Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[tsutsuji]

http://www.asahi.com/national/jiji/JJT201106240113.html although the valves are supposed to be OK this time, the absorption factor at the Kurion facility is not improving (only 1/10). Together with the Areva system, the decontamination factor for the whole facility is OK, but Tepco wants to investigate the problem.

Where it lands is not visible on the video.

A picture has been released : http://www.tepco.co.jp/en/news/110311/images/110624_1.jpg

 

[Borek]

The doomed flight of the T-Hawk can be seem in this video, shortly after the time marked 06:34 by TEPCO.

http://www.youtube.com/watch?v=_vrYWGPDRKg&feature=channel_video_title

8:34, not 6:34.

 

[imandylite]

T-Hawk Drone crashes into reactor unit 2 whilst sampling airborne nuclides.

I did a quick cut and cleaned things up. Also got a pick of the crash site (not much left of the drone)

https://www.youtube.com/watch?v=WZQ8w6IgFf4

 

[SteveElbows]

8:34, not 6:34.

Sorry for the confusion, I was talking about the timestamp that TEPCO have at the top of the screen, not the youtube time for this video.

Anyway, as TEPCO mentioned that this incident happened around 7am, I looked at later footage to see if the drone was spotted at any points later on on the video. There are a couple of moments where a dot is briefly visible in the right sort of place quite some minutes later, but as these are fleeting glimpses its not possible to say for sure, and it is not interesting viewing.

Im quite sad that it crashed, as I would like to know more about what is coming out of building 2 these days.

 

[SteveElbows]

Having seen more details about the temporary cover building for reactor 1, I quite like it.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110624e15.pdf

OK there are a few risks of things going wrong, but it should enable us to get a much better idea of what radioactive substances are still escaping, the opportunity to filter them, and better monitoring of things like the fuel pool.

 

[tsutsuji]

Im quite sad that it crashed, as I would like to know more about what is coming out of building 2 these days.

"Matsumoto said (...) a backup drone can take over the mission" : http://www.washingtonpost.com/world/asia-pacific/drone-helicopter-measuring-radiation-at-japanese-nuclear-plant-makes-emergency-landing-on-roof/2011/06/24/AGWDZmiH_story.html

http://www.asahi.com/national/jiji/JJT201106240113.html although the valves are supposed to be OK this time, the absorption factor at the Kurion facility is not improving (only 1/10). Together with the Areva system, the decontamination factor for the whole facility is OK, but Tepco wants to investigate the problem.

and here is the press release with the measurements : http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110624_04-j.pdf

 

[SteveElbows]

"Matsumoto said (...) a backup drone can take over the mission" : http://www.washingtonpost.com/world/asia-pacific/drone-helicopter-measuring-radiation-at-japanese-nuclear-plant-makes-emergency-landing-on-roof/2011/06/24/AGWDZmiH_story.html

Aha, I see that article also describes how the Japanese robot has failed on its first mission.

To be honest I am not too shocked at this news, because that robot looks rather fragile to me, like a prototype that is not ready, especially in the video they posted of it which shows it doing the things it has apparently failed to do properly today.

 

[Orcas George]

Having seen more details about the temporary cover building for reactor 1, I quite like it.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110624e15.pdf

OK there are a few risks of things going wrong, but it should enable us to get a much better idea of what radioactive substances are still escaping, the opportunity to filter them, and better monitoring of things like the fuel pool.

I do not agree. The design criteria for the structure is 25m/sec which works out to 55mph -- which I consider wildly optimistic for sheets of plastic blowing in the wind, but which is still far too low.

Considering emergency counter measure as in service period with regard to the calculation of wind pressure we adopted lowering wind velocity in recurrance interval of 10 years. The wind velocity is above the average maximum wind velocity 17m/sec..

They admit that they chose a wind velocity based on what the structure was claimed to support rather than what the actual wind at the site was and then fudge the matter by claiming that the average maximum wind nearby is 17m/sec (38mph) which gives them a good safety margin. Since it is an emergency measure somehow that makes it work. What they don't want to tell you is the maximum recorded wind at the site, which is really what you have to design to. I'm willing to bet it is more than 38mph.

So they are basing their design for a three-story plastic structure on an exposed coastline in a typhoon zone on an assumption that somehow the maximum wind they will ever see is 38mph. Building codes would be much easier if you could build to the average conditions rather than the maximum ones. Heck, I probably wouldn't even need insulation in my house if the codes worked that way!

I do not see anywhere in the report where they calculate the stress on the structure from the difference in air pressure (either positive or negative) due to the air treatment system and the gas expansion from radioalisis.

 

[~kujala~]

Analysis of the spent fuel pool water at reactor 1 is out:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110624_02-e.pdf

Numbers are a fair bit lower than for reactor 3 pool ( http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110510e12.pdf )

But way, way higher than for reactor 4 pool ( http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110509e3.pdf )

Just for a reminder... They also measured the SFP #2 skimmer surge tank (and also corrected the values of April 12th sampling of the unit #4 SFP?):
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110531e19.pdf

I am making here a small comparision for a starter (as Bq/cm3):
Isotope; SFP 1; SFP 2; SFP 3; SFP 4
Cs134; 12,000; 98,000; 140,000; 130
Cs137; 14,000; 93,000; 150,000; 140

I think it's not that simple, it can be many routes of contamination for a single pool and not the same routes for each of them?
Anyway, they didn't spray seawater into the SFP #1 (afaik), so that's one thing to make it easier.

 

[LabratSR]

TEPCO likely failed to vent No. 1 reactor at tsunami-hit nuclear plant

http://mdn.mainichi.jp/mdnnews/news/20110624p2a00m0na011000c.html

 

[desertlabs]

Okay. I'm hesitant to ask this, but what are the significance of these levels which are so "old"? What is the context with respect to today? Why isn't the power curve more steep? Am I unrealistically impatient? An intellectual exercise is great, but do we have enough information in the www to generate answers to basic questions?

I have been seeing really bizarre nuclear apologist rants and I am worried people at large may be slipping into another dimension. Trying to stay grounded.

 

[etudiant]

I do not agree. The design criteria for the structure is 25m/sec which works out to 55mph -- which I consider wildly optimistic for sheets of plastic blowing in the wind, but which is still far too low.




They admit that they chose a wind velocity based on what the structure was claimed to support rather than what the actual wind at the site was and then fudge the matter by claiming that the average maximum wind nearby is 17m/sec (38mph) which gives them a good safety margin. Since it is an emergency measure somehow that makes it work. What they don't want to tell you is the maximum recorded wind at the site, which is really what you have to design to. I'm willing to bet it is more than 38mph.

So they are basing their design for a three-story plastic structure on an exposed coastline in a typhoon zone on an assumption that somehow the maximum wind they will ever see is 38mph. Building codes would be much easier if you could build to the average conditions rather than the maximum ones. Heck, I probably wouldn't even need insulation in my house if the codes worked that way!

I do not see anywhere in the report where they calculate the stress on the structure from the difference in air pressure (either positive or negative) due to the air treatment system and the gas expansion from radioalisis.

Agree entirely that a 10 minute average wind speed is pretty useless as a design spec. Gusts do the damage on sails much more frequently than average winds.
They are probably gambling that it will last for a year or so. By then, it should be less of an issue.
Of course, that supposition flies in the face of the stated plan to cover all 4 reactor buildings this way.
In any case, other than the effort diverted, it does not look to cause much harm.

 

[elektrownik]

http://www3.nhk.or.jp/daily/english/25_08.html
Interesting:

temperature near the reactor containment vessel is so high that water inside the device's pipes has evaporated.

 

[~kujala~]

Here's how my logic goes...

There should be no debris lying in the SFP #2, should there?

So condensated steam is a good candidate, as well as contaminated seawater. This a positive scenario where one assumes that fuel is still intact.

Is there any ideas how much of the 93,000 - 98,000 Bq/cm3 of Cs137/Cs134 could have come from condensated steam alone?

For the unit #4 SFP the known maximum from contaminated seawater is only 130 - 140 Bq/cm3 (Cs134/Cs137) but for the unit #2 SFP it could be more depending on where the hoses were located. Also some of cesium may have evaporated from the unit #4?

Is there any basis at this point to conclude that the role of contaminated seawater is of no significant importance for the unit #2 and #3 SFP?

 

[SteveElbows]

Today I keep seeing press stories such as this one that refer to 11000 pages of faxes that TEPCO sent, and that NISA have now published.

http://www3.nhk.or.jp/daily/english/25_01.html

I had considerable trouble finding these documents, but finally managed to find the right page:

http://www.nisa.meti.go.jp/earthquake/plant/plant_index.html

These are faxes so it is not possible for me to translate any of them using computer translation. It is easy enough to read the charts of data, which does not seem to say much that we did not already know, but I wonder if there is anything interesting in some of the notes that are written on some pages.

For example, is there anything interesting in this document which covers stuff sent on March 15th?

http://www.nisa.meti.go.jp/earthquake/plant/1/230617-1-5.pdf

 

[SteveElbows]

Okay. I'm hesitant to ask this, but what are the significance of these levels which are so "old"? What is the context with respect to today? Why isn't the power curve more steep? Am I unrealistically impatient? An intellectual exercise is great, but do we have enough information in the www to generate answers to basic questions?

I have been seeing really bizarre nuclear apologist rants and I am worried people at large may be slipping into another dimension. Trying to stay grounded.

Not 100% sure what you mean. With a nuclear disaster such as this, we may expect to wait years to learn true answers to some of the biggest questions, and some may never be answered fully.

The pool contamination figures were brought up now because they just published results for reactor 1 pool, and it can be useful to compare these against older results from other pools. Like most of the data we have, it is not enough to form strong conclusions, as several possibilities exist which could explain the results.

Not sure what you mean about power curve, or what nuclear apologist rants you are talking about.

 

[Jorge Stolfi]

I suppose that the contamination of water in the basements and SFPs is being measured near the surface, is this correct?

But then the measurements will be meaningful only for metals whose salts are generally soluble, like cesium;as well as forr elements with very soluble anions, like the halogens. Most other elements should tend to precipitate out. Since there is little circulation in those spaces, they should accumulate as a layer of sludge (or dirtier water) at the bottom of the liquid.

Is this likely to be happening? Could it become a problem for the decontamination efforts?

 

[robinson]

There is no doubt the heavy elements are going to be a huge problem.

 

[MikeIt]

http://www3.nhk.or.jp/daily/english/25_08.html
Interesting:

BWR water level instruments sense differential pressure between a reference leg (which taps off the upper part of the RPV and is filled and held at a constant level by steam condensing in the leg) and a variable leg (which taps off the lower part of the RPV). The article is trying to say that the drywell temperature near the reference leg is so high that the water in the reference leg has either flashed to steam or evaporated out of the reference leg. As a result, the water in the reference leg is gone or much lower than when the instrument was last calibrated. This usually tends to produce an inaccurate, higher than actual water level indication. Depending on the configuration of the instrument runs, it is possible in some BWRs for certain water level instruments to show an increasing RPV water level trend when actual RPV water level is below the variable leg instrument tap. (Not a good thing.) Such was the case with 1F1 where the RPV water level data showed the core partially submerged when actual water level was downscale and probably below the bottom of active fuel. They will likely discover the same thing in 1F2 and 1F3.

 

[jim hardy]

Indeed that's how it works - zero differential means the vessel is full.

that's the nuisance of getting the drywell real hot and quickly depressurizing vessel , the reference leg may empty itself and take out that important indication. With loss of power there was no drywell cooling so it'd begin an asymptotic approach toward vessel temperature in there.
empty reference leg = false high indication = fail unsafe because you'd think you had water.
... only clue would be when you add water and the indicator doesn't respond because true level is below lower tap... and you might logically think from the high meter reading it's above the top tap instead. ever had a gas gage stuck on full?

poor guys trying to figure all this out by flashlight... they showed true grit.

however - it is easy to lose the reference leg by other means.
in this image
http://www.tepco.co.jp/en/news/110311/images/110604_10.jpg
the three blue handles above center gage are the isolation valves, left and right ones go to the vessel taps.
Middle one is the bypass around gage, called 'equalizing valve', and opening it while other two are open let's the reference leg drain into lower tap. Happens to a lot of inexperienced instrument techs. Sequence is important.
Sometimes you'll get a piece of grit in the equalizing valve's seat and it'll leak which drains the reference leg. At operating pressure the condensing steam can keep up with a real small leak in that valve. As reactor cools down(or drywell heats up) it no longer can.




one wonders how they plumbed up the fire trucks to re-flood, and what they used to judge how much water to inject.
AF.mil has some pics of US GI's machining parts for them but the captions aren't definitive enough to know what the parts were for.

 

[elektrownik]

I found some document from tepco in english, I can't find orginal version, maybe there is translation error: http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e12.pdf
There is: "status of the plant at the time of earthquake" and for unit 4: "maintenance (removing fuel)" So this is translation error ?
Also for unit 6: "rpv closed" if it is closed should it be at atmospheric pressure like now ?

 

[joewein]

I found some document from tepco in english, I can't find orginal version, maybe there is translation error: http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e12.pdf
There is: "status of the plant at the time of earthquake" and for unit 4: "maintenance (removing fuel)" So this is translation error ?
Also for unit 6: "rpv closed" if it is closed should it be at atmospheric pressure like now ?

They must have meant "fuel removed".

The definition of cold shutdown is below 100 deg C and at atmospheric pressure (because there's no steam at that temperature).

 

[joewein]

I suppose that the contamination of water in the basements and SFPs is being measured near the surface, is this correct?

But then the measurements will be meaningful only for metals whose salts are generally soluble, like cesium;as well as forr elements with very soluble anions, like the halogens. Most other elements should tend to precipitate out. Since there is little circulation in those spaces, they should accumulate as a layer of sludge (or dirtier water) at the bottom of the liquid.

Is this likely to be happening? Could it become a problem for the decontamination efforts?

I think your assumptions are correct, Jorge. They can only take a sample in an accessible spot, probably near one of the stairwells.

The less soluble salts will be more concentrated in sludge at the bottom, but overall there should be less of them in the basement because they would have been more likely to stay inside the containment to start with, simply because they were less soluble.

Most likely hot water, especially pressurized hot water (> 100 deg C) will leach out some less soluble salts from the fuel or from condensate on the containment walls, like water in a coffee maker or espresso machine. The water leaks outside via damaged seals and as it cools off in the basement some of the salts precipitate out as solubility drops with temperature.

For the water decontamination efforts that sludge is not an immediate problem, since the primary objective is to prevent contaminated water from overflowing, which can be achieved if the overall quantity is reduced. Once solubles are separated out, the cleaned water can be reused or evaporated.

In the more long term, once the goal becomes to decontaminate the buildings and pack up their radioactive inventory into containers for transport to a permanent storage site, then any sludge would have to be removed too. At that stage there might be demand for a good steam cleaning robot for the Fukushima basements.

In the near term I see little need for any human to venture into those basements.

 

[ceebs]

Aha, I see that article also describes how the Japanese robot has failed on its first mission.

To be honest I am not too shocked at this news, because that robot looks rather fragile to me, like a prototype that is not ready, especially in the video they posted of it which shows it doing the things it has apparently failed to do properly today.

So is this crash down to equipment failure? or radiation effected electronics?

 

[elektrownik]

And here: http://www3.nhk.or.jp/daily/english/26_11.html I think that they could find something not so expensive like boric acid to prevent corrosion

 

[zapperzero]

They could add any acid, but they need the boron to prevent criticality, should their worst-case scenario described in the article (racks failing due to corrosion) come true.

 

[elektrownik]

They could add any acid, but they need the boron to prevent criticality, should their worst-case scenario described in the article (racks failing due to corrosion) come true.

But why they weren't doing this until today ?

 

[Atomfritz]

But why they weren't doing this until today ?

They took water samples in May.
Then they started to add hydrazine to the water to avoid corrosion.
Now they are adding boric acid again.
I am no chemist and cannot say anything about the behavior of the neutron absorbers in the SFP.

Could it be possible that they found out that there could be potential danger of the neutron absorbers dissolving in the basic water?

If this is the case then the boron acid added again could be not only for the (official) reason to avoid fuel leaks.
It could be also to avoid criticalities when the thinning of the neutron absorbers reaches a critical threshold.

And here: http://www3.nhk.or.jp/daily/english/26_11.html I think that they could find something not so expensive like boric acid to prevent corrosion

Just assuming that other acids would be used to neutralize the water to around pH 7.
Couldn't then be a risk that if boric acid is added a later time when a criticality should happen, that it would be less efficient? Maybe due to boron precipitating out instead of staying in solution?

And, consider debris sludge and pockets also which can hamper water circulation. In case of a sudden criticality there could be a problem to get boron to critical places quickly enough. So it might be better to have it already there prophylactically.

And, then the compatibility question in regard to water decontamination.
I suppose this would be somewhat more difficult if you have not only boric acid in the water but a full cocktail of acids.

Just my unqualified thoughts.

 

[elektrownik]

@up I think so also, maybe they know more, maybe they detected some proofs of recriticality in unit 3 sfp... who know

 

[Borek]

My first thought is that it is just a KISS principle. Water is highly alkaline - that's bad, so they have to neutralize it. Boric acid is probably a thing they already have at place, it will serve multiple purposes, it is already everywhere, so they will have to deal it anyway - does it make sense to use something else and add another unknown into the equation?

 

[Jorge Stolfi]

They took water samples in May. Then they started to add hydrazine to the water to avoid corrosion. Now they are adding boric acid again.

Somewhere earlier in this thread it was said that hydrazine (which is quite toxic) is added to purified water in working reactors to fight corrosion, but in very small amounts --- parts per million or so. If that is correct, it would not make much difference to the pH.

Boric acid was initially used as a source of neutron-absorbing boron to prevent criticality. Whether it is now being added for that reason, or to adjust the water's pH, the amounts needed must be much larger. I recall that early on Areva shipped to Fukushima several tons of the stuff, enriched for boron-10. (Presumably they used boric acid at the beginning, rather than some other boron compound, because it is soluble, fairly non-toxic, and contains no extra elements -- only H and O. Now they may be using it simply because it is a mild harmless acid already at hand).

However, I cannot imagine what could have made the saltwater in the basement alkaline. Perhaps reaction between the salt and reactor metals, like steel and zirconium?

 

[Calvadosser]

(snip)

However, I cannot imagine what could have made the saltwater in the basement alkaline.

(snip)

All that radioactive cesium?

 

[joewein]

TEPCO found that the water in the pool had turned strongly alkaline, with its PH level reaching 11.2. The leaching of calcium hydrate from the debris is believed to be the cause.

I guess this is because while the concrete of the pool is protected by a steel liner and hence should not come into contact with the hot pool water, any bits of concrete knocked into the pool by the explosion will gradually dissolve.

I wonder when they first tested the pH of the pool water.

Aluminium certainly doesn't take very well to being immersed in strongly alkaline liquids. Not only does it quickly corrode the aluminium, it can also produce large amounts of hydrogen (as a teenager I used to fill balloons with hydrogen made from aluminium foil dropped into bottles filled with sodium hydroxide solution).

 

[joewein]

However, I cannot imagine what could have made the saltwater in the basement alkaline. Perhaps reaction between the salt and reactor metals, like steel and zirconium?

Unless I missed something, weren't they only talking about the spent fuel pool?

However, if it happens with calcium from concrete bits in the SFP, one should it expect it to happen in the basement too. In fact, there should be a lot more concrete in permanent contact with water in the basements than in the fuel pools. Hopefully they'll test the pH in the basements too.

 

[MadderDoc]

And here: http://www3.nhk.or.jp/daily/english/26_11.html I think that they could find something not so expensive like boric acid to prevent corrosion

Certainly any acid could be used to neutralize an alkaline solution, but using boric acid has the added benefit of tending to produce a buffered solution at about pH 7-9, right where you'd want a solution containing aluminium to be in order to avoid corrosion.

 

[Borek]

However, I cannot imagine what could have made the saltwater in the basement alkaline.

All that radioactive cesium?

Radioactivity doesn't matter. Cesium per se is not alkaline, and it doesn't react with water as it was never metallic in the first place. Could be it was present as oxide in the uranium dioxide pellets, that could produce hydroxides when reacting with water, but it also requires broken fuel rods - my understanding is that so far we have no idea if they were broken or not.

No idea what they mean by "calcium hydrate", as far as I can tell there is no such compound.

 

[joewein]

No idea what they mean by "calcium hydrate", as far as I can tell there is no such compound.

Presumably calcium hydroxide.

 

[Fine]

However the following document does contain some pictures that I don't think I've seen before, outside reactor 3 building (demolished the damaged vehicle entrance tunnel by the looks of it). And also, joy of joys, a view of the site looking down from the top of the slope where the webcam is, so that we can actually see the ground around the reactors and further to the left of reactor 1 than normal. Its not very high res within this pdf, but it still gives me a much improved sense of the state of a good chunk of the site these days. (that photo, or rather 3 photos stitched together, is on page 13)

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110617e4.pdf

There is a very interesting intesting picture of reactor 3 on Pg 7. what is the semi-circular structure/debris toward the upper left of the photo ? A reactor pit plug ? Sorry for the speculation but I sure would like to have some expert eyeballs and opinions on this.

 

[SteveElbows]

There is a very interesting intesting picture of reactor 3 on Pg 7. what is the semi-circular structure/debris toward the upper left of the photo ? A reactor pit plug ? Sorry for the speculation but I sure would like to have some expert eyeballs and opinions on this.

Well that photo is fairly old now, and so this question has come up before. Although it is hard to make out too much in that photo with certainty, it seems pretty likely that the concrete you see is simply far too small to be a reactor plug.

 

[Fine]

I know it is old but I have been carefully following the threads and have not seen any discussion at all about it. If it isn't a plug what is it ? I still think this the best view of reactor 3 that I have seen.

 

[Orcas George]

I would guess that it has something to do with the seawater that they were pumping (did they pump seawater into SFP #3?) Not the seawater itself although it is more alkaline than pure water, but all of the sea creatures that they sucked up at the same time. Crabs excrete ammonia, for example.

The plankton filter in front of an RO system gets really nasty (and puts a foul taste in the water) if you don't change it often. If they have tons of plankton, seaweed, brine shrimp, etc. in the bottom of the pool then chemistry changes are not surprising.

I feel like they are a juggler trying to hold up a bunch of spinning plates into the air.

By the way, have they started treating the water yet? I thought it was urgent...

 

[ManuBZH]

By the way, have they started treating the water yet? I thought it was urgent...

According to this news report: http://www3.nhk.or.jp/daily/english/26_16.html , they have processed 5400t of water already and aim to start their "full-scale operation" tomorrow. Then, we'll see if the system is stable on the long-run...

 

[tsutsuji]

According to this news report: http://www3.nhk.or.jp/daily/english/26_16.html , they have processed 5400t of water already and aim to start their "full-scale operation" tomorrow. Then, we'll see if the system is stable on the long-run...

The 5400 tons are decontaminated, but not all of it is desalinated. http://www3.nhk.or.jp/news/html/20110627/t10013780371000.html says 600 tons have been desalinated.

http://www.chunichi.co.jp/s/article/2011062690220051.html : Between June 20th and June 26th, 5178 tons were decontaminated at a 49.7 ton/hour flow. But the system was kept idle during a total of 38 hours of flushing. As a result, the average flow was 863 tons per day, falling short of the originally planned 1200 tons per day.

 

[elektrownik]

Can anyone explain me why unit 5 plots are so strange ? It was normal, but something changed between 6/24 and 6/25: http://www.tepco.co.jp/nu/fukushima-np/f1/images/11062612_temp_data_56u-j.pdf

 

[MadderDoc]

Can anyone explain me why unit 5 plots are so strange ? It was normal, but something changed between 6/24 and 6/25: http://www.tepco.co.jp/nu/fukushima-np/f1/images/11062612_temp_data_56u-j.pdf

It looks to me like the sfp previously was cooled by a system shared with the RPV, and has now been switched to use its own cooling system.

 

[MadderDoc]

There is a very interesting intesting picture of reactor 3 on Pg 7. what is the semi-circular structure/debris toward the upper left of the photo ? A reactor pit plug ? Sorry for the speculation but I sure would like to have some expert eyeballs and opinions on this.

Many unit 3 photos from many angles have been scrutinized by many people. The chance of a reactor pit plug sized and shaped object lying about somewhere in unit 3, with relatively free view to it as suggested by the photo your are referring to seems very small.

 

[tsutsuji]

Can anyone explain me why unit 5 plots are so strange ? It was normal, but something changed between 6/24 and 6/25: http://www.tepco.co.jp/nu/fukushima-np/f1/images/11062612_temp_data_56u-j.pdf

I don't remember if he was talking about unit 5 or unit 6, but the other day, if my understanding is correct, Mr Nishiyama of the NISA said that there was no need any longer to share the same cooling system between the spent fuel pool and the reactor. So from now on, the spent fuel pool and the reactor will be cooled simultaneously instead of flip-flopping.

For unit 5 http://www.nisa.meti.go.jp/english/press/2011/06/en20110626-1-2.pdf page 12 says "June 24 16:35 Cooling of the Spent Fuel Pool was started using the Fuel Pool Cooling and Clean-up System."

 

[elektrownik]

It looks to me like the sfp previously was cooled by a system shared with the RPV, and has now been switched to use its own cooling system.

[STRIKE]But there is change in rpv plot for unit 5 also ?[/STRIKE]
@up I see now, thanks !
I found some new contamination data (english): http://www.acro.eu.org/RAP110620-OCJ%2801%29-v1.pdf

 

[MadderDoc]

Unless I missed something, weren't they only talking about the spent fuel pool?

However, if it happens with calcium from concrete bits in the SFP, one should it expect it to happen in the basement too. In fact, there should be a lot more concrete in permanent contact with water in the basements than in the fuel pools. Hopefully they'll test the pH in the basements too.

The surface-near layer of concrete structures weathers and becomes less alkaline as it reacts with the carbondioxide of the atmosphere, while concrete bits produced by the explosion would feature fresh concrete surfaces which are considerably more alkaline.

 

[joewein]

I don't remember if he was talking about unit 5 or unit 6, but the other day, if my understanding is correct, Mr Nishiyama of the NISA said that there was no need any longer to share the same cooling system between the spent fuel pool and the reactor. So from now on, the spent fuel pool and the reactor will be cooled simultaneously instead of flip-flopping.

The diagram indicates that in unit 6, the same cooling system is still being shared between the RPV and the fuel pool, as you can see the temperature of one going up whenever the other is going down.