Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[jlduh]

Thank you. Thanks to your pictures, I think I could see all of them, except those for unit 4. Have they been wiped out by the tsunami, or have they already been removed for cleanup or repair ?

Their absence is conspicuous on :
http://www.netimago.com/image_202942.html


Are you sure ? Looking at that picture, it is difficult to say if the blue structure is close or far enough behind.

Well, on this other picture taken March 12, after the tsunami, you see that in the area close to intake N°4, there were some blue covers at the intake, and i think this tend to make e think that they were doing some repair in this area when the tsunami hit.

http://www.netimago.com/image_202962.html

But this is a guess, also based on the fact that N°4 was stopped.

For the blue structure, i don't know if it hit or not the pumps at N°5 but fore sure there has been some damage on this structure.

At first, when the accident happened, i heard in the news that they lost first the cold source, then the electrical power. I don't know if all the pumps were still fully functionnal after the tsunami, in addition to loss of electrical power, in fact...

 

[Maxion]

I agree. I was talking about the withe dots for example in this picture already posted, which are a totally different subject than the fringing in the satellite image, as i mentionned it...

http://www.netimago.com/image_202891.html

Yeah, I kind-of ignored that subject because those white dots are definitely an image artifact that I have never seen before. The color white comes when the bayer-filter registers all three color channels as fully saturated. The only artifact that comes close is hot pixels when shooting with high ISOs and long exposure, but they aren't white, or very rarely are.

 

[jlduh]

More detailed analysis of accumulated turbine building water from march sampling finally published:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110522_04-e.pdf

Any comments?

For experts: how can you interpret that water from N°1 is significantly less contaminated (orders of magnitude lower for most isotopes) than N°2 and N°3, and that Ba-140, La-140 (short half life) and Sr 89 and 90 are much lower in this N°1 water (see page 3 of pdf)?

Is La-140 a daughter isotope in the decay process of other elements?

 

[ModelX]

Yeah, I kind-of ignored that subject because those white dots are definitely an image artifact that I have never seen before. The color white comes when the bayer-filter registers all three color channels as fully saturated. The only artifact that comes close is hot pixels when shooting with high ISOs and long exposure, but they aren't white, or very rarely are.

The "funny" pixels are not always white. It looks like impulse noise affecting one or more color components to me. I've seen artifacts like these when the CCD power source had noise or when there was some RF interference. There can be several places where the noise could be introduced: in CCD, in ADC converter or when transfering digital data from imager to the processing system. Sometimes the data transfers are done using YUV data channels, so a single bit off could change the overall luminance or color. It's not at all certain that radiation is causing this.

 

[jarvik]

Yep. Ruthenium, Strontium, Uranium and Plutonium present. That's used fuel, basically. It needs to have melted down for this stuff to be mobilized, I think.

The U, Pu and Ru are below detection limits as the are all reported as < X.

While there certainly is Radioactive Sr present in large amounts (3rd table), most of the Sr in table 2 (by mass) will be stable Sr from sea water.

Sea water will also contain trace amounts of U, though that leads me to my 3rd point, the detection limits in table 2 are two high to be useful from the point of view of detecting fuel failure etc.

Crap load of 134/137Cs and 90Sr to deal with for long-term clean up though. Pity the table didn't give volume estimates of the various "pools" so we could easily convert this to total inventories of the isotopic activities.

 

[Maxion]

The "funny" pixels are not always white. It looks like impulse noise affecting one or more color components to me. I've seen artifacts like these when the CCD power source had noise or when there was some RF interference. There can be several places where the noise could be introduced: in CCD, in ADC converter or when transfering digital data from imager to the processing system. Sometimes the data transfers are done using YUV data channels, so a single bit off could change the overall luminance or color. It's not at all certain that radiation is causing this.

I never said it was ;) I tried to ignore the subject because my knowledge of how an image is formed on a sensor and it's path to becoming a RAW or JPG is quite limited. I do know that it is not caused by the cameras normal operation under normal operating conditions.

 

[jarvik]

For experts: how can you interpret that water from N°1 is significantly less contaminated (orders of magnitude lower for most isotopes) than N°2 and N°3, and that Ba-140, La-140 (short half life) and Sr 89 and 90 are much lower in this N°1 water (see page 3 of pdf)?

Is La-140 a daughter isotope in the decay process of other elements?

I'd like to hear an expert on this too,

My non-expert thinking is the I and Cs isotopes are more volatile and more readily escape the fuel than Sr so the increased Sr in # 2 and 3 likely means much greater damage to fuel and containment for those units.

 

[jpquantin]

The U, Pu and Ru are below detection limits as the are all reported as < X.

One can question this "<". For U in page 2 they explicitly stated "ND" (not detected?). Moreover for Zr in page 2, the detection limits would not be the same for each sample analyzed ... (I understand Italic numbers as being recalculated from analysis of diluted solutions).

Is it plausible that JAEA may not be able to detect concentration lower than 1.2 mg per liter for Pu?

 

[tsutsuji]

Note 2: At DAINI plant, which is newer, they added some buildings close to the sea but to me, these pumps are still outside, close to these buildings (the 3 aligned white/grey circles each time)

http://www.netimago.com/image_202950.html

Some details about Daini are provided in this article :

Unit 3 was undamaged and continued to cold shutdown status, but the other units suffered flooding to pump rooms where equipment transfers heat from the reactor circuit to the sea - the ultimate heat sink.
http://www.world-nuclear-news.org/RS_Insight_to_Fukushima_engineering_challenges_1803112.html

I wonder how enough seawater pumps at Daini unit 3 could remain safe after being flooded by the OP+6m ~ OP+14m wave reported and depicted on dramatic pictures at http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110409e10.pdf, if they are located outdoors. How can we explain the Daini unit 3 miracle ?

The following attachments are from , a video explaining how the Tokai NPP (located further South in Ibaraki prefecture) survived the March 11th tsunami. The video says that the seawater pumps are enclosed in "more than 6 m" high walls, while the tsunami wave was only "more than 5 m" high. Two pumps survived. The third pump didn't survive because its wall was still under construction and not finished.

Tokai NPP's pump protecting wall is also depicted on a diagram at http://www.asahi.com/photonews/gallery/infographics/110330_toukai2.html and on photographs at http://mytown.asahi.com/areanews/ibaraki/TKY201104190562.html (according to that article, the seawater pumps are also providing cooling for the emergency diesel engines ; One diesel engine stopped because the seawater pump for that engine was flooded through a hole in the wall. The reason for the existence of the hole is that the wall was under construction ; If the wall had been 70 cm lower, the Tokai NPP might have had the same destiny as Fukushima Daiichi)

 

[jarvik]

One can question this "<". For U in page 2 they explicitly stated "ND" (not detected?). Moreover for Zr in page 2, the detection limits would not be the same for each sample analyzed ... (I understand Italic numbers as being recalculated from analysis of diluted solutions).

Is it plausible that JAEA may not be able to detect concentration lower than 1.2 mg per liter for Pu?

Oh I thought it was odd that U was given as ND while most others are reported as <X. The analsyis here is evidently a relatively rough chemical analysis as only the major ions of sea water are given values (Na, Ca, Cl etc) as even expected minor ions like Si are only given <X. From my own experience an analyitical lab will give you an actual value OR give you <X where x is the detection limit in question.

I'm not sure I follow you on the Zr, the < X value is the same for all straight samples and reduced by the dilution factor as appropariate for dilution runs.

The inability to detect Pu I think is another reflection of this being a wet chemical method and not a radiometric method which would be far superior at detecting Pu.

In all honesty the detection limits seem piss poor for the question that will obviously be asked from the data (fuel failure?) but more appropriate for asking what % is sea water and water % is fresh water sourced in each sampling pool.

For a comparison I recently have gotten some chemical elemental (30 elements) analysis data back for some work I'm doing and looking at it the reported detection limits vary by element but for example they have a detection limit of 0.05 mg U /kg soil and 0.5 mg Mo/kg soil for the lab we went with. Seems far better than Tepcos lab sadly.

 

[zapperzero]

Is La-140 a daughter isotope in the decay process of other elements?

Yes. It is daughter of Ba-140, which in turn can be found in the decay chains of both U-238 and U-235, iirc. But I can't find a chart so... let's wait for the experts.

 

[jarvik]

Yes. It is daughter of Ba-140, which in turn can be found in the decay chains of both U-238 and U-235, iirc. But I can't find a chart so... let's wait for the experts.

Er.. you mean fission product of U I expect.

 

[zapperzero]

Er.. you mean fission product of U I expect.

Err. Yes. Found a chart as well :D

http://www-nds.iaea.org/sgnucdat/c3.htm

 

[Jorge Stolfi]

This. From the live feed. No zooming and no cropping on my part.

Sigh. Try to locate the *pillars*. Do NOT use the outline of the building (walls, corners and roof) since it is obscured by hanging debris, sagging beams, paint spots and such. Then check the pipes in the tower.

 

[Jorge Stolfi]

2 for N°1, 3 for N°2 to 4 but at N°4, because they were doing maintenance on the core, it seems they were also doing maintenance on the pumps because they seem to be removed on this picture.

I think that the missing pumps were swept away by the tsunami. One of them (an isolated pump due west from unit #2) is still lying on its side, not far away from its presumed base. I would guess that the other missing ones were rolled into the sea by the receding wave.

 

[tsutsuji]

[PLAIN]http://www.yomiuri.co.jp/photo/20110419-495936-1-L.jpg
Diagram from http://www.yomiuri.co.jp/science/news/20110419-OYT1T01008.htm

It shows that in order that the contaminated water moved from unit 2 does not leak into the ground water, it will not be allowed to fill more than the second basement floor of the process main building.

 

[zapperzero]

Sigh. Try to locate the *pillars*. Do NOT use the outline of the building (walls, corners and roof) since it is obscured by hanging debris, sagging beams, paint spots and such. Then check the pipes in the tower.

I see I have a reputation which is following me , and it's not a good reputation

Anyway. I was interested in the pictures because you can just make out a gantry crane and the huge beam it travels on. Second pic shows a tower that is rarely present in the feed.

 

[tsutsuji]

Note 2: At DAINI plant, which is newer, they added some buildings close to the sea but to me, these pumps are still outside, close to these buildings (the 3 aligned white/grey circles each time)

http://www.netimago.com/image_202950.html

[URL]http://www.asahi.com/national/update/0405/images/TKY201104050670.jpg[/URL]
This diagram is taken from http://www.asahi.com/national/update/0405/TKY201104050625.html

The upper part is Fukushima Daiichi.
The lower part is Fukushima Daini.

The horizontal red rectangles are the emergency diesel generators.
The small vertical red pins are named "seawater pump"
The quadrilateral shape around Daini's seawater pump is named "seawater pump building"
扉 is "door".

According to this diagram, at least the pumps sending seawater to provide cooling for the diesel generators are indoors at Daini. Perhaps only these pumps are indoors while the other pumps are outdoors ?

 

[~kujala~]

For experts: how can you interpret that water from N°1 is significantly less contaminated (orders of magnitude lower for most isotopes) than N°2 and N°3, and that Ba-140, La-140 (short half life) and Sr 89 and 90 are much lower in this N°1 water (see page 3 of pdf)?

I am a non-expert but still trying to answer this one as I have a theory.
They did not spray sea water to unit #1 SFP.
AFAIK the first spray they did (and all sprays after that) were done using fresh water.
March 31st 13:03～16:04 Water spray by Concrete Pump Truck (Fresh water) ...

The really contaminated water in the unit #1 could be in the basement of the reactor building whereas the water in the basement of the turbine building could have come mainly from tsunami/SFP sprayings. Also perhaps some groundwater has leaked in but not enough to affect the levels of contamination heavily.

Once they measure SFP contamination levels in #1 it could further confirm this kind of theory.
The expected result would be to see low-level contamination in #1 SFP.

 

[Joe Neubarth]

http://atmc.jp/plant/rad/

Where in each plant are those outrageous Sieverts per Hour readings coming from? Is it in the control centers? Is there something wrong with the data? Does Sv/hr in Japan mean something different from what I think it means. The readings from Unit Five and Unit Six are frightening considering that they were in cold shutdown at the time of the Tsunami.

 

[elektrownik]

http://atmc.jp/plant/rad/

Where in each plant are those outrageous Sieverts per Hour readings coming from. Is it in the control centers? Is there something wrong with the data? Does Sv/hr in Japan mean something different from what I think it means.

First plot is for unit 1, and if you will read tepco data you will see that there was big radiation jump in drywell, but we don't know if this is correct, sensor can be damaged, if data is correct than this could be corium which get into drywell from RPV
http://www.tepco.co.jp/nu/fukushima-np/f1/images/11052306_level_pr_data_1u-j.pdf

 

[tsutsuji]

The following article http://astand.asahi.com/magazine/judiciary/articles/2011051100015.html?iref=chumoku expresses the view that most diesel generators at Fukushima Daiichi are water-cooled : "The tsunami hit the seawater pumps and water intake became impossible. As a consequence, the 10 water-cooled emergency diesel generators stopped (...) Unit 2, unit 4 and unit 6 have one air-cooled emergency diesel generator each. (...) Those at unit 2 and unit 4 failed too. They are located high above sea level, which raises the possibility that what failed was the metal-clad switchgear which acts as the electric power receiving end at the building"

A photograph showing seawater pumps being removed for inspection at Ikata NPP can be viewed at : http://mytown.asahi.com/areanews/ehime/OSK201105190135.html

 

[Uagrepus]

The "fringin" on the highlights in the photo is with 99% certancy an optical effect caused by the Earth's atmosphere coupled with the extreme optics needed to get images like this from Earth orbit.

Thanks for your interpretation. So there is 1% left those colored sparkles are optical effects simply from oil? ;-)

-->
http://www.netimago.com/image_202942.html

I have to look for similar fringed spots in satellite photos of the mexican gulf desaster ...

EDIT: Colored sparkles found here, American Samoa Tsunami, no radioactivity needed :
http://www.flickr.com/photos/digitalglobe-imagery/3969593680/sizes/l/in/photostream/

 

[ottomane]

First plot is for unit 1, and if you will read tepco data you will see that there was big radiation jump in drywell, but we don't know if this is correct, sensor can be damaged, if data is correct than this could be corium which get into drywell from RPV
http://www.tepco.co.jp/nu/fukushima-np/f1/images/11052306_level_pr_data_1u-j.pdf

Ouch. Let's hope only the sensor broke. We'll know soon.

Btw.: Can such values be reached without recriticality?

 

[AntonL]

radiation measurement live from Japan
μSv/h

Iitate village, Fukushima pref
39.5 km away from Fukushima Daiichi
http://www.ustream.tv/channel/8000164

Fukushima city, Fukushima pref
67 km away from Fukushima Daiichi
http://www.ustream.tv/channel/8060606

Hokida, Fukushima city, Fukushima pref
http://www.ustream.tv/channel/8073183

Miyagi pref
http://www.ustream.tv/channel/7954538

near Sendai station, Miyagi pref
http://www.ustream.tv/channel/8126354

Mito city, Ibaraki pref
http://www.ustream.tv/channel/7574817

Adachi ward, Tokyo
seismometer(L) & radiation measurement(R)
http://www.ustream.tv/channel/7754813

Shinjuku ward, Tokyo
http://www.ustream.tv/channel/7943728

Tsurumaki, Setagaya ward, Tokyo
http://www.ustream.tv/channel/8278742

Asakusa, Taito ward, Tokyo
http://www.ustream.tv/channel/7658661

Asakusabashi, Taio ward, Tokyo
http://www.ustream.tv/channel/7873981

Katsushika ward, Tokyo
http://www.ustream.tv/channel/7373757

north Tokyo
200km away from Fukushima Daiichi
http://www.ustream.tv/channel/7485012

Kashiwa city, Chiba pref
http://www.ustream.tv/channel/7555976

Chiba city, Chiba pref
http://www.ustream.tv/channel/7960747

Inage ward, Chiba pref
http://www.ustream.tv/channel/7691874

Yachimata city, Chiba pref
http://www.ustream.tv/channel/8211793

Ichinomiya seaside area, Chiba pref
http://www.ustream.tv/channel/7817633

Kuki city, Saitama pref
http://www.ustream.tv/channel/7800484

Yamato city, Kanagawa pref
http://www.ustream.tv/channel/8315787

Tsuru city, Yamanashi pref
http://www.ustream.tv/channel/8244010

Ueda city, Nagano pref
http://www.ustream.tv/channel/7545780

Shijokarasuyama, Kyoto city, Kyoto
http://www.ustream.tv/channel/7752205

Kita ward, Osaka
http://www.ustream.tv/channel/7752284

Kakogawa city, Hyogo pref
http://www.ustream.tv/channel/8207434

 

[AntonL]

Broken pipes discovered at Hamaoka's No. 5 nuclear reactor
http://www.asahi.com/english/TKY201105210146.html

[PLAIN]http://www.asahicom.jp/english/images/TKY201105210310.jpg

At least 20 of the approximately 21,000 titanium pipes, which are 0.5 millimeters thick and have a diameter of 3 centimeters, had cracks or holes in them.

The damage appears to have been caused by the end cap of a nearby pipe, which came off and was found on the ground. It possibly became dislodged due to worn welds, but the details are yet to be confirmed, according to a Chubu Electric official

 

[zapperzero]

radiation measurement live from Japan
μSv/h

Iitate village, Fukushima pref
39.5 km away from Fukushima Daiichi
http://www.ustream.tv/channel/8000164

Thanks! This one in Iitate is on a 30-second average mode, varying wildly between 0.4 and 0.9 uSv/h

Many seem uncalibrated, though :(. One is dead, no battery :P.

 

[Atomfritz]

Yeah, I kind-of ignored that subject because those white dots are definitely an image artifact that I have never seen before. The color white comes when the bayer-filter registers all three color channels as fully saturated. The only artifact that comes close is hot pixels when shooting with high ISOs and long exposure, but they aren't white, or very rarely are.

The "funny" pixels are not always white. It looks like impulse noise affecting one or more color components to me. I've seen artifacts like these when the CCD power source had noise or when there was some RF interference. There can be several places where the noise could be introduced: in CCD, in ADC converter or when transfering digital data from imager to the processing system. Sometimes the data transfers are done using YUV data channels, so a single bit off could change the overall luminance or color. It's not at all certain that radiation is causing this.

Maybe it's not certain, but it is very probable that the suspicious "bad pixels" are caused by radiation.

Some background to this: Dynamic circuitry, like DRAMs and many processors is very sensitive to radiation from structure micron size about short before the megachips' era.

About 25 years ago, DRAM chips producers began commonly to provide the chips with a thin dense coating directly on the finished die to protect the small charges of the data storage capacitors from getting altered by particles and photons emitted just by the plastic casing of the chips.
This is reflected in the soft error specifications of the DRAM manufacturers.

However, little proven facts are available regarding modern consumer digital cameras and the effects of radiation.

Here an interesting article of a Cambridge University team working on a radiation-hardened camera sensor, explaining some of the radiation effect in the semiconductor: http://iopscience.iop.org/1748-0221/6/03/C03003/pdf/1748-0221_6_03_C03003.pdf

I found another report on evaluating CCD camera sensors for use in highly irradiated accelerator areas, regarding both durability and temporary image distortions.

They used a TRIGA research reactor as radiation source to find out if a CCD camera can survive usage in an accelerator.

They found out that some camera sensors can survive up to 100 Gy, but also that temporary image distortions ("pixels" for those who hate this word ;) ) definitely show up very clearly at 100 mSv/h.

http://img852.imageshack.us/img852/3290/hotspotcamera.jpg

For the detailed report please see here: http://www.isprs.org/proceedings/XXXVI/part5/paper/MARB_645.pdf

So I think that the strange spots you can very clearly see in the high-resolution picture linked here ( http://www.tepco.co.jp/en/news/110311/images/110519_3_4.jpg ) are still quite interesting.

We have to consider that the men walked in areas up to around 2 Sv/h!

Maybe it is just that we just don't get shown the really disturbing images completely speckled with radiation noise that one could expect at 2 Sv?

 

[Bodge]

Ouch. Let's hope only the sensor broke. We'll know soon.

Btw.: Can such values be reached without recriticality?

Not according to TEPCO.

http://www.tepco.co.jp/en/press/corp-com/release/11042713-e.html"

So it's either:

a.) Sensor malfunction
or
b.) A "transient criticality".

What does the supporting evidence suggest?

 

[Grumalg]

Iodine is too volatile to stay in open place for that long. Besides this is not an iodine color.

In my experience it's not *that* volatile. The temperature where it melts is 113C and sublimation occurs about 113.7C at the triple point, and I doubt that rubble pile is that hot.

I've handled Iodine crystals a fair bit, and they don't evaporate away at normal temperatures. I've melted/sublimated it into purple vapors and seen what surfaces the vapor deposits on look like and how such deposits persist for extended periods.

The resulting deposits from those vapors have often appeared similar in color to what shows in the picture depending on the nature of the surface and how heavy the deposit. The resulting colors I've seen have ranged from light red/brown through dark bluish purple (almost dark enough to look black).

Not saying it has to be Iodine, but I don't think it's all that far fetched that Iodine deposits could discolor things that were exposed to it as a vapor, nor that such deposits could persist at temperatures below 100C.

The real question is whether the Iodine vapor was present in sufficient concentration to form a visible deposit. That I'm not so sure about.

 

[etudiant]

Maybe it's not certain, but it is very probable that the suspicious "bad pixels" are caused by radiation.

Some background to this: Dynamic circuitry, like DRAMs and many processors is very sensitive to radiation from structure micron size about short before the megachips' era.

About 25 years ago, DRAM chips producers began commonly to provide the chips with a thin dense coating directly on the finished die to protect the small charges of the data storage capacitors from getting altered by particles and photons emitted just by the plastic casing of the chips.
This is reflected in the soft error specifications of the DRAM manufacturers.

However, little proven facts are available regarding modern consumer digital cameras and the effects of radiation.

Here an interesting article of a Cambridge University team working on a radiation-hardened camera sensor, explaining some of the radiation effect in the semiconductor: http://iopscience.iop.org/1748-0221/6/03/C03003/pdf/1748-0221_6_03_C03003.pdf

I found another report on evaluating CCD camera sensors for use in highly irradiated accelerator areas, regarding both durability and temporary image distortions.

They used a TRIGA research reactor as radiation source to find out if a CCD camera can survive usage in an accelerator.

They found out that some camera sensors can survive up to 100 Gy, but also that temporary image distortions ("pixels" for those who hate this word ;) ) definitely show up very clearly at 100 mSv/h.

http://img852.imageshack.us/img852/3290/hotspotcamera.jpg

For the detailed report please see here: http://www.isprs.org/proceedings/XXXVI/part5/paper/MARB_645.pdf

So I think that the strange spots you can very clearly see in the high-resolution picture linked here ( http://www.tepco.co.jp/en/news/110311/images/110519_3_4.jpg ) are still quite interesting.

We have to consider that the men walked in areas up to around 2 Sv/h!

Maybe it is just that we just don't get shown the really disturbing images completely speckled with radiation noise that one could expect at 2 Sv?

Afaik, the radiation tests on sensors were done with the sensor directly exposed to the radiation.
That is quite different from the situation when taking a photo. The sensor then is behind a massive lens, which is opaque to all but visible and near IR light. Alpha and beta radiation is excluded therefore, plus it would take quite energetic gamma rays to register on one of these CCD sensors. These would simply be passing through the lens and would not be focused by it.
There may be extreme radiation hot spots on the site, but they will not be found using conventional photographs. A scanning radioactive source meter would be more promising, but these are pretty primitive designs and not especially easy to deploy.

 

[StrangeBeauty]

Ouch. Let's hope only the sensor broke. We'll know soon.

Btw.: Can such values be reached without recriticality?

Not according to TEPCO.

http://www.tepco.co.jp/en/press/corp-com/release/11042713-e.html"

So it's either:

a.) Sensor malfunction
or
b.) A "transient criticality".

What does the supporting evidence suggest?

Is it possible that a fresh blob of corium just dropped into the area near the sensor?

 

[jlduh]

Thanks! This one in Iitate is on a 30-second average mode, varying wildly between 0.4 and 0.9 uSv/h

Many seem uncalibrated, though :(. One is dead, no battery :P.

Well, now in Iitate i read more than 4,2 (I guess microSievert/h)... Which is much more.

 

[SteveElbows]

http://atmc.jp/plant/rad/

Where in each plant are those outrageous Sieverts per Hour readings coming from? Is it in the control centers? Is there something wrong with the data? Does Sv/hr in Japan mean something different from what I think it means. The readings from Unit Five and Unit Six are frightening considering that they were in cold shutdown at the time of the Tsunami.

The graphs on that site are not good, plenty of errors.

For a start for unit 1 they say that one CAMS reading is from D/W and other from S/C. Its not true, both the sets of data they are showing are for D/W, and they are not showing any S/C readings. TEPCO publish 2 D/W readings and 2 S/C readings, and it is important to note that the unit 1 D/W readings were unavailable for many days due to presumed sensor problems, and indeed the sensor that has recently shows 201 Sv/h has also spiked to high values in the past, so don't know whether to trust it.

As for Units 5 and 6, the site is complete rubbish, it is using wrong data. There are no CAMS readings for reactors 5 and 6, and I have worked out what data it is using by mistake. These numbers are the reported temperatures of the spent fuel pools at units 5 & 6 and should certainly not be in Sv/h. Here is the raw data that I can get to match up, eg look at pool temps at 12:00 on 21st and they match the bogus Sv/h readings on that graph site:

http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/11052306_temp_data_56u-e.pdf

So I would not recommend using that atmc.jp site, use TEPCOs data.

http://www.tepco.co.jp/en/nu/fukushima-np/index-e.html

As for why some of the real numbers are also high, well this equipment is inside containment and is designed to detect fuel melting, so its not surprising that some numbers are high. Yes if many of these higher numbers were from outside containment then this would indeed be cause for great alarm, but they arent, so don't panic.

 

[Bodge]

Is it possible that a fresh blob of corium just dropped into the area near the sensor?

If I'm understanding it correctly, the TEPCO doc I linked to precludes the possibility of anything in the drywell being *that* radioactive after ~1600 hours.