Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[jlduh]

I think i downloaded some pdf document related to geological studies in F-1 weeks ago, they are in japanese and also shows the location where they bored some 300m below ground level around the npp, there are a lot of pages but i don't understand the subject and the my proficiency in the language is not that good.

Maybe we could try an automatic translation, if you can attach or upload the doc?

I found on tepco site these docs explaining the kind of survey they did:

http://www.tepco.co.jp/en/press/corp-com/release/betu07_e/images/071105e1.pdf

http://www.tepco.co.jp/en/press/corp-com/release/betu07_e/images/071127a.pdf

http://www.tepco.co.jp/en/press/corp-com/release/betu07_e/images/070817e2.pdf

The results would be VERY interesting...

 

[tsutsuji]

They say they did new geological surveys at Fukushima, they were due to June 2009 i think. But i can't find these studies.

Here are some various Fukushima Daichi earthquake safety related reports

http://www.nisa.meti.go.jp/shingikai/107/4/1/001/a1-2-4.pdf (13 May 2008)

http://www.nisa.meti.go.jp/shingikai/107/4/1/005/a5-2-1-1.pdf (31 July 2008)

http://www.nisa.meti.go.jp/shingikai/107/4/1/019/a19-2-1.pdf (15 May 2009)

http://www.nsc.go.jp/senmon/shidai/taishin_godo_WG1/taishin_godo_WG1_09/siryo-9-1-1.pdf (22 May 2009)

http://www.pref.fukushima.jp/nuclear/info/pdf_files/100714-13.pdf (22 February 2010)

http://www.tepco.co.jp/nu/material/files/ka10070602.pdf (6 July 2010)

http://www.pref.fukushima.jp/nuclear/info/pdf_files/100805-1.pdf (August 2010)

Speaking about post-2007-quake retrofits, does anyone know the location of the newly built (summer 2010) "Seismic isolated building" within the Fukushima Daichi plant ?

 

[mamoru]

Speaking about post-2007-quake retrofits, does anyone know the location of the newly built (summer 2010) "Seismic isolated building" within the Fukushima Daichi plant ?

[URL]http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/f1_lmap-e.gif[/URL]

[URL]http://www.tepco.co.jp/nu/f1-np/pavilion/images/mensin_2.jpg[/URL]

 

[mamoru]

Concerning Tepco reassessment of seismic safety data which was required after the Kariwa plant event, read this Tepco communication for shareholders:

http://www.docstoc.com/docs/41609714/Creating-Disaster-resistant-Nuclear-Power-Stations

They say they did new geological surveys at Fukushima, they were due to June 2009 i think. But i can't find these studies.

They should be called something like "Fukushima Daiichi Units Geological Survey Seismic Safety Assessment"...

Maybe a japanese member could try to find this by googling some of these key words in japanese?

"www.tepco.co.jp/nu/material/files/fg09062401.pdf"[/URL]

 

[Jorge Stolfi]

Ground shaking is amplified in soft sediments and dampened in hard rock...

Not to defend TEPCO, but we must keep in mind that the safe design criteria for buildings of this type are diferent from those of ordinary apartment/office buildings. I recall reding the words 'floating foundation' somewhere, perhaps in a TEPCO document. Instead of anchoring the building to the underlying rock, or driving deep piles into the ground, the idea is to build the basement as a big stiff box that 'floats' on the soil/rock below. That way, if the ground cracks, deforms, liquefies, or shakes too much, the building may move or sink a bit but is less likely to crack or collapse.

In any case, building on bedrock (granite or other volcanic rock) will not help if the rock cracks and shears during a big earthquake. (Recall that the cause of the earthquake was a 500 km long crack that caused two pieces of that 'solid bedrock' to slide tens of meters past each other.) Anchoring the building to the bedrock seems a rather bad idea in that case.

According to the blueprints, the thickness of the reactor building walls increases from top to bottom. The service room wall panels are perhaps 30--50 cm thick and thinly reinforced; but 2nd floor walls seem to be 1.2 meters thick, basement walls are at least 1.5 meters thick, and the basement floor slab is 4 meters thick. (That by itself would explain why the explosions did very little visible damage below the 3rd floor.)

Thus I am willing to believe that the buildings of the reactors are pretty safe against earthquakes, and suffered no damage on 11/mar. (That does not apply to the reactors proper and other equipment, of course) I have yet to see a picture of any crack or other damage to those buildings that was caused by the earthquaque itself.

In particular, I do not see any possibility of their lower levels sinking, tilting or collapsing to any significant extent, even if they were resting on top of soil rather than rock. Thus the tilting of #4 that is supposedly visible in the webcam --- and only there --- can only be an optical illusion or artifact.

The type of the underlying rock could matter for the safety of the equipment inside (mudstone results in stronger shaking than granite, it seems) and for the water leakage problem (mudstone probably has more cracks and pores).

Of course, some parts of the upper floors that were damaged by the explosions are now visibly unsafe, even against minor quakes or storms. (Could a tornado blow away the loosely-hanging wall panels of #3 and #4?)

 

[Jorge Stolfi]

Hey Madder, the chances of a ballistic object landing in that configuration, parallel with anything and just a foot away from a wall,... and not deforming it's shape are quite frankly near zero.

If the object fell in that part of the roof, it probably rolled about until it hit the wall. That would account for its position.

As for deformation, it depends on where it came from and how sturdy it is. For example, in the Air Photo Service pics one can see a large dark gray metal box that was ejected from Unit #3 and was lying on the ground, some 30 meters southwest of the building --- apparently intact.

 

[Rive]

This link shows a basic layout of the level circuit. 2 taps into the vessel connected to a differential pressure (DP) cell and transmitter. http://www.pbnc2010.org.mx/pdfs/technical/tuesday/14.00_ModelingLevelInstrumentation.pdf

The released TEPCO photo shows the techs at a whole panel of DP cells.
I don't think anyone knows for sure where these taps actually sense level in the RPV. Is the bottom tap in the shroud region or acually in the vessel itself (ie below the downcomer)??
It is also not clear if they blew back the sensing lines to make sure they were clear of any obstruction. They also should have pumped water back up to the upper condensate pot to ensure the reference leg was full. Without doing these 2 steps - the readings may still be wrong!

Well, a theoretical question. If it's not possible to trust those DP cells as water level indicators can they be turned to pressure meters of the RPV relative to the atmospheric pressure?

 

[Borek]

big stiff box that 'floats' on the soil/rock below. That way, if the ground cracks, deforms, liquefies, or shakes too much, the building may move or sink a bit but is less likely to crack or collapse.

In particular, I do not see any possibility of their lower levels sinking, tilting or collapsing to any significant extent, even if they were resting on top of soil rather than rock. Thus the tilting of #4 that is supposedly visible in the webcam --- and only there --- can only be an optical illusion or artifact.

The way I see it - if they float as rigid boxes, it is quite possible they can tilt without damage.

 

[rowmag]

ROWMAG, read my updated post as I provide a second english link in the "safety" section:

https://www.physicsforums.com/showpost.php?p=3306751&postcount=7594

Thanks, but the Japanese site does not mirror the English one at all. Really everything has been stripped away and replaced by disaster-related information.

 

[Jorge Stolfi]

The chunk has a very different appearence than on the other pictures I posted, where it looks clearly to be concrete, on this one it's not so clear but the rendering of the picture is bizarre. What is really surprising is the small amount of damages around or under it, like if it was delicately put there!

If it is the chunk I am thinking, then it is clearly one of the service floor wall panels --- some 5-7 meters across but perhaps only 30-40 cm thick. The following picture shows it clearly, and shows that it did bend the metal railings above the pipes. If it came from #4, its position and the lack of damage to the pipes are easy to explain. If it came from #3, it may have hit something else (such as the wall of #4 or of its turbine building) before landing there.

http://www.ic.unicamp.br/~stolfi/EX...isc4/drone/hires/aerial-2011-3-30-1-11-12.jpg
http://www.ic.unicamp.br/~stolfi/EX...isc4/drone/hires/aerial-2011-3-30-0-20-11.jpg

 

[tsutsuji]

IEEE Spectrum interviewed Tsuneo Futami, former superintendent of the plant, from 1997 to 2000 :

second concern is the strength of spent fuel pools’ reinforced concrete. Usually we have to keep the temperature inside the spent fuel pools under 60 degrees Celsius or so. A high temperature decreases the strength of reinforced concrete.
http://spectrum.ieee.org/tech-talk/...ale-of-the-accident-was-beyond-my-imagination

...

thanks

 

[ottomane]

I am following this thread now for a long time and I have to thank you all for the fantastic work done. I learned a lot about reactors and the thinks happening in Fukushima.

During the last days the situation has changed. Many expected this before, but now it is official: R1 and probably also R2 and R3 had full meltdowns with at least the core of R1 burning holes in and/or leaving the RPV (I guess the same must have happened to R2 and R3 too).

http://www.bbc.co.uk/news/world-asia-pacific-13423230"

Based on these news (to TEPCO this must be very old news) I would like to know what you think may happen now. Some things I read today in the net:

1. We may experience a China Syndrone as written by Time.com. Core will explode when hitting ground water soon. Or burns deep into Earth's crust triggering a volcano (wtf! I cannot believe this could happen).
2. The core drops at some day into the 3000t of water in the basement causing an explosion of several megatons distributing the core in a wide area. Maybe Japan (or more) will be inhabitable afterwards.
3. The core will stay in the basement and slowly cool down. H2 explosions are the only threat.
4. What else? What do you think will happen now?

From my understanding of the building design, the "lost" water is not directly located under the RPV and there is a concrete wall which may stop the corium from dropping into the basement. What do you think?

I know this is pure speculation, so please excuse me if this is the wrong place to ask. But finally we got some information we can use to extrapolate potential future scenarios.

 

[gmax137]

Siting plants at higher levels would not help for that aspect of a tsunami. Are power plants designed to handle the lows?

The cooling inlets may fall dry for 15 minutes, due to distant earthquakes that would not scram the reactor. Can a reactor at full power survive that?

Very interesting question.
The heat of vaporization is about 2000 joules/gram. So a 1 gigawatt plant at full cry would need to vaporize 3 gigajoules worth of water every second, or about 1.5 million grams of water, about 1.5 tons worth. The 15 minute dry spell would vaporize 1350 tons of water. That seems a manageable amount, about equal to the water quantity in SFP 4. No idea if the reactors are designed to have that much reserve capacity though.

Yes. Assuming loss of offsite power. Diesels will be tripped if they try to satrt without cooling water which will protect them during the drawdown period. The high pressure DC systems can inject cooling water for long enough for the drawdown period. At Fukushima that is the isolation condenser at unit 1 and the RCIC and HPCI systems at the other plants. If the water returns and the diesels are undamaged from the tsunami they can be started and then the low pressure AC systems will also be available. The Fukushima event made this scenario impossible due to failure to protect safety systems from the tsunami or from flooding.

An important thing to recognize is that the reactor would trip regardless of the distance to the earthquake - if the sea recedes from the intake area, then the large circulating water pumps that push the normal cooling water through the condenser would run dry, the condenser pressure would increase, and the turbine would trip. This loss of load would lead to a direct reactor trip, or if that failed to occur, then an indirect trip on high pressure in the reactor (among others). So, there is no need to boil off the full reactor power for more than a few seconds.

 

[SteveElbows]

Are you talking about the graph page 41/66 of http://www.tepco.co.jp/nu/fukushima-np/plant-data/f1_8_Parameter_graph.pdf ?

3 data are between 8 and 12 MPa, but it is difficult for me to read the date more precisely than sometime between March 18th and March 23rd.

I am interested in any interpretation of what happened at any unit late on March 20th or early in the morning on March 21st, because I am curious about the radioactivity peak recorded in Mito at 6 AM on the morning of March 21st, as in most cities in Eastern Japan on that date, which I believe is also connected to the "don't give tap water to babies" crisis in Tokyo during the following days (http://www.guardian.co.uk/world/2011/mar/23/tokyo-water-unsafe-infants ).

My previous posts on that topic :
https://www.physicsforums.com/showthread.php?p=3258585#post3258585 (with Mito 6 AM March 21st peak attachment)
https://www.physicsforums.com/showthread.php?p=3258806#post3258806 (about the gap in Tepco data)

For what it's worth, I posted about Kenichi Ohmae's somewhat isolated view of black smoke being something serious at https://www.physicsforums.com/showthread.php?p=3229089&highlight=Ohmae#post3229089

You can see the data in table form, where it is easy to read the exact values around March 21st.

However there is a problem. Yesterday Tepcos links to modern graphs, tables of data, and csv files did not just contain very recent data like they normally do, they were much larger and contained data going all the way back to before the 20th march. But today the same links have returned to their normal state, just showing data from recent days in may. So I cannot give you links to this information, maybe someone can reupload the data or find different urls?

Here is my post where I talked to someone about this new data yesterday, but as I said the links in it don't give the info I was talking about anymore :(

https://www.physicsforums.com/showpost.php?p=3305309&postcount=7502

In recent messages here I have been disagreeing with someone else about whether the smoke events of 21st march may be responsible for the increased radiation detected far away just a few hours later. I was blaming the weather. Well, I do not mean to sound so certain about this at all. Its only that I do not want to rule the weather out completely, because I checked messages I posted at a different forum around 19th-20th march to remind myself what was being said then. Stories were already appearing in the press about food and water contamination by the 19th march. And I posted messages with concern about the weather that was coming.

For example on March 19th at 21:53 JST I said on another forum:

I don't like the weather forecast and plume prediction models for the days ahead. It looks like wind is likely to be taking stuff inland and there is also rain for many places, especially on Monday. Will have to wait for newer readings from further afield to see if this shows up, certainly expect it to if any significant quantity of stuff is still escaping into the sky, which seems kinda likely.

Also, when I look at radiation data from the Fukushima plant itself, there had been spikes on dates such as 18th, so we should probably not be looking at the march 21st events in isolation. Its been a while since I looked at the radiation data from this time though, so I will look again soon to see if I have forgotten something.

 

[SteveElbows]

Many expected this before, but now it is official: R1 and probably also R2 and R3 had full meltdowns with at least the core of R1 burning holes in and/or leaving the RPV (I guess the same must have happened to R2 and R3 too).

Based on these news (to TEPCO this must be very old news) I would like to know what you think may happen now. Some things I read today in the net:

1. We may experience a China Syndrone as written by Time.com. Core will explode when hitting ground water soon. Or burns deep into Earth's crust triggering a volcano (wtf! I cannot believe this could happen).
2. The core drops at some day into the 3000t of water in the basement causing an explosion of several megatons distributing the core in a wide area. Maybe Japan (or more) will be inhabitable afterwards.
3. The core will stay in the basement and slowly cool down. H2 explosions are the only threat.
4. What else? What do you think will happen now?

From my understanding of the building design, the "lost" water is not directly located under the RPV and there is a concrete wall which may stop the corium from dropping into the basement. What do you think?

I know this is pure speculation, so please excuse me if this is the wrong place to ask. But finally we got some information we can use to extrapolate potential future scenarios.

If you follow thread for a long time then I am a bit surprised you have not read plenty here about China syndrome and some of the other doomsday core scenarios. The very silly China syndrome is almost universally laughed at, but other things like criticality, and how far the core may already have fallen are still open to debate.

Should also note that meltdown is not a precise technical term, so means different things to different people. Official story is still only at the stage where the fuel has all melted, but still remains in the reactor pressure vessel (even though it has made some holes in it). You are missing the next stage from your list, the core next has to fall into the containment vessel, and then melt through the containment vessel, before it gets to the concrete that you speak of. Until we learn more about how much of the core may have left the reactor pressure vessel, we should not skip ahead to thinking of it being in the basement.

Be especially careful with term 'full meltdown' because to some people full just means all fuel melted, but to others it may imply full meltdown through bottom of reactor vessel & then through drywell containment.

 

[TCups]

Have the recent large volume of new data released by TEPCO shed any further light on the questions of:
1) the possible origin of the explosion of Bldg 3 (ie, origin from the primary containment?), or
2) the nature of the radiation spike resulting from the explosion of Bldg 3 (ie, sudden criticality vs. some other mechanism of apparent littoral explosion in SFP3 with gamma shine)?

Apologies in advance for a busy schedule and relative lack of mental acuity for meaningful interpretation of the large volume of technical data on the reactors that was released. Thanks.

 

[SteveElbows]

What do people think of Tepcos roadmap update then? Several english documents available here:

http://www.tepco.co.jp/en/press/corp-com/release/11051703-e.html

TEPCO have made it sound like progress is going quite well. Spin aside, and to be fair, the documents remind us that there has actually been some real progress in certain areas. I was quite surprised to see that if I have read the document properly, fuel pool 3 has water injected through normal cooling system, for example.

http://www.tepco.co.jp/en/press/corp-com/release/11051703-e.html

Aside from that the main change is what we expected, reactor 1 plan to fill containment with water not yet completely erased from the roadmap, but the recirculation of water plan now takes priority at that reactor.

 

[ottomane]

If you follow thread for a long time then I am a bit surprised you have not read plenty here about China syndrome and some of the other doomsday core scenarios. The very silly China syndrome is almost universally laughed at, but other things like criticality, and how far the core may already have fallen are still open to debate.

I know that the China Syndrome in its basic idea is nonsense, but a core melting through the basement into some meters of Earth can not be ruled out, was my understanding so far.

Should also note that meltdown is not a precise technical term, so means different things to different people. Official story is still only at the stage where the fuel has all melted, but still remains in the reactor pressure vessel (even though it has made some holes in it). You are missing the next stage from your list, the core next has to fall into the containment vessel, and then melt through the containment vessel, before it gets to the concrete that you speak of. Until we learn more about how much of the core may have left the reactor pressure vessel, we should not skip ahead to thinking of it being in the basement.

Be especially careful with term 'full meltdown' because to some people full just means all fuel melted, but to others it may imply full meltdown through bottom of reactor vessel & then through drywell containment.

But: How can the core melt holes into the RPV without falling out afterwards at least partially?

 

[Caniche]

Spiffing .AOK Just as expected:rofl:

 

[bill-green]

HEllo, Yes, the Russians learned a lot and should have been consulted earlier,... though as I understand it the mechanisms and type of cleanup needed are very different. There's a good vid on YT that says they eventually pumped Liq. N2 into the ground under the reactor,... and the evaporating N2 gas "put the fire out"
The corium there seems to have melted the sand they poured on and it cooled and solidified before reaching water table...
However the Russians had an open reactor, on which to dump sand.
I think not knowing the state of the three CORES here is the main problem... How can you know what to do... I hope modern reactors have a radiation proof camera looking at the state of the core incase this happens again.

Exactly and btw thanks for your reply.

I'm not a nuclear engineer, but read a lot about Chernobyl, after the fukishima accident and how close they/we were (Chernobyl) to an even bigger incident, that eventually transpired.

The whole of northern Europe uninhabitable type of incident. IF the corium core had hit the water table.

They took drastic measures to ensure this didn't happen and were succesful.

Is this type of incident a possible scenario in this case or is there not enough information to conclude.

Thanks

 

[bill-green]

Forgive me I should read the latest posts before posting as my questions have already been asked and somewhat answered
Thanks for all the info here and take care all

 

[MadderDoc]

Have the recent large volume of new data released by TEPCO shed any further light on the questions of:
1) the possible origin of the explosion of Bldg 3 (ie, origin from the primary containment?),

We had reasons to believe that the primary containment was, or got, involved also before we had these additional data, With the extra data we have just more reason to believe so. I do not think data can point to the origin of the explosive event. It remains a possibility that the origin could have been somewhere else, and the excursion from the primary containment was a secondary effect.

or
2) the nature of the radiation spike resulting from the explosion of Bldg 3 (ie, sudden criticality vs. some other mechanism of apparent littoral explosion in SFP3 with gamma shine)?

CAMS readings are absent in the dataset, from shortly before the explosion and until 3 days after, so we can still say nothing about the effect it may have had on those readings.

 

[MadderDoc]

>..>
I am interested in any interpretation of what happened at any unit late on March 20th or early in the morning on March 21st, because I am curious about the radioactivity peak recorded in Mito at 6 AM on the morning of March 21st, as in most cities in Eastern Japan on that date<..>

I think it is fair to say that the new data set indicates an untoward event occurring in unit 3 about 2am on March 21st. This is something we have been so far completely oblivious about. It happened during the nighttime, so there's no imagery of the event, and for the relevant period of this event, we also had no access to data until now.

 

[SteveElbows]

Have the recent large volume of new data released by TEPCO shed any further light on the questions of:
1) the possible origin of the explosion of Bldg 3 (ie, origin from the primary containment?), or
2) the nature of the radiation spike resulting from the explosion of Bldg 3 (ie, sudden criticality vs. some other mechanism of apparent littoral explosion in SFP3 with gamma shine)?

The main problem with the data and these questions is the time period that the data covers. There were 2 important releases of data in recent days.

One set filled in some gaps at various times later on, for example around 18th-19th march onwards when they managed to switch on lots of additional temperature sensors at reactor 3. We already had a lot of this data but some corrections were made and some gaps were filled in, but I think this was more notable for reactor 2 at an earlier time period, think I mentioned this yesterday.

The other set was a large quantity of data about lots of reactor parameters during the earthquake and in the hour or so that followed afterwards. So this data is from too early a period to tell you about the explosions. Its probably of most interest to those who want to see how water levels and emergency systems responded to the earthquake and tsunami. Press stories indicate that the data shows the emergency cooling at reactor 1 being turned off. But there is also data showing what things such as the RCIC were doing in the first hour or so. Problem with much of this data is we need to know what happened in the many emergency hours that followed, but this data is not available.

 

[NUCENG]

An important thing to recognize is that the reactor would trip regardless of the distance to the earthquake - if the sea recedes from the intake area, then the large circulating water pumps that push the normal cooling water through the condenser would run dry, the condenser pressure would increase, and the turbine would trip. This loss of load would lead to a direct reactor trip, or if that failed to occur, then an indirect trip on high pressure in the reactor (among others). So, there is no need to boil off the full reactor power for more than a few seconds.

Thanks, that is a good amplification on my post. I should have covered the trip.

 

[razzz]

Sure you could build a floating box with 20 foot thick walls all around, doesn't mean it can't be shaken. Do you want to put your really thick walled floating box on sand or solid rock? See the difference yet?

 

[SteveElbows]

I think it is fair to say that the new data set indicates an untoward event occurring in unit 3 about 2am on March 21st. This is something we have been so far completely oblivious about. It happened during the nighttime, so there's no imagery of the event, and for the relevant period of this event, we also had no access to data until now.

To be honest it is not true that data about this event was new to us yesterday. Plenty of people had likely seen some of this data in graph form already, although it may not have been noticed because of the larger messy temperature etc picture seen on reactor 3 graphs both before and after 21st. And the data that showed huge pressure spike from one sensor at 01:25, 01:45 and 02:30 had certainly been seen before by some people on this forum, because someone found old version of this data on the internet and posted about it here a while back, but again I am not sure if anyone noticed the pressure spike early on 21st march.

The problem I still have with this event is that there are no interesting changes to CAMS readings around this period, and simply because there was so much going on during the week of the 20th march that it is hard to know what to rule out. I have already talked about weather, and I believe tepco webcam archive images from around 20th will show that it rained on site. They had been connecting power up to various things at various reactors. When they got temperature sensors working at reactor 3 around 19th march, they saw scary temperatures and I think they implemented additional cooling within a few days. And by the end of the week we heard about basement water at reactor 3 because workers trod in it. And even now I think I am missing out plenty more things that happened that week.

Im not trying to dismiss the march 21st event, but given these things, and the fact that there also seemed to be spikes in radiation levels on site in the days before 21st, we should not try to look at this event in relative isolation. Its not so easy because as mentioned the interesting temperature measurements are unavailable until 19th march, so there is a gap in our knowledge about key early days of problems at reactor 3.

 

[I_P]

This, elektrownik, is a most interesting document. It includes far more datapoints than I have seen before, including during the most interesting moments. I've previously estimated the pressure drop within the containment during the explosion of unit 3 to be >=0.1 MPa. Based on this document, the estimate of DW pressure drop must be revised to >=0.4MPa.

It is also news to me from this document, that the RPV during the period of the 'black smoke event' on March 21st briefly peaked out at >12MPa, before it dropped back abruptly and went down to to atmospheric. My,my.

I think it is fair to say that the new data set indicates an untoward event occurring in unit 3 about 2am on March 21st. This is something we have been so far completely oblivious about. It happened during the nighttime, so there's no imagery of the event, and for the relevant period of this event, we also had no access to data until now.

At the time (20th) TEPCO said that they were considering venting unit 3 due to rising pressure. Later they said that the situation had resolved itself and they didn't need to vent... Yes, of course they didn't because the pressure dropped to atmospheric after the 'resolution', whatever it was.

 

[MadderDoc]

Hey Madder, the chances of a ballistic object landing in that configuration, parallel with anything and just a foot away from a wall,... and not deforming it's shape are quite frankly near zero.

That's a perfect non-argument. The a priori chances of its landing in _any_ particular configuration is near zero.

C'mon... it was installed there before anything happenned.

Why do you think so?

 

[SteveElbows]

But: How can the core melt holes into the RPV without falling out afterwards at least partially?

Its a good question. I am not sure if TEPCO have tried to answer it, but from everything I have read this seems to be the position they currently take on this matter, as talked about a lot in the news at the weekend.

It maybe that they actually mean that most of the core is still in the reactor pressure vessel, and that they do not exclude possibility that a little bit of it escaped.

It could be that they mean very tiny holes. Or holes that are above the level where the corium now lives, but still low enough down that water they pump in escapes.

Or some combination of the above in conjunction with the idea that the corium didnt melt the reactor vessel itself, but rather something that is normally connected to the reactor pressure vessel, but melts more easily, and leaves a gap where it was before it melted.

I assume the main reason we don't hear far more talk about the core no longer being in the reactor, is the temperature levels of the reactor vessels. They are still hot, so we assume something is still there to heat them. But this is far from my area of expertise so other people could say better about this stuff.

 

[RealWing]

Siting plants at higher levels would not help for that aspect of a tsunami. Are power plants designed to handle the lows?

The cooling inlets may fall dry for 15 minutes, due to distant earthquakes that would not scram the reactor. Can a reactor at full power survive that?

Are you referring to the pre-tsunami event where the sea level receeds - or a different event that causes a drop in sea level at the cooling water intakes?

In either scenario, if the water level drops at the cooling water intakes, the pumps will likely trip on low suction levels (if so equipped) or just stop pumping. This will quickly cause a loss of the turbine condenser cooling water flow, condenser vacuum quickly deterorates and causes a turbine trip which cross trips the reactor.

In other words, a low sea level will result in a fairly quick reactor trip. Then one has to deal with decay heat via RCIC or isolation condensers.

 

[MadderDoc]

If the object fell in that part of the roof, it probably rolled about until it hit the wall. That would account for its position.

As for deformation, it depends on where it came from and how sturdy it is. For example, in the Air Photo Service pics one can see a large dark gray metal box that was ejected from Unit #3 and was lying on the ground, some 30 meters southwest of the building --- apparently intact.

I'd be grateful if you'd point it out on a photo. To understand the explosion it is potentially useful to look at fragments ejected.

As regards the grey cylinder, in this video , right at the end, there is a brief sequence showing a firetruck spraying water to the roof, apparently in the direction of the object (two frames are attached, one before, and one after the firetruck starts spraying.

I ask forgiveness for presenting you to a video of this low quality, it is horrible, but it is the only source I know of which includes this particular sequence.

The video starts out with a brief sequence from the helicopter video shortly after the tsunami. There are better sources for this sequence.

The rest of the video appears to have been made by someone with the Tokyo Fire Department Hyper Rescue Unit. It shows bits and pieces of the emergency response at unit 3 of the Hyper Rescue Unit, around midnight between March 18 and March 19. The bits and pieces are timestamped throughout.

Parts of this sequence have better sources, but this source contains a few sequences which are not included there (in the sequence in which the photographer sits tight in the dark, in an apparently high radiation environment, with his camera showing a multitude of variations of radiation blips on the otherwise mainly dark background.)

Finally there is this brief sequence at the end, in which we see one of the trucks of the Hyper Rescue Unit spraying water to the roof close to the grey cylinder. The timestamp for this sequence is March 19 14:08.

 

[RealWing]

Well, a theoretical question. If it's not possible to trust those DP cells as water level indicators can they be turned to pressure meters of the RPV relative to the atmospheric pressure?

Not really. Level transmitters are designed and calibrated to sense a differential pressure of a few cm's or meters of water. To measure actual pressures of many Kpa or Mpa, you need a different transmitter with a much larger range.

They have several separate lines running into the reactor vessel to measure pressure via pressure transmitters..

 

[MadderDoc]

At the time (20th) TEPCO said that they were considering venting unit 3 due to rising pressure. Later they said that the situation had resolved itself and they didn't need to vent... Yes, of course they didn't because the pressure dropped to atmospheric after the 'resolution', whatever it was.

Please, can I ask of your source of this information?

 

[jlduh]

If it is the chunk I am thinking, then it is clearly one of the service floor wall panels --- some 5-7 meters across but perhaps only 30-40 cm thick. The following picture shows it clearly, and shows that it did bend the metal railings above the pipes. If it came from #4, its position and the lack of damage to the pipes are easy to explain. If it came from #3, it may have hit something else (such as the wall of #4 or of its turbine building) before landing there.

http://www.ic.unicamp.br/~stolfi/EX...isc4/drone/hires/aerial-2011-3-30-1-11-12.jpg
http://www.ic.unicamp.br/~stolfi/EX...isc4/drone/hires/aerial-2011-3-30-0-20-11.jpg

This is this one but how do you interpret this view from the south from where the thickness seems huge:

http://www.netimago.com/image_201109.html

EDIT: hummm i think i got trapped by an optical illusion when i viewed it from this side... What i interpreted as thickness was in fact length seen from perspective angle i think!

The quality of your images seems better than mine and now i see better the shape of this object which is not so thick than i saw it. Damn optical illusion