Fukushima Japan Earthquake: nuclear plants Fukushima part 2

[Rive]

... it could mean the water level was that high and soluble fission products were deposited there.

That is a really good idea. It could also explain why is the radiation level seems to be so different at so close places.

 

[Jeremy Thomson]

I'm looking to refute a YouTube video that states "uncontrollable fission is continuing under the site"
I'm sure if this were the case there would be reports from the CTBTO (Comprehensive Test Ban treaty Organistion) of elevated readings of noble fission products (Xenon 135). Does anyone know if the CTBTO publishes the station data anywhere on the web?

Thank you,
Jeremy Thomson

 

[Rive]

I'm looking to refute a YouTube video that states "uncontrollable fission is continuing under the site"
I'm sure if this were the case there would be reports from the CTBTO (Comprehensive Test Ban treaty Organistion) of elevated readings of noble fission products (Xenon 135). Does anyone know if the CTBTO publishes the station data anywhere on the web?

Thank you,
Jeremy Thomson

Hi,

First: if you think that you can clear the thing then don't be disappointed if no success. Debunking some Fukushima clickbait theories is just as impossible as winning against some fake-moon-landing conspiracy stuff. That video is just awful stupid. No connection between the video and the voice, no background for the claims, no scientific base for anything - just a pile of rubbish.

Second: natural fission is always happening and cannot be controlled. It happens at the nature too. Maybe it'll be about some 'criticality' event? If so, the nature of the thing is not limited to Xe135. The most noticeable effect is the increase in heat production and in the direct radiation. So what you have to look for is a peak in CAMS radiation monitors, followed by a sudden temperature increase, and the increase in noble gas output is just a confirmation.

Third: here you can find some data, both actual and historical.

 

[Sotan]

http://photo.tepco.co.jp/date/2017/201702-j/170227-01j.html
5 short films presenting the pedestal area in Unit 5 PCV - to serve as reference for the incoming robot investigation of the correspondent area in the PCV of Unit 1.

 

[turi]

Work at unit 3 SFP continues:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170302_08-j.pdf
Reduction of water injection in Units 1, 2 and 3:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170302_05-j.pdf

 

[etudiant]

The 'Simply Info' site reports that consideration is being given to tunneling under the reactors and then drilling up through their base to extract the fuel remains.
http://www.fukuleaks.org/web/?p=16176

It is not obvious whether this is the preferred concept, but it does indicate that a very wide range of options is being considered.
Clearly some planning is under way for what would be a decades long retrieval effort.
Given the obvious difficulties, one wonders whether these studies are simply preparing the public for
the less costly and less fraught 'seal and abandon in place' alternative.

 

[LabratSR]

Tepco will send an investigative robot inside unit #1 PCV next Tuesday.

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170309_01-e.pdf

 

[Sotan]

They ran into some trouble right from the start, with a cable drum that didn't work properly and (probably) cut a cable which caused loss of image from a camera. They will replace the cable drum assembly "starting on 16th" and then resume the preparations for inserting the robot. They said in Monday's press conference that first results (some still photos most likely) will probably be released the day after inserting the robot, so I say we might expect something on 17th or - more likely - on 18th.

http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170315_05-j.pdf

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170318_03-j.pdf
(in Japanese)

Just one page, presenting the starting of the robotic investigation of Unit 1 PCV.
Thick blue line on the top-left diagram shows the (short) path traveled today by the robot.
At top right there are two small photos - one taken as the robot is being lowered from the access pipe onto the grating platform, the other as the robot has taken the U shape and started rolling onto the grating.
Photo at lower right shows workers in action.
Lower left gives the main objectives of the first part of the inspection:
at D0 - try to assess whether there is fuel debris spilling over from the sump pit;
at D1, D2 - try to assess whethere there is fuel debris flown through the opening of the pedestal;
at D3 - try to see if the fuel debris has got in contact with the PVC wall;
at BG - take radiation measurements to serve as "background" or control, to be compared with measurements taken at D0~D3.

Slightly larger photos here:
http://photo.tepco.co.jp/date/2017/201703-j/170318-01j.html

 

[Sotan]

On March 19 a new 4-page quick report has been added by IRID/Tepco, regarding the inspection of Unit 1 PCV.
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170319_02-j.pdf (in Japanese)

Page 1 shows little new content compared to the previous report. The two photos at top-right are new; one was taken with the right-hand camera on the robot and shows the gratings; the other one was taken with the camera/radiation meter unit lowered through the grating, just before getting submerged in water.

Page 2, right side:
- one photo taken under water;
- tentative results regarding radiation dose: 7.8 Sv/h on the grating; 1.5 Sv/h when the measurement unit was lowered at the lowest point (more than 1m above the bottom of the PCV, still working out the precise depth). They are now analyzing imagery and radiation measurements in order to evaluate the state of the bottom of the PCV.

Pages 3 and 4 are there just to show that there were no changes in plant parameters and no effects on the surroundings, during the investigation. Trying to avoid mistaken interpretations that happened in the past, the red text at top of Page 4 states "a value of 7.8 Sv/h has been measured during this investigation. That only means that a radiation measurement has now been taken in a place inside the PCV, which could not be accessed since the accident, but became accessible now. It does not mean that a new phenomenon/event has occurred".

 

[Sotan]

New report from IRID/Tepco, dated 21 Mar - on the ongoing investigation of Unit 1 PCV
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170321_03-j.pdf (in Japanese)

Page numbered 0
- The robot continued to move from D0 to BG and then to D1 point (Mar 19)
- Top-right: View of the grating and view of the surface of water, just before submerging of the camera/radiation meter

Page 1
- Top-right: Underwater view taken in point BG. Radiation dose on the grating: 3.8 Sv/h. Radiation at the lowest point reached with the underwater camera/radiation meter (about 30 cm above PCV floor): 11 Sv/h. Radiation dose values and height above floor are tentative values.

Page 2
- The robot continued to move from D1 to D2 point (Mar 20)
- Top-right: View of the grating and view of the surface of water, just before submerging of the camera/radiation meter

Page 3
- Top-right: Image taken underwater at D2. Also, radiation measurement in D2 was 12 Sv/h on the grating and 6.3 Sv/h underwater at the lowest point reached (about 1m above PCV floor). Values are tentative.

Page 4
- Access route from D2 to D3 was narrow/risky so for the time being they returned the robot to D1. On Mar 21 they will re-try D3 (which is close to the opening in the pedestal wall), then go back to D1 and continue the measurements there.

Page 5-7
- Emphasizing the existing shielding by steel and concrete, the fact that there are no changes in plant parameters and the fact that this investigation and its findings do not mean additional threats for the surroundings.

Slightly larger photos here:
http://photo.tepco.co.jp/date/2017/201703-j/170321-01.html

Edit: After checking other sites in the last couple of hours, it appears that they decided to extend the investigation another day - that is on 22 March too, to gather more data. What they got until now is still inconclusive, they still don't have a direct confirmation of the location and state of fuel debris, and they couldn't get really close to the floor in places of interest, fearing the sensor will get stuck. So - one more day.

 

[nikkkom]

If you step back a bit (stop thinking about everyday details of the investigation, look at a bigger picture), what could be the plan for dealing with the station?

The fuel can and should be unloaded from the pools.
Everything exterior to PCVs can be cleaned up and where beneficial, partially dismantled.

But what next with the PCVs and everything inside? What with basements?

BTW, is Japanese public opinion softening up to an idea of eventual restart of Units 5 and 6? IIUC, they are essentially undamaged and in working shape?

 

[etudiant]

I don't think there can be any clarity for the long term as yet.
The cleanup will run as outlined for the next few years, so hopefully early in the 2020s the SFPs will be emptied and the location of the corium will be known.
By that time, the political and social picture will also have evolved, but who knows in which direction.
Fukushima looks to become the Hanford of Japan, a perpetual clean up project, because the recognition that the site be best encapsulated and left to itself is politically unacceptable.

 

[turi]

BTW, is Japanese public opinion softening up to an idea of eventual restart of Units 5 and 6? IIUC, they are essentially undamaged and in working shape?

I can't imagine TEPCO restarting units 5 & 6. They are using them (or at least unit 5) for testing equipment to be used in units 1-3. They have drilled various holes etc. TEPCO has other nuclear power stations waiting for reactivation, getting the safety updates and paper work for them done is more than enough work and has a higher potential for a positive return on investment.

 

[Rive]

BTW, is Japanese public opinion softening up to an idea of eventual restart of Units 5 and 6? IIUC, they are essentially undamaged and in working shape?

That's not practical. To operate a NPP you need a lot of auxiliary stuff/area around the reactor and the turbine building: like you can see the pre-disaster pictures about Fukushima.
After the tsunami all these areas were sacrificed in order the restoration work.
To restart U5 and U6 a lot of work would be needed, and the conflict with the restoration work would be unavoidable.
I think the best is to write them off.

 

[nikkkom]

That's not practical. To operate a NPP you need a lot of auxiliary stuff/area around the reactor and the turbine building: like you can see the pre-disaster pictures about Fukushima.
After the tsunami all these areas were sacrificed in order the restoration work.

I looked at the Google map and area around Units 5/6 does not look significantly altered.
Fields of water tanks, debris storage areas and such are located mostly inland from Units 1-4. not up north along the coast where Units 5/6 are.

 

[Sotan]

- From what I have seen there is no talk whatsoever about a possible restart of Units 5-6 at Fukushima plant.
- I agree with etudiant's post above, for now they have a plan and are sticking with it and trying to give it their best; nobody says the plan itself cannot be changed, but they will probably consider that later (maybe after removing all the spent fuel).

- Today there's a new post of IRID/Tepco, about the investigation of Unit 1 PCV. (The investigation is over and the robot has been retrieved.)
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170323_05-j.pdf (in Japanese)
- Photo on page 1 shows intensive image blurring when the camera/radiation sensor gets very close to the bottom of the PCV.
- Photo on page 2 has been shown before, looks a little enhanced now, but seems (at least to me) to show a rather clean area on the bottom.
- Photo on page 3 shows... I don't know what it shows :/
It is a bit frustrating, I think we need to wait for more materials and results to be released.

Edit: (quoting a Mainichi article)
Tepco announced on February 23 that it was impossible to confirm the nuclear fuel melted in the core melt accident from the images obtained as a result of the internal investigation of Fukushima Daiichi No. 1 Reactor containment vessel from March 18th to 22nd. They will analyze the animation and radiation data obtained in the survey and announce final findings on March 27th.

 

[Sotan]

Correction: Above, obviously, I should have written "Tepco announced on March 23...", not February.

 

[Charles Smalls]

Hi guys

I was curious about the large amount of sediment or 'sand' that the recent robot observations of Unit 1 found inside the containment vessel. It is well known that concrete exposed to high temperatures can undergo a process of spalling, where the heat causes individual constituents in the concrete to expand at different rates causing small explosions in the material and debris goes popping off.
You can see the process here:



and a much more dramatic example here:



Is it possible that the sand/sediment we see in the latest footage is from this process where the fuel has met the CV concrete floor and caused this large amount of spalled material? I have read the sediment may be from seawater injection/flooding but I'm not sure how probable that is. Is there any special material or liner in the CV concrete mix that would prevent the spalling process?

Many thanks for your insights and expertise as always.

 

[turi]

New info on unit 1 examination: http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170327_14-j.pdf

[...]
Is it possible that the sand/sediment we see in the latest footage is from this process where the fuel has met the CV concrete floor and caused this large amount of spalled material?[...]

I am no expert on concrete, so no opinion on this from me. But I could imagine that the sand/sediment we can see could be metal oxides from farther up, oxidized zirconium and the like.

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170327_14-j.pdf (in Japanese)
Updated report on the robot investigation of Unit 1 PCV.
A lot of the content has been presented in previous reports so I will mention just a few new aspects:
- Page numbered 5, "blue" object filmed on the floor (Photo D0-3) is a "fallen object".
- Page 6, photo at top left: "pre-existing structure"; bottom left: "fallen object"; bottom right: "fallen object(s)".
- Page 7: Radiation dose measurements in various points, on the grating (first row of the table) and at the lowest point reached by the hanging measurement unit (second row in the table, height from floor also noted).
- Page 8: graphs showing the variation of the measured dose as a function of the height from PCV floor, in various points BG, D0...D3. Group of numerous points in the left are for underwater measurements. Then there are a few measurements right at water surface (at almost 2m on X axis) and a few more on the grating (at 3.5m on X axis).
- Page 9, conclusions:
- This was the first opportunity to film the bottom of the PCV around the area of the opening in the pedestal wall. It was also possible to verify that radiation doses increase as we get closer to the PCV bottom.
- Sediment was observed on the bottom of the PCV, around pipes etc. Research/analysis on the nature of the sediment will continue.
- It was attempted to get close and film the sediment at point D2. From the fact that the sediment did not rise/float into the water it is deduced that it does have a considerable weight.
- When the measuring unit enters the w3ater, the radiation dose decreases, however it rises as the unit gets closer to the bottom.
- The height (measured from the bottom) where the radiation values appear to increase varies from one point to another. (There are many hypotheses for the cause of this phenomenon. The sediment could be the radiation source, there could be a strong source sticking to the bottom under the sediment, there could be fuel debris close to the PCV bottom...)
- The radiation doses measured on the grating did not differ much from those observed in April 2015, and no major destruction of the structures was observed.
- The analysis of the images and data will continue.
- Page 12: shows, in section, several of the places where the underwater measurement unit was lowered. Emphasis on the PLR pipes. (Radiation doses of 5.9 to 9.4 Sv/h, according to Page 7).
- Page 14: shielding with lead plates in the area of the PLR pipes.

Edit: slightly larger photos and a 300 Mb movie - here:
http://photo.tepco.co.jp/date/2017/201703-j/170327-01j.html

 

[Sotan]

A couple of things I understood from watching the robot video and the press conference related to this last report.

- What they meant to convey by the diagrams of Page 12-14:
When they lowered the underwater measurement unit in the area of points D1-D2, they had to stop at a height of about 90 cm from he floow, because there was already a surface of sediment at that height. Incidentally, those points where the unit had to stop also coincide roughly with the top of the PLR pipe as shown in Page 12. Add to this - as seen on page 14, which by the way is a photo of Unit 1 during scheduled maintenance work - the fact that on the side of that particular portion of the PLR there was, installed by design, a shield made of lead panels. So, there is a possibility that that shield collapsed or melted partially and fell over the PLR pipe, and what now appears to be a "90 cm thick layer of sediment", in which they ran into when lowering the measurement unit, is in fact a sheet of lead that fell om the PLR and is covered with some dust. They hope to learn more about this sediment and its thickness by further analyzing the imagery taken.
The diagram onm page 13 shows another place which appears in the film/photos, namely the valve wheel that is photographed pretty clearly close to the bottom of the PCV. That is one place where they managed to get as low as 30 cm above the floor.

- On page 6, the top right photo shows a weird yellowish stain at D2 (3), which I couldn't figure out earlier what it meant and I thought it might be due to high radiation. It appears that is an effect of getting very very close to the filmed surface (of the sediment), so that the LEDs that provide light cannot actually illuminate the center area enough for an image to form. So it's just a shadow.

- The video images at D1(2) (around 05:15 in the video) transiently show a black mass at the edge of the field of view, which perhaps would deserve more investigation.

- There is some light stuff floating in the water - but they are still happy with it's transparency, it could have been worse, as it is it allows a reasonable viewing.

- They hope to carry out the final step of this investigation - taking a sample of the water/sediment - ini the following days, as soon as preparations are done.

- They are making progress - even if slowly - with the robot for Unit 3, which they hope to be able to send in the PCV sometime this summer.

 

[Rive]

Is it possible that the sand/sediment we see in the latest footage is from this process where the fuel has met the CV concrete floor and caused this large amount of spalled material?

In case of U1 it's likely that all the core material escaped the RPV, so some kind of interaction with the concrete floor is expected.
However: I expect it within that well-like concrete structure. But the actual investigation is about the floor around that structure, not inside.
I don't know how mobile the materilas from MCCI are, but this amount of sediment just feels wrong.

 

[Sotan]

How much sediment do we actually expect?

Wikipedia says the core contained roughly: Uranium dioxide 78.3 tons; Zirconium 32.7 tons; Steel 12.5 tons; Boron carbide 590 kilogram; Inconel 1 ton.
A simple calculation based strictly on the density of the first 3 materials gave me a total volume of about 10 cubic meters.
With the pedestal having an internal diameter of 5 meters, if all those materials melted and went to the bottom (let's ignore the opening in the pedestal at this time) I get a height of the "cylindrical layer of debris" of about 50 centimeters, if it behaved like a liquid and filled all the space evenly.
Since it probably didn't behave exactly like that, we can assume an uneven distribution (actually suggested by the latest investigation too).
So 90 cm might not be that out of scale after all? But if so, how come the radiation values are so low (with water and all, Tepco spokespersons said if that was fuel debris the values close to the sediment layer should have been higher).

...would somebody please check my calculations :)

 

[Rive]

But it's not about core debris, but about burnt concrete what became mobilized and relocated from inside of the pedestal to outside.

There was some calculations: in case of complete core relocation it was ~ 70cm deep penetration in concrete as I recall. I'll try to dig this up later.

 

[Sotan]

Right, Rive - I forgot that the melted stuff attacked and bore into the concrete base.
Oversimplification of course... Plus the opening in the pedestal clearly allows some (a lot?) of materials to get out into the PCV.
But unless there was a lot of vaporization of solids, It seems to me that most of the mentioned volumes should still be laying somewhere around there.

 

[Rive]

Actually I did forgot one thing - it's possible that if inside of the pedestal had an aggressive water input then that could relocate the mobolized sediment and deposit it on the outside.

 

[Sotan]

Well at least you had the locations right.
Unfortunately I was speaking of the sediment height inside the pedestal - whereas this time's investigation and the reported "90 cm debris?" were all outside of the pedestal wall... I will step back, clearly I don't know enough. I can't even begin to imagine the physical processes that took place in those moments in the pedestal area.

 

[Charles Smalls]

How much sediment do we actually expect?

With the pedestal having an internal diameter of 5 meters, if all those [fuel] materials melted and went to the bottom (let's ignore the opening in the pedestal at this time) I get a height of the "cylindrical layer of debris" of about 50 centimetres.

The opening in the pedestal and it's location may have a lot to do with these weird sediment/sand images.
In the TEPCO report, location D2 is where the camera observed the thickest sediment deposits:

If this material was from concrete heat spalling, this would make sense because D2 is directly opposite the pedestal opening and the first place the core melt would have spread after leaving the pedestal. If the PVC proper was dry, this is where the core-concrete interaction would have begun.

Page 1 of the TEPCO report seems to show similar thinking:

On the right they show a gray puddle exiting the pedestal via the yellow doorway into the PVC proper. If this was fuel melt encountering the concrete floor, you would expect erosion/spalling to take place heavily here. On the floor above they show the robot in position D2 where it was when it lowered the camera and captured the sediment images.

- On page 6, the top right photo shows a weird yellowish stain at D2 (3), which I couldn't figure out earlier what it meant and I thought it might be due to high radiation. It appears that is an effect of getting very very close to the filmed surface (of the sediment)

This is the part that doesn't add up. On the video it looks like they basically lower the camera all the way down until it hits the surface of the sediment. If it was a loose amalgamation of materials as spalled concrete normally is, I would have expected this impact to have thrown some of the sediment into suspension and clouded the water. It could be that the material is too heavy to be dislodged by such a light impact or maybe it formed a depression which the camera didn't pick up. I would be very interested to learn more on the make up of the sand/sediment i.e. particle sizes and whether it is loose material or a solidified mass.

 

[jim hardy]

Wait until there's a handful of the stuff gathered up to analyze.

I was never inside a BWR containment..

In mine there's normal dust . Cable trays were all sprayed with fireproofing material "FlameMastic" a fibrous mix of something akin to latex paint and i think asbestos.

I would think inside a containment that's been subjected to prolonged loss of cooling and pressure-cooker steam a lot of mud would result from soggy thermal insulation , peeled paint, maybe even melted pvc electrical insulation . Seawater injection had to carry in a lot of solids if only salt .

Were i looking for Corium i'd turn off the lights and look in the water for telltalle blue glow of Cerenkov .