Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[NUCENG]

You have a point there. However, I was not thinking so much of the experiences we have had so far (the number of which is fortunately very limited), but rather the design bases of the containments. If you don't have large enough volume to accommodate all hydrogen produced by cladding oxidation, a full meltdown will probably result into a release. And if you don't have filters in the vent line, you will probably have a rather large release (and even if you have filters, they will not be able to catch noble gases or organic iodine, unless it's a large dry bed instead of the more compact wet scrubber type).

If you don't have a core catcher, and your containment does not allow for flooding of the drywell in case of melt-through (either due to the pools sitting lower than the drywell or due to fear of steam explosions), you have difficulty controlling the core-concrete interaction, which may result into a containment failure.

Etc. My point was simply that if a full-scale meltdown is not included in the original design basis of the containment, it's difficult to prove it can prevent release in 99 % of the cases, which would be a plausible target for new reactor designs.

I understand, and agree in general that existing plants may not be the best design for safety. So I work to ensure that their operation as as low risk as I can provide. I would prefer to see new designed plants with all their safety advances being built so we can retire the older designs. I would hope that advances to intelligent grid design to increase the potential sor reliable addition of wind and solar generation sources. And I hope Miss America finally gets world peace. We only fail if we quit trying.

 

[jmelson]

There has never been a nuclear accident in any US Naval Nuclear Propulsion Plant or prototype.

Are you sure about that? There was a serious accident that cost 3 lives and destroyed a
reactor at Idaho National Engineering Lab in, I believe, 1958. I believe this was a prototype
of a Naval power reactor. The fuel was nearly spent and due for exchange, and therefore the
reactor was very touchy. An operator was apparently lifting a control rod to attach it to the control
rod drive after an unattended shutdown. It was sticking, and he lifted it too far, causing a rapid
power excursion and exploding the RPV. The three operators in the facility were burned by radioactive steam and died. This should be a fairly well-known accident.

Jon

 

[nikkkom]

Are you sure about that? There was a serious accident that cost 3 lives and destroyed a
reactor at Idaho National Engineering Lab in, I believe, 1958. I believe this was a prototype
of a Naval power reactor. The fuel was nearly spent and due for exchange, and therefore the
reactor was very touchy. An operator was apparently lifting a control rod to attach it to the control
rod drive after an unattended shutdown. It was sticking, and he lifted it too far, causing a rapid
power excursion and exploding the RPV. The three operators in the facility were burned by radioactive steam and died. This should be a fairly well-known accident.

http://en.wikipedia.org/wiki/SL-1

It wasn't a Navy program. It was an Army program.

 

[westfield]

I am open minded on the cause of damage on Unit 4.

Initially I received information that operators believed a second explosion had occurred in Unit 3. Other theories were of steam explosions, which I never found convincing. We basically rehjected that theory because we couldn't find photographic changes in unit 3 indicating a second explosion. Then the possibility of hydrogen from damaged fuel in a drained spent fuel pool was proposed based on NRC statements that the pool was empty. That was proved wrong by photos showing no significant damage. For a while people were looking for welding gases supporting the shroud chane project or lubricating oils as sources for the explosion.

The next theory was radiolysis of water in the spent fuel pool. Calculations were made that showed that was possible if the pool was boiling. There was some good work on this by other posters.

Then TEPCO postulated the Unit 3 source via the stack piping. Apparently that has gained credence by the photos and inspections of the debris on the 3rd and 4th floors. It is relatively easy to see a difference between an explosion inside ducting and ducting that has benn crushed or damaged from an exterior explosion. The isometric sketches of the SBGT ducting seems consistent. We don't really know when the exterior duct failed on the side of unit 3. Recent information confirms the dampers fail open and there are no backdraft damper. The explosion of unit 3 could have followed a period when the hydrogen was present with increasing hydrogen concentrations and pressure forcing hydrogen into unit 4 or the explosion itself may have been the driving force. The explosion may not have been propagated to unit 4 because the hydrogen concentration in the ducting was to rich for deflagration or detonation. The timelag before the Unit 4 explosion could have been awaiting an ignition source or dilution to a combustible or explosive mixture.

In summary I still have unanswered questions. to change the maybes into facts. If I have to answer your question, I will default to "Mythbusters" terminology and say it is somewhere neither BUSTED, nor CONFIRMED, but somewhere between POSSIBLE, and PLAUSIBLE.

NUCENG, I understand large (main) generators are cooled using hydrogen gas circulated through the windings. Would you or anyone with NPP generator knowledge care to comment on this hydrogen system being a possible source of Unit #4's hydrogen buildup?

Apart from the hydrogen that is circulated through the generator while its running there would also be hydrogen generation systems and\or bottled hydrogen on-site to provide the initial charge of hydrogen on start-up and then "make up" while the generator is running.

I realize that Unit #4 was not running and the generator casing would presumably be inerted however that still leaves the hydrogen generation system or "bottled" hydrogen somewhere onsite. I wish I could find a drawing which indicates where this is located. One would tend to think if it's anywhere inside of Unit #4 it would be in the Turbine building however one would not normally expect the EDG's to be located where they are at fuku ichici so I for one wouldn't be surprised if the generator cooling hydrogen system is somewhere "surprising" as well.

Edit : I guess without knowledge of the actual location of the main generator cooling hydrogen at fuku-ichici Unit #4 we are in the dark. FWIW, on the Oyster Creek Turbine Building general layout drawings there are hydrogen gas bottles shown in the TB loading dock. That location would seem to eliminate that hydrogen as a possible source leaking into the RB.
Again, having some drawings of the fukushima plant would be rather handy in these discussions.

 

[dezzert]

NUCENG, thank you very much for that response. I truly appreciate it.

Then TEPCO postulated the Unit 3 source via the stack piping. Apparently that has gained credence by the photos and inspections of the debris on the 3rd and 4th floors. It is relatively easy to see a difference between an explosion inside ducting and ducting that has benn crushed or damaged from an exterior explosion. The isometric sketches of the SBGT ducting seems consistent.

Yes, but could the exhaust system pick up emissions from lower in the building and not from the SGTS. The reason I ask this is because of the pulse/explosion that is believed to have occurred in R2 at the same time as the R4 blast, and because of the damage to the SGTS valve in the basement of R2 after the R3 blast. Schematics of the plant show an extensive tunnel system (both piping and electrical) connecting numerous points within the R1 to R4 compound. Studying the R3 blast extensively there appear to be numerous expulsions, cloud bursts, emanating from the switching yard up to 12 seconds after the main pulse from R3. Could R3s explosion have blown open this tunneling system allowing communication between the reactors underground.

We don't really know when the exterior duct failed on the side of unit 3.

With only the DigitalGlobe sat photos to go by that's going to be hard to determine, but Id have to say from the looks of the exhaust line from R3 after the blast, Id say its likely at the same time.

Recent information confirms the dampers fail open and there are no backdraft damper. The explosion of unit 3 could have followed a period when the hydrogen was present with increasing hydrogen concentrations and pressure forcing hydrogen into unit 4 or the explosion itself may have been the driving force. The explosion may not have been propagated to unit 4 because the hydrogen concentration in the ducting was to rich for deflagration or detonation. The timelag before the Unit 4 explosion could have been awaiting an ignition source or dilution to a combustible or explosive mixture.

Like you I include possible to this scenario but then go the other way to not probable. Knee jerk reaction. The only possibility to me is if the R3 blast blew the valves shut.

 

[dezzert]

Unfortunately, I do not know how to make the future predicatable or to prevent furure calamities. I do know that 7 Billion people cannot be sustained on this Earth without technology and a stable society. Providing safe and reliable energy is essential for preserving that stability. Right now I do not think we have any other alternative than to include nuclear power in the mix of energy sources.

In the early eighties, peak winter, I visited a geek friend in the mountains of southern Mendocino Co. California for a week. He built a beautiful house with every inch of roof covered with solar panels, and not far away, a wind generator all hooked to a huge battery collection for electricity. For hot water he had panels on the southside below the house and a water line connected to the back of his wood stove feeding a large heat tank in the attic. For cooking he had both a wood and gas stove, but in the winter only uses the gas side for hot coffee water in the morning. He also had a back up nat gas generator and nat gas on demand water heater, which again were seldom used. For cooling his house in the summer, he had a 2 ft pipe that ran from a group of trees, 6 feet underground, and into his house. He said it worked unbelievably well and I believe him.

During my stay there was a massive storm that knocked out the grid throughout the northern bay area into his area. That morning, while drinking a cup of coffee, I watched his good enough sized (24"?) TV picking up the bay area stations via antenna, talking about the blackout. As I sat there, listening to his son play music on his stereo upstairs, and my friend taking a hot bath that was steaming up the bathroom, and watching flooding scenes in downtown Santa Rosa, I had an epiphany. This was the future.

Now we need to actually make it the future.

 

[jmelson]

http://en.wikipedia.org/wiki/SL-1

It wasn't a Navy program. It was an Army program.

Yup, apparently so, although they did train some Navy people at the same site.
Well, I remembered most of the details without too much error.

Jon

 

[jmelson]

NUCENG, I understand large (main) generators are cooled using hydrogen gas circulated through the windings. Would you or anyone with NPP generator knowledge care to comment on this hydrogen system being a possible source of Unit #4's hydrogen buildup?

Well, that would have been in the turbine building, not the reactor building. There have been some alternator hydrogen fires in the US, but I haven't heard of "explosions" due to the hydrogen coolant.
Of course, an earthquake can affect any system.

Jon

 

[westfield]

Well, that would have been in the turbine building, not the reactor building. There have been some alternator hydrogen fires in the US, but I haven't heard of "explosions" due to the hydrogen coolant.
Of course, an earthquake can affect any system.

Jon

Indeed that system is presumably located in the TB but considering the SGTS hydrogen scenario involves another entirely separate building, a different scenario involving an attached building doesn't seem out of the realms of possibility.

While not quite related to what we are talking about here you may be interested in this accident - http://www.powerplantforum.com/generator-auxiliary-systems/460-hydrogen-explosion-accident-u-s-lessons.html

If there are gen cooling related systems happen to be near the western end of the TB it's not a giant leap to see a potential scenario where hydrogen has leaked and instead of making its way throughout the TB it has insteadmade its way up through into the RB - this is post a major earthquake as you say. Oyster Creek drawings indicate HVAC ducting extends throughout the TB.

Thankyou for the reply.

Edit: PS, I'm not trying to sell this idea, just wanted to explore it. Didn't seem too outragous to me when the SGTS theory is the current leading one.

 

[nikkkom]

In the early eighties, peak winter, I visited a geek friend in the mountains of southern Mendocino Co. California for a week. He built a beautiful house with every inch of roof covered with solar panels,

Solar panels. Reasonably efficient. Reasonably durable. In early eighties. Really?

and not far away, a wind generator all hooked to a huge battery collection for electricity. For hot water he had panels on the southside below the house

Which he needed to not forget to drain before winter sets in. Meaning - in winter it doesn't work.

Come to think about it, where did your friend in the mountains got the clean, drinkable water from in the first place?

and a water line connected to the back of his wood stove feeding a large heat tank in the attic. For cooking he had both a wood and gas stove, but in the winter only uses the gas side for hot coffee water in the morning. He also had a back up nat gas generator and nat gas on demand water heater, which again were seldom used.

He must be enjoying everyday trips to forest for wood. Not everyone would like to do it. Not in Manhattan, for sure.

During my stay there was a massive storm that knocked out the grid throughout the northern bay area into his area. That morning, while drinking a cup of coffee, I watched his good enough sized (24"?) TV picking up the bay area stations via antenna, talking about the blackout. As I sat there, listening to his son play music on his stereo upstairs, and my friend taking a hot bath that was steaming up the bathroom, and watching flooding scenes in downtown Santa Rosa, I had an epiphany. This was the future.

Wind generator doesn't work in massive storms. Solar power is likely not available too. Unless you have a submarine-sized battery (very expensive), you can't operate TVs and stereos for long.

Heating a full bath of hot water would take helluva lot of wood. For people who need to collect that wood by hand, I bet not many would engage in such wasteful use of it (unless they are masochists).

In short, you need to stop making up stories. Of course, Internet is full of people engaging in mental masturbations of all imaginable kinds...

 

[NUCENG]

Are you sure about that? There was a serious accident that cost 3 lives and destroyed a
reactor at Idaho National Engineering Lab in, I believe, 1958. I believe this was a prototype
of a Naval power reactor. The fuel was nearly spent and due for exchange, and therefore the
reactor was very touchy. An operator was apparently lifting a control rod to attach it to the control
rod drive after an unattended shutdown. It was sticking, and he lifted it too far, causing a rapid
power excursion and exploding the RPV. The three operators in the facility were burned by radioactive steam and died. This should be a fairly well-known accident.

Jon

You are referring to the SL-1 reactor accident a DOD/US Army prototype for use in small land-based facilities such as northern radar sites. It was NOT a Naval Reactors project.

 

[NUCENG]

NUCENG, I understand large (main) generators are cooled using hydrogen gas circulated through the windings. Would you or anyone with NPP generator knowledge care to comment on this hydrogen system being a possible source of Unit #4's hydrogen buildup?

Apart from the hydrogen that is circulated through the generator while its running there would also be hydrogen generation systems and\or bottled hydrogen on-site to provide the initial charge of hydrogen on start-up and then "make up" while the generator is running.

I realize that Unit #4 was not running and the generator casing would presumably be inerted however that still leaves the hydrogen generation system or "bottled" hydrogen somewhere onsite. I wish I could find a drawing which indicates where this is located. One would tend to think if it's anywhere inside of Unit #4 it would be in the Turbine building however one would not normally expect the EDG's to be located where they are at fuku ichici so I for one wouldn't be surprised if the generator cooling hydrogen system is somewhere "surprising" as well.

Edit : I guess without knowledge of the actual location of the main generator cooling hydrogen at fuku-ichici Unit #4 we are in the dark. FWIW, on the Oyster Creek Turbine Building general layout drawings there are hydrogen gas bottles shown in the TB loading dock. That location would seem to eliminate that hydrogen as a possible source leaking into the RB.
Again, having some drawings of the fukushima plant would be rather handy in these discussions.

The turbine hydrogen is stored in tanks and feeds the turbine generator cooling sysstem locatated in the turbine building. It was the reactor building that was damaged. Very unlikely to be the cause.

 

[NUCENG]

In the early eighties, peak winter, I visited a geek friend in the mountains of southern Mendocino Co. California for a week. He built a beautiful house with every inch of roof covered with solar panels, and not far away, a wind generator all hooked to a huge battery collection for electricity. For hot water he had panels on the southside below the house and a water line connected to the back of his wood stove feeding a large heat tank in the attic. For cooking he had both a wood and gas stove, but in the winter only uses the gas side for hot coffee water in the morning. He also had a back up nat gas generator and nat gas on demand water heater, which again were seldom used. For cooling his house in the summer, he had a 2 ft pipe that ran from a group of trees, 6 feet underground, and into his house. He said it worked unbelievably well and I believe him.

During my stay there was a massive storm that knocked out the grid throughout the northern bay area into his area. That morning, while drinking a cup of coffee, I watched his good enough sized (24"?) TV picking up the bay area stations via antenna, talking about the blackout. As I sat there, listening to his son play music on his stereo upstairs, and my friend taking a hot bath that was steaming up the bathroom, and watching flooding scenes in downtown Santa Rosa, I had an epiphany. This was the future.

Now we need to actually make it the future.

Idyllic! Does he grow his own food? Where does he get natural gas?. He must be technologically saavy, was his educational institution self powered? Is he a physician? Where does he get his solar panels? Is his application possible to duplicate in areas away from forest sources of wood? Is he truly self-sufficient in a way that can be sustained over the long haul and handed down to his children? Can this be duplicated for the rest of the world or even just for America? If not, how will he defend it when the rest of the world wants what he has and civilization has broken down?

 

[nikkkom]

Idyllic! Does he grow his own food?

How is this relevant? Nuclear plants are not growing food either.

Where does he get natural gas?. He must be technologically saavy, was his educational institution self powered? Is he a physician? Where does he get his solar panels? Is his application possible to duplicate in areas away from forest sources of wood? Is he truly self-sufficient in a way that can be sustained over the long haul and handed down to his children? Can this be duplicated for the rest of the world or even just for America? If not, how will he defend it when the rest of the world wants what he has and civilization has broken down?

NUCENG, I think your criticism is wrong. *IF* the described lifestyle was possible, it would be good.

The point is, it wasn't possible in late 80s - photovoltaics, wind turbines and batteries were not up to the task. Green home technologies (good insulation, passive heating, etc) were not actively developing. Etc. The story is incredible (in a negative sense of the word).

Such lifestyle probably is not possible even today (he'd need a humongously large battery to ride through periods when neither wind nor photovoltaic generation are working). But we are getting there.

 

[westfield]

Originally Posted by westfield
NUCENG, I understand large (main) generators are cooled using hydrogen gas circulated through the windings. Would you or anyone with NPP generator knowledge care to comment on this hydrogen system being a possible source of Unit #4's hydrogen buildup?

Apart from the hydrogen that is circulated through the generator while its running there would also be hydrogen generation systems and\or bottled hydrogen on-site to provide the initial charge of hydrogen on start-up and then "make up" while the generator is running.

I realize that Unit #4 was not running and the generator casing would presumably be inerted however that still leaves the hydrogen generation system or "bottled" hydrogen somewhere onsite. I wish I could find a drawing which indicates where this is located. One would tend to think if it's anywhere inside of Unit #4 it would be in the Turbine building however one would not normally expect the EDG's to be located where they are at fuku ichici so I for one wouldn't be surprised if the generator cooling hydrogen system is somewhere "surprising" as well.

Edit : I guess without knowledge of the actual location of the main generator cooling hydrogen at fuku-ichici Unit #4 we are in the dark. FWIW, on the Oyster Creek Turbine Building general layout drawings there are hydrogen gas bottles shown in the TB loading dock. That location would seem to eliminate that hydrogen as a possible source leaking into the RB.
Again, having some drawings of the fukushima plant would be rather handy in these discussions.

.

The turbine hydrogen is stored in tanks and feeds the turbine generator cooling sysstem locatated in the turbine building. It was the reactor building that was damaged. Very unlikely to be the cause.

I don't wish to sound impertinent but would you mind reading past the first paragraph of my post? I don't mind being shot down in flames by sound argument but with respect, saying it's very unlikely because it's in another area doesn't seem a considered response when the SGTS theory is the leading theory which is an entirely separate building.

I'm not trying to sell this idea, I'm looking for reaons that make it less plausable than the SGTS theory.

What reasons could make this source of hydrogen less plausable than hydrogen leaking from Unit #3, an entirely separate building hundreds of feet away with an open stack in the middle of the duct that connects the two. I'm hoping to learn reasons as to why it's not even been considered.


Yes the Unit #4 Turbine building and Reactor building are separate areas, but they are also obviously joined by many doors, HVAC systems, drainage systems, plenums etc. We know for certain that doors and waterproofing between areas were compromised during the Earthquake\Tsunami. We know water is leaking all around this plants basements between areas and buildings. Hydrogen seems to follow a barely plausible path in the SGTS theory, I thought this idea was just as barely plausible as well.


Anyway, forget it. I thought it might be interesting looking at a possible alternative and I get patronising brushoff, some science forum.

 

[dezzert]

Idyllic!

Absolutely. But its not something that's given to you. Its something you have to work towards. He took the technology of that time and progressed, put it to use. And it wasn't just him. It was called the back to the land movement, and out of it came the distributed power system movement, though it wasn't called that at the time. Smart people, looking for ways to make life better.

Does he grow his own food?

Of course. Best tasting veggies and fruit I've ever eaten. Cans numerous items for winter. He raises rabbits, and composts under the hutches. The meat (being vegetarian I wouldn't know) he claims is the most delicious kind. Winter time doesn't produce much though. He also has chickens and goats.

Where does he get natural gas?.

Thats one of the few things he has to rely on that he can't produce, allow he is toying with the idea. He currently has a compost privy that could produce methane, but that's still in the future.

He must be technologically saavy, was his educational institution self powered?

Cal Berkeley has some of those capabilities, but it needs to improve big time to head towards the future.

Is he a physician?

. No, but his neighbor is. However, until recently, I've never known the guy to be sick. It's one of the main pluses of living a more natural lifestyle, you don't get sick nearly as often. There is a rhythm to nature that, once in tune with, allows for much greater health.

Where does he get his solar panels?

Not sure why that stumps you and Nikkom, but alternative energy stores have been around since the 70s, and were a lot more common back then when there was a greater demand for them by the back to the land crowd. There are still quite a few around. If you need to know of any in your area Ill look them up for you.

Is his application possible to duplicate in areas away from forest sources of wood?

Not in the way he has it set up, but that's not a concern in the Pacific Northwest. Our problem is keeping the clearings open. But in areas with limited wood, or no wood, there are other methods to employ. You have to look for whatever works best in your area. It can be a lot of work structuring a holistic back to nature life style, but worth it.

Is he truly self-sufficient in a way that can be sustained over the long haul and handed down to his children? Can this be duplicated for the rest of the world or even just for America? If not, how will he defend it when the rest of the world wants what he has and civilization has broken down?

No, he is not truly self-sufficient. As I said he still has to depend on certain items. He makes trips to town for supplies. Back then he ran purely on gas. Now he has one that runs on kitchen grease and stuff like that (biodiesel) as well as a hybrid. But his footprint on this Earth is very small.

In some areas of the world his style of self-sufficiency can be duplicated. In other areas only some aspects can, but others are available that are not to him. The point is, the answers to reduce carbon production, toxic chemical production, the need for nuclear, coal or fossil fuel power plants exists, but it takes society turning the ship around and heading in that direction. Actively looking for ways to do it better. And that's where the problem lies. Society is held captive by those who make money off the grid, the most insane concept humans have ever come up with. No wonder Tesla spent his life trying to free us from it.

 

[Rive]

No, he is not truly self-sufficient.

Not even close to that. My father was old enough to feel the taste of real self-sufficiency in his youth, and he was happy that those times were passed: and I know, that those times would not fit for any green-dreamer of the internet too.

What your bro spent on that system could enhance three to five average houses (on the grid of gas and electricity) to generate CO2 emission only halved: and on the other end of the world that number would be even four times higher for that money (for those resources).

I'm a bit tired of this kind of green-dreaming.

Especially if I have to read it here.

 

[NUCENG]

How is this relevant? Nuclear plants are not growing food either.



NUCENG, I think your criticism is wrong. *IF* the described lifestyle was possible, it would be good.

The point is, it wasn't possible in late 80s - photovoltaics, wind turbines and batteries were not up to the task. Green home technologies (good insulation, passive heating, etc) were not actively developing. Etc. The story is incredible (in a negative sense of the word).

Such lifestyle probably is not possible even today (he'd need a humongously large battery to ride through periods when neither wind nor photovoltaic generation are working). But we are getting there.

No, nuclear plants don't grow food, but the provide power to farms, food processing plants, grocery stores, and home refrigeration and cooking. Gasoline and diesel food are used in agriculture and to transport food. A sinle family can appear to be independent and living a "green" lifestyle. But that family cabin is still dependent on thousands of other actvities powered by the electric grid and using other non-green power sources. Someday that may be change, but that day isn't any time soon. In the meantime the cabin in the woods lifestyle is a fairy tale, a wonderful story, but fantasy all the same.

 

[Borek]

If you want to discuss green living and fertilizing your own tomatoes in a natural way, please move to other thread, as these things have nothing to do with Japan Earthquake nor nuclear plants.

 

[NUCENG]

I don't wish to sound impertinent but would you mind reading past the first paragraph of my post? I don't mind being shot down in flames by sound argument but with respect, saying it's very unlikely because it's in another area doesn't seem a considered response when the SGTS theory is the leading theory which is an entirely separate building.

I'm not trying to sell this idea, I'm looking for reaons that make it less plausable than the SGTS theory.

What reasons could make this source of hydrogen less plausable than hydrogen leaking from Unit #3, an entirely separate building hundreds of feet away with an open stack in the middle of the duct that connects the two. I'm hoping to learn reasons as to why it's not even been considered.


Yes the Unit #4 Turbine building and Reactor building are separate areas, but they are also obviously joined by many doors, HVAC systems, drainage systems, plenums etc. We know for certain that doors and waterproofing between areas were compromised during the Earthquake\Tsunami. We know water is leaking all around this plants basements between areas and buildings. Hydrogen seems to follow a barely plausible path in the SGTS theory, I thought this idea was just as barely plausible as well.


Anyway, forget it. I thought it might be interesting looking at a possible alternative and I get patronising brushoff, some science forum.

I read your entire post, assuming otherwise is maybe, just a little bit, impertinent. If you wanted more detail, that is fair, all you had to do was ask.

I know how hydrogen is used in generator cooliing systems and they are at the far end of the turbine building from the steam tunnels that connect to the reactor building. The very high radioactivity of shortlived N-16 in steam during operation makes the steam tunnel a closed volume that separates the two buildings. That means that after power failure, the turbine building would have to be filled with hydrogen to provide a differential pressure to move into the reactor building and result in the explosion there without also blowing the turbine building apart. Storage tanks are outside the building so damage from the earthquake or tsunami would have caused leakage outside the building. The generator hydrogen cooling system is a closed system requiring only a small makeup flow of hydrogen to replace leakage. The system supply of hydrogen will isolate on excess flow from breaks inside the building.

I hope this helps you understand why I described this as unlikely. I was not trying be dismissive or to belittle your idea.

 

[jmelson]

I don't mind being shot down in flames by sound argument but with respect, saying it's very unlikely because it's in another area doesn't seem a considered response when the SGTS theory is the leading theory which is an entirely separate building.


What reasons could make this source of hydrogen less plausable than hydrogen leaking from Unit #3, an entirely separate building hundreds of feet away with an open stack in the middle of the duct that connects the two. I'm hoping to learn reasons as to why it's not even been considered.

Well, there is a fairly limited volume of hydrogen in the alternator and heat exchanger, and it is carefully controlled at just a little above atmospheric pressure, to prevent any oxygen from getting in. So, it would take something unusual to vent all this hydrogen and then transport it to the reactor building. (Yes, the earthquake was an unusual event.)

The key here is first, it is unlikely the hydrogen would be driven out of the alternator, although slow leakage would not be a surprise. Second, as it is not under pressure, what would push it all out, some days after all the equipment has been unpowered and transport it to another building? Note that some
of these buildings has pretty much open ventilation in the roofs that would prevent accumulation of large amounts of hydrogen.

So, I think it makes much more sense that pressurized hydrogen was released within the reactor building, or possibly transferred from one RB to the other RB through existing ducts. The explosions in these buildings seem like they took a LOT of hydrogen. Certainly #3 was so big a lot of people thought at one time there couldn't possibly be that much hydrogen present.

Jon

 

[Most Curious]

I wonder about the volume of hydrogen in the generator cooling system and the volume required to blow up #4 RB.

 

[tonio]

Just thinking out loud a little bit, not knowing too much about these reactors...

I understood that contaminated water from the reactors leaked towards the surroundings via underground conduits for cables and maybe also water drainage pipes. I suppose that this is normally not possible but that it could occur due to cracks in the foors or walls of the reactor buildings. Now, if water can do this, it must also be possible for (pressurized) gas.

Thus I can imagine that hydrogen-containing gas from the leaking secondary containment of R3 (or maybe R2 or R1) entered these conduits/pipes and, via the road of least resistance, entered R4 building from beneath.

 

[tsutsuji]

"Hydrogen concentration management for reactor pressure vessel in Unit 1 to 3 at Fukushima Daiichi Nuclear Power Station":

To be sure, until the nitrogen injection to reactor pressure vessel begins, steam ratio in the reactor pressure vessel will be increased to decrease hydrogen concentration. The implementation will begin on November 24.
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111124_03-e.pdf

How can they do that ? How can they increase the steam ratio in the reactor pressure vessel ? Does it mean increasing the water injection flow rate ? Do they have measuring instruments measuring that steam ratio ?

 

[NUCENG]

"Hydrogen concentration management for reactor pressure vessel in Unit 1 to 3 at Fukushima Daiichi Nuclear Power Station":



How can they do that ? How can they increase the steam ratio in the reactor pressure vessel ? Does it mean increasing the water injection flow rate ? Do they have measuring instruments measuring that steam ratio ?

From the article you linked it appears they intend to inject nitrogen directly into the pressure vessels (RPV) to flush out high hydrogen concentrations that may be there. They will continue to inject nitrogen into the containment vessel and will double the injection rate when they start injecting nitrogen into the RPV. This doubling will help keep the hydrogen concentration below combustible limits while any large concentration in the RPV is being flushed out.

Until they complete installation of the nitrogen injection path for the RPV they say they will allow the steam ratio to increase (probably by reducing cooling water flow into the vessel and allowing boiling to increase the amount of steam). They must believe that the core debris is and will remain covered by water during that process and that the reduced cooling flow will not uncover any of the corium. Increased steam will dilute the hydrogen in the vessel which they hope will prevent any combustion or explosions in the meantime.

Interesting decision, because I don't know if they really know how much of the corium is submerged and how deeply. When they try to reduce cooling flow and increase steaming rate I expect they will closely monitor radiation and isotopic releases to detect any further uncovering of fuel debris. II am guessing that they believe the possibility of further hydrogen burns or explosions is high enough to justify the risk of reducing cooling.

 

[NUCENG]

Interesting.

I though "battery-backed emergency lighting", when used in the context of nuclear power plants, means lighting *integrated with battery*. Maybe even the lamp and battery in an air- and water-tight unit. With photodiode detector which switches it on automatically when it detects darkness. You know, something designed to be fail-safe.

How naive I was...

nikkom, there are probably the typical emergency exit lights which have their own battery packs, but these lights are not general area lights that would illuminate the panels and allow operators to easily read their instruments. (Most of their instruments were out anyway.The control room general area lighting is a fairly large electrical load and would require a lot of individual batteries for simillar backup.) Thus it is likely that the control room general area lighting emergency backup poower source is either the station batteries (DC) or emergency diesel generators (AC).

Since the description of the event was complete blackout in some control rooms, and the control room lights are an essential electric load with emergency AC or DC backup, TEPCO may not even have had exit lights in the control room. So when the emergency DC and AC supplies were flooded all lighting was lost. US fire codes would not allow that omission of the emergency exit lights, so it is a lesson that needs to be corrected where it exists.

Early reports also indicated they had to scrounge for flashlights and batteries. But although loss of lighting was a complication, I really doubt it made the difference between success and meltdown.

 

[tsutsuji]

(probably by reducing cooling water flow into the vessel and allowing boiling to increase the amount of steam).

Thanks for your comments.

There is a short Yomiuri article on that topic:

http://www.yomiuri.co.jp/science/news/20111124-OYT1T01086.htm "Too much cooling is dangerous too ... start of work to increase reactor temperatures" (...) The flow rate into unit 1 will be reduced by 0.5 m³/h (from 5.5), and those into unit 2 and unit 3 by 1.5 m³/h (from 10). RPV bottom temperatures which are below 70°C at present will be raised to above 80°C. The original flow rates will be restored after nitrogen injection is enabled.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111124_02-e.pdf "Presumption of gas flow in the PCV of the Unit 2"

 

[nikkkom]

nikkom, there are probably the typical emergency exit lights which have their own battery packs, but these lights are not general area lights that would illuminate the panels and allow operators to easily read their instruments.

I am thinking more about reports about workers having to look for valves and such in completely dark rooms. That is just wrong and should not be possible on a NPP.

Early reports also indicated they had to scrounge for flashlights and batteries. But although loss of lighting was a complication, I really doubt it made the difference between success and meltdown.

Maybe it was the difference between venting early and venting late? Between having hydrogen explosions and not having them?

 

[zapperzero]

Thanks for your comments.

There is a short Yomiuri article on that topic:

http://www.yomiuri.co.jp/science/news/20111124-OYT1T01086.htm "Too much cooling is dangerous too ... start of work to increase reactor temperatures" (...) The flow rate into unit 1 will be reduced by 0.5 m³/h (from 5.5), and those into unit 2 and unit 3 by 1.5 m³/h (from 10). RPV bottom temperatures which are below 70°C at present will be raised to above 80°C. The original flow rates will be restored after nitrogen injection is enabled.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111124_02-e.pdf "Presumption of gas flow in the PCV of the Unit 2"

This means more steam, which presumably means an increase in emissions. Not so good. But then, it also means less water to process, which is somewhat beneficial.

Does anyone know if this measure is permanent, or just a stopgap until they devise another system for gas management?

 

[NUCENG]

I am thinking more about reports about workers having to look for valves and such in completely dark rooms. That is just wrong and should not be possible on a NPP.



Maybe it was the difference between venting early and venting late? Between having hydrogen explosions and not having them?

I am certain it contributed to the delay once the decision was made to vent. However the reports to date clearly show the two biggest sources of delay were in obtaining permissionto vent and deliberately waiting for evacuations to be completed before trying to vent. These factors added hours of delay.

 

[nikkkom]

I am certain it contributed to the delay once the decision was made to vent. However the reports to date clearly show the two biggest sources of delay were in obtaining permissionto vent and deliberately waiting for evacuations to be completed before trying to vent. These factors added hours of delay.

NUCENG, with all due respect, you are intelligent enough to understand that your argument does not help to defend your general position?

Let me spell it out for you.

I am not sure that lack of lighting didn't affect the outcome, but for the sake of argument let's assume it did not affect the outcome *in this particular accident*.

But on some other station, in some other event unanticipated total darkness in some room very well might hamper a crucial operation. One does not need to be a genius to acknowledge that adding reliable, fully independent battery backed emergency lighting
(a) may help A LOT in some emergencies
and
(b) is, by the standards of NPPs, a very, very, VERY cheap thing to implement. Something on the order of $100k per plant. Pocket change.

And yet, apparently it wasn't done.

So, the management of this particular NPP are not only greedy bastards who knowingly decided to skimp on tsunami protection (which is a crime, but at least I can understand the motivation - saving a few hundred millions of dollars), but also they are incompetent and lazy bastards - they didn't bother planning for a serious accident even where it did not cost them much.

 

[NUCENG]

NUCENG, with all due respect, you are intelligent enough to understand that your argument does not help to defend your general position?

Let me spell it out for you.

I am not sure that lack of lighting didn't affect the outcome, but for the sake of argument let's assume it did not affect the outcome *in this particular accident*.

But on some other station, in some other event unanticipated total darkness in some room very well might hamper a crucial operation. One does not need to be a genius to acknowledge that adding reliable, fully independent battery backed emergency lighting
(a) may help A LOT in some emergencies
and
(b) is, by the standards of NPPs, a very, very, VERY cheap thing to implement. Something on the order of $100k per plant. Pocket change.

And yet, apparently it wasn't done.

So, the management of this particular NPP are not only greedy bastards who knowingly decided to skimp on tsunami protection (which is a crime, but at least I can understand the motivation - saving a few hundred millions of dollars), but also they are incompetent and lazy bastards - they didn't bother planning for a serious accident even where it did not cost them much.

Having a bad day, nikkom? What argument? I agreed that loss of lighting was a contributing factor, and that means it needs to be evaluated. I do believe you overstate the significance of loss of lighting in the specific case of venting, based on facts about how the decision to vent was delayed. Based on what I have seen, by the time they first tried to vent the containment was overpressurized and probably leaking hydrogen gas into the reactor building. If lighting had remained fully operational, the lost safery sytems, control and instrumentation and operational delays would still have been determining factors.

If you read my posts here and on the Management and Government thread you will also see I do not defend management decisions and delays on addressing a known tsunami threat. Your colorful language does not make them more guilty.

If the final outcome is plant modificstion to protect the emergency AC and DC power supplies, or to supplement it with additional sources, the lighting problem may be solved as well, but that is not yet clear.

 

[tsutsuji]

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111122_02-j.pdf Assessment of the operation of unit 1's Isolation Condenser. An English translation will probably follow soon. I attach a partial translation of the last figure.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111122_03-e.pdf English version.

As to the cause of the suspected malfunctioning, TEPCO suggested that hydrogen generated by damaged nuclear fuel may have gathered in the piping, causing the IC's heat removal efficiency to decline.
http://mdn.mainichi.jp/mdnnews/news/20111123p2a00m0na010000c.html

 

[NUCENG]

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111122_03-e.pdf English version.

This confirms the system became at least partially gas bound, reducing the water level in the return leg to the point where cooling flow was reduced or lost. It also shows how early fuel damage started in ubit 1.

 

[nikkkom]

Having a bad day, nikkom? What argument?

In your posts you generally support a view that things in nuclear industry are okay in general. No big problems exist in NPPs operations and management wrt safety. Chernobul? Irrelevant, Russians were very careless - but we are much better than they. Fukushima? It was a big earthquake + "once in 1000 years tsunami", which exceeded what they were designing for. Looks like this (expected level of tsunami) was a mistake. Japanese were not well prepared, but we are much better than they.

That is your position, and I think it is a wrong position. US nuclear industry is certainly better wrt safety than Russians were, and is possibly somewhat better than Japanese, but not by a large margin. Instead of claiming that everything is hunky-dory, it should take a deep hard look into every detail of Fukushima lesson.

If US nuclear industry won't do it, and God forbid, there will be a meltdown in CONUS in the next 10-20 years, US nuclear power generation can kiss its *** goodbye.

 

[NUCENG]

In your posts you generally support a view that things in nuclear industry are okay in general. No big problems exist in NPPs operations and management wrt safety. Chernobul? Irrelevant, Russians were very careless - but we are much better than they. Fukushima? It was a big earthquake + "once in 1000 years tsunami", which exceeded what they were designing for. Looks like this (expected level of tsunami) was a mistake. Japanese were not well prepared, but we are much better than they.

That is your position, and I think it is a wrong position. US nuclear industry is certainly better wrt safety than Russians were, and is possibly somewhat better than Japanese, but not by a large margin. Instead of claiming that everything is hunky-dory, it should take a deep hard look into every detail of Fukushima lesson.

If US nuclear industry won't do it, and God forbid, there will be a meltdown in CONUS in the next 10-20 years, US nuclear power generation can kiss its *** goodbye.

First, and foremost your interpretation of my position is exactly that - YOUR interpretation. I respect your right to disagree, but in over 700 posts I have tried to back up my position with facts and over 30 years of nuclear power experience. Not once in all those posts have I said that everything is hunky dory or that US plants don't have any lessons to learn from Chernobyl or Fukushima.

I am pro-nuclear. That is a fact of which I am unashamed. What I have done here is first, to provide factual information about the operation of BWRs, and second, to try to balance the anti-nuclear hysteria, emotional outbursts, misstatements of fact, exagerations and outright lies that have been posted by some. Your discussions to date have tended to be thoughtful and honest even when you disagreed with me. I don't expect to change your mind, but I would hope we can draw out facts and ideas through open, honest, and RESPECTFUL discussion. I don't understand why you have suddenly gone to personal attack mode because I believe you overstated your case on the plant lighting.

Fukushima and Chernobyl are human tragedies. TMI2 put the US nuclear industry into a near fatal coma from which we were just starting to emerge. I believe nuclear power is an inevitable and vital part of our energy mix in the US for the forseeable future. I want it to be as low risk as possible and I have worked to make that happen. If you have ideas or factual observations, let's discuss them, but "I am right and you are wrong!" isn't helpful.

 

[NUCENG]

I don't wish to sound impertinent but would you mind reading past the first paragraph of my post? I don't mind being shot down in flames by sound argument but with respect, saying it's very unlikely because it's in another area doesn't seem a considered response when the SGTS theory is the leading theory which is an entirely separate building.

I'm not trying to sell this idea, I'm looking for reaons that make it less plausable than the SGTS theory.

What reasons could make this source of hydrogen less plausable than hydrogen leaking from Unit #3, an entirely separate building hundreds of feet away with an open stack in the middle of the duct that connects the two. I'm hoping to learn reasons as to why it's not even been considered.


Yes the Unit #4 Turbine building and Reactor building are separate areas, but they are also obviously joined by many doors, HVAC systems, drainage systems, plenums etc. We know for certain that doors and waterproofing between areas were compromised during the Earthquake\Tsunami. We know water is leaking all around this plants basements between areas and buildings. Hydrogen seems to follow a barely plausible path in the SGTS theory, I thought this idea was just as barely plausible as well.


Anyway, forget it. I thought it might be interesting looking at a possible alternative and I get patronising brushoff, some science forum.

I tried to respond to your PM, but you have PM replies disabled.

I just noticed your PM. Did my latest reply post help?

I know you mentioned cable tunnels and drainage systems. There are also HVAC systems. But with the loss of power to fans that would move hydrogen from the turbine building to the reactor buildin through any of these paths, the only motive force would be differential pressure in the turbine building. The turbine buildings at Fukushima weren't water tight so they clearly wouldn't have been gas tight.

I hate to confuse the issue, but there is another system which uses hydrogen gas in many BWRs. Hydrogen gas is injected into feedwater to scavenge oxygen in the reactor to reduce corrosion. Again, the hydrogen for this system is stored outside the turbine building and power loss to the condensate and feedwater pumps would make this an unlikely source as well.

Sorry for the delay in this reply. I hope I have not just been skimming posts and missing the points being made. Sometimes it is just a case of misunderstanding. There has been a lot of that on this forum, and some of it has been on my part. The great thing is that open discussion can clear that up. Thanks for participating.

 

[nikkkom]

I don't expect to change your mind, but I would hope we can draw out facts and ideas through open, honest, and RESPECTFUL discussion. I don't understand why you have suddenly gone to personal attack mode because I believe you overstated your case on the plant lighting.

I don't think I am attacking you personally. I disagree with the position of post-Fukushima PR damage control, regardless of who is taking it.

Fukushima and Chernobyl are human tragedies. TMI2 put the US nuclear industry into a near fatal coma from which we were just starting to emerge. I believe nuclear power is an inevitable and vital part of our energy mix in the US for the forseeable future. I want it to be as low risk as possible and I have worked to make that happen. If you have ideas or factual observations, let's discuss them, but "I am right and you are wrong!" isn't helpful.

I do have ideas. Such as:

* NRC should *pro-actively* fish out F1 lessons learned and implement actions to improve safety. In fact, I expected this to be done already several months ago. What do we have instead? Please go to "US NRC Post-Fukushima Actions" thread. What do we see there? "NRC just issued guidelines for estimation of maximum design basis flooding levels"? They are kidding, right? It took them ~6 months to figure out that F1 was caused by a tsunami?!? Gosh... I fear that with such "amazing" performance, NRC will lose a lot of "subtler" details as time goes by and general public is no longer interested, such as why there were no working emergency lights, why IC wasn't working, why personnel did not have accident training, why personnel failed to vent reactors/containments, why hydrogen was allowed to accumulate, etc, etc, etc.

* NRC should press Japanese into releasing an *honest* accident report. We still don't have even the simplest and most obvious questions answered, such as "what a hell happened to IC on Unit 1, why the heck it wasn't turned on?".

 

[clancy688]

"what a hell happened to IC on Unit 1, why the heck it wasn't turned on?".

There are contradicting reports, at least that's the last thing I heard.

The newest report (the INPO one) told us that the IC was shut down right after SCRAM. This happened according to the manual because at that time all EDGs were working and an active IC together with active EDGs could have cooled down the reactor vessel to fast. Which may have led to thermal induced tensions and thus damaged the vessel.

But after the tsunami had hit, power was gone and there was no way for the IC to be turned on again - for the next six hours.

 

[NUCENG]

I don't think I am attacking you personally. I disagree with the position of post-Fukushima PR damage control, regardless of who is taking it.



I do have ideas. Such as:

* NRC should *pro-actively* fish out F1 lessons learned and implement actions to improve safety. In fact, I expected this to be done already several months ago. What do we have instead? Please go to "US NRC Post-Fukushima Actions" thread. What do we see there? "NRC just issued guidelines for estimation of maximum design basis flooding levels"? They are kidding, right? It took them ~6 months to figure out that F1 was caused by a tsunami?!? Gosh... I fear that with such "amazing" performance, NRC will lose a lot of "subtler" details as time goes by and general public is no longer interested, such as why there were no working emergency lights, why IC wasn't working, why personnel did not have accident training, why personnel failed to vent reactors/containments, why hydrogen was allowed to accumulate, etc, etc, etc.

* NRC should press Japanese into releasing an *honest* accident report. We still don't have even the simplest and most obvious questions answered, such as "what a hell happened to IC on Unit 1, why the heck it wasn't turned on?".

When you misstate my position and call it so wrong that you don't need to explain why it is wrong, I don't think you are exactly respectful of my right to disagree.

Can you provide a link to the new flooding guidance? How does it differ from the following two references that are nearly 40 years old?

RG 1.59 initial version issued August 1973:
http://pbadupws.nrc.gov/docs/ML0037/ML003740388.pdf

RG 1.102 initial version issued October 1975:
http://pbadupws.nrc.gov/docs/ML0037/ML003740308.pdf

tsutsuji posted a partial translation that is pretty convincing that the problems in the IC were caused by gas binding. The source, believe it or not was TEPCO.
https://www.physicsforums.com/showpost.php?p=3635311&postcount=11798

You concludrd with : I fear that with such "amazing" performance, NRC will lose a lot of "subtler" details as time goes by and general public is no longer interested, such as why there were no working emergency lights, why IC wasn't working, why personnel did not have accident training, why personnel failed to vent reactors/containments, why hydrogen was allowed to accumulate, etc, etc, etc.

We have been discussing those topics for over 8 months. NRC has issued recomendations and is working on regulatory requirements. These things take time because they don't want to solve incorrect causes.

 

[Bandit127]

Nikkkom and NUCENG.

There is no doubt that your recent discourse is well informed. Your posts are based on knowledge and experience that most of us can only aspire to.

However, discourse it is. A thrust and parry of argument and opinion.

Yes, it forwards our knowedge and therefore it has some value. But the price we observers pay is high in trudging through each personal retort and each base derogatory term used.

In all, it does not fit the dignity of this board and I request that you take it elsewhere. Please.

 

[zapperzero]

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111128_01-e.pdf
Gas temperature in S/C of Unit 2

11/27 6:50, it was confirmed that it read approximately 84, increasing in a staircase pattern. On the other hand, it
was also confirmed that the temperature changes of the bottom of the Reactor Pressure Vessel and the
water in the pool of the Suppression Chamber were smaller than that of the inside of the Primary
Containment Vessel (Drywell) and that there was no significant change in the temperature.

 

[Astronuc]

New analysis of Fukushima core status
30 November 2011
A new analysis of the accident at Fukushima Daiichi indicates more extensive melting probably occurred at unit 1 than previously thought, although the predicted status of units 2 and 3 remains about the same.

The bulk of unit 1's nuclear fuel went through the bottom of the reactor vessel as well as about 70 centimentres of the drywell concrete below, according to the analysis released today. However, the corium did not breach the steel containment vessel 1.9 metres further down within the concrete, or the boundary of secondary containment some 7.6 metres further still.
. . . .

http://www.world-nuclear-news.org/RS_New_analysis_of_Fukushima_status_3011111.html

 

[clancy688]

http://www.world-nuclear-news.org/RS_New_analysis_of_Fukushima_status_3011111.html

Thanks for the link, Astronuc.

"The bulk"? For the bulk to disappear from the vessel, there have to be much larger leaks than previously thought of. At least I don't believe that dozens of tons of fuel- and control rods would be able to leak through a couple of holes only a few square centimeters wide. So there has to be a much larger hole.
Previous discussions regarding leaks discarded the theory of holes on that scale because of some temperature sensors at the bottom of the RPV, some of which still were "alive". Which's highly unlikely if the core came marching through. So how does this new analysis fit with those sensors still reporting?

 

[tsutsuji]

http://mainichi.jp/select/today/news/20111201k0000m040066000c.html According to a study made by the Institute of Applied Energy (Ministry of Economy and Industry) released on 30 November, between 85% and 90% of unit 1's fuel fell down into the primary containment vessel. According to their estimate, fuel cladding tubes were damaged 5 hours 31 minutes after emergency shutdown, and the RPV bottom was damaged 7 hours 21 minutes after emergency shutdown. At units 2 and 3 about 70% of the fuel fell down into PCV. In another study, Tepco says that "considerable amount" of fuel fell down into PCV at unit 1, without saying exactly how much, and that at units 2 and 3, "some of the fuel" fell down into PCV. In all three units, core-concrete reaction took place according to Tepco. At unit 1, a maximum 65 cm depth of concrete was eroded, which, in the worse case, leaves only a 37 cm thick layer of concrete between melted fuel and the PCV's steel bottom. As there is a 7.6 m thick layer of concrete below that, the ground has not been reached by the melted fuel. The contaminated water is believed to leak through, for example, interstices in pipes. A 12 cm depth of concrete was eroded at unit 2, and 20 cm at unit 3.

Tepco's handouts on this topic (Japanese) :

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_07-j.pdf Estimate of fuel damage

Fuel damage workshop :
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_09-j.pdf Condition of fuel
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_03-j.pdf Plant behaviour after accident
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_04-j.pdf Improvement and assessment of JAEA model based on real conditions
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_05-j.pdf List of approaches to grasp fuel condition
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111130_06-j.pdf MAAP analysis and core-concrete reaction study

http://www.yomiuri.co.jp/science/news/20111130-OYT1T01135.htm According to the Institute of Applied Energy study, up to 2 m of concrete was eroded at unit 1. It leaves open the possibility that the RPV, which is supported by concrete, is inclined. According to a JNES study, although unit 1's RPV is damaged, units 2 and 3's RPVs are not damaged.

http://www.asahi.com/national/update/1130/TKY201111300697.html Tepco announced the results of a study saying that most of unit 1's fuel has fallen into the PCV. The melted fuel has been stopped, but part of the concrete is eroded. As the melted fuel is still 37 cm above PCV bottom, there is no "China syndrome". At units 2 and 3 most of the fuel is still in the RPV. Tepco, which had previously admitted that some of the fuel was leaking from the RPV, is now recognizing that the fuel condition is worse than that. At Three Mile Island in 1979, the fuel had remained inside RPV.

http://www.jiji.com/jc/c?g=soc&k=2011113000590 According to Tepco, it is estimated that "considerable amount" of fuel at unit 1, "some fuel" at units 2 and 3 fell from RPV into PCV. Those results were released at the "Technical workshop on core damage estimates" held by the NISA. According to Tepco, nearly all of unit 1's fuel fell down into PCV. In case all of unit 1's fuel has fallen into PCV, the depth of eroded concrete is 65 cm.

 

[Astronuc]

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111122_03-e.pdf English version.

Thanks for the link, Astronuc.

"The bulk"? For the bulk to disappear from the vessel, there have to be much larger leaks than previously thought of. At least I don't believe that dozens of tons of fuel- and control rods would be able to leak through a couple of holes only a few square centimeters wide. So there has to be a much larger hole.
Previous discussions regarding leaks discarded the theory of holes on that scale because of some temperature sensors at the bottom of the RPV, some of which still were "alive". Which's highly unlikely if the core came marching through. So how does this new analysis fit with those sensors still reporting?

See the links posted by tsutsuji.

Related article in Nuclear Engineering International (Nov 28, based on Nov 22 handouts from Tepco, those cited by tsutsuji) - http://www.neimagazine.com/story.asp?storyCode=2061233


Bear in mind, it is an analysis, not the result of observing the RPV and core. The analysis would imply essentially complete loss of cooling of the core, i.e., nearly adiabatic conditions, and effectively no water in the bottom plenum, or rather no make up. The article reports this for unit 1. It appears that Units 2 and 3 had some loss of the core, possibly through vessel penetrations, e.g., control rod drive mechanisms.

Even without melting, if a lot of fuel reacted with the coolant, there could have been dissolution of the fuel which could have washed out. The effect would have been more or less the same, namely the loss of gaseous and volatile fission products to the containment and vent systems.


I'd like to read the report.

 

[tonio]

A question for the experienced nuclear engineers.

As far as I understood, during the meltdown most or all the fuel elements in the RPV's lost their zirconium cladding. Thus a mixture of UO2 and reaction products, both in the RPV’s and at the bottom of the secondary containment, was exposed to cooling water that probably dissolved most or all of the more soluble/volatile reaction products (a.o. Cesium?) and part of the less soluble reaction products. As a result, a significant part (most?) of the radioactivity entered the cooling water and spread with it though the reactor buildings, trough the cooling systems and into the soil and the sea.

Wouldn’t it be much better that, in case of a meltdown, the fuel would be allowed to exit the RPV and the leak onto a thick layer of some kind of metal with a moderate boiling point (lower than that of concrete and steel) which it then would melt and mix with? The surface of such a pool of metal/fuel mixture could subsequently be cooled and solidified with cooling water, minimizing the dissolution of radioactive reaction products in the passing cooling water.

 

[clancy688]

It's called Core Catcher.

 

[Rive]

...According to a study made by the Institute of Applied Energy (Ministry of Economy and Industry) released on 30 November, between 85% and 90% of unit 1's fuel fell down into the primary containment vessel.

I have a gut feeling that (this time) they are overestimated it. According to the temperature and water feed graphs of U1-U3 there is not so much difference between the units.

Don't shoot, it's just a gut feeling

 

[tsutsuji]

http://www3.nhk.or.jp/news/html/20111201/t10014325321000.html In the Tepco study the worse case for unit 2 is 57% of the fuel falling down into PCV, creating a 12 cm deep concrete erosion. For unit 3 the worse case is 63% of the fuel falling down into PCV, creating a 20 cm deep concrete erosion. Tepco explained that those results have no consequence on the achievement of the below 100°C "cold shutdown". But as in unit 1 there is only about 40 cm of water at the bottom of PCV, it is questionable if cooling is stable enough and if it can be juged that "cold shutdown" is achieved.

http://news.tbs.co.jp/20111130/newseye/tbs_newseye4890525.html The study results that were shown today are nothing more than estimates. Recently, reactor temperature did not rise as expected although the water injection rate had been reduced. The recovery work is expected to go on, as if groping one's way in the dark.