Fukushima Japan Earthquake: nuclear plants Fukushima part 2

[Sotan]

Interesting, Rive.
To me the fact that the blocks moved looked like a positive indication of steam release or some other explosive action from the inside, as I imagined that the hydrogen explosion could have only pushed down on the well plug...
I didn't know vacuum after the explosion can do that?!

 

[Rive]

I can't be sure, too many things depends on how many space there is below those blocks. But it would fit with the low radiation.

This kind of 'blast effect negative phase' (you can google it) is generally associated with nuclear or thermobaric weapons/explosions and can be quite strong.

Ps.: as I think about this, the vacuum effect of a hydrogen explosion might be quite remarkable, since the result is water (vapour)? This would also fit. But again, I can't be sure, so it's just an idea. Might be completely baseless.

 

[Hiddencamper]

The shield plugs are on top of the drywell head. You can stand on top of the plugs during operation with virtually no dose from the reactor. They are massive plugs.

The dose rates suggest that there was leakage from the drywell head into the area under the plugs.

As for vacuum, no idea why. A hydrogen explosion causes the blowout panels to break away. If the explosion was between the drywell head and plugs I suppose it's not impossible. But those drywell shield plugs are not a pressure retaining boundary. They are only for shielding and allow the drywell head cavity to be dry during operation.

 

[Rive]

The shield plugs are on top of the drywell head. You can stand on top of the plugs during operation with virtually no dose from the reactor. They are massive plugs.

The dose rates suggest that there was leakage from the drywell head into the area under the plugs.

As for vacuum, no idea why. A hydrogen explosion causes the blowout panels to break away. If the explosion was between the drywell head and plugs I suppose it's not impossible. But those drywell shield plugs are not a pressure retaining boundary. They are only for shielding and allow the drywell head cavity to be dry during operation.

The radiation level on operating floor in U2 and U3 is around 200-800+ mS/h as I recall, and definitely has a peak around the plug.
The radiation level on the operating floor of U1 is below 100mS/h and has no peak around the plug.

For me this suggests that for U2 and U3 the drywell cap has failed and there was leakage through the plug.
However, in case of U1 for me this suggests that there was no leakage through the plug: the hydrogen (and the contaminated steam) come on a different way (so it could contaminate the whole floor without peaks).

Regarding the vacuum part: when an explosion occurs, right after the expanding phase the center rapidly cools down (in case of hydrogen: the water partially condensates) and so creating a low pressure area. Since that shield plug was actually right below the center, it means that after the explosion the plug had atmospheric pressure below and partial vacuum above. The maximal lifting force would be ~ 1000 ton (I hope I did the math correctly).
Of course it was just partial vacuum, so the actual lifting force was surely lower.

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/roadmap/images1/images2/d161124_08-j.pdf
(in Japanese)
TEPCO / IRID report on the progress towards the planned investigation of the interior of Unit 2 PCV through the X-6 penetration

Very short summary:

The concept of the planned investigation has been presented before: send in a robot through the X-6 penetration, continue via the CRD rails, drive over the platform, look up towards the control rods and down towards the pedestal.

You might recall that the area of the lid of the X-6 penetration was found to be strongly radioactive, and decontamination operations didn't go very well. Therefore, they have to cut a hole in the lid to gain access into the penetration, using a complicated procedure, aided by specially constructed equipment (an "isolation mechanism" comes first and clings onto the X-l penetration lid using strong metal clamps, then a shielding structure is attached to it, followed by the hole-cutting machine. The "isolation mechanism" contains a ball valve and its role is to allow pumping in pressurized nitrogen, to keep dust and PCV air from coming out during the hole-cutting operation. The valve will then remain closed after the retraction of the hole-cutting machine.

They have already used the equipment on a model and confirmed it's capabilities.

Highest radiation reading recorded inside the PCV in March 2012: 73 Sv/h (page numbered 9)

This time the robot will be preceded by a device for clearing away sediments (sediments in the area were observed during the last investigation).

The operation is scheduled to start sometime in January next year.

 

[etudiant]

It is evident that this work is far beyond the capabilities of any utility, even as substantial a one as TEPCO once was.
It seems more akin to a major government engineering research effort.
Does TEPCO really still contribute anything useful to the work here?

 

[Sotan]

IRID (International Research Institute for Nuclear Decommissioning) is listed at the top of the report shown in my previous post...
This diagram from IRID site is suggestive for the complicated relations that have formed around the Fukushima Daiichi issue. TEPCO still plays a role, they have to carry out all the work on site (certainly together with contractors, sometimes) and provide all the data and feedback - but undoubtedly other factors are involved, especially in R&D:

As for the relationship between TEPCO and the Government, these recent articles may be explanatory:
http://asia.nikkei.com/Politics-Eco...y-involved-in-Fukushima-plant-decommissioning
http://asia.nikkei.com/Japan-Update/Tepco-seen-staying-under-government-control-for-some-time

 

[etudiant]

A very informative diagram, thank you!
The structure seems very complex, so quick decisions within it would be very difficult to reach. Presumably that is by design, there is no emergency now, but rather a very complicated problem with no existing precedent. Exploring the ramifications of decisions carefully before acting seems a sensible priority.

 

[turi]

The unit 3 spent fuel pool is getting a part of a new roof: http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2016/images/handouts_161220_01-e.pdf. The new roof will house a new fuel handling machine.

 

[etudiant]

Very impressive work is getting accomplished here.
The focus on the SFPs of the reactors makes eminent sense, they hold a large inventory of fissile materials that needs to be put into safe storage.
It is interesting that the reactor with the most physical damage is getting the priority for the SFP cleanup, perhaps because access was easier as a result of the explosion. I
It does show that Japan has a realistic plan for removing the unmelted nuclear material from the site within the next few years.
The larger challenge of locating and removing the corium is not time critical and can be safely deferred until later in the coming decade.

 

[Sotan]

An image taken during the cutting of a hole in the door of the X6 penetration of Unit 2 PCV:
http://photo.tepco.co.jp/date/2016/201612-j/161224-01j.html

Image and a movie with the X6 penetration after the hole is done:
http://photo.tepco.co.jp/date/2016/201612-j/161226-01j.html

 

[turi]

Thanks, Sotan. Tepco usually has a press release together with the new images and videos. Oddly I can't seem to find one this time.

 

[etudiant]

Toshiba is apparently facing a multi billion dollar writedown from its acquisition of the CBI nuclear business in the US.
I have to think that this is traumatic for a company already struggling with the nuclear issues in Japan.
Presumably the Japanese government will take note of the risk that these setbacks will undermine Toshiba's ability to adequately support the Fukushima cleanup.
Is there any discussion regarding this prospect in Japan by the various players involved?
If Toshiba can solve the problems currently dogging its nuclear program, it will have a near global leadership in the segment, as France and the UK have faltered.
Does Japan still support nuclear as a strategic priority or had Fukushima ended that?

 

[Sotan]

The future of nuclear industry in Japan is a very complicated issue, etudiant; lots of articles come up from a simple search, and some people might say this is not the best place to discuss it.
It depends who you ask, as there's the usual conflicting views of government and industry (who want to go forward) and activists and opposing groups (who want/hope to be able do make do with sun and wind and waves as energy sources).
I'll just put two links here, one describing the government's rather reluctant and unhappy decision to scrap Monju:
http://www.japantimes.co.jp/news/20...ey-cog-japans-nuclear-energy-policy-scrapped/
and one speaking of a (secret?) government initiative to establish... Monju's successor:
http://www.asahi.com/ajw/articles/AJ201612010046.html
These seem to suggest the continuation of government's support for a strong nuclear component in Japan's energy policy - but also underline the difficulties that come from public distrust and opposition after the Fukushima plant accident.
As always, the tone of such articles depends very much on the newspaper's position on the matter, and I only listed these two as examples of what's being talked... even though I know it doesn't completely cover what you asked.
- A more detailed, numbers-filled and updated material on (nuclear) energy policy in Japan can be accessed here:
http://www.world-nuclear.org/inform...ofiles/countries-g-n/japan-nuclear-power.aspx

 

[Sotan]

Thanks, Sotan. Tepco usually has a press release together with the new images and videos. Oddly I can't seem to find one this time.

No turi I couldn't find one either.
There's this document submitted to NRA on Dec 22 which detaliates the Unit 2 PCV investigation plan and the hole opening operation (in Japanese only)
http://www.nsr.go.jp/data/000173970.pdf
Looks like they will move on to the actual investigation right after the New Year.

 

[etudiant]

The future of nuclear industry in Japan is a very complicated issue, etudiant; lots of articles come up from a simple search, and some people might say this is not the best place to discuss it.
It depends who you ask, as there's the usual conflicting views of government and industry (who want to go forward) and activists and opposing groups (who want/hope to be able do make do with sun and wind and waves as energy sources).
I'll just put two links here, one describing the government's rather reluctant and unhappy decision to scrap Monju:
http://www.japantimes.co.jp/news/20...ey-cog-japans-nuclear-energy-policy-scrapped/
and one speaking of a (secret?) government initiative to establish... Monju's successor:
http://www.asahi.com/ajw/articles/AJ201612010046.html
These seem to suggest the continuation of government's support for a strong nuclear component in Japan's energy policy - but also underline the difficulties that come from public distrust and opposition after the Fukushima plant accident.
As always, the tone of such articles depends very much on the newspaper's position on the matter, and I only listed these two as examples of what's being talked... even though I know it doesn't completely cover what you asked.
- A more detailed, numbers-filled and updated material on (nuclear) energy policy in Japan can be accessed here:
http://www.world-nuclear.org/inform...ofiles/countries-g-n/japan-nuclear-power.aspx

Thank you, Sotan-san, for your very informative response.
It does seem clear that Japan is attempting to build a new public consensus using more realistic cost estimates that recognize nuclear accidents can be hugely costly. I've not seen anything comparable from any other country or source, real efforts to include the cost of a failure into the rate calculations.
Clearly the various parties are all trying to build a solution acceptable both in terms of economic as well as social parameters. If Japan can find that balance, I'd think the future would be very bright for Toshiba as well.

 

[turi]

This is not really news, but today I have realized that the Google Maps images of the area are quite up to date (the unit 1 temporary roof cover has already been removed): https://www.google.com/maps/@37.4207748,141.0323845,3073a,20y,0.81h/data=!3m1!1e3

 

[LabratSR]

Video - "The Current Situation at Fukushima Daiichi NPS" - January 2017 version

http://www.tepco.co.jp/en/news/library/archive-e.html?video_uuid=o6iw41m6&catid=61795

 

[turi]

For those interested in some problem solving, Tepco has posted some challenges: https://tepco.cuusoo.com/#challenges

 

[Sotan]

New info on the planned investigation of Unit 2 PCV
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170123_05-j.pdf
(in Japanese)

Page 2 shows again the 7 steps of the plan. Step 3 is done already, step 4 (a preliminary check of the X-6 penetration and CRD rails) is set for Jan 24, and a similar preliminary check of the pedestal area is scheduled for Jan 26. Step 6 may or may not be needed (depending on the presence/absence/state of sediments on the route of the robot). Step 7 is the insertion of the robot for the actual investigation.

Page 3 gives details on Step 4 and 5 (the preliminary checks mentioned above). In Step 4 they will manually insert a guide pipe carrying a tilt camera at the tip, to check the state of the X-6 penetration and CRD rails. Step 5 is a similar check but aimed at the pedestal area, mainly to see what (if any) issues are posed by the sediments present in the area. The guide-pipe in Step 5 is "extendable", if that's the word.

Page 4 shows the planned device and method for cleaning sediments from the route along the CRD rails to be used later on by the investigation robot. It uses a high pressure water jet for that purpose, and there is also a "scraper" for the stuff that water can't blow away.

Pages 5-6 show the robot used in the final step of the investigation and give specifications of the various cameras it carries.

 

[Sotan]

In addition to the previous post:
At the bottom of this page there are the links to two very short but informative videos showing the X-6 penetration and the route that the robot will have to follow, as they appear in Unit 5.
http://photo.tepco.co.jp/date/2017/201701-j/170123-01j.html
Awesome view of the pedestal and bottom part of the control rods...
How will Unit 2's pedestal look?

 

[Sotan]

Unfortunately they had a bit of trouble today and stopped the operations related to Step 4 mentioned 2 posts above (the preliminary investigation of the state of the X-6 penetration and CRD rails).
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170125_06-j.pdf (in Japanese)

They did not succeed in inserting the guide pipe through the front seal installed at the entrance of the X-6 penetration. The presumed cause is the hardening of the O-rings of the seal due to the temperature which is lower than at the time of the training. The result is that much more force appeared to be needed in order to insert the pipe, and they preferred to stop.

The will warm up the front seal using a heater, soften the O-rings and reduce the resistance - and attempt again, tomorrow (Jan 26). Step 5 too will probably be delayed accordingly.

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170126_14-j.pdf
(in Japanese)
They performed the "Step 4" mentioned above; this document gives some of the results, including some photos.
Page 7 contains the conclusions:
- They confirmed that there is room enough to insert the 110 mm diameter guide pipe for the next investigation.
- There are no obstacles on/around the CRD rails to prevent them for doing the next step (pedestal area preliminary check).
- Hazy imaging in the area of the entrance to the pedestal space, but this will probably not prevent the next step (which will be carried out as soon as preparations are ready).

P.S. Great video at the bottom of this page:
http://photo.tepco.co.jp/date/2017/201701-j/170126-01j.html

 

[Sotan]

http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170130_01-j.pdf
(in Japanese)

2-page quick report with results of the second preliminary investigation - in the area of the pedestal of Unit 2 PCV.

On the left side of each page there is the photo of Unit 5, for reference. On the right side there are images taken in Unit 2.
Page 1 - right side: upper photo is of the "slot opening", not sure of the translation; lower photo shows the "flat bar" area, with a piece of grating missing (!) on the left side of the photo.
Page 2 - right side: upper photo is of the "CRD housing support"; lower photo is of the "flat bar".

-------------
I can find no interpretation or explanations... and the photos are so scarce, I wish we had more of them and maybe a video... but I will venture and say, what if that so-called "sediment" is... corium? Maybe the material was so fluid that in many places it simply flowed through the grating without melting it, and among the control bar mechanisms? Maybe a larger lump, colder and unable to go "through" the grating, took down that portion of grating with it, simply by weight. Could the "sediment" be corium remains that stuck to the grating?
Also, under such conditions, navigating a robot over that grating (with missing parts and all) will be a nightmare...

 

[jim hardy]

Wow Sotan THANKS !

Was there a mention of the radiation field in there , or robot stay time ? I'd expect Corium would be so active, hundreds of Seiverts / hr, as to wreck the robot's electronics .

 

[Sotan]

No Jim, no other info in that short report.
I got so excited - because we (well... they) are certainly getting closer, that I forgot how radioactive corium should be.
On the other hand, based on the film released in Step 4 preliminary investigation, inserting the guide pipe with camera in the tip, and talking just a few pictures around, could have been a matter of minutes. So it's hard to say.

I am sure we will get more info soon, they must be analyzing much more results than those in this quick report.

 

[Sotan]

http://www.businesslive.co.za/bd/wo...-find-could-be-a-big-breakthrough-in-cleanup/
"Tokyo — Tokyo Electric Power (Tepco), the operator of Japan’s wrecked Fukushima nuclear plant, has found possible nuclear fuel debris below the damaged No2 reactor, one of three that had meltdowns in the 2011 disaster, public broadcaster NHK reported on Monday."

Also here
http://asia.nikkei.com/Business/Companies/Possible-nuclear-fuel-debris-sighted-under-damaged-Fukushima-reactor

NHK short video - I cannot see it, maybe you can see the "black mass" they are talking about in these images:
http://www3.nhk.or.jp/news/html/20170130/k10010857621000.html

By now it's all over the internet but no new photos released.

 

[Hiddencamper]

http://www.businesslive.co.za/bd/wo...-find-could-be-a-big-breakthrough-in-cleanup/
"Tokyo — Tokyo Electric Power (Tepco), the operator of Japan’s wrecked Fukushima nuclear plant, has found possible nuclear fuel debris below the damaged No2 reactor, one of three that had meltdowns in the 2011 disaster, public broadcaster NHK reported on Monday."

Also here
http://asia.nikkei.com/Business/Companies/Possible-nuclear-fuel-debris-sighted-under-damaged-Fukushima-reactor

NHK short video - I cannot see it, maybe you can see the "black mass" they are talking about in these images:
http://www3.nhk.or.jp/news/html/20170130/k10010857621000.html

By now it's all over the internet but no new photos released.

From the nhk link, at 26 seconds you see the wrecked crd support housing. You see a normal one at 1:26.

It's hard to tell exactly because without seeing the robot go in, I don't have a lot of context for where we are looking. But that support housing is directly below the vessel and core. It's designed so if the control rod drives eject from the core due to a weld failure that the rod cannot move more than a few inches because the housing will absorb the impact. And the support housing looks pretty messed up.The first 10 seconds the camera is looking sideways and down at the grating below where workers would be walking. There is grating and a rotating platform used for servicing control rods during an outage. You can see debris wrapped around the grating.

 

[Sotan]

Thank you Hiddencamper, I will take a look when I get home.
I saw a short material on NHK news television.
The reason there is no info about radiation is simply because the (guide) pipe used in this preliminary search only carried a camera and no radiation meter. The robot to be inserted later will carry such a device.
Also, from the text reports I expected a large black mass, but actually it seems they refer to smaller fragments scattered on the grating which can be seen in the released photos. They mentioned that molten fuel was probably 2000 or even 3000 degrees Celsius and yet in many parts the steel grating is not molten - yet part of the grating is missing, was it molten? carried away? which speaks about the complicated dynamics of the flow that took place in those moments.
One new aspect I learned/saw was that lots of water drops are coming down through the control rod installations and falling down onto the pedestal, obviously from the cooling water seeping through the holes left in the bottom of the RPV by the molten fuel.

 

[turi]

English press release from Tepco:
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170130_01-e.pdf
http://photo.tepco.co.jp/en/date/2017/201701-e/170130-01e.html

New self assessment report:
http://www.tepco.co.jp/en/press/corp-com/release/2017/1369451_10469.html