Japan Earthquake: nuclear plants Fukushima part 2

In summary, there was a magnitude-5.3 earthquake that hit Japan's Fukushima prefecture, causing damage to the nuclear power plant. There is no indication that the earthquake has caused any damage to the plant's containment units, but Tepco is reinforcing the monitoring of the plant in response to the discovery of 5 loose bolts. There has been no news about the plant's fuel rods since the earthquake, but it is hoped that fuel fishing will begin in Unit 4 soon.
  • #701
Rive said:
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).

With the reactor breached, adding water means any that spills out goes into the containment, where the fuel debris should be.

I mean, there's no reason you can't inject to the dry well spray spargers, but injecting to the reactor core guarantees you get any debris in there too.

If you stop injecting, between lowering level and heating up water you run the risk of airborne contamination. Not desirable. The water also acts as shielding.
 
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  • #702
Is the fuel still generating that much heat?
We're now 4 years since the accident, how much residual activity does the fuel have.
There was a curve, from MIT I think, that projected the decay heat. The levels by now should be much less than earlier if that chart was accurate.

I'm sort of thinking of the Chernobyl 'Elephants Foot' as a model, a mass of congealed fuel, containment steel and concrete material. Is that still unrealistic?
 
  • #703
I can't say for certain. Remember the elephant's foot mixed with a ton of sand from around the reactor, which my understanding is that it helped to change its structure and allow it to solidify.

The fuel still releases heat. It's "safe" if it's uncovered with water, but you lose the shielding effect and now have airborne potential. Keeping it submerged prevents those issues.

It's not enough heat to do damage but it can be problematic in other ways.
 
  • #704
etudiant said:
Is the fuel still generating that much heat?
It is not. Generally, it takes 3-5 years for fuel to be ready for dry storage after removed from the core. However, it's not just about the heat generation. It's now a melted mass, with much lower surface/mass ratio, so it still can be/go hot if the cooling is not adequate.

Also, the mentioned 'elephant foot' started to crumble after some years. So corium indeed hase some potential to go airborne with time.
 
  • #705
I think it's just inertia.
If you change anything and something bad happens, you are getting the blame.
 
  • #707
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150629_05-j.pdf
This is a report regarding the preparations being made for that A2 investigation of PCV of Unit 2. (There is a previous post about this operation on page 35 of this thread.)
It is in Japanese only but still worth taking a look.

Page 2 shows that they have removed most of the concrete blocks located in the front of the X-6 penetration, using a remote controlled robot.

Page 4 shows the results of radiation dose measurements around X6 penetration. Highest recorded value was 1197 mSv/h (informative value only, considering that the apparatus used for measurement has a maximum scale value of 999 mSv/h). They believe that only about 100 mSv/h is direct radiation coming from the inside of the PCV - the rest being due to various contamination of the area. They plan to clean and shield the area as best as they can before starting investigation work.

Page 5 shows a very interesting photo: something melted and leaked through the bolted flange/lid that covers the X-6 penetration pipe. Some of the matter is still hanging down from the lid, some of it has fallen on the floor. They speculate that the matter is composed of rubber-like material from the O-ring that seals that lid as well as from the cables located inside the pipe, as well as, maybe, other stuff.
 
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  • #709
I'm very glad to hear that it worked.
Some people were skeptical but it worked.
One worry less.
 
  • #710
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150701_05-j.pdf
(in Japanese)
Tepco report regarding the removal of spent fuel from the SFP of Unit 3

Page 2 – concept of the cover to be installed over the Reactor 3 building in order to remove the spent fuel from the SFP
Page 3 – overall view of the planned setting of the installations for spent fuel removal
Page 4 – tentative schedule. Red line is today. The cover should be in place at the end of 2017 and then the removal of the 566 bundles of fuel from the SFP should begin.
Page 5 – images showing the process of cover construction
Page 6 – radiation dose rates on the operating floor of Unit 3 (in fact, at floor + 5m height) at present are around 220 mSv/h in the area of the shield plug
Page 7 – radiation doses at operating floor + 50cm height.
Page 8 – expected radiation doses when the decontamination of the area is over – at operating floor + 50cm height.
Page 9 – explanations on the measures for decontamination and reduction of the radiation dose prior to actually starting the assembling work for the building cover and in the early stages of the assembly operations. Setting shielded “waiting areas” for workers to be protected from radiation when not actually involved in work.
Page 10 – images with the building cover during trial assembly.
Page 11 – they explain how they arrived at those expected values of radiation “after the decontamination is over”
Page 12 – measures for protection of the workers from radiation during the installation of the bridge for the transportation of the fuel bundles. The actual installation is to be done in one day, using 4 teams of 15 workers each, each team working for 1 hour and making use of various methods for shielding the workers, as seen in Page 13 too. Steel plates of 150mm thickness will reduce the radiation dose to 1/100 of whatever is around. Thinner plates (50mm thick) offering shielding to 1/3 of the ambient radiation dose will be used in cages and covers that can be moved and placed around by crane.
Page 14 contents some final remarks on further decontamination to be done, followed by radiation measurements and evaluation and then by the finalizing of the work plan and schedule for cover installation.
Pages 15~ are additional materials used in the preparation of the report.
Page 27: photo of the operating floor taken on Dec 8, 2014.
 
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  • #711
Sotan said:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150701_05-j.pdf
(in Japanese)
Tepco report regarding the removal of spent fuel from the SFP of Unit 3

Seems that a very large amount of serious preparation is under way. Japan is working the problem diligently.
Still, the image of the cleared top of reactor 3 was sobering, especially when combined with the radiation map.
This has a long ways to go.
 
  • #712
I found this link on another related site:
http://www.jaif.or.jp/en/toshiba-and-irid-develop-small-robot-to-investigate-fukushima-daiichi-2-pcv-interior/

There is a video with the new robot working on a mock-up, quite interesting.
 
  • #713
etudiant said:
Seems that a very large amount of serious preparation is under way. Japan is working the problem diligently.

Yes, looks promising. Top of SFP is almost completely free of debris.

Still, the image of the cleared top of reactor 3 was sobering, especially when combined with the radiation map.
This has a long ways to go.

220 mSv/h is not high.
Remember the base of vent stack which has ~10000mSv/h...
 
  • #714
nikkkom said:
Yes, looks promising. Top of SFP is almost completely free of debris.
220 mSv/h is not high.
Remember the base of vent stack which has ~10000mSv/h...

There are much hotter spots indeed, but 220 mSv/hr is 4x the annual permitted dose for US radiation workers, so still too hot to allow longer term use of work teams.
 
  • #715
nikkkom said:
220 mSv/h is not high.

comparatively it's not, as noted. ~ 22 R /hr? Our stay time would be under ten minutes , you'd get three months' worth of exposure in that time.
 
  • #716
jim hardy said:
comparatively it's not, as noted. ~ 22 R /hr? Our stay time would be under ten minutes , you'd get three months' worth of exposure in that time.

Yeah, that's a stupid high dose. Keep deconning.
 
  • #717
Unit 1 cover is being dismantled:
http://mainichi.jp/english/english/newsselect/news/20150728p2g00m0dm069000c.html

Fisheries agree for purified subdrain water to be released to the sea:
http://mainichi.jp/english/english/newsselect/news/20150728p2a00m0na016000c.html
 
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  • #718
Has TEPCO sent the scorpion robot down the CRD cattle chute yet? I was really looking forward to that footage.
 
  • #720
http://www3.nhk.or.jp/news/genpatsu-fukushima/20150731/0440_robot.html
(Article in Japanese on the NHK site)

The investigation of the interior of the PCV of Reactor 2 at Fukushima Daiichi plant, which was tentatively scheduled for sometime next month, might be postponed towards December or even later in the worst case scenario, due to difficulties in planning the operation.

Tepco says the radiation level in the area of the PCV penetration pipe that is to serve for robot access - where they have been removing those concrete blocks - is high and using remote-controlled machines they haven't yet been able to remove all the blocks which appear stuck. They are trying to loosen them using chemical substances but at the same time they are considering whether it will be required to design stronger remote-controlled equipment. If it turns out that this is absolutely required, the investigation may be pushed towards December or even later. Even if they succeed to remove the stuck concrete blocks, the decontamination will still take some time, so August seems to be no longer a possibility for sending the robot in.

------------
http://www3.nhk.or.jp/news/genpatsu-fukushima/20150730/2123_trench.html
(Article in Japanese on the NHK site)

Tepco announces that on July 30th all the highly contaminated water from the trenches at Fukushima Daiichi has been removed and they are now filling the last portions of the pits and trenches with concrete (to be done in ~10 days or so). Thus one of the highest risks of contamination of the ocean has finally been averted.

-------------
http://www3.nhk.or.jp/news/genpatsu-fukushima/20150730/0402_gareki.html
(Article in Japanese on the NHK site)

The lifting of the collapsed FHM wreckage from the SFP of Unit 3 (mentioned by LabratSR above) is scheduled for August 2.
 
  • #721
Sotan said:
The lifting of the collapsed FHM wreckage from the SFP of Unit 3 (mentioned by LabratSR above) is scheduled for August 2.

Wow, that is a major event.
I'm impressed that the access to Unit 3 is good enough to allow a 20 ton piece to be extracted from a very tricky and potentially hugely hazardous position.
Frankly, none of the spindly crane structures that dot the site seem adequate to me to control this kind of a bulky and unbalanced load within the centimeter accuracy that is required. I just hope it does not worsen the problem.
If however this can be managed, it would certainly make the Unit 3 cleanup timeline more credible.
 
  • #724
turi said:
In English: http://www.tepco.co.jp/en/press/corp-com/release/2015/1256671_6844.html

Thank you, Sotan and Turi, for posting this. Kudos to the workers who pulled this off and the engineers who planned out the operation.
It is a substantial step forward, as this piece was preventing the cleanup from moving ahead.
Japan is gradually chipping away at this problem with innovation, smarts and money. It is impressive.
 
  • #725
hoping for photographs... ! Been following since "that awful day"

Saw a very good Nova a few nights ago about it.
In fact they had two whole nights dedicated to Uranium - check PBS website
 
  • #726
Jim,
Thank you for the heads up on the Nova program.

Meanwhile, there are pictures and a video here: http://www.fukuleaks.org/web/?p=14930
 
  • #730
etudiant said:
Thank you, Sotan and Turi, for posting this...

turi said:
More pictures and video:...

Yes, thank you for posting this. The weather looks awful in that video.
 
  • #731
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150804_05-j.pdf
2-page Tepco report in Japanese with results of a quick video inspection of SFP of Unit 3 after removing the FHM.
They found that 4 fuel bundles that had been right under the FHM have had their handles deformed to some extent.
(there's a photo of those handles in the report.)

Apart from that, radiation monitoring before, during and after FHM removal indicated that, at least, the FHM removal operation did not cause any extra damage to the fuel bundles stored in the SFP and no additional release of radioactive materials in the environment.
 
  • #732
Sotan said:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2015/images/handouts_150804_05-j.pdf
2-page Tepco report in Japanese with results of a quick video inspection of SFP of Unit 3 after removing the FHM.
They found that 4 fuel bundles that had been right under the FHM have had their handles deformed to some extent.
(there's a photo of those handles in the report.)

Apart from that, radiation monitoring before, during and after FHM removal indicated that, at least, the FHM removal operation did not cause any extra damage to the fuel bundles stored in the SFP and no additional release of radioactive materials in the environment.
More pictures: http://photo.tepco.co.jp/en/date/2015/201508-e/150804-01e.html
There's quite a bit of rubble to be removed.
 
  • #733
turi said:
...not available in your region... I could try a VPN solution, I'll see. Thanks anyway.

Works for me using the free version of Cyberghost and a USA VPN.
 
  • #734
The bail handles on GE fuel are really robust. I'm concerned there may be some fuel element deformation in those bundles. Depending on he bundle, there are 4 - 8 tie rods that are used simply to hold the bundle together, and are what structurally support the bail handle, and transfer lifting force from the bail handle to the lower tie plate. If the load bent the handle, there's a decent chance of cracking the fuel elements in the bundle or at a minimum deforming them.
 
  • #735
That may help explain why TEPCO has such an elaborate structure planned for lifting out the fuel assemblies.
Barring damage, it is hard to see why 4+ year old spent fuel assemblies could not be hoisted out as is individually. There is no one within a couple of hundred feet of the SFP, so an intact fuel assembly would be no hazard.
 

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