Japan Earthquake: nuclear plants Fukushima part 2

[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.