Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[jim hardy]

MJRacer

Re your separation by oil ---
you obviously have experience ... thank you for contributing.

i pray you are on to something. Those guys deserve a break.

If oil has affinity for these contaminants, (and why not? oil has great surface tension)

perhaps the answer was embarassingly simple - dairy equipment , modern version of the old hand-cranked cream separator , might do the pretreatment job. Sure would be nice to have 90% of the contamination bottled up in a few drums of oil . They could be wrapped in lead sheet and handled with forklifts.

Your elegant solution would be right in line with Mother Nature's sense of humor.

i'm watching for that one.

thanks -

old jim

 

[Orcas George]

Tepco plans to destroy the treatment system:

The leak was found at 9PM on June 18 by the worker conducting the inspection. The safety valve [rupture disk] of the oil/technetium unit was broken, and there was water between the cylinder [vessel] that contains zeolite and the container that holds the cylinder. The safety valve is designed to break when the pressure inside the vessel gets high. TEPCO believes it may be the result of having to repeatedly start and stop the pump. The purpose of the safety valve is to prevent the hydrogen leak during the system halt. TEPCO is considering closing the valve leading to the safety valve during the operation.

http://ex-skf.blogspot.com/

Can I shout "NO" loud enough for them to hear me in Japan? You do not do this. If a fuse blows, you do not replace it with a straght wire unless you want to burn up your house. It is the same with water pressure.

The problem that they are facing is called "water hammer." It is a well known phenomon. All they need to do is put an inverted cylinder into the system to absorb the shock from start up/shut down. There are better solutions but this is what they have time for. It is possible that there are water hammer arresters in the system and they are simply flooded and need to be drained. If there is nothing to deal with water hammer in the system, then Kurion is a bunch of snake oil salesmen.

 

[MiceAndMen]

It's good to see the IAEA is as committed to transparency as ever. The 151 IAEA member states will meet this week in Vienna for 5 days.

IAEA Director General Yukiya Amano called the ministerial meeting to learn lessons from the March 11 Fukushima accident and plot strategies to improve nuclear safety.

http://www.bloomberg.com/news/2011-06-20/fukushima-disaster-failures-kept-behind-closed-doors-at-un-atomic-meeting.html

 

[GJBRKS]

http://www3.nhk.or.jp/daily/english/20_13.html

Tokyo Electric Power Company, or TEPCO, halted the filtering system only 5 hours after it went into full operation on Friday. Readings around one of the system's devices indicated higher-than-expected radiation levels.

TEPCO engineers suspect that the density of radioactive substances in the contaminated water was greater than had been predicted.

They initially thought that the device had absorbed large volumes of oil and sludge containing radioactive material. But in a test conducted on Sunday, high radiation levels were registered for equipment set to the lowest of 3 absorption levels.

In another test on Monday, TEPCO adjusted the flow of the contaminated water through the equipment.

This is bad if the initial monthly change has to be revised to 5 hours due to an elevated density ...
2 orders of magnitude shift in projected contamination ?
What would this do for the schedule ?
I suspect they do not know yet why , and this would be the simplest explanation , allthough it then means they were wrong on the total level of contamination from the start

 

[joewein]

The sensible thing to do would be to progress from the lightly radioactive water used last week for testing to the next more radioactive water in storage.

At the end of the day, one cubic meter freed up is a cubic meter, doesn't matter how contaminated it was if it can now be reused for cooling instead of 500 t of additional water per day from the dam.

You don't want to have the most radioactive water from the unit 2 basement in the system while you still iron out the kinks. I assume that's what they would be doing too. Even more surprising then when they should declare that things are going wrong because the water was too radioactive!

 

[MadderDoc]

This confirms the leak between the reactor pit and the pool between March 15 and 20, which is assumed to have saved the fuel in the pool from worse damage.

I am wondering how much of the temperature of the water in the reactor pit can be explained by heat conduction through the gate separating them. The reactor well itself sits insulated inside the containment, so not that much heat should flow via its walls.

Right, I am wondering about that too, joewein. Suppose we once knew ( or thought we knew) that the gate between pit and pool was closed and watertight, and someone came to this forum with the theory that the pit heat signature in the thermographs could be explained by conduction of heat through the gate, would he be taken seriously? I don't think he would.

 

[tsutsuji]

Tokyo Shinbun has the results of the tests performed at the Water purifying facility : http://www.tokyo-np.co.jp/article/national/news/CK2011062002000169.html?ref=rank

Definitions of the tests :
(1) removing any material from the tower
(2) filling the tower with a chemical agent that takes oil
(3) filling with zeolite

The test is performed for 4 hours using highly contaminated water.

Radiation measured during the test
(1) 11.55 mSv/h
(2) 4.85 mSv/h
(3) 6.60 mSv/h

Radiation measured after flushing
(1) 0.4 mSv/h
(2) 0.4 mSv/h
(3) 1.74 mSv/h

"From these differences, TEPCO concludes that while zeolite absorbs radioactive substances to some degree, there is a high probability that the measuring instrument on the surface of the tower combines the high radiation coming from the contaminated water".

 

[razzz]

http://www3.nhk.or.jp/daily/english/20_13.html



This is bad if the initial monthly change has to be revised to 5 hours due to an elevated density ...
2 orders of magnitude shift in projected contamination ?
What would this do for the schedule ?
I suspect they do not know yet why , and this would be the simplest explanation , allthough it then means they were wrong on the total level of contamination from the start

Storing radioactive water in an oil tanker is looking better by the minute. I'd being laying the transfer pipe offshore right now just in case.

Anyone have a better idea to keep the site workable?

 

[tsutsuji]

A series of diagrams explaining the water level problem in the reactor and in the pit of unit 4 : http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110620_02-e.pdf

("Unit 1" is a translation mistake. Compare with Japanese version : http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110620_02-j.pdf )

A series of large size pictures from the early days of the accident : http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110620_05-j.pdf ( meant to be viewed together with the first response report http://www.tepco.co.jp/en/press/corp-com/release/11061805-e.html )

Page 5 : a stray tank blocking a road.
The last picture seems to be the black or grayish smoke event at unit 3 on March 21st (although it is merely captioned as "unit 3 outer view after explosion")

 

[MadderDoc]

westfield, joewein, thank you for considerations and your inputs to this question:

I wonder if anyone here has been able to identify where this photo was taken?

http://www.tepco.co.jp/en/news/110311/images/110611_05.jpg
<..>

Considering everything I end up with, albeit not conclusively, that the camera is in the 4th floor of unit 4, somewhat west of the center of the floor, and pointing NNE, towards the panel in the north wall that was blown out by the events on March 15th, If true this has certain implications: There is light coming from above, that implies there must be non-design holes in the servicefloor above. There is light coming in apparently through a missing panel to the west of the aforementioned blown out panel. This implies some further deconstruction either intentionally or intentionally with removal of panel(s) has occurred on the north wall of the building. (and this can be confirmed looking at some of the most recent photos shot from the ground).

The machinery seen to the right along the wall would, I believe, most likely be the M/G sets for the reactor circulation pumps. There has been reported fires in the 4th floor in a most confusing way involving the oil from the M/G sets of either or both units 3 and 4. However there is afaics no evidence of a lubricant fire in this photo.

 

[SteveElbows]

The sensible thing to do would be to progress from the lightly radioactive water used last week for testing to the next more radioactive water in storage.

At the end of the day, one cubic meter freed up is a cubic meter, doesn't matter how contaminated it was if it can now be reused for cooling instead of 500 t of additional water per day from the dam.

You don't want to have the most radioactive water from the unit 2 basement in the system while you still iron out the kinks. I assume that's what they would be doing too. Even more surprising then when they should declare that things are going wrong because the water was too radioactive!

I think the problem is that its the highly contaminated water that they are running out of storage capacity for, dealing with the less contaminated stuff does not really help them in the struggle to prevent overflow. So far I think they only have permission to store the highly contaminated water in a few locations, and those are pretty much full.

They were so desperate that the other day they even tried to move some water from reactor 2 to reactor 1 condenser, but I believe a pump failed so it didnt happen.

I imagine it is well possible that they will end up trying to store highly contaminated water elsewhere, as a last resort against site flooding/escape into sea, but I guess they will leave this till the last minute as storing very radioactive water in less than ideal locations probably comes with new risks.

 

[SteveElbows]

It's good to see the IAEA is as committed to transparency as ever. The 151 IAEA member states will meet this week in Vienna for 5 days.
http://www.bloomberg.com/news/2011-06-20/fukushima-disaster-failures-kept-behind-closed-doors-at-un-atomic-meeting.html

I will likely talk about this in the more political thread later today.

In the meantime I had completely missed the fact that there is a video of the IAEA visit to the plant, I had only seen the photo before:



I don't think I had realized how wet the dry cask storage building got before I saw this video.

 

[ThomS]

People got around 10 particles each in Tokyo. The data is from air filters in Japan and the West Coast.

How do you know that? Source?

Many thanks.

 

[zapperzero]

The last picture seems to be the black or grayish smoke event at unit 3 on March 21st (although it is merely captioned as "unit 3 outer view after explosion")

There's a concrete mixer truck in that picture. I wonder what it's doing there.

 

[joewein]

There's a concrete mixer truck in that picture. I wonder what it's doing there.

There are other possible explanations, but during one annual Japanese earthquake drill (1 September, Great Kanto quake anniversary) I have seen concrete mixers demonstrated as emergency water transport vehicles to help fire fighting. They can carry several tons of water and can pour it into pumps.

This idea came out of the Kobe earthquake, where the majority of victims did not die in the quake but subsequently burnt to death in fires when the mains hydrants broke and there was no water for putting out fires.

It might be something different, but the dark smoke from unit 3 next to it reminds me of that.

 

[Jorge Stolfi]

Tokyo Shinbun has the results of the tests performed at the Water purifying
Radiation measured during the test
(1) 11.55 mSv/h
(2) 4.85 mSv/h
(3) 6.60 mSv/h

Radiation measured after flushing
(1) 0.4 mSv/h
(2) 0.4 mSv/h
(3) 1.74 mSv/h

"From these differences, TEPCO concludes that while zeolite absorbs radioactive substances to some degree, there is a high probability that the measuring instrument on the surface of the tower combines the high radiation coming from the contaminated water".

I don't know what to make of these numbers. Is this good news or bad news?

 

[joewein]

I don't know what to make of these numbers. Is this good news or bad news?

The way I read it, it means the filters measure highly radioactive after operating for a while not because they've absorbed a lot of isotopes already but because they're soaked in plenty of highly radioactive water that has yet to pass several more purification steps. Once you flush out that water the levels are much lower again.

Did I understand the numbers correctly?

 

[etudiant]

If it is that simple, then they can just raise the threshold from 4 to 8 mSv, knowing that 4mSv come from the entrained water.
Just need to be sure to backwash before changing out thye filters./

 

[MadderDoc]

There's a concrete mixer truck in that picture. I wonder what it's doing there.

Probably nothing. It's in the same position as it was in imagery taken shortly after the tsunami.

 

[tsutsuji]

Tepco is now working to figure out how the process of removing radioactive material can be evened out among the six cartridges.
http://online.wsj.com/article/SB10001424052702303936704576397220194086998.html

Each cartridge has its own radiation sensor. If they manage to lower the radiation on the first cartridge by using a filtering material that is less efficient, then I guess the high radiation problem might occur on the second cartridge. Also they may want to ignore the sensors while the contaminated water is inside, then perform flushing on a regular basis and read the sensors only during the intervals when flushing is performed.

 

[SteveElbows]

OK here is IAEA documentation from their conference:

http://www-pub.iaea.org/MTCD/Meetings/cn200_documentation.asp

I believe the 3rd and 4th links are the report to IAEA by Japan, which we have already seen.

The 2nd link on the page contains the long IAEA report. I've not read it all yet, but after reaching page 44 I tentatively conclude that its what we may have expected, in that there is nothing much new in it at all. This is not too surprising as its mostly based on documents we have already seen, and it is not exactly crammed with technical detail. The language used when describing events is generally easier to understand, so I suppose there is a chance that it will clear up some ambiguities, but don't expect much really.

 

[MadderDoc]

<..> there is nothing much new in it at all.

Considering this is supposed to be a report of a 'fact finding mission' that's already a pretty damning thing to say. It's a watered out soup of already known facts and banalities bound in virtual brown leather and a fine IAEA logo, a total waste of time. I'd rather rehash an old T-Hawk video.

 

[etudiant]

Considering this is supposed to be a report of a 'fact finding mission' that's already a pretty damning thing to say. It's a watered out soup of already known facts and banalities bound in virtual brown leather and a fine IAEA logo, a total waste of time. I'd rather rehash an old T-Hawk video.

It is sad that the world's nuclear leadership is so frightened of the political process that it speaks only bromides. It relinquishes its chance to state its case by default.
A compelling argument can be made for nuclear power, especially if all the externalities such as mercury emissions from coal or water contamination from drilling are factored in. Yet the nuclear industry goes on pretending that it must be 99.44% pure, just like Ivory Soap. This nonsense is destructive to the credibility of the industry as well as to the emergence of better safety practices.
The essential truth is that problems denied are automatically magnified. The better approach is to 'paint it red', make it super conspicuous so that you have to deal with it in a way that everyone understands, even if they do not agree with it. That may mean early retirement for the Mk 1 reactors, because they are too vulnerable, but better an amputation than whole body gangrene.
My $0.02.

 

[zapperzero]

I suppose there is a chance that it will clear up some ambiguities, but don't expect much really.

Oh, I wouldn't say that. From
http://www-pub.iaea.org/MTCD/Meetin...tion/cn200_Final-Fukushima-Mission_Report.pdf

Conclusion 3: There were insufficient defence-in-depth provisions for tsunami hazards. In particular:
 although tsunami hazards were considered both in the site evaluation and the design of the Fukushima Dai-ichi NPP as described during the meetings and the expected tsunami height was increased to 5.7 m (without changing the licensing documents) after 2002, the tsunami hazard was underestimated;
 thus, considering that in reality a ‘dry site’ was not provided for these operating NPPs, the additional protective measures taken as result of the evaluation conducted after 2002 were not sufficient to cope with the high tsunami run up values and all associated hazardous phenomena (hydrodynamic forces and dynamic impact of large debris with high energy);
 moreover, those additional protective measures were not reviewed and approved by the regulatory authority;

The resulting ground acceleration at Units 1, 4 and 6 did not exceed the standard seismic ground motion, whereas at Units 2, 3 and 5, the resulting ground acceleration did exceed the standard seismic ground motion. The tsunami exceeded the design basis at all units.

Alignment of the valves to vent the Unit 2 containment was carried out on 13 March by opening an air operated valve using an air cylinder and another valve with AC power supplied by an engine generator. After the Unit 3 explosion, discussed below, the valve was rendered inoperable. The operators then attempted to open another air operated valve to establish the vent path. An engine driven air compressor and AC power supplied by an engine generator were used and the valve appeared to open slightly. However, the successful venting of the Unit 2 containment could not be verified.

The heat transfer path from the core and the spent fuel pool to the ultimate heat sink is very important. The ultimate heat sink of Fukushima Dai-ni NPP units 1-4 is sea water of Pacific Ocean, there are two trains of heat removal system for each unit, their seawater cooling system (RHR-S) are located in the relevant Heat Exchange Building (Hx/B), the motor of the RHR-S is located in 1F pump room (4 m above the sea level), and their power centres are located in the B1F control panel of Hx/B. Due to the tsunami (maximum run-up height of approximately 14 m) on 11 March, all of them except RHR-S-3B are submerged and damaged, so the path to removal the decay heat in the core and spent fuel pool to the ultimate heat sink (Pacific ocean) is broken. The survival of RHR-S-3B is just due to luck that is why unit 3 can reach cold shutdown state more early than Unit 1, 2, 4. The site superintendent reported the central and local governments nuclear emergency situation because the temperature of the suppression pools of Unit 1,2,4 became more than 100 ℃ during accident, but afterward with temporary power cable laid and urgent procurement of motors, one train of RHRS, RHRC, EECW for each unit of Unit 1,2,4 has recovered and restarted. Up to now, all units of Fukushima Dai-ni have reached cold shut states.

At Dai-ichi the events progressed much too fast for operators to respond in an organized manner. Normally the mission times of IC/RCIC should have given the operators some time before the core was exposed and radiation levels increased making several reactor areas inaccessible. It is not clear if and why these systems did not function the way they should have.

Unavailability of measurements has resulted in initiating urgent protection action based on the plant status. The fast changing plant circumstances made it imperative to take several consecutive measures (mostly evacuations) to protect the residents. Long term sheltering was not in line with international practice and has been abandoned and the notions of ―deliberate evacuation‖ and ―evacuation-prepared area‖ were introduced instead.
4 – LESSONS LEARNED __/__/2011 1. Use of long term sheltering (―in-house evacuation‖) was an unusual and not fully justified action that will need further analysis in the future.

On 15 March MEXT became the central agency for environmental monitoring. From 18 March the monitoring has been enhanced and reinforced (aerial, oceanic, land). Some important support from IAEA and US-DOE contributed to the improvement. Sophisticated monitoring equipments are in use (mobile units, aircraft, ships…). The most significant exposure ways are currently monitored, including land, marine and sky. Monitoring items include:
IAEA
136
o Dose rate. Fixed post and mobile units, aircrafts and ships
o Integrated dose at fixed monitoring posts
o Radionuclide analyses (mainly I-131 and Cs-137)
 Dust, soil, pond water, weed
 Drinking water, fallout (47 Prefectures)
 Sea water and sea bottom soil

bolding mine

EDIT: I am loath to parse it again, but another important thing they are saying is the IC in unit one and the RCIC in units 2 and 3 failed - i.e. ceased to perform their function adequately way earlier than they should have.

 

[MiceAndMen]

OK here is IAEA documentation from their conference:

http://www-pub.iaea.org/MTCD/Meetings/cn200_documentation.asp

I believe the 3rd and 4th links are the report to IAEA by Japan, which we have already seen.

The 2nd link on the page contains the long IAEA report. I've not read it all yet, but after reaching page 44 I tentatively conclude that its what we may have expected, in that there is nothing much new in it at all. This is not too surprising as its mostly based on documents we have already seen, and it is not exactly crammed with technical detail. The language used when describing events is generally easier to understand, so I suppose there is a chance that it will clear up some ambiguities, but don't expect much really.

Thanks for finding the link to the report. It answers, in part, why we saw so few pictures of the IAEA team at the Dai-ichi plant. They were there for less than 4 hours according to page 146 (page 148 of the pdf). The day before, they spent 5 hours at the Dai-ini plant. Apparently most of their time was spent in meetings and technical discussions, which is reasonable I guess.

In hindsight, we knew very little in the first hours and days after 11 March, but re-reading the first couple of pages in this thread is very enlightening in a not-good sort of way. Extraordinary events have taken place that were thought to have an infinitesimal chance of occurring.

 

[etudiant]

Thanks for finding the link to the report. It answers, in part, why we saw so few pictures of the IAEA team at the Dai-ichi plant. They were there for less than 4 hours according to page 146 (page 148 of the pdf). The day before, they spent 5 hours at the Dai-ini plant. Apparently most of their time was spent in meetings and technical discussions, which is reasonable I guess.

In hindsight, we knew very little in the first hours and days after 11 March, but re-reading the first couple of pages in this thread is very enlightening in a not-good sort of way. Extraordinary events have taken place that were thought to have an infinitesimal chance of occurring.

The surprise to me was that there existed detailed analyses done by the NRC that indicated a meltdown within half a day of loosing cooling. Awareness of that little detail would have put everyone on the same page very early.
Whether it would have changed any actions or outcomes is a separate issue.

 

[imandylite]

UK Government secret documents on the Fukushima Disaster released through freedom of information request.

http://www.guardian.co.uk/science/2011/jun/20/japan-earthquake-and-tsunami-japan"

http://www.scribd.com/fullscreen/58313487?access_key=key-1amf2uutax7h93geh699"

Many interesting details in the documents - some talked about here.

 

[MadderDoc]

Oh, I wouldn't say that. From
http://www-pub.iaea.org/MTCD/Meetin...tion/cn200_Final-Fukushima-Mission_Report.pdf

<..snipped a lot> just kept this tidbit from what you quoted which illustrates well why I am disgusted with this 'fact finding mission' report.

After the Unit 3 explosion, discussed below, the valve was rendered inoperable.

So, what fact is expressed here? Is it perchance an expression of cause and effect? Or is it an expression of timing of events? The answer is blowing in the wind.

Also this piece of gold, not one of those you quoted:

Because of the lack of
instrumentation and high radiation levels, the water levels in the SFPs of Units 1–4 could not
be determined in the first several days of the accident. However, the explosions at the site
destroyed the reactor building roofs of Units 1, 3 and 4, providing access to the SFPs.

So, are we to understand that high radiation at the plant already from the morning of March the 12th made it impossible to send a man to each service floor to check the situation around the pools? Is that a fact or is it hokum? Are we to understand that absent the saving grace of three explosions it would have been impossible to gain 'access' to those pools? Access? Exactly what kind of 'access' are we talking about? Access in the sense that one now could (only) look into the pools from a safe distance in a helicopter, what kind of access is that?

Yes I am sure I am overreacting. Calm down old bear.

 

[tsutsuji]

Areva's water purification system possesses its own oil removal system and would be able to perform the whole purification task alone, should the Kurion system become unavailable : http://www.sciencesetavenir.fr/actu...-traitement-peine-a-demarrer-a-fukushima.html

 

[~kujala~]

I just noticed something... I thought earlier that if there was a flow of contaminated groundwater into the sea we would see this in the radioactive levels of seawater (= increasing levels). Well, this happens to be a completely false idea:

"Underground water flows at a speed of about 5 to 10 centimeters a day, so we have more than a year before it reaches the shore."

http://mdn.mainichi.jp/perspectives/column/archive/news/2011/06/20110620p2a00m0na005000c.html

This means basically that if the deeper groundwater (= groundwater below the sub-drains) is now heavily polluted it could take a year until we will see the radioactive levels of seawater rising...

Could this be the reason (besides money) that TEPCO is not talking so much about the groundwater contamination? They think they have time.

 

[SteveElbows]

Oh, I wouldn't say that. From
http://www-pub.iaea.org/MTCD/Meetin...tion/cn200_Final-Fukushima-Mission_Report.pdf

bolding mine

EDIT: I am loath to parse it again, but another important thing they are saying is the IC in unit one and the RCIC in units 2 and 3 failed - i.e. ceased to perform their function adequately way earlier than they should have.

A large amount of the stuff you highlighted is not actually brand new information. But it might be the first time that some of the information is presented in a way that means something to many people. As well as language issues, TEPCO & Japanese authorities have sometimes failed to explain the significance of certain details they announce, to weave such details into the bigger picture in a helpful way.

In any case a lot of my complaint that there isn't much new information is not really supposed to be a criticism of the IAEA report, just a reflection of the fact that the detailed documents upon which most of this reporting is based were already made available to us in prior weeks.

Anyway, the large number of 'lessons learned' in these documents seem mostly sensible, although its hard not to laugh or cry about some of them, the very idea that we had not learned these lessons until now! For example on page 113:

The presence of high radiation fields in the plant needs to be considered to ensure manual actions can be executed under accident conditions.

This is a pretty good example of a wider failing that becomes apparent as we read all of these lessons. Safety systems & procedures are designed to try to prevent things from getting bad, but are not much use once things reach a certain bad point. This is painfully clear with areas such as instrumentation, shocking how blind the operators were to the conditions at crucial moments due to instrument failure, and lack of relaible data continues to hamper the quest for knowledge to this date.

 

[SteveElbows]

<..snipped a lot> just kept this tidbit from what you quoted which illustrates well why I am disgusted with this 'fact finding mission' report.



So, what fact is expressed here? Is it perchance an expression of cause and effect? Or is it an expression of timing of events? The answer is blowing in the wind.

Look elsewhere for the underlying facts, and just treat the IAEA stuff as a useful additional narrative. I am pretty sure that in some of the more technical documentation we've discussed here in recent weeks, there was reference to certain equipment at reactor 2 being taken out of action by the explosion at 3, and I would assume this is what they are referring to. I don't have time to find the exact detail right now but will post it when I next stumble upon it.

So, are we to understand that high radiation at the plant already from the morning of March the 12th made it impossible to send a man to each service floor to check the situation around the pools? Is that a fact or is it hokum? Are we to understand that absent the saving grace of three explosions it would have been impossible to gain 'access' to those pools? Access? Exactly what kind of 'access' are we talking about? Access in the sense that one now could (only) look into the pools from a safe distance in a helicopter, what kind of access is that?

Yes I am sure I am overreacting. Calm down old bear.

They are a bit vague on the timescale. The pools may not have been in a dangerous state early on, and so the need to check them would come days later, once things on site had got much trickier and where they may not have been keen to have humans present on service floors in any of the reactors. We don't really have much detail on the realities of this, eg we still don't know if humans removed the reactor 2 building blowout panel or not. Earthquakes causing pool water sloshing is a known issue that has had to be dealt with in the past, though I doubt it would cause enough water loss to cause pool shielding issues. If an earthquake caused additional damage to pool integrity then water may drop to a level where shielding becomes an issue much more quickly.

As for access, I think they mean access to spray water. Its a valid point even if it seems absurd when viewed from certain angles. If a pool with plenty of heat like reactor 4's was in urgent need of more water, and normal means to inject water was unavailable, and the building was still intact, then that would be a bigger problem than what they actually had to deal with. Sure, it is possible to argue that if the building had not exploded in the first place, it is more likely that more normal methods for injecting water (some pipes) would still be available, which is why I say it is a silly point in some ways.

 

[Most Curious]

Has anyone seen a time line of when building radiation levels became too high to allow human entry? I would assume shortly after fuel damage began, prior to explosions, that rad levels were already way too high for entry.

I base this on very hot reactors degrading containment seals early in the accident, loss of suppression function when pools were reported at 100C followed within a few hours by severe contamination as the fuel rod integrity was lost.

IOW, I suspect conditions were right for severe building contamination as soon as fuel damage began. At that point would anyone have ventured to the service floor for ANY reason?

 

[MadderDoc]

Look elsewhere for the underlying facts, and just treat the IAEA stuff as a useful additional narrative.

IMO you are much to kind. I'd say: look elsewhere as close to the original stuff as you can get, and treat the IAEA report as you would a poorly recompressed video coming with lost information and wooly artefacts.

They are a bit vague on the timescale. <..>

Definitely, but the worst is that they are producing pretentious nonsense, which lures the positively inclined reader into fetching some sense from his own head to fill in the void. Naturally said positive reader will then think that it was the nonsense that made the sense, not himself. Quite like when people have come here to insist there is smoke from reactors which they have dreamt up from looking at compression artefacts with a smoke-positive mind.

 

[joewein]

Could this be the reason (besides money) that TEPCO is not talking so much about the groundwater contamination? They think they have time.

TEPCO is considering walls to be built into the ground around the plant to isolate the groundwater.

See text and illustrations on page 11 on:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110617e4.pdf

II. Mitigation
(4) Groundwater
(...)

Countermeasure [68]
Examination of shielding wall of groundwater

- Considering underground water flow based on seepage analysis

<next step>
-Implement most appropriate method to shield underground water by evaluating water shield effect, earthquake resistance, durability, etc.
-Implement study for optimization of shielding section, installation plan and construction schedule