Fukushima Japan Earthquake: nuclear plants Fukushima part 2

[Gary7]

The muon "x-ray" of Fukushima #1 showed no fuel in the reactor.

http://mainichi.jp/english/english/newsselect/news/20150320p2g00m0dm028000c.html

Edit: This article (below) has a visual... may be slightly more interesting than the previous.
http://mainichi.jp/english/english/newsselect/news/20150320p2a00m0na013000c.html

 

[LabratSR]

Here is TEPCO's release on the Muon imagery. The future investigation plans outlined at the bottom are interesting.

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2015/images/handouts_150319_01-e.pdf

 

[Sotan]

On Mar 26 Tepco announced that there is a possibility that the sunk FHM in Spent Fuel Pool of Unit 3 might be in contact with (and perhaps has caused some damage) to the gate that separates the pool from the reactor well.

In order to better understand the situation as they are planning to remove the dropped FHM the investigated the area using the cameras used in the debris removal operatin, from the air and from underwater. A report on this is available here (in Japanes only):
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150406_04-j.pdf

Apparently there are 2 gates that separate the SFP from the reactor well, designated as G1 (towards the pool) and G2 (towards the reactor well). G1 appears to be in good state, well fixed in its supports and its seal seems functional - in agreement with the fact that no loss of SFP water has been observed in time. However, G2 seems to have been changed shape/position during the accident. The FHM was found to have no contact with the gate, except for some thin sheet of metal touching it somewhere. They will use the information in the operation for removing the FHM from the SFP.

---------------------

As you know the muon imagery has brought new evidence suggesting that the fuel in Unit one has melted and relocated toward the base of the reactor (not clear where exactly). They are now planning important investigation around the pedestal of Reactor 1. This document shows the outline of the operation and its schedule (sorry, only in Japanese):
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150406_03-j.pdf
The investigation consists of sending one shape-changing robot (equipped with camera, thermometer and radiation measurement device) through the 100mm diameter X-100B penetration and then have it walk over the grating located at first floor inside the PCV.
The robot investigation is planned for April 10 and 13 - perhaps the action is split in two as somewhere in the document it is stated that the robot will take a clockwise route up to a point, and then an anti-clockwise route for the remaining portion.
The results will be used, among other, in the planning of another investigation - this time down lower, outside of the pedestal.

 

[Rive]

Apparently there are 2 gates that separate the SFP from the reactor well, designated as G1 (towards the pool) and G2 (towards the reactor well). G1 appears to be in good state, well fixed in its supports and its seal seems functional - in agreement with the fact that no loss of SFP water has been observed in time. However, G2 seems to have been changed shape/position during the accident.

Quite interesting. Especially, because on the early days one of the main steam/heat sources around the U3 reactor well was rather close to those gates.

Ps.: it was said at one point that the steam there is just 'rainwater on the hot plate', but my personal opinion is, that the damage on the drywell/PCV cap there could be more extended than just the expected temporal leaking.

 

[Sotan]

By what mechanism do you think the G2 gate could have been damaged, while G1 escaped unharmed?
I don't have a clear image of the geometry of the area, but would it be possible for the falling FHM to hit, with some corner or some piece of its structure, the G2 gate, while (by total chance) missing gate G1? A beam or other object falling right in the space between gate G2 and the inside of the drywell and causing a wedge effect which practically dislocated one side of the G2 gate?

 

[Rive]

Here is the geometry, from the linked document:
http://keptarhely.eu/view.php?file=20150408v00gqxhsl.png

The 'steaming' locations, from the early days:
http://keptarhely.eu/view.php?file=20150408v00gtevln.jpeg
(The one on the right is not really visible, but I remember where it is - in the corner of the equipment pool and the drywell :) )

The same locations on a 'fresh' picture, with the pool gates visible:
http://keptarhely.eu/view.php?file=20150408v00gzoofr.jpeg

What I have in mind is, that steam pressure might be a reason of the relocation of the G2 pool: such event would not affect G1 (which is also has the water pressure on one side as advantage).

Of course right now it's just speculation.

 

[Sotan]

English material from Tepco presenting the Unit 1 PCV investigation by robot which has probably started today:

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2015/images/handouts_150406_01-e.pdf

 

[Sorai]

English material from Tepco presenting the Unit 1 PCV investigation by robot which has probably started today:

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2015/images/handouts_150406_01-e.pdf

It seems the robot got stuck a few hours after going into Unit 1:

"The robot entered the containment vessel through piping on April 10 at 9:30 a.m. It began its journey around the netted first floor of the vessel at 11:20 a.m. to measure the temperature and radiation levels while transmitting images of the surrounding conditions. But after covering about two-thirds of its planned route, the robot came to a standstill after 2 p.m.

According to an IRID official, the operators tugged on the robot's cable and sent instructions for it to change shape, but it still would not move. The robot’s camera, dosimeter and temperature gauge were not damaged, and the robot was still capable of transmitting data."
​

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201504110035

 

[Sotan]

I am reading Tepco's press release (in Japanese) http://www.tepco.co.jp/cc/press/2015/1249672_6818.html

Indeed, the robot got stuck, doesn't look like it can be recovers, so tomorrow (April 13) they are going to cut it's cable.
Such a result was considered, and cutting the cable was one of the possible outcomes.
They are also postponing the other half of the investigation, in which they were planning to use a second robot to go the other half of the grating.

They did get some valuable data though. The robot managed to go two thirds of its intended route and covered 14 out of the intended measurement and imaging points.

 

[westfield]

Here is the geometry, from the linked document:
http://keptarhely.eu/view.php?file=20150408v00gqxhsl.png

The 'steaming' locations, from the early days:
http://keptarhely.eu/view.php?file=20150408v00gtevln.jpeg
(The one on the right is not really visible, but I remember where it is - in the corner of the equipment pool and the drywell :) )

The same locations on a 'fresh' picture, with the pool gates visible:
http://keptarhely.eu/view.php?file=20150408v00gzoofr.jpeg

What I have in mind is, that steam pressure might be a reason of the relocation of the G2 pool: such event would not affect G1 (which is also has the water pressure on one side as advantage).

Of course right now it's just speculation.

If we are having a stab at this then I think the steaming was the symptom of the problem, not the cause.

Have a look at the red circled keyway on the right in this image that you linked -
http://keptarhely.eu/view.php?file=20150408v00gzoofr.jpeg

Its one of the steaming locations but more alarming is how displaced the keyway is in relation to the gate. I noticed this years ago and to me it was perhaps a hint that the whole "ring" around the top of the containment vessel is fractured. At the time we couldn't see that the middle section of concrete "lid" over the containment vessel had been broken in half by the falling overhead crane, it must have placed enormous stain on that ring of concrete that normally supports it.

I think the sort of damage that has created that displacement on the big concrete gate to the DS pool (or whatever you would like to call that pool) could also allow the SFP "G2" gate to simply fall out of its track over on the other side. Its not clear enough to see if that's the case though.

P.S> Just be be clear - I am certainly not saying this has anything to do with a containment failure, this is just the concrete ring around the top of the containment vessel I'm referring to in relation to the U3 SFP "G2" Gate displacement.

 

[Gary7]

Video from the robot inspection of Unit #1 is up on YouTube. (Video is from a Japanese news program. Feel free to remove if it is against forum rules).


The still photos are also getting a lot of attention from the papers as well. They say the robot encountered radiation of between 7 and 9.7 sieverts inside the unit (which was in line with Tepco's estimates). Ambient temperature was between 17.8 and 20.2 Celsius.
http://www.tokyo-np.co.jp/article/national/news/CK2015041402000134.html

 

[Sotan]

- Even if it is very early, I would be interested to hear the comments of the knowledgeable people in this forum about what is seen in that video.
What is that yellowish stuff that can be seen on the grating here and there?

- Tepco has a PDF report with some explanations (in Japanese but worth a look as figures and photos make it almost understandable):
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150413_02-j.pdf

-Page 2 shows the intended route of the robot, out of X-100B penetration and then to the right (anti-clockwise) toward investigation points B0...B17. (The other route, clockwise, from C0 to C11, planned for the other robot, can also be seen.)
-Page 3 mentions that the actual course (blue line) had to be corrected because of obstacles fallen on the grating, and that the robot got stuck somewhere around point B14. Green X signs mark the place of major obstacles. The 20mm scale shown on photos helps understand the size of some of those fallen objects (I don't know why but from the video I wrongly assumed they were much larger).
- Page 4: report on results regarding objectives 1 to 3 of the present investigation. (1) Access opening in the grating towards the lower floor was found to be in good condition, without major obstacles (in view of the planned investigation of the basis of the pedestal). (2) CRD rail (?) was not reached but there is some filming of CRD from the last point where the robot was active (images being processed now). (I don't know why this CRD rail was a major objective, I don't even know what it is.) (3) Along the traveled route no major destruction was observed; the HVH, PLR piping, walls of the pedestal showed no signs of major damage. Temperature and radiation values were measured along the way. (I don't know right now what HVH, PLR abbreviations stand for.)
- Page 5: Again we see the opening planned to be used to lower the robot down towards the basis of the pedestal. No major obstacles in the area.
- Page 6: Images from point B7. No major damage on the PLR piping (insulation). However there is some insulation material (?) fallen down on the grating.
- Page 7: View of the outside wall of the pedestal, in good shape (B3). View of the outside of the "machinery hatch" (?), in good shape, no major damage (B2).
- Page 8: Views from B1 point. No major destruction of HVH (D).
- Page 9: Radiation and temperature measurements.
- Page 10: In the narrowest portion of the route (between points B14 and B15) an obstacled was found and an alternative route was chosen. That's when the robot got stuck. But it managed to take some images in the direction of the CRD. Probable cause - robot rollers stuck in some uneven place formed between preexisting piping and the grating.
- Page 11: They measured about 10 Sv/h and under and are happy to see that the camera resisted 2-3 hours under such conditions. The second part of the investigation is being reconsidered to make use of the information achieved until now. A tentative schedule shows 13 to 17 April as the time window for this second attempt.
- Page 12: Mockup image showing the place where the robot got stuck.
- Page 13: Mockup image showing the CRD rail.

 

[Sotan]

- Correction to yesterday's post:
"Page 11: They measured about 10 Sv/h and under and are happy to see that the camera resisted 2-3 DAYS (not hours) under such conditions." (my apologies)

- There's a new pdf on Tepco's site (in Japanese) showing the planning o fthe second half of the investigation - using the clockwise route, which is probably under way as I post this.
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150415_01-j.pdf

- Page 3: some new hypotheses about how the first robot got stuck. Probably one roller was rotating in the air as it caught an empty space, a wider gap in the grating, combined with a difference in height. They plan to advance more slowly (since the robot can last for 2-3 days at least) and more carefully this time.

 

[Rive]

Its one of the steaming locations but more alarming is how displaced the keyway is in relation to the gate.

I could not decide if it's really a relocation or just there is no rubble there to fill the hole.

Page 3: some new hypotheses about how the first robot got stuck. Probably one roller was rotating in the air as it caught an empty space, a wider gap in the grating, combined with a difference in height.

Ouch. That would be a really stupid mistake. They already lost a robot in U2 for another such 'facepalm'.

 

[jim hardy]

- Page 11: They measured about 10 Sv/h and under and are happy to see that the camera resisted 2-3 hours under such conditions.

A few tens of sv is about where NMOS semiconductors should start degrading from radiation.

"Page 11: They measured about 10 Sv/h and under and are happy to see that the camera resisted 2-3 DAYS (not hours) under such conditions." (my apologies)

Thanks for the update. I was puzzled why they'd not use parts with better rad tolerance. Now it appears they did, which makes sense...

 

[Sotan]

Indeed, jim hardy, once again really sorry about that.

The second part of the investigation went well until now (based on the daily report in Japanese, http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150415_07-j.pdf)

- at 10:00 they started the operation of sending the robot into the PCV;
- at 11:15 the robot arrived on the grating;
- at 11:43 it started to advance on the grating;
- at 15:43 it had checked 6 of the 11 imaging points established in advance.

The investigation is set to continue on April 16 starting at 09:30.

 

[jim hardy]

really sorry about that.

For heaven's sake don't apologize - i feel very grateful for your effort !
Thank you for all the great information you translated.

 

[Hiddencamper]

The CRD (control rod drive) rails are used to move control rod mechanical drive units to/from underneath the vessel. If the robot got there it could turn and probably get a view of under the vessel to see the damage.

 

[Sotan]

Thanks Hiddencamper, that explains why they were so interested in the CRD rail area.
(On the mockup the thing designated as CRD rail didn't look very interesting.)
They said the first robot took some images towards that CRD and that they are working on analyzing those images (perhaps enhancing them) but nothing else was made public after that.

Not much news today either, only a pdf (in Japanese) at http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150416_04-j.pdf
showing the first half of robot #2's travel clockwise.
They say the HVH(D) and (E) as well as the PLR area showed no signs of major damage.
Radiation dose rate was between 6.7 and 8.3 Sv/h and temperature was 19.4-19.6 Celsius.
The pdf contains only a few foggy images.

 

[Sotan]

Actually a few hours later the continuation of the report mentioned above was also published (in Japanese) on Tepco's site:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150417_10-j.pdf
It presents findings from the robot's going to the remaining C6-C11 spots planned for investigation.
No significant damage was observed (on PLR pumps, PCV walls etc.).
Radiation dose was between 4.7 and 6.2 Sv/h, temperature between 20.7-21.1 Celsius.

 

[jim hardy]

Radiation dose rate was between 6.7 and 8.3 Sv/h and temperature was 19.4-19.6 Celsius.

What's normal rad level down there?
Underneath our PWR at shutdown was maybe 1/1000th that much, unless the traveling incore probes were parked there.

I assume BWR is similar, and they'd have been parked there when earthquake struck?

 

[Sotan]

This page of Mainichi Shinbun newspaper has a link to video from the second robot:
http://mainichi.jp/feature/20110311/news/20150418k0000m040048000c.html
I can't confirm cause I can't see it where I am now.

Edit:
It's on youtube too:


Robot camera repeatedly attempts to look down, through the grating.
Very interesting images, perhaps somebody can venture and tell us what we are seeing (is that water surface down there? is that melted metal towards the end?)

http://news.biglobe.ne.jp/domestic/0417/mai_150417_2974683460.html
This site says it is the surface of the water below the grating.
They also mention that these images were shot on April 15, and that robot #2 will also investigate the state of stuck robot #1 on April 18th (?? couldn't find this latter part on any other of the Japanese news sites; later edit: found something similar on NHK site).

http://getnews.jp/archives/921641
Water was confirmed visually on the bottom of the PCV for the first time. It is believed that the water level is at 2.8m above the bottom of the vessel.

http://www3.nhk.or.jp/news/html/20150417/k10010052131000.html
(This is from NHK site.)
Water on the bottom of the PCV was clearly visible in the images, and metal is highly corroded.
The apparent level of the water - 2.8m from the bottom - is in agreement with previous estimations.
The amount of rust and surface degradation of the grating and installations speaks about the high temperatures that occurred during the accident. (All those machines had had painted surfaces, whereas now all the paint seems to have gone.)
Robot #2 is still in the PCV and tepco will attempt its recovery after April 18 but before that they will try to use #2 for some extra investigation of the area where robot #1 was working at the time it got stuck.

 

[nikkkom]

It's been constantly wet there for four years, what paint can survive that?

Is this a novel program to remove corium (and everything else) by dissolution? I'm only half joking...

 

[Cire]

The image at 0:59 into that last video looks exactly like what you see when a pot of lead cools and hardens.

It looks like there is a shelf under the grate at that location.

 

[Hiddencamper]

What's normal rad level down there?
Underneath our PWR at shutdown was maybe 1/1000th that much, unless the traveling incore probes were parked there.

I assume BWR is similar, and they'd have been parked there when earthquake struck?

The drywell dose rates are highly location dependent. General areas are usually on the 10s or mR to low 100s. Near piping you get higher rates. Between the bioshield and the reactor up to 5 Rem. higher dose near the recirculaton and reactor cleanup valves and elbows, especially in plants with fuel failures.

In the subpile (directly under the vessel) with all neutron instruments inserted it's barely a high rad area, but if any NI is withdrawn dose rates are in the hundreds of mR

 

[Hiddencamper]

I don't know what PLR stands for, but that's the reactor recirculaton piping. No damage helps to support no LOCA at unit 1, which would also support the analysis tepco has done.

With no LOCA, if unit 1's IC remained in service it likely would have retained adequate core cooling.

 

[Sotan]

Indeed I found a list of abbreviations which states that PLR = Primary loop recirculation system.

 

[Sotan]

The image at 0:59 into that last video looks exactly like what you see when a pot of lead cools and hardens.

It looks like there is a shelf under the grate at that location.

That was what I thought too when I saw it.

http://mainichi.jp/english/english/newsselect/news/20150417p2a00m0na010000c.html
This report mentions "Meanwhile, parts of lead curtains used to reduce the radiation impact on pipes and other equipment were seen fallen on the steel mesh floor."
Maybe its molten lead indeed?

--------------------
Not related to the above post, but for some perspective, here's how the inside of the PCV of Unit 4 at Tepco's Kashiwazaki-Kariya Plant looks:

 

[Hiddencamper]

Just to mention the kashiwazaki plant is an ABWR design and has a larger containment system. It's like the mark II and Mark III had a baby.

The mark I containment is more compact. The one in the video is so spaceous, also well lit and clean which is unusual. Drywells are usually gloomy.

It probably wasn't molten lead. Probably the lead is still there, and the plastic like material around the lead melted.

 

[jim hardy]

lead melts at 621F 327C

http://www.ianbradshaw.co.uk/multimedia/fukushima/tepco.html

maybe early on...?

 

[Sotan]

Tepco report of April 20 (in Japanese) about the second robot
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150420_02-j.pdf

- They used the second robot to investigate the position of the cable left on site from the first robot. Interestingly, while most of the cable sits on the grating, there is a portion around the middle of the course ran by robot 1, where it is hanging in the air; coincidentally, that is also the place where the opening to be used go to the lower floor is located. Unclear from the document how high in the air or how it got into that position. They conclude that the cable poses no additional difficulty to the next planned investigation aimed at the bottom of the PCV.

- The first robot was found to be stuck as expected, with one roller fallen into a gap between grating frames, in a narrow place formed near a pillar. The same pillar will have to be avoided next time, if they are to continue to try for the CRD rail area. They believe there is a path, this time turning right at that pillar, not left (left is no longer usable anyway because of the stuck #1 robot). The path looks awfully narrow though.

- They decided to abandon the second robot too because a camera failed, probably due to the effect of radiation, and they are unable to confirm visually that the robot changes shape properly before being pulled back into the X-100B penetration pipe. (They don't want to risk blocking that pipe by pulling in the robot without proper shape confirmation.) The #2 robot was parked safely in a place where it won't hinder subsequent investigations, somewhere near point C3.

- Radiation dose values were between 4.1 and 5.9 Sv/h; temperatures between 17.9 and 20.4 degrees Celsius.

 

[Gary7]

Another burst of video from Fukushima. This one appeared on CNN complete with lurid headline (which they have since toned down)
http://edition.cnn.com/videos/world/2015/04/20/vos-fukushima-nuclear-plant.tepco

 

[elektrownik]

In this video there is a moment where radiation reading spikes to ~40Sv/h, could this be correct or this can be some sensor error ?

 

[Hiddencamper]

I definitely think 40 Sv/hr is possible in there. However the robot wasn't really moving and it jumped so fast that it's hard to really know if that particular measurement was real or not.

 

[Cire]

In this video there is a moment where radiation reading spikes to ~40Sv/h, could this be correct or this can be some sensor error ?

If you watch the video right when the value spikes there is a hiccup in the video feed. I think you what happened was a power transient/glitch or equivalent that spiked the system for a few miliseconds. You see the heavy averaging of the radiation value as it starts to drift back down. So probably during the hiccup some very large impulse value was put into the averaging and it just took a few seconds for it to trend out.

 

[Sotan]

This page http://en.dccc-program.jp/2015/04/09/?p=401 shows the present developmental stage of 11 R&D projects comprised in a program called “Conceptual Study of Innovative Approach for Fuel Debris Retrieval and Feasibility Study of Essential Technologies”. I might have posted similar links in the past, but these I think are updated versions (as of April 9 to be exact).

The projects are grouped into 3 categories:
- 1. Conceptual Study of Innovative Approach for Fuel Debris Retrieval (4 Projects)
- 2. Feasibility Study of Visual and Measurement Technology for Innovative Approach (4 Projects)
- 3. Feasibility Study of Fuel Debris Cutting and Dust Collection for Innovative Approach (3 Projects)

The 11 links lead to very concentrated 1-page pdf reports prepared by the various companies and consortia that are working on these matters.
Might be an interesting read.
Many of the research projects focus on the hypothesis that working under water shielding will not be possible.
One notion that was novel to me (might have simply missed it before): one project proposes to use "steel balls" as a shielding material in the last stage of fuel debris removal (from the pedestal area).

 

[Sotan]

The latest verison of "Medium and Longterm Roadmap" report of Tepco has been posted on April 30:
http://www.tepco.co.jp/decommision/planaction/roadmap/index-j.html

As usual there are a lot of documents in there, for now only in Japanese - hopefully to be translated into English in a month or so (at least they did in the past).

This time there is a new document called the "Strategic Plan", a massive 240 page report on all current issues at Fukushima Daiichi, which I am sure will be a good read once available in English. The Roadmap remains as a more general framework which defines the goals to be reached and the activities that need to be carried out; the Strategic Plan aims to be a much more concrete document, going into details, explaining the options and choosing from among them etc.
It is available in Japanese at http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/d150430_14-j.pdf

This is actually the "2015" version of the Strategic Plan - to be amended as required based on the actual situation of the plant and the most up-to-date information and data acquired. The entity in charge with the Strategic Plan is the "Nuclear Damage Compensation and Decommissioning Facilitation Corporation" or NDF, established in August 2014.

I only had time for a quick glance through it, but I did notice the stress on the need to plan in advance for the things that are going to happen soon (or even those happening not so soon) according to the Roadmap. For example, a lot of space is given to the presentation of the envisaged methods for accessing the RPV and PCV areas, together with the information available at the present regarding the location of the melted fuel. This allows to define one or more "most plausible" scenarios for accessing and removing the melted fuel (and the submersed method, as you know, is no longer the only method considered). As time goes by and more information gathers, hopefully a decision on the chosen method/scenario will be able to be made by the deadline stipulated by the Roadmap (first half of 2018). But things that are further down the road (such as storing the fuel debris, or all the contaminated materials that have accumulated and will continue to accumulate on the site) are also considered, as they are as important to be planned ahead.

...it is difficult to select something from it right now; I definitely was most interested in all the chapters (pages 95 to 192) dedicated to dealing with the fuel debris (a lot of examples, including photos, are based on what was found at Three Miles Island). I can only hope that this document is translated in English as soon as possible.

 

[nikkkom]

It's good that they have read TMI report. They must have an idea now how immensely difficult fuel removal would be. TMI struggled to remove fuel from a reactor that *did not* lose integrity of its outer shell. Here we have three reactors which melted through.

I think it does not make sense to remove the fuel. The fuel has no value. It can't be stolen from where it is now. The danger is only that it can leak. If the concern is that it may leak, how about thoroughly insulating it in place so that it can't leak?

 

[LabratSR]

Small robot to enter Fukushima No. 2 reactor

"“The robot is built to withstand 1,000 sieverts, so it should be able to operate for about 10 hours,” a Toshiba employee in charge of the project said."

http://the-japan-news.com/news/article/0002126853

 

[Sotan]

A new post in Japanese on Tepco's site led me to these pages in English at the IAEA home page:

IAEA Delivers Major Report on Fukushima Accident to Member States
(it seems this accident report is not a public document? there's no link to it anyway.}

IAEA Issues Report on Fukushima Decommissioning Review
Includes this link to the IAEA report (PDF document) after the recent evaluation mission to Fukushima Daiichi.

 

[turi]

IAEA Delivers Major Report on Fukushima Accident to Member States
(it seems this accident report is not a public document? there's no link to it anyway.}

The release is planned for September (though it doesn't say whether it will be a public release):

The IAEA’s Board of Governors will consider the report at their next regular meeting in June, before its planned subsequent release at the 59th session of the Agency’s General Conference in September, the annual gathering of IAEA Member States.

 

[turi]

A new prompt report:
http://www.tepco.co.jp/en/press/corp-com/release/2015/1250926_6844.html

• Measured radioactivity spike on March 20, 2011 likely caused by changed wind direction.
• Failed venting of unit 2: Failure of rupture disk to rupture still a possible cause. Data inconclusive.
• PCV of unit 1 became hot at the top: Cooling devices for spraying the top are a countermeasure option.

 

[turi]

There has been an update regarding the treatment of contaminated water:
http://www.tepco.co.jp/en/decommision/planaction/alps/index-e.html
http://www.tepco.co.jp/en/press/corp-com/release/2015/1251076_6844.html
Almost all water has been treated for Strontium, 2/3 of the water has also gone through ALPS. The remaining 3% of untreated water will take more time to treat as it has a high calcium and magnesium content and/or is at the ground of tanks to be disassembled (where the installed pumps can't remove it completely).

 

[turi]

An even newer press release now announces that the water with high salt concentration has been treated as well and that only the water at the bottom of emptied tanks remains to be treated for strontium:
http://www.tepco.co.jp/en/press/corp-com/release/2015/1251105_6844.html

Addendum: The second link in my post above is wrong (the text is correct), it should be:
http://www.tepco.co.jp/en/press/corp-com/release/2015/1251076_6844.html

 

[Sotan]

Tepco report dated May 28 (in Japanese):
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150528_01-j.pdf

They measured again the water level in PCV Unit 1. Water level was found to be about 1000 mm under the grating. It was 650 mm under the grating when measured previously, in October 2011. They speculate about this difference and what it can tell us about the water leaks. The water level is established dynamically as a balance between the water that is poured into cool the fuel and fuel debris, and the water leaked out of the PCV and S/C (two such leaks have been identified already, the "sand cushion drain line" and the "bellows of the vacuum break line" in the suppression chamber). They used to pour in 5 tons of cooling water each hour before November 2011 - but only 4.5 tons per hour after that, so the water level difference could be explained by that. They also make some calculations which suggest that the "holes" causing the leaks mentioned above could amount to 2.4 square centimeters and 0.47 square centimeters, respectively (these numbers sound incredibly small, but I suppose a lot of water can leak through there... Not to mention that there may be other holes too, not found yet.)

 

[Sotan]

A new Mid-to-Long Term Roadmap report (dated May 28) consisting of a set of documents is posted on Tepco website. In Japanese only.

This one document refers to preparations and activities carried out in view of the future removal of fuel debris:
http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/d150528_11-j.pdf

Starting with page number 5 there is a presentation of the planned investigation of the inside of the PCV of Reactor 2.

Basically the investigations has 4 stages (A1 to A4 – page 5).
A1 is the investigation of the state of the CRD rail and it has been done in August 2013.
A2 refers to the platform located inside the pedestal room – and this is the stage further detailed in the present document.
A3 (planned for 2016) refers to the same platform inside the pedestal room, with accent on the region located right under the CRDs.
A4 will focus on the situation of the bottom of the pedestal room.

(page 6) A2 investigation will aim, first of all, to check the situation of cables found in penetration X-6 and if/how they can be avoided, as well as the state of the first part of the CRD rail.
Then a guiding pipe (100 mm) will be inserted in the 115mm X-6 penetration, and through this pipe a crawler robot (with lights, cameras, temperature and radiation measuring devices) will get in.

(page 7) Items to be checked in this investigation (tentative)
Item 1 is the situation of cables inside X-6 penetration
Items 2-1 through 2-5 refer to checking the state of the CRD rail (in preparation for investigations A3 and A4) as well as identification of possible fallen objects located on the platform inside the pedestal
Items 3-1 and 3-2 are the ones that will make use of the crawler robot and refer to the state of the platform and of the lower part of the CRD rail. (Also include checking the position and state of the “CRD changing machine”).

(page 8) Tentative schedule of investigation A2. Training in May, on-site preparations till June 11, then the work will begin to remove the wall of concrete blocks placed in front of X-6 penetration – to end on July 9.
In parallel preparations and training with the devices used for investigation, and the actual opening of X-6 and start of investigation planned after the concrete blocks are removed.

(page 9) Explanation regarding the wall of concrete blocks placed in front of X-6 penetration. There are about 138 such concrete blocks that will have to be removed by remote-controlled devices. (There are abouit 10 mSv/h in the space in front of the concrete blocks wall.) Heaviest block is believed to weigh about 36 kg.

(page 10) Outline of the operation for removing the concrete blocks
It will be done using a machine (robot) controlled from the distance.
Removing one block will probably take about 15 minutes.
There will be a radiation dose measuring device on the manipulating arm of the robot, to sense any sharp changes in radiation, just in case. The radiation dose is expected to increase when removing these blocks (their main purpose seems to be shielding?), therefore a replacement shield (steel plate 100 mm thick) will be placed appropriately.

(page 11) Enumerates some risks related to this operation and envisioned ways to deal with them. Operation errors, blocks dropped, failures of the robot mechanisms, unexpected rise of radiation dose, stumbling on blocks heavier or larger than anticipated…

-------------------------------------
The document goes on then with another subject: muon imaging results.

Page 16~: a muon measurement image computed after 96 days of data gathering. Better image with less noise, smaller statistical errors and better clarity. The conclusion is the same though – no fuel left in the reactor core.

 

[etudiant]

Tepco report dated May 28 (in Japanese):
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150528_01-j.pdf

They measured again the water level in PCV Unit 1. Water level was found to be about 1000 mm under the grating. It was 650 mm under the grating when measured previously, in October 2011. They speculate about this difference and what it can tell us about the water leaks. The water level is established dynamically as a balance between the water that is poured into cool the fuel and fuel debris, and the water leaked out of the PCV and S/C (two such leaks have been identified already, the "sand cushion drain line" and the "bellows of the vacuum break line" in the suppression chamber). They used to pour in 5 tons of cooling water each hour before November 2011 - but only 4.5 tons per hour after that, so the water level difference could be explained by that. They also make some calculations which suggest that the "holes" causing the leaks mentioned above could amount to 2.4 square centimeters and 0.47 square centimeters, respectively (these numbers sound incredibly small, but I suppose a lot of water can leak through there... Not to mention that there may be other holes too, not found yet.)

Why the continuing water injection if the evidence is that the fuel is no longer in the reactor? Presumably that fuel now sits well below the current water level.
Seen that there is now enough water processing capacity, would it not be better to draw down the water level in the plant so that ground water flows in rather than having contaminated water flow out?

 

[Sotan]

I always underlined I am no specialist, but regarding your question etudiant:
Perhaps they continue to pour in water exactly in order to keep the fuel submerged - wherever it is? I mean, it still needs cooling, doesn't it? Presumably, stopping the water injection would lead to further retraction of the water level, through the leaks, and thus expose the fuel.
If cooling is no longer needed then it's a different story...

 

[etudiant]

I always underlined I am no specialist, but regarding your question etudiant:
Perhaps they continue to pour in water exactly in order to keep the fuel submerged - wherever it is? I mean, it still needs cooling, doesn't it? Presumably, stopping the water injection would lead to further retraction of the water level, through the leaks, and thus expose the fuel.
If cooling is no longer needed then it's a different story...

Thank you for your added thoughts. I'm no specialist either, just trying to see the logic here and the TEPCO releases don't address the question.
There is essentially no fuel left in reactor 1, so what is getting cooled?
That blob of fuel material is now down way below the water surface, somewhere in the pedestal., so it is not reached by the injections.
Of course we do not have muon pictures of reactors 2 and 3, so maybe the situation there is different.
Perhaps the idea is that as things are currently reasonably stable, no change should be made.

 

[Rive]

Why the continuing water injection if the evidence is that the fuel is no longer in the reactor?

The main fuel mass is down, but there is no guarantee that some debris is not left there above water level.

Also, with adding 'clean' water and removing contaminated water, the average contamination level in the basement water is decreasing (as I recall, a year ago it was ~ two decades lower than in the beginning).