6/plot-un1-full.png
Any hope this could just be some H2O vapor ?

And (if the question has not been raised yet) : 7 atm is a very high pressure, I thought the desin was for 4 atm ... why inject nitrogen under such circumstances ?

Pressure would increase if the temperature of the gas increased. Nitrogen is there to provide for an inert, non-combustible environment. Of course, if there is a leak, then the nitrogen leaks as well.

Well, the design pressure is greater than 4 atm, but the operating limit would be specified at 4 atm to ensure that the containment had sufficient margin to failure. Theoretically, the concrete the steel liner should hold to about 7 atm, although the concrete might start cracking (leaking).

Leak-before-break is a typical approach to designing containment systems.

 

[TCups]

And here is further confirmation of your hypothesis. Nice job.
http://english.kyodonews.jp/news/2011/04/83613.html

Well, it sounds like both news stories arise from reporting of the same conference, so it isn't independent "confirmation". And while it is interesting to think it may be something like what actually happened, I might characterize what was reported as "evidence for" rather than "confirmation of" the earlier hypothesis.

 

[tadjik]

Pressure would increase if the temperature of the gas increased. Nitrogen is there to provide for an inert, non-combustible environment. Of course, if there is a leak, then the nitrogen leaks as well.

Well, the design pressure is greater than 4 atm, but the operating limit would be specified at 4 atm to ensure that the containment had sufficient margin to failure. Theoretically, the concrete the steel liner should hold to about 7 atm, although the concrete might start cracking (leaking).

Leak-before-break is a typical approach to designing containment systems.

OK, I understand for nitrogen. Thanks.

But the source gives temperature slowly going down; of course, they can think the data are wrong but it seems to me the 2 measures are "coherent" both in time and between them.
On the other hand, it does not exclude increase elsewhere in the system, of course.

 

[|Fred]

http://english.kyodonews.jp/news/2011/04/83613.html

=> in which way to you find it confirms anything?

edit: which

 

[georgiworld]

http://english.kyodonews.jp/news/2011/04/83613.html

=> in witch way to you find it confirms anything?

I may be mistaken in reading between the lines but as I read the article the managers of the disaster are attempting to prevent a repeat of what happened in Reactor3

According to the article "Nishiyama said past hydrogen explosions have likely occurred due to hydrogen accumulation caused by the reaction of melted fuel rods' zirconium with steam from the coolant water".

It also states that
"The utility has been pouring massive amounts of water into the reactors and their spent nuclear fuel pools as a stopgap measure to cool them down. But the measure is causing ''side effects,'' such as the detection of contaminated water in various parts of the nuclear complex and some leakage into the sea."

TCups points out "That big old steel reactor vessel sets on a pedestal like a long, skinny boiled egg. It is made of heavy steel, and it is full of water and one of the densest things I know of -- uranium.

Furthermore he states

"If the lateral acceleration forces exceed the design parameters, the pressure vessel risks becoming the upside down clanger in a giant bell shaking at about a 9 on the Richter scale."

The key vulnerable structure if that happens is the high pressure steam outlet pipe. If that cracks or leaks, then you have high pressure steam and shortly thereafter, hydrogen in the primary containment"

 

[Astronuc]

One can find there assessment reported in the NY Times here:

http://djysrv.blogspot.com/2011/04/nrc-threat-assessment-of-fukushima.html