Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[MadderDoc]

Time zone difference when/where tagging??

The time is given as UTC time. UTC time is very much equal to GMT, it should be the same in whatever which time zone you may be. Assuming the encoding/tagging computer time setting had a minus one day offset error would move the encoding time from 22h48m before the event (impossible), to 1h12m after the event (possible, maybe plausible).

 

[elektrownik]

reactor 3 water level going down (-1950 -2300), temperature up, and they injecting 15,5m3/h now...

 

[NUCENG]

NUCENG, thanks for your detailed answers. So, from what you wrote it seems most likely to me that they brought the core shroud in through the refueling tunnel/entrace. It seems to involve fewer complications to use the existing building features than to construct new openings in the building. Also, no such round hole in the roof can be seen in unit 4. Further, a square hole would probably have been easier to cut into the roof than a round one.

Follow-up question (just curious): Do we know what was the status of the core shroud replacement in unit 4?

Also, NUCENG, with all your inside knowledge, would you mind commenting on my question about why the SFPs in these type of BWRs are apparently not covered with concrete shield plugs during normal operation, which I had already brought up twice in this thread, but no one has picked up on it yet?

Just followup. I haven't found any discussions of covering spent fuel pools. So the following points are just ideas that may be involved.

1. If they were covered at Fukushima it may have made it harder to add water to the spent fuel pools.
   
2. Spent fuels are warm due to decay heat. There would be a hot moist environment below a cover. That could accelerate corrosion or degradation of concrete.
   
3. Covering the pools may increase the demand on fuel pool cooling systems by preventing evaporation cooling at the surface of the pool. It also might result in faster heatup following a loss of Fuel pool cooling.
5. Concrete covers would be heavy loads and would have to be put on and taken off frequently. That could be a higher risk to the spent fuel that a seismic event.
6. Covering pools could allow gas buildup under the cover.
7. Currently fuel pool level is easily visible. Failure of level instrumentation while the pool is covered could be a problem.

I haven't found any discussion of design basis that would require a cover. The exclusion of debris and dirt is handled by loose parts programs, skimmers, and filtration on pool water. Obviously, if the roof caves in these systems aren't up to that task.

 

[Rive]

Just followup. I haven't found any discussions of covering spent fuel pools.

Some NPPs has separate pools to receive fuel casks. These pools are connected with the main pool by channels, as it can be seen on the general BWR GE MK1 drawing. I've checked this SFP-covering thing through my NPP-pictures collection, and these additional pools looks missing on some pictures, even if that NPP has such pools.

Of course it's possible that I made some mistakes during collecting the pictures, but maybe it worth to consider if these covers belongs to the additional pools.

 

[swl]

reactor 3 water level going down (-1950 -2300), temperature up, and they injecting 15,5m3/h now...

Sounds bad. What was the source of data?

 

[jlduh]

Just followup. I haven't found any discussions of covering spent fuel pools. So the following points are just ideas that may be involved.

1. If they were covered at Fukushima it may have made it harder to add water to the spent fuel pools.
   
2. Spent fuels are warm due to decay heat. There would be a hot moist environment below a cover. That could accelerate corrosion or degradation of concrete.
   
3. Covering the pools may increase the demand on fuel pool cooling systems by preventing evaporation cooling at the surface of the pool. It also might result in faster heatup following a loss of Fuel pool cooling.
5. Concrete covers would be heavy loads and would have to be put on and taken off frequently. That could be a higher risk to the spent fuel that a seismic event.
6. Covering pools could allow gas buildup under the cover.
7. Currently fuel pool level is easily visible. Failure of level instrumentation while the pool is covered could be a problem.

I haven't found any discussion of design basis that would require a cover. The exclusion of debris and dirt is handled by loose parts programs, skimmers, and filtration on pool water. Obviously, if the roof caves in these systems aren't up to that task.

An article on this subject of sabotage or terrorism and SFPs:

http://belfercenter.ksg.harvard.edu/publication/364/radiological_terrorism.html

 

[NUCENG]

Some NPPs has separate pools to receive fuel casks. These pools are connected with the main pool by channels, as it can be seen on the general BWR GE MK1 drawing. I've checked this SFP-covering thing through my NPP-pictures collection, and these additional pools looks missing on some pictures, even if that NPP has such pools.

Of course it's possible that I made some mistakes during collecting the pictures, but maybe it worth to consider if these covers belongs to the additional pools.

I have not seen any covered spent fuel pools in the plants I have visited, toured, or worked at. Nor have I found reguatory mentions of covered pools in US or International websites. There may be such pools, I just found nothing definitive, so I tried to think of reasons why covering a pool might be problematic - thus my list in the previous post.

The OP pdObq was asking a question that he had apparently asked before without response. I think he assumed a cover might have protected the fuel in the pools at Fukushimafrom the debris from the explosions. It is a legitimate question that deserves an answer. I'm hoping my post may trigger some discussion about whether covering fuel pools would be a good idea based on what happened at Fukushima.

 

[Rive]

...

Maybe I made a mistake - I thought that this thread is the followup of the SFP coverings found on some equipment weight/movement list. What I intended to say is that maybe those covers belongs to the additional (cask receive) pools and channels, because on some pictures they are visible, but they looks missing or covered on some other pictures.

Sorry for the confusion.

 

[Samy24]

Because of the rising temperatures they may fear criticality in unit 3.

At 2:33 pm on May 15, we started injecting boric acid through the fire
extinction system.

http://www.tepco.co.jp/en/press/corp-com/release/11051503-e.html"

 

[NUCENG]

It was already reported in March that Technicium99m was found.
In one German media is thus based on criticality.
Often the argument of the rapidly declining decay heat is given. Normally, should have reassured the nuclei after two months of cooling.
Nevertheless, the temperature in the reactors.
For me, the rise in temperature is an indication of criticality and thus increasing or constant temperature, despite cooling.
Perhaps the corium has formed a skin. The corium is washed with water from the outside. The boron in the water can not flush the corium. Thus its effect is irrelevant.

Sorry my bad english.

Kind regards

http://www.taz.de/1/archiv/print-ar...sort=sw&dig=2011/03/29/a0082&cHash=96559c9d6c

I hope I understand your question. Tc-99m has a half life of only 6 hours and was still being measured in late March. You are asking if that would support a conclusion that the reactor had gone recritical. Tc99m is also being produced by a decay chain of other fission products from Rb99 to Sr99 to Y99 to Zr99 to Nb99 to Mo99 to Tc99m and Tc99 due to beta decay. It also has inputs from beta, neutron decays of Rb100, Sr100, and Y100. Most of these parent isotopes have half lives in seconds or fractions of seconds and are gone in about 30 minutes. However Mo99 has a 66 hour half life and will continue producing measureable Tc99m for about 30 days post-shutdown. So only measureable Tc99m or increases in sampes after the middle of April would need to be investigated seriously for evidence of criticality.

Rising temperatures may be due to poor cooling, and don't need criticality to happen. If the corium does have a skin and water is only cooling the skin the corium deeper in the pile would not have an effective moderator to permit thermal fission. Boron in water outside the skin would continue to absorb neutrons preventing them from being reflected back into the corium. So although there may be a lot of uranium in the corium mass it may still be lacking in thermal neutrons for fission.

 

[NUCENG]

Maybe I made a mistake - I thought that this thread is the followup of the SFP coverings found on some equipment weight/movement list. What I intended to say is that maybe those covers belongs to the additional (cask receive) pools and channels, because on some pictures they are visible, but they looks missing or covered on some other pictures.

Sorry for the confusion.

No problem. I wasn't aware of anything like an equipment weight movement list.

I have found a trick. In most posts, that are replies and quote a previous post you will see something like "Originally Posted by Rive" followed by a blue icon. Click that blue icon and it will take you to the previous post so you may be able to see more about the discussion.

 

[default.user]

I hope I understand your question. Tc-99m has a half life of only 6 hours and was still being measured in late March. You are asking if that would support a conclusion that the reactor had gone recritical. Tc99m is also being produced by a decay chain of other fission products from Rb99 to Sr99 to Y99 to Zr99 to Nb99 to Mo99 to Tc99m and Tc99 due to beta decay. It also has inputs from beta, neutron decays of Rb100, Sr100, and Y100. Most of these parent isotopes have half lives in seconds or fractions of seconds and are gone in about 30 minutes. However Mo99 has a 66 hour half life and will continue producing measureable Tc99m for about 30 days post-shutdown. So only measureable Tc99m or increases in sampes after the middle of April would need to be investigated seriously for evidence of criticality.

Rising temperatures may be due to poor cooling, and don't need criticality to happen. If the corium does have a skin and water is only cooling the skin the corium deeper in the pile would not have an effective moderator to permit thermal fission. Boron in water outside the skin would continue to absorb neutrons preventing them from being reflected back into the corium. So although there may be a lot of uranium in the corium mass it may still be lacking in thermal neutrons for fission.

Thanks for the remarks.

I'm also not a physicist.
I would like to argue that alone is the fuel in a reactor at least 50 tons. Probably even more.
I wonder how big the dermis to be.
I doubt that the borated cold water may exert its physical function in this mass of corium.
One must also bear in mind is that the entire inventory [steel parts, etc.] also melted.
The corium should therefore weigh more than 50 tons.
I have no idea what effects the different densities of the molten substance on the overall status of the corium.
Can we might take the Earth as a role model? A uranium core and around it melted steel and other metals.
If the dermis reacts with the concrete, will be added further layers.
I would imagine that the criticality cause the temperature of the corium remains constant.
The criticality is not comparable to a nuclear explosion.
Ranging from power might not be sufficient to destroy the outer skin. But it is enough to keep the temperature constant.

As an example, I would argue that it was time to time to criticality in processing plants. Connected with the dead.
Criticality does not imply a nuclear explosion.

It prevents the cooling process and can perhaps even calculated. If the neutron balances were recorded properly, should be detectable, how much Fissile material is included in the corium and how long have expected criticality.

Excuse my theoretical ideas.

 

[clancy688]

Because of the rising temperatures they may fear criticality in unit 3.



http://www.tepco.co.jp/en/press/corp-com/release/11051503-e.html"

Despite raised water inflow the temperature is rising, the water level is decreasing and now they are injecting boron.

What are the drywell and wetwell radiation sensors saying? Is there another kind of explanation for that kind of behavior, perhaps a rupture at piping / the RPV?
I don't know much of nuclear chain reactions, but how dould it be possible that a corium puddle stayed put for two months and then suddenly got critical?

 

[elektrownik]

Despite raised water inflow the temperature is rising, the water level is decreasing and now they are injecting boron.

What are the drywell and wetwell radiation sensors saying? Is there another kind of explanation for that kind of behavior, perhaps a rupture at piping / the RPV?
I don't know much of nuclear chain reactions, but how dould it be possible that a corium puddle stayed put for two months and then suddenly got critical?

Hard to say but they injecting water via two different ways science few days, at last one of them should be undamaged and working, It is possible that core or its part melt from RPV to drywell so water is leaking like in reactor 1, in case of recricitality, tepco would not use boron if it wouldn't be required, the problem is that almost all temperatures are going up, unit 1 and 2 is more stable in this case, so there is something different with unit 3

 

[etudiant]

reactor 3 water level going down (-1950 -2300), temperature up, and they injecting 15,5m3/h now...

The experience to date and the reactor 3 temperature data suggests a lump of partly melted core material, mixed with salt, encrusted near the bottom of the RPV. Presumably the worst case event would be a melt through with the core lump deposited into a flooded drywell, generating a large steam explosion.
Is this a realistic scenario and is there enough data that the scale of the steam generation can be modeled?

 

[mrcurious]

Despite raised water inflow the temperature is rising, the water level is decreasing and now they are injecting boron.

May this be an indication the holes in the bottom of the RPV are getting larger and the leak rate has now exceeded the refill rate? If so, eventually the RPV will drain completely no matter how much water is injected.

Any opinions on what happens then?

 

[mrcurious]

The experience to date and the reactor 3 temperature data suggests a lump of partly melted core material, mixed with salt, encrusted near the bottom of the RPV. Presumably the worst case event would be a melt through with the core lump deposited into a flooded drywell, generating a large steam explosion.
Is this a realistic scenario and is there enough data that the scale of the steam generation can be modeled?

But the "lump" is already sitting in a pool of water with no steam explosion. If it has been dripping through the holes in the RPV until now, and even if it drops in a lump, it still is going from one water medium to another. Would a steam explosion require a dry lump of corium super heated to several thousand degrees prior to being introduced into a water pool?

 

[TCups]

REGARDING THE VISIBILITY OF THE FIREBALL AND IGNITION OUTSIDE OF BLDG 3 CONTAINMENT

I think no one can claim to have actually seen the ignition. It would seem to me to be an extraordinary claim that the ignition point was outside the building. I would like to hear about the supposed mechanism for such occurrence before even considering it.

IMO, I believe I could see ignition occurring outside of Bldg 3. See the prior images I posted some time back. The nature of video compression and image compression is complicated. It is interesting to me that I am not able to reproduce this resolution on one of the later generations or perhaps different copy of the explosion of Unit 3, but my initial review of the video, IMO, was pretty clearly a white puff then a very brief expanding and contracting fireball quite distinct and separate from the other components of the explosion. A discussion of this and other observations about the video and a link to the original video, preceded the quotation with images below, I believe.

REGARDING COMPRESSION ARTIFACT AND RESOLUTION

Just for grins, here are the actual pixels I am able to resolve, not from the video, but from the links to the frame grabs I posted. ROI is the initial white puff and red fire ball.

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture2-1.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture3-1.png

http://i306.photobucket.com/albums/nn270/tcups/Fukushima%20Foto%20Files/Picture4-1.png

Not great, but more than 8 pixels for sure. Plus the tower just to the left will give an idea of edge artifact and contrast resolution.

"Seeing" is different from confirming and explaining the mechanism, I suppose. But my simple explanation would be that the oxygen available for the initial explosion in the primary containment (if that is what had occurred) had been consumed, that very hot steam and hydrogen gas were being jetted, and that contact with air outside of the building with a higher concentration of oxygen outside of the building allowed ignition (re-ignition?) of the ejected gas. Someone earlier posted a video of a similar effect observed in a fireball exiting a mine explosion, I believe.

 

[etudiant]

But the "lump" is already sitting in a pool of water with no steam explosion. If it has been dripping through the holes in the RPV until now, and even if it drops in a lump, it still is going from one water medium to another. Would a steam explosion require a dry lump of corium super heated to several thousand degrees prior to being introduced into a water pool?

The thought is that the transition from the RPV to the drywell breaks up the lump and exposes the molten material currently inside a crust. So the question is how much impact from the heat in 50-100 tons of molten reactor fuel, not assuming any incremental contributions from implausible recriticalities.

 

[elektrownik]

Meltdown occurred at Fukushima No. 1 reactor 16 hrs after March 11 quake
TOKYO, May 15, Kyodo

A nuclear fuel meltdown at the No. 1 reactor of the crisis-hit Fukushima Daiichi power plant is believed to have occurred around 16 hours after the March 11 quake and tsunami crippled the complex in northeastern Japan, Tokyo Electric Power Co. said Sunday.

http://english.kyodonews.jp/news/2011/05/91207.html

 

[clancy688]

http://english.kyodonews.jp/news/2011/05/91207.html

That's odd.

3/11 - 14:46: Tohoku earthquake
3/11 - 15:41: Tsunami impact
3/11 - 16:36: Battery failure in Unit 1
3/11 - 17:07: Isolation Condenser active in Unit 1
3/12 - 05:30: Unit 1 primary containment pressure 820 kPa
3/12 - 06:46: +16 hours
3/12 - 10:17: Venting of Unit 1
3/12 - 11:20: Fuel rods 90 cm exposed in Unit 1
3/12 - 15:36: Explosion of Unit 1

The meltdown occurred before venting and before the fuel rods got exposed?

 

[PietKuip]

"A nuclear fuel meltdown at the No. 1 reactor of the crisis-hit Fukushima Daiichi power plant is believed to have occurred around 16 hours after the March 11 quake and tsunami crippled the complex in northeastern Japan, Tokyo Electric Power Co. said Sunday."
http://english.kyodonews.jp/news/2011/05/91207.html

That was when all the industry experts told us in TV that such a thing was impossible.

 

[clancy688]

That was when all the industry experts told us in TV that such a thing was impossible.

Then you should've watched german tv... quite the opposite.

 

[mrcurious]

The thought is that the transition from the RPV to the drywell breaks up the lump and exposes the molten material currently inside a crust. So the question is how much impact from the heat in 50-100 tons of molten reactor fuel, not assuming any incremental contributions from implausible recriticalities.

Understood. But the exposed molten material is dripping into the containment filled with water in small portions, not in one 50-100 ton mass. Will that make a difference?

If the majority of the large mass is still in the RPV, is there a possibility it could burn through the bottom in one quick event and if so what temp might that mass be when it drops into the water pool in the containment?

I guess I'm trying to determine the possibility of a large steam explosion sending the corium into the atmosphere. Next up might be determining if and when the corium mass burns through the concrete in the PCV and onto the floor of the reactor building, then from there into the basement with the 4.2 meters of standing water.

 

[SteveElbows]

That's odd.

3/11 - 14:46: Tohoku earthquake
3/11 - 15:41: Tsunami impact
3/11 - 16:36: Battery failure in Unit 1
3/11 - 17:07: Isolation Condenser active in Unit 1
3/12 - 05:30: Unit 1 primary containment pressure 820 kPa
3/12 - 06:46: +16 hours
3/12 - 10:17: Venting of Unit 1
3/12 - 11:20: Fuel rods 90 cm exposed in Unit 1
3/12 - 15:36: Explosion of Unit 1

The meltdown occurred before venting and before the fuel rods got exposed?

Someone on this thread found some reactor data from early on, and it shows far more detail about when the fuel rods were exposed. The last reading where the level was above the top of the fuel was at 07:30, showing +600mm and +200mm. There was then a gap in the readings, and the next available ones at 08:30 showed reading A at 0mm and reading B at -400mm. By 08:49 it was measured at -300mm and -550mm. So the 11:20am levels were not the beginning of fuel exposure.

 

[clancy688]

So the 11:20am levels were not the beginning of fuel exposure.

Of course not. But even with the readings cited by you, meltdown would have occurred before the fuel rods got uncovered.

 

[bytepirate]

That's odd.

3/11 - 14:46: Tohoku earthquake
3/11 - 15:41: Tsunami impact
3/11 - 16:36: Battery failure in Unit 1
3/11 - 17:07: Isolation Condenser active in Unit 1
3/12 - 05:30: Unit 1 primary containment pressure 820 kPa
3/12 - 06:46: +16 hours
3/12 - 10:17: Venting of Unit 1
3/12 - 11:20: Fuel rods 90 cm exposed in Unit 1
3/12 - 15:36: Explosion of Unit 1

The meltdown occurred before venting and before the fuel rods got exposed?

obviously, they are using a different data set:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110515e10.pdf
water level at bottom of fuel at 19:30 on 3/11

i am not sure, where the other data set, that stolfi et al are using originates from.

'On the other hand, as the temperature of the RPV of Unit 1 is in the range of 100°C - 120°C, stable cooling is being achieved'

looking at the #3 data, this is a little scary...

 

[SteveElbows]

obviously, they are using a different data set:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110515e10.pdf
water level at bottom of fuel at 19:30 on 3/11

i am not sure, where the other data set, that stolfi et al are using originates from.

It may well be the same data, but recalibrated.

The data I was going on about which showed fuel uncovered by 08:30 on the 12th, did have very big gaps in it the previous evening. And now that they have recalibrated the A readings, the subsequent data which showed levels above the top of the fuel was likely totally wrong, and they have adjusted accordingly.

Thanks for finding the official document about this stuff, its very interesting, and we should just forget all about the '16 hours' that Kyodo story mentions.

 

[SteveElbows]

Thanks for finding the official document about this stuff, its very interesting, and we should just forget all about the '16 hours' that Kyodo story mentions.

Oops, I worded that badly. What I meant is that 16 hours is not when fuel began to be uncovered, the document shows that this is when they think the fuel fell to the rpv bottom.

 

[clancy688]

obviously, they are using a different data set:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110515e10.pdf
water level at bottom of fuel at 19:30 on 3/11

Thank you very much! That data sheet is VERY interesting. I think the data Stolfi and others used came from NISA or TEPCO.

looking at the #3 data, this is a little scary...

For me it's rather scary what happens with a BWR/3 when emergency power supply fails - it's immediately doomed.
Fast decrease in water height started only minutes after power failure. Only two hours later the top of the fuel was uncovered. And three and a half hours later the fuel was completely uncovered. Which means that the passive cooling equipment (Isolation Condenser) was totally useless. There are not many BWR/3 or older in use... I asked wikipedia, one is in spain, the rest in the USA: Dresden NPP (2x), Monticello NPP (1x), Nine Mile Point NPP (1x, BWR/2), Oyster Creek (1x, BWR/2), Pilgrim NPP (1x), Quad Cities NPP (2x) and Santa Maria de Garona NPP in Spain (1x). I think the operators of those plants should make sure now that there's always emergency power available... without relying on passive cooling systems.
Now I'm interested in such a report regarding Unit 2 and 3... showing if the BWR/4 design with RCIC was considerably better in providing emergency cooling. One question for the physicists: core temperature began rising very fast, but once it reached 2900 degrees it suddenly stopped rising. Why? I'd expect a temperature graph resembling a function of ln(x), not such a sudden stop.

And another question (for everybody): What's the data TEPCO used for that sheet, and where did it come from? It doesn't seem to be an estimate, since there are bumps in those graphs, indicating they are build on accurate data.

Thanks for finding the official document about this stuff, its very interesting, and we should just forget all about the '16 hours' that Kyodo story mentions.

But the document states exactly that 16 hours after the earthquake, the core had totally molten down. Look at the four images at page 3.

 

[ernal_student]

The meltdown occurred before venting and before the fuel rods got exposed?

It might help to recall the details with this excerpt from the accumulated information on the related wikipedia page:

On 11 March at 14:46 JST, unit 1 scrammed successfully in response to the earthquake though evacuated workers reported violent shaking and burst pipes within the reactor building. All generated electrical power was lost following the tsunami leaving only emergency batteries, able to run some of the monitoring and control systems. At 15:42, TEPCO declared a "Nuclear Emergency Situation" for units 1 and 2 because "reactor water coolant injection could not be confirmed for the emergency core cooling systems." [...]

After the loss of site power, unit 1 initially continued cooling using the isolation condenser system; by midnight water levels in the reactor were falling and TEPCO gave warnings of the possibility of radioactive releases. In the early hours of 12 March, TEPCO reported that radiation levels were rising in the turbine building for unit 1 and that it was considering venting some of the mounting pressure into the atmosphere, which could result in the release of some radioactivity. Chief Cabinet Secretary Yukio Edano stated later in the morning the amount of potential radiation would be small and that the prevailing winds were blowing out to sea. At 02:00 JST, the pressure inside the reactor containment was reported to be 600 kPa (6 bar or 87 psi), 200 kPa higher than under normal conditions. At 05:30 JST, the pressure inside reactor 1 was reported to be 2.1 times the "design capacity", 820 kPa.Isolation cooling ceased to operate between midnight and 11:00 JST 12 March, at which point TEPCO started relieving pressure and injecting water. One employee working inside unit 1 at this time received a radiation dose of 106 mSv and was later sent to a hospital to have his condition assessed.

Rising heat within the containment area led to increasing pressure. Electricity was needed for both the cooling water pumps and ventilation fans used to drive gases through heat exchangers within the containment. Releasing gases from the reactor is necessary if pressure becomes too high and has the benefit of cooling the reactor as water boils off but this also means cooling water is being lost and must be replaced. If there was no damage to the fuel elements, water inside the reactor should be only slightly radioactive.

In a press release at 07:00 JST 12 March, TEPCO stated, "Measurement of radioactive material (iodine, etc.) by monitoring car indicates increasing value compared to normal level. One of the monitoring posts is also indicating higher than normal level." Dose rates recorded on the main gate rose from 69 nGy/h (for gamma radiation, equivalent to 69 nSv/h) at 04:00 JST, 12 March, to 866 nGy/h 40 minutes later, before hitting a peak of 0.3855 mSv/h at 10:30 JST.

At 13:30 JST, workers detected radioactive caesium-137 and iodine-131 near reactor 1, which indicated some of the core's fuel had been damaged. Cooling water levels had fallen so much that parts of the nuclear fuel rods were exposed and partial melting might have occurred. Radiation levels at the site boundary exceeded the regulatory limits. [...]

At 15:36 JST on 12 March, there was an explosion in the reactor building at unit 1.

The press release came out at what is now considered the approximate time of the meltdown - during the period of increased gamma radiation.

 

[intric8]

"Does anyone have any reliable info on the nuclear plants - the reports on the news seem garbled to me."

Weeks ago, someone mentioned the very first message in this thread (above), and how things have changed so little with Tepco that this comment is still very appropriate today.

Ringing truer than ever.

 

[triumph61]

According to Tepco, hyrogen produced in the overheating of the reactor core at Unit 3 flowed through a gas treatment line and entered Unit No. 4 due to a breakdown of valves. Hydrogen leaked from ducts in the second, third and fourth floors of the reactor building at Unit 4 and ignited a massive explosion.

http://online.wsj.com/article/SB10001424052748703509104576325110776621604.html

 

[clancy688]

According to Tepco, hyrogen produced in the overheating of the reactor core at Unit 3 flowed through a gas treatment line and entered Unit No. 4 due to a breakdown of valves. Hydrogen leaked from ducts in the second, third and fourth floors of the reactor building at Unit 4 and ignited a massive explosion.

http://online.wsj.com/article/SB10001424052748703509104576325110776621604.html

Did they actually solve the Unit 4 explosion mystery? Sounds to good to be true... hence it can't be true! (just kidding... but what's up with them... suddenly releasing informations)

 

[AntonL]

According to Tepco, hyrogen produced in the overheating of the reactor core at Unit 3 flowed through a gas treatment line and entered Unit No. 4 due to a breakdown of valves. Hydrogen leaked from ducts in the second, third and fourth floors of the reactor building at Unit 4 and ignited a massive explosion.

http://online.wsj.com/article/SB10001424052748703509104576325110776621604.html

Did they actually solve the Unit 4 explosion mystery? Sounds to good to be true... hence it can't be true! (just kidding... but what's up with them... suddenly releasing informations)

Tepco have been reading this forum for ideas, I postulated this a month ago

But where does the Hydrogen come from for the explosion, forum members here agree that the explosion centre was lower down in the building on the north side, which does make sense because of the observed damage.

For that scenario I can also give a very imaginative explanation. When unit 3 was vented, could unit 4 have pumped hydrogen steam into unit 3. Unit 3 and 4 share a common exhaust stack and there was no power for fans to work to aid the exhaust procedure, Furthemore, we do not know if there are any dampers in the system and if installed I would imagine they fail open when power is lost.

Lets assume unit 3 pumped unit 4 full of steam and hydrogen, this would then be into the suppression chamber, then H2 will leak into the primary containment chamber, it would not immediately escape to the roof, as there is a seal between the reactor vessel and PCV so that PCV is not flooded during fuel transfer. The Hydrogen could have leaked out through the access hatch which would not have been sealed due to the maintenance taking place, This access hatch is on the ground floor, which is the right level for a lower explosion centre. The only question why the long delay between units 3 and 4 exploding.

and again later

this new underwater video of SFP4 certainly seems to rule out that SFP4 boiled dry and Hydrogen produced by overheating fuel rods and, so how did the Hydrogen get into reactor 4 building? In my opinion, only two possibilities remain:
1. Hydrogen being pumped into the building during venting of unit 3. Unit 3 and 4 share a common exhaust stack and there was no power for fans to work to aid the exhaust procedure.
2. Radiolysis of water as perhttps://www.physicsforums.com/showpost.php?p=3287847&postcount=6068"

Do you have any other ideas?

 

[PietKuip]

One question for the physicists: core temperature began rising very fast, but once it reached 2900 degrees it suddenly stopped rising. Why? I'd expect a temperature graph resembling a function of ln(x), not such a sudden stop.

It stops at the boiling point of corium. The boiling point of iron is 2750 ºC.

 

[StrangeBeauty]

(just kidding... but what's up with them... suddenly releasing informations)

The cynic in me says the answer is "Please don't look at #3 too closely right now! Oh look! #1 melted down 16 in hrs two months ago! #4 was blown up by #3!" The "shiny object distraction technique" in action. I hope I'm very wrong. :)

 

[clancy688]

It stops at the boiling point of corium. The boiling point of iron is 2750 ºC.

Thanks. And how could they measure those numbers?And another question: Where do I get up to date sensor data of Unit 3?

 

[PietKuip]

Thanks. And how could they measure those numbers?

These are calculations. The timing is made to fit the measured temperatures at different places.

 

[clancy688]

These are calculations. The timing is made to fit the measured temperatures at different places.

I meant, where did they get the numbers to build their graphs in the TEPCO press release regarding the melt down. The graphs shown there don't look as if they were done with calculation data.

 

[|Fred]

Then you should've watched german tv... quite the opposite.

As far as the opinion given in this board was concerned, the exact expertise was (if I recall corectly) " if there is water in the RCV then meltdown is unlikely ". The available data indicated there was some watter.

I do believe that the given statement still stand

 

[GJBRKS]

obviously, they are using a different data set:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110515e10.pdf
water level at bottom of fuel at 19:30 on 3/11

i am not sure, where the other data set, that stolfi et al are using originates from.

'On the other hand, as the temperature of the RPV of Unit 1 is in the range of 100°C - 120°C, stable cooling is being achieved'

looking at the #3 data, this is a little scary...

Wow , that link finally makes it clear where to find the D/W HVH temperature sensor :

http://img220.imageshack.us/img220/1281/tempsensors.jpg

And if its BELOW the RPV , then the increasing temperature reading for Unit 3 ( up to 197 Celsius from 125 Celsius within 24 hours) could mean that corium has breached into the containment just now ...

 

[Astronuc]

obviously, they are using a different data set:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110515e10.pdf
water level at bottom of fuel at 19:30 on 3/11

i am not sure, where the other data set, that stolfi et al are using originates from.

'On the other hand, as the temperature of the RPV of Unit 1 is in the range of 100°C - 120°C, stable cooling is being achieved'

looking at the #3 data, this is a little scary...

I should point out that the 110515e10.pdf is an analysis - a model - and may not reflect physical reality, which is often the case in licensing/safety analysis. Effectively, to get to fuel pellet melting, they would have to assume near adiabatic conditions.

They also claim to have water in the bottom of the RPV, but not the core. The progression seems somewhat unreal.

 

[Godzilla1985]

Eh, come on. Given TEPCO's own statements concerning #1 in that WSJ article, do you really think any of those gauges can be trusted? #3 probably had a full meltdown after 16 hours as well, and the corium dropped through some time around the 21st of March when that thick black smoke appeared...

 

[~kujala~]

Nice work, Anton!
(BTW: I remember there were some counterarguments against your theory. Now that TEPCO has adopted your theory is there any more validity in these counterarguments? TEPCO engineers must know their plants so their evaluations about possible theories have a certain level of assertiveness, which the outsiders lack.)

 

[triumph61]

The work to install a supporting structure for the floor of the
Spent Fuel Pool of Unit 4 was started. (From May 9.)


http://www.nisa.meti.go.jp/english/files/en20110510-1-1.pdf

Has someone checked the Situation IN Unit 4??

 

[AntonL]

looking at the #3 data, this is a little scary...

[PLAIN]http://k.min.us/iNbS.JPG

 

[GJBRKS]

Eh, come on. Given TEPCO's own statements concerning #1 in that WSJ article, do you really think any of those gauges can be trusted? #3 probably had a full meltdown after 16 hours as well, and the corium dropped through some time around the 21st of March when that thick black smoke appeared...

You talking to me ? ...

 

[jim hardy]

Somebody mentioned that 3 & 4 shared a vent stack.
If that's so,

unit 4 with its substantial heat source in the spent fuel pool should have established a "draft" up its tall stack just from the warm humid air coming off the pool.
No different than your fireplace chimney just lots taller.
Natural circulation, warm light moist air rises. Moist air is lighter than dry air even at same temperature.

That would cause a natural draft from 3 to 4 through whatever remained of 3's ventilation systems so long as the dampers stayed open.

 

[elektrownik]

Interesting that unit 3 temperature going down after boron injection...