Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[jensjakob]

Even though it is a BWR6 reactor, this guide can provide hints to many answers on FUkushima configuration:
http://www4.ncsu.edu/~doster/NE405/Manuals/BWR6GeneralDescription.pdf

 

[|Fred]

2. A reactor pressure vessel is a massive heat sink. I believe the drywell on both reactor 1 and 2 where flooded early on in the process; providing addition temperature relief. This doesn't include the water that has been injected since the start of the accident..

Thank you Nuceng and Cire for those anwsers, you mention that the drywell (primary containment in concrete if I'm not mistaken) Has been flooded. I've seen this "idea" on the paper written by or for Areva.
But I haven't seen any statement , indications or explanation by the Japanese authorities or tepco that they did so ...
Is is a standard procedure ? how did they get some water there and when..

E.g. to receive a dose of 1 mSv in 50 years it requires about ingestion of about 80000 Bequerel of Caesium 137 but only about inhalation of 15 Bq of Plutonium. The activity in Bq in the environment is relatively simple to determine.

I think this statement is wrong there is a 20 factor ponderation between alpha and beta, please correct me a dose of 1mSv it would require contact with a 10 000 Bq source of 137Cs or a 500 Bq source of Pu

 

[Bodge]

So, is it currently feasible for there to be a large steam explosion in (under) any of reactors 1-3?

Could there be corium in an unbreached RPV, suspended above a saturated area?

 

[Bodge]

I'm looking at Reactor 1 in particular.

But, in any reactor, could the conditions above still conceivably develop in the next few days?

 

[Astronuc]

Thank you Nuceng and Cire for those anwsers, you mention that the drywell (primary containment in concrete if I'm not mistaken) Has been flooded. I've seen this "idea" on the paper written by or for Areva.
But I haven't seen any statement , indications or explanation by the Japanese authorities or tepco that they did so ...
Is is a standard procedure ? how did they get some water there and when..

A contact at GE indicate that flooding containment is standard op in the case of a LOCA.

I would expect that TEPCO flooded containments on Units 1, 2 and 3 - in addition to getting water into the pressure vessel in order to reflood the core as much as possible.

 

[Cire]

Thank you Nuceng and Cire for those anwsers, you mention that the drywell (primary containment in concrete if I'm not mistaken) Has been flooded. I've seen this "idea" on the paper written by or for Areva.
But I haven't seen any statement , indications or explanation by the Japanese authorities or tepco that they did so ...
Is is a standard procedure ? how did they get some water there and when..

Here is a 1995 Paper by ECN on the IAEA website about flooding the drywell.. It's a good read.http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/27/036/27036479.pdf"


Quoted from the abstract:

In case of a severe reactor accident inside a Nuclear Power Plant (NPP), the
worst case scenario includes melt-down of a significant part of the core.
Without any counter measures, this will lead to failure of the Reactor
Pressure Vessel (RPV). In order to prevent failure of the RPV, the decay heat
generated by the corium pool has to be removed from the vessel at such rates
that excessive temperature rise of the vessel wall is averted.
Recently, flooding of the lower drywell or external (ex-vessel) flooding has
been suggested as a possible accident management strategy, with the purpose
to cool the relocated heat generating corium pool in such a way that vessel
failure is prevented.

My understanding is you flood the dry well by activating the fire suppression system in that area and not turning it off until you flood the area. I'm looking for the source material I read that stated the dry well was flooded. When I find it I'll be sure to link to it.

 

[Astronuc]

I was thinking more about unit #4, wondering if a solution could have been in the core at the time of the quake? And, if so, would the solution (if leaked back into SFP through failed gate seal) contribute to more rapid heating by dissolving or weakening the cladding on the spent fuel rods?

In a BWR, there would be no solution in SFP water or the reactor cavity. It's flooded with clean water, which is cooled and filtered.

I would expect that the gate was open, but I don't know as I'm not familiar with their procedures. Unit 4 was shutdown since Nov 30, 2010, and for whatever reasons, they do exceptionally long maintenance outages. The core had been cooling for 101 days at the time of the quake. The thermal burden should have been about 2.75 MW.

Most US plants try to minimize outage length. Some utilities have it down to about 15-17 days every 18 mo or 24 mo depending on the unit, although many units probably do it more like 20-30 days.

The earthquake certainly could have caused a structural failure somewhere in the pool or containment structure.

Some of the Kashiwazaki-Kariwa units sustained damaged from the Niigata earthquake, and Chubu's Hamaoka Units 1 & 2 were shutdown and decommissioned prior to the Suruga Bay earthquake of Aug 11, 2009.

 

[AtomicWombat]

An other question, I've heard this sentence: "because Plutonium is so dense and heavy, IT CANNOT go very far and be transported to a great distance from its source point, so it should stay around the vicinity of the plant".

I know it's a very dense element, but is this sentence 100% true?

Plutonium oxide is insoluble in almost everything, so it won't get into the food or water supply.

Plutonium (in its oxide form) is most dangerous when it is in fine particles of airborne dust. I see it as a little like asbestos. If in some accident a large amount of asbestos dust was to spread over an inhabited area, there would be a long term expectation of elevated rates of mesothelioma. The mechanisms and resulting cancers are different with plutonium (lung & bone cancers and leukemia) but it's that form of risk.

http://www.nvmp.org/pluto4.htm"

"If somebody inhales plutonium dust, he won't notice anything special. Only 10 to 50 years later is it possible that lung and bone cancer may develop. "

"Plutonium is not dangerous outside the body."

"...during fires in the US nuclear weapons complex Rocky Flats near Denver in 1957 and 1969 clouds of smoke containing plutonium dust spread over the town. However, the expected "epidemic" of lung cancer and congenital defects did not occur. Probably the plutonium dust did not reach the population because it came down quickly and became firmly adhered to the soil. Besides, extra cases of cancer or birth-defects in babies are difficult to distinguish from what people acquire "naturally". "

"Atmospheric testing between 1945 and 1963 brought 4.2 tons of plutonium dust directly into the environment. ... In theory 7,900 cases of cancer may have been caused by this plutonium. "

"Plutonium can go off when it is piled up, a 'criticality' disaster. ... The smoke coming out of the burning pile may lodge tiny particles containing plutonium deep in the lungs. Fall-out from an explosion of an atomic bomb also contains plutonium dust, and so does the smoke of a nuclear disaster like 'Chernobyl' and 'Windscale' "

 

[Astronuc]

About 15 years ago, I met one to two guys who experienced glove box explosions while working with Pu. The accidents has happened in the 70's, and he was still doing well in the 90's. He had had glass and Pu solution embedded in his face, neck and chest. As far as I know he's still alive, but I'll have to check.

 

[rhody]

About 15 years ago, I met one to two guys who experienced glove box explosions while working with Pu. The accidents has happened in the 70's, and he was still doing well in the 90's. He had had glass and Pu solution embedded in his face, neck and chest. As far as I know he's still alive, but I'll have to check.

Astronuc,

If someone suspects they have inhaled plutonium, are there medical or radiological tests to confirm it ?

Rhody...

 

[AtomicWombat]

Michio Kaku trying to calm fears and reassure people:

http://www.youtube.com/watch?v=qdq4l58VoLI&feature=player_detailpage

 

[rhody]

Michio Kaku trying to calm fears and reassure people:

http://www.youtube.com/watch?v=qdq4l58VoLI&feature=player_detailpage

AW,

He stirs the masses and at the same time putting himself front and center... Wait, did I just say that ! Doesn't he have a new book out as well, Wait, did I say that too !

Rhody... :yuck:

 

[Astronuc]

Michio Kaku trying to calm fears and reassure people:

http://www.youtube.com/watch?v=qdq4l58VoLI&feature=player_detailpage

If they abandon ship?! Free fall?! :grumpy:

Um - we don't do that.


Incidentally from JNES http://ompldr.org/vN3VhMQ

 

[AntonL]

KYODO 11:04 30 March
NEWS ADVISORY: Radioactive iodine 3,355 times legal limit found in seawater near plant

So the trenches are overflowing

for the past detailed seawater analysis up to 28 march can be http://www.meti.go.jp/press/20110329013/20110329013-2.pdf"

and http://www.meti.go.jp/press/20110330002/20110330002-4.pdf" supporting the news advisory

and again Tc-99m 6 hour half life is detected - I hope measuring error

 

[ailog]

Any news on the fresh water that the US navy is/has barged to the site? Is it being put to use? I havn't seen anything about it recently.

 

[Astronuc]

From World Nuclear News:

A good description of the Fukushima event - http://www.world-nuclear.org/info/fukushima_accident_inf129.html

I've been wondering about the ground motion and accelerations. Apparently not all the data are collected and/or processed, but from WNN,

http://www.world-nuclear-news.org/RS_Fukushima_faced_14-metre_tsunami_2303113.html

More detailed data of the ground acceleration rates caused by the magnitude 9.0 earthquake have also been made available by Tepco. Although not all the data has yet been collected, they record very powerful tremors that exceed the design basis in one dimension.

At Daiichi there is still no data for units 1, 2 and 5, but available figures put the maximum acceleration as 507 gal from east to west at unit 3. The design basis for this was 441 gal. Other readings were below design basis, although east-west readings at unit 6 of 431 gal approached the design basis of 448 gal.

At the Daini plant, ground accelerations ranged from 186 gal in the vertical plane at unit 1 to 277 gal from north to south at unit 3, as recorded by sensors in the reactor building foundation. The range of design basis figures is a spread from 415 gal to 512 gal.

No mention of unit 4.

From - http://www.world-nuclear.org/info/inf18.html

Japan's Nuclear & Industrial Safety Agency eventually declared the accident as Level 5 on INES scale - an accident with wider consequences, the same level as Three Mile Island in 1979. The design basis acceleration for both Fukushima plants had been upgraded in 2008, and is now quoted at horizontal 441-489 Gal for Daiichi and 415-434 Gal for Daini. The recorded data for Daiichi are still being analysed, but it appears that 507 Gal was the maximum for it, and 251 Gal for Daini. (Ground acceleration was around 2000 Gal a few kilometres north, on sediments.)

 

[AntonL]

New idea - wrap the structures in special cloth to filter radio-activity

I suppose http://www.christojeanneclaude.net/wc.shtml" will be asked to help with the design - nobody more experienced.

From below info graphic:
But more important the highly radio-active water unit 2 to be shipped off-site - and then?

[URL]http://www.asahi.com/special/10005/images/TKY201103290521.jpg[/URL]

　Fukushima Daiichi nuclear power plant at TEPCO, 1,3,4 a rocket blew the building, Kan, the Cabinet is considering measures to prevent radioactive material dispersal of a special cloth to cover it. To ensure that working conditions for recovery and stable power supply to cool the reactors. Water pollution measures, including high levels of radioactivity leaking into the turbine building basement, is also out with a plan to collect contaminated water tankers. TEPCO has struggled to win work, they need to recognize more ambitious plans.

Yes a neat "out of the box idea" as an example of ambitious plan

 

[Reno Deano]

BWRs have an astounding number of penetrations (CRDMs and reactor instrumentation) coming through the bottom of the reactor vessel. A CRDM ejection is a remote possibility. But if the CRDM seismic supports failed, that could be the breach.

 

[razzz]

BWRs have an astounding number of penetrations (CRDMs and reactor instrumentation) coming through the bottom of the reactor vessel. A CRDM ejection is a remote possibility. But if the CRDM seismic supports failed, that could be the breach.

Apparently a 'leaky loop' is acceptable in this design since avenues are built-in. Maybe the graphite rod don't morph into rough diamonds due to heat but their seals sure can fail.

Too bad now that it is a problem just trying to keep the working environment safe. The contaminated cooling water or seawater is of secondary importance whether it discharged into the Pacific or tanker ship, as trying to keep the hot spots cool and keep the cool spots from becoming hot spot is of utmost importance. Even if they can keep the situation static, it's a waiting game.

I'd probably be unloading the (slightly) off site major spent fuel pond and then unload unit 5&6 ponds getting ready for the day that unit 4 pond can be unloaded...I don't even know if these things are possible.

 

[NUCENG]

Thank you Nuceng and Cire for those anwsers, you mention that the drywell (primary containment in concrete if I'm not mistaken) Has been flooded. I've seen this "idea" on the paper written by or for Areva.
But I haven't seen any statement , indications or explanation by the Japanese authorities or tepco that they did so ...
Is is a standard procedure ? how did they get some water there and when..


Early on TEPCO reports indicated that they were injecting seawater into the reactor pressure vessel. My Bad. I misremembered reading that they had been performing containment flood. However looking at the TEPCO updates since 11 March, I cannot confirm that. So my speculation of a steam explosion was invalid. However if melt-throu does occur, the interaction with containment concrete will be revealed by the activation and release of concrete materials.

I will do better job of checking my WAGs.

 

[Gilles]

Sorry, I come here only from time to time (plus jet lag ..) and I may have missed part of the discussion, but it seems that interesting observations can be done on these graphs

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/v8/Main.html

Obviously explosions happened after the sudden decrease of pressure in React 2 and 3, and most likely 1, probably to the voluntary depressurizing to allow water to flow in the reactor - releasing a huge amount of steam and hydrogen that had been produced very early after the failure of cooling systems. Then in R1 and 3, temperature remained very high (300 or 400 °C) whereas the pressure was only a few bars -indicating that places where temperatures were measured were out of water, and overheated by fuel rods much hotter than the boiling point at this pressure. Probable oxidation and maybe fusion have occurred continuously then. Can it be that the vessels were totally dry at this time ? R2 was steadily around atmospheric pressure and 100 °C - probably boiling water covering the fuel. Around the 20th of March a significative decrease of temperature occured. Is it due to the arrival of fresh water in the vessel - although no variation of water level was recorded, but may be they're measured in the confinement around the vessel - or may be to the melting of upper parts of fuel rods that gathered in the liquid phase, solidifying here ? A new rise of temperature in R2 these last days is worrying - does it mean that water is again very low ?

 

[rmattila]

Thank you Nuceng and Cire for those anwsers, you mention that the drywell (primary containment in concrete if I'm not mistaken) Has been flooded. I've seen this "idea" on the paper written by or for Areva.
But I haven't seen any statement , indications or explanation by the Japanese authorities or tepco that they did so ...
Is is a standard procedure ? how did they get some water there and when..


Early on TEPCO reports indicated that they were injecting seawater into the reactor pressure vessel. My Bad. I misremembered reading that they had been performing containment flood. However looking at the TEPCO updates since 11 March, I cannot confirm that. So my speculation of a steam explosion was invalid. However if melt-throu does occur, the interaction with containment concrete will be revealed by the activation and release of concrete materials.

I will do better job of checking my WAGs.

As far as I have followed the situation, in the early JAIF raports it was mentioned that water injection to core at all units was continuing, water injection to unit 1 containment vessel was "done", and to units 2-3 "to be decided".

In later JAIF reports, up until March 21, water injection to containment vessels 1 and 3 was reported to be "continuing (Seawater)", and for unit 2 "to be decided". On March 22, they changed the status to "confirming" on units 1 and 3 and "to be decided (Seawater)" on unit 2. On the latest releases, the status on units 1 and 3 containment vessel is stated as "to be confirmed".

Based on that mixed information, I'm not sure if anyone outside Tepco has an accurate idea whether water has so far been injected to any of the containment vessels on purpose. It seems that there has been a constant confusion of the terms "reactor pressure vessel" and "containment", with different combinations such as "core containment vessel" etc. being seen in different reports.

 

[AntonL]

Based on that mixed information, I'm not sure if anyone outside Tepco has an accurate idea whether water has so far been injected to any of the containment vessels on purpose. It seems that there has been a constant confusion of the terms "reactor pressure vessel" and "containment", with different combinations such as "core containment vessel" etc. being seen in different reports.

Assuming that heat generated in reactor is only from residual heat from the decay of the isotopes, I have observed that water volume injected is 200% to 400% of water required to boil that heat away.

This leads me to conclude that the indicated flow rates are the combination of
1) Water injection into reactor vessel
2) Water spray in PCV to condense some of the steam generated

that could explain the huge amount of water now being leaked/released into the basements.

According to pressure readings released
reactor vessel: Unit 1 OK as >.3MPa_g high pressure Unit 2 & 3 breached zero and even negative

Primary Containment Vessel - all units OK as high pressure

leads me to believe a controlled discharge of water from PCV into the basement area - naughty naughty especially with below report from two days ago:

Edano said he has received a report that the radioactive substances are assumed to be either condensed steam from the reactor containment vessel or radioactive substances diluted by the water released into those facilities as part of cooling efforts

"released into those facilities as part of cooling effort"
What does that mean !
Surely they know the consequences !

 

[|Fred]

You are in deed right "Water injection to Containment Vessel" is mentioned on the JAIF reports
http://www.jaif.or.jp/english/news_index.php

What is a bit misleading is that the status change from "done" to "confirm" to "to de decided" to "confirming" to "to be confirmed" etc.. in a confusing order as the status is present without logical link to past action like "to be confirmed" rather than "resuming to be confirmed"

 

[|Fred]

Analyse of the day
http://www.meti.go.jp/press/20110330002/20110330002-5.pdf
http://www.meti.go.jp/press/20110330002/20110330002-4.pdf

140La 8.1 10^-2 Bq/cm^3 .. 1.6 days half life ..
132Te 1.8 Bq/cm^3 ...
129Te 21 Bq/cm^3
129mTe 4.1Bq/cm^3
110mAg 3.6 10^-2 BQ/cm^3 They specify a half life of 250 days for this element , what deos "m" stand for Silver 110 half life is suppose to be a few seconds?

 

[havemercy]

According to french IRSN yesterday' release, the people in charge have put sand bags and concrete to prevent the water to flow from the Trench to the ocean :


http://www.irsn.fr/FR/Actualites_pr...Seisme-Japon_Point-situation-29032011-12h.pdf

 

[AntonL]

Analyse of the day
http://www.meti.go.jp/press/20110330002/20110330002-5.pdf
http://www.meti.go.jp/press/20110330002/20110330002-4.pdf

140La 8.1 10^-2 Bq/cm^3 .. 1.6 days half life ..
132Te 1.8 Bq/cm^3 ...
129Te 21 Bq/cm^3
129?Te 4.1Bq/cm^3

As asked earlier:
Tc-99m 6 hour half life - :uhh:

 

[|Fred]

I think you asked or hoped Tc-99m was a mistake / measuring error.
now we have multiple measuring error, It could indicate that the probability of them not being error, increased.

Quick summary

If we have a reactor core vessel breached immersed into a concrete containment vessel filled with watter but leaking.. where do we go from there ?

If currently off line cooling system managed to be switched on , do we have simultaion of cooling a breached core vessel

If we can not provide additional cooling to the core vessel what are the options ?


I'm reading this 15 years old paper http://www.oecd-nea.org/nsd/docs/1994/csni-r1994-6.pdf .. might provide awnsers

 

[AntonL]

They specify a half life of 250 days for this element , what deos "m" stand for Silver 110 half life is suppose to be a few seconds?

m stands for "metastable". What that means for your isotope is another whole question. Check out http://en.wikipedia.org/wiki/Metastable

Some energetic states of an atomic nucleus (having distinct spatial mass, charge, spin, isospin distributions) are much longer-lived than others (nuclear isomers of the same isotope).

 

[jlduh]

Don't know who is this guy Michio Kaku but even if he is saying what he says in a very dramatic manner (theatral speaking), i have the unclear but deep feeling since some time now that what he is talking about, about this kind of domino effect, cannot just been forgotten or expelled from minds. We saw that every time there is an evolution where more radioactivity is released, this creates huge problems for workers to stay around and continue their work: there has been several evacuations, and with the news about the (very) contaminated water in the basements, this delays even more the process to put in place a cooling process using installed equipment (not to say that it may also just annihilates any possibility to do it this way, and also to get close to the reactor or pressure vessel from the bottom).

So the point is that any worsening of the release of radioactivity (by air through breaches, or by huge amount of water now) pushes a little bit further, meter by meter,the volume around the installations into which worker cannot enter (at least for no more than a given short time) to do the work. This is the big problem with nuclear accidents i think: the source is at the core but it generates more and more repulsive contaminants that creates a problem (increased distance) to attack the problem... at the core! I think it specific to nuclear accident like that, for example a fire even huge, like in Russian forests, is destroying it's own fuel (once it is burnt, it stops) and so the battle is always at the peripheral lines which can be approached to some extent (it is also very meteo dependent ,if rain comes it helps). I see a very different scenario in case of nuclear accidents like this one.

So i think at this point, nobody can for sure reject the idea that IF radiations worsens (gradually or suddenly with for example an other explosion), then the safe or let's say bearable limit (for humans) around the cores will be expanded, the no man's land volume around them will increase and what is saying is that then, this can be an on going process implying that human made operation (including cooling of reactors) could not been done at some point.

Then the domino effect is "possible":from "reactors" to "pools on reactors", then to "common pool on site", then to the "two other reactors on site", then why not two the "second Daini plant which is 12 miles south"?

Every time some human presence is required to maintain one part of the installation "functionning", and that this man cannot stay there because of increased radiation, then this is a possible problem. Except if everything is fully automatic and continue to work without damage (?) or if bio-robots (sacrified men like at Tchernobyl?) are an option in this case?

What I'm just saying is that even if this guy is putting it in words that are a little bit too dramatic to be scientific, totally true, what he is saying cannot just be refuted like that, except if we someone can show that this domino game is NOT possible.

So let's demonstrate it's not possible?

 

[Gilles]

Analyse of the day
http://www.meti.go.jp/press/20110330002/20110330002-5.pdf
http://www.meti.go.jp/press/20110330002/20110330002-4.pdf

140La 8.1 10^-2 Bq/cm^3 .. 1.6 days half life ..
132Te 1.8 Bq/cm^3 ...
129Te 21 Bq/cm^3
129mTe 4.1Bq/cm^3
110mAg 3.6 10^-2 BQ/cm^3 They specify a half life of 250 days for this element , what deos "m" stand for Silver 110 half life is suppose to be a few seconds?

yes, m stands for metastable - excited but somewhat stable nuclear spin states. What I don't know is if the half-life is given for beta decay only or for the some of all decay modes including transition to the stable Ag110 ?

and Tc-99m is produced by the decay of Mo-99, which has a longer half-life of 66 hours - however it should have fairly disappeared if no fission had occurred for 20 days = 480 hours. Looks pretty hot inside.

 

[DrDu]

and again Tc-99m 6 hour half life is detected - I hope measuring error

What's the problem with Tc-99m having 6 hour half life?

 

[jlduh]

Hummmm, is this guy (TEPCO chairman) actually living on another planet?

He added that the No.1 through 4 reactors would eventually have to be shut down for good.

http://www3.nhk.or.jp/daily/english/30_28.html

Does it mean that he had still some hopes that they could be restarted? Damn, if they only could be shut down FOR GOOD, that would be the best news from 2 weeks, especially for the workers on site...

These kinds of "understatements and distortions" of reality bother me and make me feel very angry to say the least. How can we trust people with this kind of language, really?

Ok i know we're getting political. But HE started! Sorry.

 

[jlduh]

Achille's heel revisited...

Kaieda urges safety steps at other nuclear plants

Japan's industry minister has urged power companies across the country to secure emergency energy sources for their nuclear power stations.

Banri Kaieda told reporters on Wednesday that the accident at the Fukushima Daiichi plant was due to a failure to secure emergency electricity and a loss of cooling systems at the reactors.

Kaieda urged utility companies to secure mobile generators as a source of emergency power that can safely cool nuclear reactors, and to ensure water-supply routes for fire engines.

He demanded that the companies confirm emergency steps and conduct drills within a month, or stop operating their nuclear power plants.

Kaieda added that putting an immediate end to operations at nuclear power plants is out of the question, because Japan relies on them for about 30 percent of its electricity.

NHK has learned that 90 percent of the 15 nuclear power stations nationwide, excluding the 2 quake-hit plants in Fukushima, have decided to introduce new emergency power generators, including mobile generators.

Some utilities have already conducted simulations for cooling procedures based on a scenario in which emergency generators have failed to work at their nuclear reactors.
Wednesday, March 30, 2011 16:57 +0900 (JST)

http://www3.nhk.or.jp/daily/english/30_27.html

 

[AntonL]

Hummmm, is this guy (TEPCO chairman) actually living on another planet?

He added that the No.1 through 4 reactors would eventually have to be shut down for good.

http://www3.nhk.or.jp/daily/english/30_28.html

Does it mean that he had still some hopes that they could be restarted? Damn, if they only could be shut down FOR GOOD, that would be the best news from 2 weeks, especially for the workers on site...

These kinds of "understatements and distortions" of reality bother me and make me feel very angry to say the least. How can we trust people with this kind of language, really?

Ok i know we're getting political. But HE started! Sorry.

Please see this in context - even talking to reporters this is an announcement to Tepco share holders which he has to do sometime as responsibility to the shareholders and stock exchange regulations, normal business practice and not because he only realized it today. It also makes decision making for the accident manager easier - no economic pressure to preserve