Fukushima Japan Earthquake: nuclear plants Fukushima part 2

[Hiddencamper]

Two questions/thoughts

Isn't the entire containment flooded with water?

If so, why isn't the water shielding the camera from the radiation?

If it is, (both underwater, and shielding is happening), then wouldn't the actual radiation source be much much higher than they are calculating?

Related question, what is the dose rate (Svr/hr) for nuclear fuel that has spent 6 years cooling?

As in, if the fuel rods had been cooling for 6 years in a spent fuel pond, how radioactive would they be?

And is this rate being measured in reactor 2 the same?

The severe accident guidelines have you flood containment to backfill the hole in the reactor following a rupture. The immediate concern is to establish minimum debris submergence level (get the core slag under water). Then flood up to try and establish core cooling. Once you've flooded containment you could feasibly open up the drywell head and vessel head and "look down" into the core.

In this case, there is containment system damage causing water to spill out. So until they find and plug those leaks they will be unable to use normal means for shielding the core slag.

Note: post Fukushima severe accident guidelines have changed and do not emphasize immediate debris submergence for mark 1/2 containments. The goal is to establish minimum debris cooling injection rates to prevent a rapid steam pressure rise in the drywell and to preserve the suppression pool as a water scrubbed release path.

 

[turi]

English reports on debris removal work (probably based on Sotan's work ):
http://www.tepco.co.jp/en/press/corp-com/release/2017/1375551_10469.html
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170209_01-e.pdf
http://photo.tepco.co.jp/en/date/2017/201702-e/170209-01e.html

English summary of newest quarterly report:
http://www.tepco.co.jp/en/press/corp-com/release/2017/1375451_10469.html
Summary of summary:

• SFP fuel removal planned in 2018 for Unit 3 and in 2020 for Unit 1, preparatory work underway.
• Ice wall: Amount of water pumped up daily has declined from 400 cubic meters to 140 cubic meters.

Report in Japanese:
http://www.tepco.co.jp/press/release/2017/pdf1/170210j0102.pdf

 

[Sotan]

Thank you turi.

I just want to refer to the last link you posted above, the 91-page long report in Japanese. The title would sound something like "Progress of the reform plan on nuclear power safety" and aims to show the work Tepco is doing to generaly improve the safety level in its three nuclear facilities (Fukushima Daiichi, Fukushima Daini, Kashiwazaki-Kariwa plants, the last one, world's largest nuclear power plant, still employing 6000 workers and hoping to restart production some day). I only browsed through it enough to see that there's not much new content related to the mainly technical scope of this thread, so... I don't think I will quote anything of it in here.

 

[turi]

IRID released a document showing a robot called "PMORPH" for investigating Unit 1:
http://irid.or.jp/en/topics/pcv内部調査／1号機原子炉格納容器内部調査（ペデ/

 

[F X]

The containment is not flooded with water.

Seriously? So the fuel is just sitting somewhere, in air? For how long?

 

[turi]

Seriously? So the fuel is just sitting somewhere, in air? For how long?

Since 2011. More under constant rain than just air though.

 

[jim hardy]

Seriously? So the fuel is just sitting somewhere, in air? For how long?

Don't get excited until they find it. The tempest might still be in the teapot.

 

[turi]

Newly stitched together images from Unit 2, courtesy of IRID:
http://photo.tepco.co.jp/date/2017/201702-j/170215-01j.html

Edit: To me, if I interpret the pictures correctly, it looks as if the alternative route to the left for the inspection robot isn't feasible as well. Something that could take hold of the middle beam would be necessary, but that would be a much more complex robot (or probably an electro magnet or two could help).

 

[Sotan]

The link posted by turi above leads to a PDF report in which Tepco shows us the options that they are considering these days, regarding the final step of the planned investigation of PCV/pedestal of Unit 2, namely the step which involves sending in the "scorpion" robot equipped with cameras, thermometer and radiation meter.
Pages 1-3 you've seen them before, they show the general concept, object and steps of this investigation. (Page numbers as inscribed at bottom-right corner)
Pages 4-6 compile various information obtained in previous steps - including a few newly stitched and reprocessed images. Page 5 underlines the gap (45 to 140 mm wide) that exists between the end of the CRD rails and the grating platform. White dotted line on Page 6 shows a possible route for inserting the robot (which, as you have seen in a presentation video, is capable of crossing some gaps).
Page 7 mentions that additional information could be obtained by performing this final step, with the robot taking over from where the sediment-cleaning robot stopped. The scorpion robot is shown, with its front and back camera, thermometer and radiation measuring device (which by the way still has a plus/minus 20% error). The latter device, installed in a "corrugated tube" (?) practically tied to the power cable of the robot, will be in contact with the sediment and therefore the reading will not be purely, 100%, air radiation dose.
Pages 8 and 9 show the two investigation options that they are considering, with pros and cons:

Page 8: In case they send the robot only down to the end of the CRD rails:
- they will be able to peek at the pedestal installations from an even lower point of view, getting info about the state of the hardware and the features of the sediment;
- they will measure temperature and radiation dose;
- if the device gets in trouble while crawling over the sediment, they can pull it back using the power cable. The robot might end up unable to proceed, due to: long tracks; relatively large weight; changes in the center of gravity due to manoeuvering the back-end camera.
Even if the robot does not make it to the final destination (end of the CRD rails) it would still contribute useful new data.

Page 9: In case they attempt to send the robot onto the grating platform:
- they would get more images of the holes in the grating, as well as of the bottom of the lower part of the reactor, and be able to assess the state of the CRD housings, of the sediment etc.;
- they will measure temperature and radiation dose;
However:
- the access is difficult and risky; the robot might end up unable to advance or - even worse - fall through the holes;
- while crossing the gap the robot will be in its fully extended configuration, so no images will be available from the back-end camera to help with planning the best route; they will depend only on images from the front camera;
- if the robot falls down through some opening, it might be impossible to retrieve just by pulling the power cables;
- as the investigation is the main priority, if the time needed to retrieve the robot becomes a limiting factor they might simply leave the robot in, at the end.

Finally page 10 gives some general perspective of the grating platform which is the object of this whole 7-step investigation. Red areas show places where grating has fallen, blue is safe grating, grey is unexplored area.

--------------
Same link given by turi above also leads to this second report, also in Japanese only, which is an attempt from Tepco to put the announced radiation doses into some perspective. They explain on page 1 that radiation is stopped/diminished by shielding (lead, iron, concrete...), by distance, and by the passage of time. On page 2 they point towards the place where the 650 Sv/h was estimated the other day, further explaining that the people operating the guiding pipes in this investigation, behind the shield, were subjected to only 6 mSv/h, while the value measured at the monitoring post located at the fence of Tepco's land shows only 2 microSv/h. All these are intended to show that there's no danger for the public, and even for the workers they do all they can to reduce exposure.

 

[turi]

Thank you Sotan! The PDF links weren't present when I've seen the images. Note to self: Recheck TEPCO's photo pages periodically.
Edit: English version link, currently without PDF links:
http://photo.tepco.co.jp/en/date/2017/201702-e/170215-01e.html

 

[turi]

Video, Images and PDF of newest robot excursion into unit 2:
http://photo.tepco.co.jp/date/2017/201702-j/170216-01j.html

Edit: I didn't see it in the video but on what little I understood from the PDF, the robot was left there (while the cabling was pulled back?), in the video at the end it looks as if the robot can't move and its crawlers slip. After some image stitching we should have more details, there are quite a few details previously not visible in the video.

Edit 2: English link:
http://photo.tepco.co.jp/en/date/2017/201702-e/170216-01e.html

 

[turi]

Press conference regarding the latest robot excursion:
http://www.tepco.co.jp/tepconews/library/archive-j.html?video_uuid=mt9v8ewx&catid=69619
Has anyone a good theory on what kind of material could be on that control rod drive exchange rail which causes the high radiation readings? Why is it where it is? Did it come from above (and another opening/crack in the pressure vessel) or did it somehow get there from inside the pedestal?

 

[Sotan]

Post #1133 of jim hardy (on page 57) gives the best hypothesis in my opinion.
The radioactive material is not on the CRD rail, but somewhere above it. Such as in... a pipe, that comes from the RPV. "a fuel fragment in one of them [pipes] would shine right through the pipe wall." to quote jim.

---------
Watched about half of the press conference too.
- Even before that, while checking the online Japanese press, I noticed disappointment and found the word "failure" here and there. In the press conference the speaker underlines that they are still happy with the wealth of information that they got, even though things didn't go as well as they had wished.
- The published video is only a few minutes, but they got much more. The robot went in around 08:00, went quickly over the clean area, in 20-30 min began having trouble with the left track, then until 13:00 they tried various manoeuvers with it until they gave up, so it was not an easy or rushed decision. Even after that, they took another 1.5 hours of video of the area, using the powerful lighting and camera in the tail of the scorpion. They are happy with the quality of the image (it should look much better after some processing).

 

[Hiddencamper]

Post #1133 of jim hardy (on page 57) gives the best hypothesis in my opinion.
The radioactive material is not on the CRD rail, but somewhere above it. Such as in... a pipe, that comes from the RPV. "a fuel fragment in one of them [pipes] would shine right through the pipe wall." to quote jim.

---------
Watched about half of the press conference too.
- Even before that, while checking the online Japanese press, I noticed disappointment and found the word "failure" here and there. In the press conference the speaker underlines that they are still happy with the wealth of information that they got, even though things didn't go as well as they had wished.
- The published video is only a few minutes, but they got much more. The robot went in around 08:00, went quickly over the clean area, in 20-30 min began having trouble with the left track, then until 13:00 they tried various manoeuvers with it until they gave up, so it was not an easy or rushed decision. Even after that, they took another 1.5 hours of video of the area, using the powerful lighting and camera in the tail of the scorpion. They are happy with the quality of the image (it should look much better after some processing).

There are SRV downcomers all around the containment, and we know that they had at attempted to get at least 1 SRV open while fuel damage was occurring. I believe they had some success too, but 1 SRV isn't sufficient to fully depressurize.

 

[turi]

Thanks. Does that fit with the higher dose rate from the radiation sensor (more sensitive towards the rail, if I have understood this correctly) versus the estimated dose rate from the camera?

 

[jim hardy]

Thanks for the kind words, Sotan

No shortage of pipes in there

Does anybody know if Nuclear News did a cutaway of Fukushima ?

PS
Hiddencamper's SRV line is what i was thinking, too.

Do I remember correctly "Neutrons at the Gate" were during attempts to depressurize and reflood? Been almost six years now...

 

[turi]

Do I remember correctly "Neutrons at the Gate" were during attempts to depressurize and reflood? Been almost six years now...

"[...]over three days from March 13 and is equivalent to 0.01 to 0.02 microsieverts per hour[...]" from http://www.japantimes.co.jp/news/2011/03/24/news/neutron-beam-observed-13-times/ is all I could find between tons of pseudo-science-noise. The Wikipedia-Timeline for March 14 says for Unit 2:

• 13:15: The reactor core isolation cooling system for reactor 2 stops and, shortly afterwards, the water level within the reactor starts falling.[20]
• 18:00 (approximate): The water level in reactor 2 reaches the top of the fuel.[20]
• 20:00: Core damage starts occurring in reactor 2.[20]

 

[Sotan]

I'll add just a bit to finish the reporting on the press conference after the latest inspection of Unit 2 PCV.
- At one point a reporter asks what would happen to the whole work process at Fukushima Daiichi if Toshiba (at least its nuclear section) would go bankrupt. The speaker didn't really have an answer, they haven't really considered such a possibility.
- Much doubt remains about the nature of the sediment, which puzzles reporters and everybody else. Lower radiation values this time... the fact that temperature in the area is low (same as in the whole PCV), isn't that an indication that it is not corium/fuel debris? The speaker said they can't yet give an answer. They will continue to examine images, compare them to corium samples known from Cernobil and Three Miles Island, do all sorts of analyses.
- The lower value reported this time for the radiation dose in approximately the same spot as before was the source of many questions. In the end - which value is the correct one? The speaker tried to explain that it's not that simple; different methods, even small differences in location and shielding may cause very different results. They consider them "similar enough", of the order of hundreds of Sv/h. Another reporter wondered if such variations may signify that something radioactive is physically moving around in the PCV, or maybe it has somethign to do with the cooling water going in different directions at different times - but the speaker dismissed this as a very low probability hypothesis, things are pretty much stable at this time in the PCV.
- One reporter was intrigued why this time the camera lasted for 6 hours without problems, considering it was similar to the one that went dark after only 2 hours in the case of the sediment-cleaning robot. Again, no concrete answer, so many factors could have affected the cameras in the two instances.

 

[jim hardy]

"[...]over three days from March 13 and is equivalent to 0.01 to 0.02 microsieverts per hour[...]" from http://www.japantimes.co.jp/news/2011/03/24/news/neutron-beam-observed-13-times/ is all I could find between tons of pseudo-science-noise. The Wikipedia-Timeline for March 14 says for Unit 2:

• 13:15: The reactor core isolation cooling system for reactor 2 stops and, shortly afterwards, the water level within the reactor starts falling.[20]
• 18:00 (approximate): The water level in reactor 2 reaches the top of the fuel.[20]
• 20:00: Core damage starts occurring in reactor 2.[20]

Thanks Turi
that Japan Times article jogged my memory
what the reporters called "beams" were hardly what we'd call "beams", they were instead miniscule upscale readings on neutron monitors out at the entrance gate . I remember checking wind direction it was in direction from plants to gate, and concluding to my satisfaction some fission fragments had gone up the stack during some venting during reflood.

Tepco said the neutron beam measured about 1.5 km southwest of the plant’s Nos. 1 and 2 reactors over three days from March 13 and is equivalent to 0.01 to 0.02 microsieverts per hour. This is not a dangerous level of radiation, it added.

That's not a lot of neutrons.

 

[Sotan]

• 20:00: Core damage starts occurring in reactor 2.[20]

There were a lot more neutrons a little later, though, if this wikipedia page is correct?

"At 21:37 JST, the measured dose rates at the gate of the plant reached a maximum of 3.13 mSv/h, which was enough to reach the annual limit for non-nuclear workers in twenty minutes,[50] but had fallen back to 0.326 mSv/h by 22:35.[52]"

 

[Hiddencamper]

Didn't an explosion occur around then on unit 3 or 4?

There was an info graphic with all the spikes and what they correlated with

 

[Sotan]

I have saved the official IAEA report of the Fukushima accident.
Checking the event timeline for Unit 2: Unit 1 explosion was on March 12 at 15:36; Unit 3 explosion happened on 14 Mar at 11:01. So both these had already happened by the time discussed above (evening of March 14). The explosion on Unit 4 occurred next day at around 06:14.

Quoting from the vol. 1 of the technical report, about Unit 2:

A revised estimation at 15:57 [March 14] indicated that the reactor water level would reach TAF (uncovering the
core) at around 17:30, based on the presumed time of the loss of the RCIC system. By 16:00, a
containment vent path had not yet been re-established, and it was clear that achieving a successful
venting was going to take some time. With uncovering the core predicted to be imminent, it was
decided at 16:28 to depressurize the RPV by release through the SRV to the SC, to enable water
injection, whilst recognizing the potential adverse impact on the confinement as a result of the release
of steam from the reactor into the containment as there was no venting path to ensure PCV integrity in
case of further over pressurization.

The first attempt to open the SRV from the switch in the MCR at 16:34 failed.114 After several further
unsuccessful attempts with five different SRVs, operators opened an SRV at 18:02. Additional SRVs
had to be opened, before the RPV pressure dropped to about 0.65 MPa (6.5 bar) at 19:03 (from about
7 MPa (70 bar) at 16:34), which was below the fire engine pump discharge pressure. During this
pressure relief, there was no apparent increase in the PCV pressure. On the other hand, the rapid
pressure drop caused the water inside the RPV to flash to steam and, without make-up water injection,
the water level continued to drop.115

[...]

At 20:30, the RPV pressure started to rise again, exceeding 1.0 MPa (10 bar) at 21:00. Two more
SRVs were opened, so that the RPV pressure started to drop at 21:20. The RPV pressure rose
repeatedly afterwards, and water injection was considered to have been interrupted.
At 21:55, the containment atmospheric monitoring system (CAMS) — radiation monitoring
equipment inside the PCV — was restored and its readings showed significantly elevated radiation
levels in the DW and SC compared with the earlier readings at 15:15, prior to the CAMS going offline.
The radiation level increase was 5000-fold (from 1.08 mSv/h to 5360 mSv/h) in the containment
atmosphere (the DW) and 40-fold (from 10.3 mSv/h to 383 mSv/h) in the SC section of the
containment. Additionally, neutrons had been detected between 21:00 on 14 March and 01:40 on
15 March, by a mobile radiation monitor near the main gate (approximately 1 km away from the RBs
of Units 1, 2 and 3). The measured neutron dose rates were 0.01–0.02 μSv/h.118

Note 118*:
It was thought by TEPCO that the neutrons came from the spontaneous fission of actinides that were released following
core damage in one of the three reactors, probably from Unit 2 [5].

[...]

At 06:14 [March 15], the sound of an explosion was heard on site, and tremors were felt in the MCR. This was
followed by a drop in the Unit 2 SC pressure indication, which went off scale. The MCR initially
reported to the ERC that the indicated SC pressure was at nearly atmospheric pressure, as zero bar
was displayed in the MCR indicator at 06:30, inferring potential loss of the confinement function.
After re-checking the readings, however, it appeared that the DW pressure was still at 0.73 MPa
(7.3 bar) and the SC pressure went off scale.

This information indicated a possible containment vessel failure and the possibility of uncontrolled
releases from Unit 2. On this basis, the on-site ERC ordered all personnel in all the units to
temporarily evacuate to the seismically isolated building where the on-site ERC was located. At about
the same time as the event associated with the Unit 2 SC, an explosion in the upper part of the Unit 4
RB was observed by the evacuating personnel.119

 

[turi]

New detailed info on Unit 1 hydrogen explosion (long pdf and animations):
http://photo.tepco.co.jp/date/2017/201702-j/170217-01j.html

 

[Astronuc]

I have saved the official IAEA report of the Fukushima accident.

There are numerous reports from the IAEA and AESJ, and other institutions.

https://www.iaea.org/newscenter/focus/fukushima/status-update - plenty of update reports

2015 Report - http://www-pub.iaea.org/books/iaeabooks/10962/the-fukushima-daiichi-accident

I'm not sure what 'highest' radiation level means in the context of recent specific events, but there are likely locations of high activity associated with pieces of fuel or activated materials from the core. It's difficult to know what exactly happened with core; some believe the fuel melted, which is possible, but the fuel could have chemically reacted (and oxidized) with whatever water was able to get into the core. The hydrogen has to be produced by reaction of the water with metals and fuel. One likely reaction is Zr + H₂O => ZrO₂ + 2H₂, which is expected. The UO₂ fuel goes through several oxidation states, but ultimately to UO₃, which is readily soluble.

Another presentation from 2015.
https://ceiden.com/wp-content/uploads/2015/01/3-SekimuraPresentation20150115all.pdf

There was a presentation - APS Division Nuclear Physics Hawaii Meeting, 2014.
http://adsabs.harvard.edu/abs/2014APS..DNPAA2002S

The Atomic Energy Society of Japan (AESJ) published the Final Report of the AESJ Investigation Committee on Fukushima Daiichi NPS Accident in March 2014. The AESJ is responsible to identify the underlying root causes of the accident through technical surveys and analyses, and to offer solutions for nuclear safety. At the Fukushima Daiichi, Units 1 to 3, which were under operation, were automatically shut down at 14:46 on March 11, 2011 by the Tohoku District-off the Pacific Ocean Earthquake. About 50 minutes later, the tsunami flooded and destroyed the emergency diesel generators, the seawater cooling pumps, the electric wiring system and the DC power for Units 1, 2 and 4, resulting in loss of all power except for an air-cooled emergency diesel generator at Unit 6. Unit 3 lost all AC power, and later lost DC before dawn of March 13. Cooling the reactors and monitoring the results were heavily dependent on electricity for high-pressure water injection, depressurizing the reactor, low pressure water injection, and following continuous cooling. In Unit 3, for example, recent re-evaluation in August 2014 by TEPCO shows that no cooling water was injected into the reactor core region after 8 PM on March 12, leading to the fuel melting from 5:30 AM on March 13. Even though seawater was injected from fire engines afterwards, the rupture of pressure vessel was caused and the majority of melted fuel dropped into the containment vessel of Unit 3. The estimation of amount of radioactive materials such as Xe-133, I-131, Cs-137 and Cs-134, emitted to the environment from Units 1 to 3 is discussed in the presentation. Direct causes of the accident identified in the AESJ Report were, 1) inadequate tsunami measures, 2) inadequate severe accident management measures and 3) inadequate emergency response, post-accident management/mitigation, and recovery measures. These were caused by the following underlying factors, i.e., a) lack of awareness on the roles and responsibilities by experts, b) shortfalls in establishing safety measures and fostering safety awareness by utilities, c) lack of safety awareness by the regulatory body, d) inadequacies in attitude of learning from efforts and collaborations in the international community, and e) shortage of qualified personnel to ensure safety and inadequacies in organization and management framework.

 

[jim hardy]

Photos in those reports are better resolution than i remember from 2011.

Thanks !

 

[turi]

A lot of handouts today on various topics (some of them the usual daily ones, others with more in depth information):
http://www.tepco.co.jp/nu/fukushima-np/handouts/index-j.html

Among them a lot of information about the work at Unit 3, including radiation measurements:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170220_02-j.pdf

 

[Sotan]

Indeed lots of documents - a more recent one presenting the plans to test, in the following days, a British-made "multicopter", a remote-controlled drone that can fly over the buildings and record high resolution images and radiation dose values and plot them as three dimensional maps.

The second link posted by turi above speaks about progress in the preparations for installing the building cover and crane that will serve to remove the spent fuel from Unit 3.
I just wanted to point out pages number 8-9: impressive reduction of the radiation dose values after the installation of shielding on the operation floor.
Same conclusion can be drawn from the comparative images taken with a "gamma camera" in March 2014, March 2016 and December 2016.

 

[I_P]

etudiant, Hiddencamper, and Sotan, thanks for the feedback. Sotan, the report was helpful. The complete story of what happened during the accident won't be known for some time as it has not been possible yet to enter critical areas within the damaged units - correct? 5k+ workers/day average... What was the staffing level when they were operational?

Edit: should have quoted the post I was responding to on p56

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/roadmap/2017/images1/d170223_08-j.pdf (in Japanese)
A report on two subjects: first part covers the recent investigation of PCV of Unit 2, while the second half is about the planned investigation of PCV of Unit 1.

- Regarding the first part there is not much new in this report. Just a couple of new facts that I noticed:
- The cables found inside X6 penetration had their "chloropren gum" covers gone, which means that the temperature in that area exceeded 300 ^o Celsius at some point.
- The "deposit" or "sediment" is roughly of three types: a black paste, thin pieces of material, and peble/rock sized stuff.

- The second part begins on page numbered 17 as given by Adobe Reader, which is also page 0 of this second part.
- The water level is higher in this unit. They will send a robot in using the X-100B penetration, which is located higher than the X6 that was used in Unit 2. The robot will go in through a pipe, fall down on the "1st floor grating", go around the pedestal about 180 degrees and drop a camera/radiation sensor, through the grating, through air and later on through water, to examine an area right below the pedestal opening (Page 1). That is because they assume much more fuel (most of it?) melted in this unit, so it might have spilled over through the pedestal opening.
- Page 4 gives the first step of this investigation: the replacement of the guiding pipe which is inserted at this moment in that penetration. Must be replaced because the end of it has some bellow which might impede the advancement of the robot.
- Page 5 shows something new, a graph that plots the radiation dose measured in air vs the distance from the pedestal floor; based on how those values will plot, compared to the so-called "background values" corresponding to measurements made on the pedestal floor, they will be able to indirectly assess the presence (or absence) of melted fuel debris/corium in that area.
- Page 6 shows the intended route as seen from above, and the main points of interest: D0, check for signs of debris spilled from the "drain sump"; D1-D2, check for debris spilled from the pedestal opening; D3, check whether the debris has made contact with the PCV wall (shell).
- Page 7 shows the robot.
- Page 8 shows Step 2, the insertion of the self-propelled robot. Page 9 lists the main improvements made on the robot since the last investigation (April 2015), when it got stuck in a ditch and the cameras performed unsatisfactorily.
- Page 10-11 show another new aspect: Step 3, the prelevation of a sample from the sediment that was observed disturbed and floating through water during the last investigation, when the camera approached the bottom of the vessel. A suction hose will be lowered through the same route and used to take a sample of the water and sediment. (Rather small particles of the later, considering that there's a sieve at the tip.)
- Finally page 12 gives the schedule: step 1 to begin in the first days of March, the robot will go in around the middle of the month, and the sample will be taken sometime at the end of March.
- Page 13 shows a few aspects regarding training on mockups.

 

[Astronuc]

On Sunday, February 19, Asahi Shimbun reports "Radiation levels at Fukushima reactor puzzle nuclear experts"
http://www.asahi.com/ajw/articles/AJ201702190042.html

Based on the images, TEPCO estimated 530 sieverts per hour at a point almost halfway between the metal grating directly beneath the pressure vessel and the wall of the containment vessel. Black lumps on the grating are believed to be melted fuel.

A different robot sent in on Feb. 9 to take pictures and prepare for Sasori’s mission estimated 650 sieverts per hour near the same spot.

It would help to have an idea of what elements (radioisotopes) are responsible for the activity. If it is compounds of U/Pu it would mean fuel somehow got there, or if it is Cs/Sr, it could mean the water level was that high and soluble fission products were deposited there. It would help if they did gamma spectroscopy.

Speculation about molten fuel outside of containment are not helpful, especially when analogies to lava pouring into the sea are not consistent with observation.