Fukushima Japan Earthquake: nuclear plants Fukushima part 2

Click For Summary
A magnitude-5.3 earthquake struck Fukushima, Japan, prompting concerns due to its proximity to the damaged nuclear power plant from the 2011 disaster. The U.S. Geological Survey reported the quake occurred at a depth of about 13 miles, but no tsunami warning was issued. Discussions in the forum highlighted ongoing issues with tank leaks at the plant, with TEPCO discovering loosened bolts and corrosion, complicating monitoring efforts. There are plans for fuel removal from Unit 4, but similar structures will be needed for Units 1 and 3 to ensure safe decontamination. The forum also addressed the need for improved groundwater management and the establishment of a specialist team to tackle contamination risks.
  • #451
Some components we were aware on the early days regarding the rubble on top of U3 can be seen here in operation:
http://photo.tepco.co.jp/index-j.html

For example the 'spanner':
140528_05.jpg
 
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  • #452
That above is a photo from the opening of Reactor 1 in Fukushima Daini plant.
More info and photos in this report (in Japanese): http://www.tepco.co.jp/nu/f2-np/handouts/j140528a-j.pdf
They started the operation on May 12th and finished on May 27th.
On June 2 they plan to start removing the fuel assemblies and transport them to the common fuel pool.
They also list several issues they discovered upon removing all those lids: friction marks in the contact areas between the concrete hatch and its support; and damages to some of the bolts that hold in place the cover of the bellows mounted between the PCV and the building floor. Apparently 6 bolts were found ruptured, and one broken piece of one bolt is missing (although it cannot get anywhere into the reactor vessel, by construction). They conclude that all these damages found on inspection are not affecting the functions of the facility.
 
  • #453
I was wondering how the level of contamination in the exclusion zones for Fukushima and Chernobyl would compare to that of a hypothetical dirty bomb the intelligence agencies say we should all fear so much, when I came across this gem.

From Wikipedia:

"For the majority involved in an RDD incident, the radiation health risks (i.e. increased probability of developing cancer later in life due to radiation exposure) are small, comparable to the health risk from smoking five packages of cigarettes on a daily basis."

http://en.wikipedia.org/wiki/Dirty_bomb

Doesn't the author see the contradiction in this statement?

Either the risk is small and equivalent to smoking no cigarettes per day, or it is extreme and the equivalent of smoking five packs per day. (This would easily take at least twenty years off the average persons lifespan, I smoked two packs per day and developed mouth cancer at the ripe old age of 51, fortunately they operated and got it all and I have been cancer free for 6 years now.)

Someone on this forum once suggested I should use Wikipedia for a source before asking what he thought was a simple question. It is drivel such as that quoted above why I don't trust Wikipedia.

So I will ask the question here, where there are knowledgeable people who's answers I know I can trust, does anyone here know what the comparables may be.

Yes I know there are many unknown factors such as radiological materials used and dispersion methods etc., but a rough comparison.
 
  • #454
Sotan, are the decommissioning the Daini site? (Trying to understand why they are removing all the fuel)
 
  • #455
There are people/organizations calling for the decommissioning of Daini too, but after a quick search I couldn't find anything about such a decision having been taken. I will search more.

My impression after reading the last report, where Tepco underlines that "all these damages found upon inspection are not affecting the functions of the facility", is that they are at least planning to have it back working again.
 
  • #456
Hiddencamper said:
Sotan, are the decommissioning the Daini site? (Trying to understand why they are removing all the fuel)
As I know there is no decision yet. Right now they are trying to clean and patch it up for a through, complete inspection. As the already found problems (described by Sotan - thanks) suggests, it should be a really through inspection - including maybe x-ray checks of every joints even in the RPV.

I think the "They conclude that all these damages found on inspection are not affecting the functions of the facility. " there in real means: it'll continue to look like a power plant (practically they refer to the actual functions...).
 
  • #457
I think Rive is right. I found articles with more political than technical content which speak about some parties calling for the decommissioning of Daini too, but there's no sign of a decision to decommission.

Also, as Rive says, they are doing all sorts of inspections and checks in Daini.
Here are some more examples.
http://www.tepco.co.jp/nu/f2-np/handouts/j140526a-j.pdf
This brochure (in Japanese) shows some of the work going on at Daini.
Opening the reactor of Unit 1 is announced, in preparation to move the fuel to the spent fuel pool. However, they don’t say exactly why they are doing it. They just mention it’s the first time to open the reactor after 3/11, therefore they are being extra careful.
They are also thoroughly checking the Diesel generators.
They have also inspected the spent fuel pool and found two metallic items which shouldn't have been there. A hook with a piece of wire attached to it, and a ~55cm thing looking like a piece of pipe which turned out to contained scrapped parts of some mobile neutron detectors used in the past. You can see these two items on the last page of this report of March 18:
http://www.tepco.co.jp/nu/f2-np/press_f2/2013/pdfdata/j140318a-j.pdf
The neutron detectors were removed from the reactor after finishing their life, put into that pipe and meant to be scrapped, but fell into the SFP during transportation. Finding these two items prompted similar inspections of spent fuel pools of units 2-4 too, where they also found a number of 10 foreign items (bolts, pieces of wire, washers). You can see some of them at this link: http://photo.tepco.co.jp/date/2014/201403-j/140328-03j.html. TEPCO stresses that they are not posing any risk for the spent fuel assemblies.

The brochure ends with this: we will continue to ensure the safe cold shutdown state of the plant.

In another document they show some conclusions of the investigations regarding the foreign bodies found in the spent fuel pools.
http://www.tepco.co.jp/nu/f2-np/press_f2/2014/pdfdata/j140515a-j.pdf
The big hook with wire attached to it, found in SPF 1, might have fallen there during maintenance works sometime in 1992.
The piece of pipe with those straps if material used in neutron detectors was linked to some detectors used until 1998. The scrapped parts were kept temporarily hanged with a piece of wire next to the wall of the SFP until 1992, then all were gathered in a box, meant to be taken to some final storage place. This one item must have fallen to the bottom of the SFP during those operations.

TEPCO underlines that in April 2004 they have introduced new, tougher their rules aimed at preventing the fall of foreign objects in the SFP, and mention that new measures will be taken to prevent such incidents in the future.
---------------
At Daiichi they have tons and tons of debris in spent fuel pools, so this talk of a few bolts and items might seem exaggerated, but I suppose they have to explain even the smallest thing now.

Personally I was a bit surprised to see how dirty the bottom of the SFP is (but, of course, I don’t know anything about this, maybe it’s normal):
http://photo.tepco.co.jp/library/140328_03/140328_08.JPG

(sorry for the long post)
 
  • #458
http://www.tepco.co.jp/nu/fukushima-np/handouts/2014/images/handouts_140530_13-j.pdf
(in Japanese)

This is the report on the investigation of the other half of the S/C torus at Unit 1 in Fukushima Daiichi (see post #451).

The robot couldn't go all the way, due to a piece of metal sheet (insulation cover) that was fallen on the catwalk in the area named X-5G (South). Interestingly, this is also the area that was found to be dirtier than others, AND it showed increased radioactivity. In other areas they measured 200-500 mSv/h, but around X-5G the value reached 2400 mSv/h (see page 4 of the report).

They didn't find any additional water leaks in the areas inspected this time.
 
  • #459
Welp. Seems like they found another hole. Also, there's rust in places, so water must have been there for a while at least.
 
  • #461
I am not aware of an English version of that document - in fact I don't think there is one, these massive ones take time to translate and sometimes it's never done. I’ll try to “browse” it for you. (Edit when I finished: obviously I am not satisfied with this and you probably won’t be either, but… too little time and too much material, I really don’t know how I could do better. For now. Hopefully they will manage to translate this material, properly and entirely, in English…)

This chapter shows new results regarding the internal situation of the reactors, based on advances/improvements in the analysis of the accident progression.

Opening remarks (p. 277):
- although vital for the decommissioning of the reactors, at present there is insufficient information available regarding the location of the (core?) debris;
- direct detection/observation would be the preferable method for verifying core debris location, but unfortunately such an approach will not be possible before 2019;
- for this reason, every effort must be done to analyze all available information in order to evaluate the position and state of the debris;
- however, there are unsolved aspects regarding the progression of the accident, as well as limits in the possibilities offered by analysis. As a result, there is uncertainty regarding the results of the analysis;
- a continuous effort is being made to improve the model of BWR, aiming to reduce the scope of that uncertainty. Therefore, the conclusions of the analysis may change when new input becomes available;

P. 278 – the participants in the study/project; (note: I found http://www.iaea.org/NuclearPower/Downloadable/Meetings/2013/2013-06-18-06-20-TWG-NPTD/30-japan-postfukushima.pdf that the MAAP5 model is related to Toshiba and Hitachi-GE; SAMPSON (is developed by) a group from IAE)

P. 279 – improvements in the MAAP5 code model (several new hypotheses regarding the flow ways of the molten fuel, regarding the lower plenum situation, the PCV situation – including interactions with concrete, etc),. For example, the model now considers that the molten fuel didn’t flow down in a single flow – but perhaps in several currents or pathways.

P. 280 – improvements in the SAMPSON model
- a more detailed model of stratification due to temperature and of the threedimensional flows of water in the PCV; - a better model of flows and interactions in the lower plenum, etc…

P. 281 – simulations of the amount of molten material fallen to the lower plenum – before and after model improvements…

P. 282 – specific traits and roles of MAAP and SAMPSON code models (each of them has strong and weak areas)…

P. 283 – the two models and their (expected) outcomes in 2013, 2014, 2015 regarding the core debris

P. 284 – the two models have been put to work using the most recent information derived by Tepco regarding the progression of the accident in Reactors 1-3. Four events are especially considered: the moment when the water level in the reactor went down to the top of the fuel bars; when the fuel started to get damaged (over 1200 Celsius); when the fuel started to melt (over 2500 Celsius); when the RPV began to be damaged. Pages 285 and over present the results of the analysis using the two models.

P. 285 – An example using the progression of the accident in Reactor 3. A better match of the measured data is obtained using the improved models.

P. 286 – Analysis of the accident in Reactor 1 using MAAP; a table with the four main events and the times when they occurred. 91 tons of debris expected on the pedestal and 89 tons on the floor of the drywell.

P. 287 – Reactor 1 accident – SAMPSON analysis. 72 tons of fuel is still in the core, and 88 tons (fuel/debris) are on the pedestal floor.

P. 288 – Reactor 2 accident, MAAP analysis. 97 tons of fuel/debris on the pedestal floor, 142 tons on the drywell floor.

P. 289 – Reactor 2 accident, SAMPSON analysis. 152 tons of fuel still in the core, 74 tons of fuel/debris on the pedestal floor.

P. 290 – Reactor 3 accident, MAAP analysis. 58 tons of fuel/debris on the pedestal floor, 164 tons on the drywell floor.

P. 291 – Reactor 3 accident, SAMPSON analysis. 144 tons of fuel in the core; 82 tons of fuel/debris on the pedestal floor.

P. 292 – Recap of results.
- MAAP analysis indicates that in all three reactors all the fuel has left the core region into the other zones of the PCV and spread inclusively to the floor of the drywell.
- SAMPSON analysis indicates that in all three reactors part of the fuel is still in the RPV/core, but due to RPV damage part of the fuel has flown down to the drywell floor.
- There’s something I don’t understand well because I don’t know what jet pumps are: “molten material in the core -> damage to the shroud -> jet pumps -> possible flow (of molten material?) into the lower plenum”
- molten material might have resolidified inside the pipes for guding control rods and inside the fuel support structures;
- it is possible that there is fuel debris on the drywell floor;
- it is possible that there is fuel debris on the pedestal (and) “sump pit”;
Goals for the future:
- a better grasp of the strong points and differences between MAAP and SAMPSON models in order to exploit them more efficiently;
- continue to reduce uncertainties and improve models.

P. 293 – Some of Tepco’s views (1/2)
- regarding the possibility of shroud damage… Did the molten material flow on the shroud side, or on the “core support metal plate?” side… Or both ways. A lot of uncertainty here. In Reactor 2, when the flow of cooling water pumped into the shroud side was increased, a rise in pressure was observed, which indicates that the water level outside the shroud increased, and they conclude there is a high possibility that the shroud is intact in this unit. The same cannot be said about Reactors 1 and 3.
- about the possibility of “shell attack” (damage of PCV shell by falling molten material). Molten material has high fluidity and tends to spread quickly/ easily, so the possibility of it reaching the floor/wall of PCV cannot be denied (need to inspect PCV thoroughly). However, “shell attack” means the penetration of the PCV wall by the molten material, but considering that radiation levels consistent with such a scenario were not witnessed, they tend to believe there is no data yet to support such a scenario;

P. 294 – Some of Tepco’s views (2/2)
- about new results compared to previous results (they used to consider from SAMPSON that in Unit 1 there was no fall of molten material). MAAP and SAMPSON have different views on the deterioration of the Zr coatings; SAMPSON leads to lower results in heat outputs and therefore tends to conclude that more material has remained in the cores;
- about new results compared to previous results (previous MAAP results indicated all core material had fallen down to the floor). The MAAP model has a tendency to do that, if material starts falling to the floor then all of it ends falling – which doesn’t exactly agree with actualk measured parameters; Also, any molten fuel fallen and solidified into the guiding pipes for control rods remains stuck there, and this is taken into consideration into the new improved MAAP. SAMPSON too indicates that if such molten material has solidified in the guidance pipes of control rods, then there is possible molten fuel debris on top of the “speed limiting device of the control rods”, which is considered a significant result.

Conclusion: although there is no big change in the assumptions Tepco makes on the location and state of fuel debris in the cores and PCV’s, they believe new valuable information has emerged regarding the possibility of solidified fuel being present in the “metalic support structures for the fuel”(I’m sure there is a better term for this…) as well as new information regarding the location of the debris.

P. 295-299 – a CFD experiment on the flow and spreading of molten material; a mockup experiment on the effect of sea water coming in contact with molten core material; some other studies and general remarks on cooperation between various entities

P. 314~ Research aimed at stopping the leaks and making the PCV waterproof… Many tests aimed at stopping leaks of the S/C torus, but also in the areas of bellows (expansion joints) and PCV penetrations that might be leaking.
 
  • #464
Uh, Sotan, that was a lot of work... Thank you very much.

Actually I thought you might find the original stuff somewhere or some references within the Tepco site (as it was reorganized I have a feeling it's more about hiding stuff than providing it, especially in english), not providing the translations by yourself :-)

As I understand the jet pumps are some passive piping within the RPV but outside the shroud: they mix the return water flow with the water already present in the RPV to provide constant and homogenous flow of water inside the shroud.

The whole 'breaking the shroud' scenario is new for me.

Thanks again.
 
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  • #465
No worries Rive, I wouldn't do it if I didn't like it :) As long as it helps in any way.

Those simulations and models... They may be very important, they may be a waste of time. Doesn't seem like they can know for sure where the molten fuel is and in what proportion or state, but I suppose when they open the reactors they will be able to say how accurate their simulations were, and that might be useful in the future. I have looked up what I could on the Three Mile Island accident and I know they were in a similar situation and they didn't really know what's in the RPV until they really went in.

I was disappointed to learn that direct investigation of reactor cores will not be possible until 2019 or after...

I was impressed with the amounts of fuel that will have to be dealt with. So many tons and tons mentioned there...

Just browsing through such a huge document makes me shiver with the tremendous amount of work that is carried out, and the huge tasks that await.

And I agree the Tepco site is hard to follow sometimes. For example, I had no idea there is a part of it which deals with updates on Fukushima Daini; that pic you posted, of the "spanner", led me to all those reports regarding the inspection of spent fuel pools at Daini.
 
  • #467
Re: simulations.
They are just that. I haven't seen a simulation that closely reproduces the plant parameters as recorded during the accident yet so...
Re: inspection
I don't know why they give 2019 as a deadline. Perhaps they plan to plug the various holes and flood the RPVs completely by then, so robots won't have to deal with much radiation. I don't really understand why knowing where the fuel is doesn't seem to be a priority, or why it is impossible to pick a water line (perhaps even one of those currently being used to, you know, put water into the reactors) and push a borescope through.
 
  • #468
This short NHK article actually is actually relevant to what you say zapperzero.
http://www3.nhk.or.jp/nhkworld/newsline/nuclearwatch/20140521.html
They are trying to do just that - go in through a pipe line. Apparently it takes them longer than we (and they) would like. But they might use this robot before the end of 2014.

Perhaps 2019 is thought of as the deadline to open the reactors?
 
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  • #469
From Sotan's link:
TEPCO's engineers want to start using their robot by the end of 2014. They'll begin by studying how the high levels of radiation and humidity inside the vessel affect the device. The data they collect will then be used to work on more advanced prototypes.

they have to build the tools they'll need to build the robots to do this.

In 1990's,run-of-the-mill electronics was radiation-wise only an order of magnitude tougher than humans, Rad-Hardened stuff maybe 400X . I don't know what they can do now.

To me it's mind boggling .
 
  • #470
I have been posting a lot of links recently, I hope this doesn't become an annoyance (let me know if it does).

But I sometimes find interesting documents and I wonder if you have seen them. I always look forward to comments from people with knowledge in the field (I have very little of that).

"Dismantlement of Unit 1 Reactor Building Cover for Fuel Removal at Fukushima Daiichi Nuclear Power Station", dated May 9, 2014. This one is in English and may be worth a look.

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2013/images/handouts_130509_07-e.pdf
 
  • #471
I have been posting a lot of links recently, I hope this doesn't become an annoyance (let me know if it does).
speaking for myself, i appreciate it. You do a service by 'filtering' them.

i've been anxious to see into the vessels.

I always look forward to comments from people with knowledge in the field (I have very little of that).

i'm no expert but i did work in a plant (pwr) for some years so had some familiarity with the terminology . As the incident unfolded it was "shock and awe" for me because i had believed it simply impossible to lose irretrievably all electric power.
Once it sunk in that had happened , things appeared to go pretty much as in severe accident analyses which assume that loss for initiating event.

It may be academic just how far the core melts progressed but it'll be interesting to see how close the computer models came. They've got to do those robot inspections to figure out how to approach them. There are fields in there that'd be instant death for a human and short term for a semiconductor based robot .

But what really counts is the ounces of prevention that will come from these tons of cure it's taking to clean up.

old jim
 
  • #472
jim hardy said:
speaking for myself, i appreciate it. You do a service by 'filtering' them.

But what really counts is the ounces of prevention that will come from these tons of cure it's taking to clean up.

old jim

Sotan, I strongly second that appreciation. The summaries you supply are very much appreciated.

Separately, the real challenge is to make sure that those ounces of prevention really become ingrained into procedure.
Safety standards erode over time, because of budget pressures and inertia. The WIPP disaster, due to safety doors wired open for convenience and liquid wastes made acceptable by immobilizing them in kitty litter, illustrates that process. No tsunami took place and no red lines were crossed, afaik, but a safe facility lost the ounce of prevention and became contaminated and unsafe. How does industry prevent that from happening again?
 
  • #473
jim hardy said:
speaking for myself, i appreciate it. You do a service by 'filtering' them.
old jim


I too agree with Jim. IMHO part of the benefit of this forum is many view points and many "collectors" of information. The comments of those involved in the industry are very valuable but those not involved but with a "nose" for related information is also very valuable.


Plainly, please keep up what you are doing Sotan, we appreciate it..
 
  • #474
(Thank you all for the kind and reassuring words.)

On the METI (Ministry of Economy, Trade and Industry) site I found this English translation of the "mid- and long-term roadmap report" of 24 April 2014. While it is not the newest, it can still be a good read, I think, so I post it for those who have not seen it:

www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20140424-e.pdf
 
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  • #475
Sotan said:
(Thank you all for the kind and reassuring words.)

On the METI (Ministry of Economy, Trade and Industry) site I found this English translation of the "mid- and long-term roadmap report" of 24 April 2014. While it is not the newest, it can still be a good read, I think, so I post it for those who have not seen it:

www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20140424-e.pdf

Thanks, this helps for a reasonable English update and also can help to navigate around more recent Japanese versions.
 
  • #476
Sotan said:
I have been posting a lot of links recently, I hope this doesn't become an annoyance (let me know if it does).

It is quite the opposite of an annoyance. Please accept my humble thanks for all that you do.
 
  • #479
turi said:
2/3 of the fuel bundles from the SPF of unit 4 have been moved to the common fuel pool. Last week three transports have taken place (usually two seem be the norm per week).

http://www.tepco.co.jp/nu/fukushima-np/removal4u/index-j.html
(Edit: Link added)

... importantly, within that it is 1012 spent fuel bundles out of 1331 moved, 76% done
link to english version

And yes, Tepco have been running at just over 2 cask moves per week, something like 2 - 2 - 2 - 3.
 
  • #480
http://www.tepco.co.jp/nu/fukushima-np/handouts/2014/images/handouts_140609_05-j.pdf
(in Japanese)

On June 9th they report success in installing a new thermometer in Reactor 2 PCV. You might recall that they failed at the first attempt, when the device and cables got caught somewhere in the grating inside the PCV; they removed it and tried again with better planning, and this time they succeeded.

The new device reaches down to 150 mm from the bottom of the PCV and measures temperature in 5 places at different heights. They were also able to measure the water level in the PCV, which is ~300 mm from the bottom. Temperature is 33.5 Celsius in the air space and 35.6 Celsius in the water.
 

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