Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[sheffters]

This gives rise to frustration and the opinion in some minds that TEPCO are witholding information. In fact, TEPCO are only witholding interpolation and opinion. Rightly in my mind.

They don't help themselves though in the eyes of the world. They can do it when they want to.

"Explosive sound and white smoke were confirmed after the big quake occurred at 3:36 pm on March 12. It was assumed to be hydrogen explosion."

So why not state the facts and the most likely cause to save all the speculation? They could best guess (aka assume or similar wording) based on what they know.

They could also employ some decent translators. Some of their phrasing is ridiculous. Surely between TEPCO, IAEA, NISA, JAIF and a whole host of others international bodies they have someone who understands the nuclear lingo and can translate effectively.

Ian.

 

[Most Curious]

While the guidance requirements seem to be pretty effective, they are not totally robust.
If memory serves, the Besse Davis reactor vessel had the head almost corroded through, as no one asked where the copious rust in the water was coming from. More seriously, slowly emergent problems such as the risks posed by overfilled spent fuel pools do not seem to be surfaced very effectively. Is there an industry mechanism to help bring such generic problems to the foreground?

IIRC the Davis Besse head was corroded from the OUTSIDE, therefore no evidence would have existed in the coolant.

 

[etudiant]

IIRC the Davis Besse head was corroded from the OUTSIDE, therefore no evidence would have existed in the coolant.

You are of course correct and I was mistaken. The reference should have been to the boric acid buildup around the head.
The gory details are in this report:
http://www.nrc.gov/reactors/operati...essons-learned-files/lltf-rpt-ml022760172.pdf

 

[NUCENG]

You said:




What is wrong with it? Wrong that you regret that *after this disaster* (word "now" in the above quote has that meaning), there is a "need to make sure it doesn't happen somewhere else". Which is WRONG, THIS NEED WAS THERE EVEN BEFORE THE DISASTER. Waiting for a disaster to happen in order to start looking at the problems seriously is WRONG.

How can I say this even more clearly?



Wrong again. I don't have to prove that plants are unsafe. It's the other war around - the nuclear industry must prove to the satisfaction of the people that they are safe.

There is a direct parallel with Challenger disaster. Engineers who voiced concerns about O-ring erosion were asked to provide a proof that O-rings can be breached. Rogers Report specifically points out that managers were dead wrong about it. Shuttle can be launched not when engineers can't prove it's unsafe to do so, it can be launched only if engineers are sure that it is reasonably safe to do so!

Your believe that everything is shiny in France, Russia and US just because this disaster happened in Japan, not those countries. I am not so sure about it.

I read post-disaster reports after both Shuttle disasters, I know how stubborn people may be in (self)deception about safety when it comes to multi-billion projects. NASA managed to self-hypnotize itself into believing Shuttles are safe even after NASA itself dramatically proved it's not true.

We are basically in port-Challenger state right now in regards to NPPs, and unless we start to do something differently now, we are going to get Columbia.

The reaction of worldwide nuclear community up to now is mostly PR. PR is not going to convince me. I need to see deeds, not words.

"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled", said Richard Feynman, and I fully agree with him.

While you are trying to parse words and change the meaning of what I wrote, have you figured out what the definition of is is? ;-}

I agreed with you that the need was there before the accident. Quote: "You are right that the need was there, and it wasn't done." Do you also want to argue with yourself? Does agreeing with you make me "stubborn and self-deceptive"?

It does appear you didn't read my post because I specifically said I could not answer for France and Russia.

I did not ask you to prove plants were unsafe. Again, if you look at my previous posts you will find that I don't believe the word safe is meaningful. Risk is meaningful and nothing in life is risk free. The shuttle disasters demonstrate that point well. As new risks were discovered they were fixed. Risks include human errors. But the benefite of space exploration were balanced against the clear risks and the program continued.

I asked you to discuss concrete steps being taken by industry and referenced in my earlier posts. I've explained that American nuclear plants and regulators continuously review design bases and new information and operating experience. We are not "waiting around for a disaster." You don't believe that and you want to win the argument simply by labeling me as "WRONG." If you continue with rants that don't add to the PF forum I will report them to mentors for deletion. I would much rather discuss specifics. I can't do anything about your fears, opinions, and feelings.

Give it a try, you might learn something. Even better, I might learn something.

 

[tsutsuji]

http://www.yomiuri.co.jp/science/news/20110706-OYT1T00400.htm Parts of the cover structure for unit 1 have arrived at the plant harbour this morning after being brought by boat from Onahama Port. They are two 35 ton concrete foundation stones. They are going to be unloaded by crane.

http://www3.nhk.or.jp/news/html/20110706/t10014003071000.html Tepco wants to calculate by the end of this month an estimation of the radiation emitted by the reactor building(s). The purpose is to be able to compare the figures and measure the effect before and after the cover has been completed.

http://www.nikkei.com/news/category...3E2E2E2E2E2E2;at=DGXZZO0195591008122009000000 3 workers have been sent to hospital today ; 2 are workers in their twenties suffering from hyperthermia, one laying cables at unit 1's turbine building, the other controlling entrance and exit at the West Gate. The third one is a heavy equipment operator working near unit 4 who slipped in a stair.

http://www.nikkei.com/news/category...39F9FE2E2E2E2;at=DGXZZO0195165008122009000000 Tepco is unveiling a plan to build a new water treatment system to be completed by spring or summer of 2012. The plan is to purify water in each reactor rather than go on sharing the present water treatment facility with its 4 km long pipes. The reactors will require cooling by water injection for years before the fuel can be removed (at Three Mile Island it took 10 years). The present water treatment facility has been designed with a durability of one year.

http://sankei.jp.msn.com/economy/news/110705/biz11070516200015-n1.htm Interview of Areva vice president Dominique Mockly in Paris on 4 July : Areva will supply Tepco with evaporation equipment for the final treatment of the contaminated water.

http://www3.nhk.or.jp/news/html/20110706/t10014013131000.html The water treatment facility achieved a utilization rate slightly above 80% during the week up to 5 July. But it was only 55% before that, as the facility encountered a number of issues on 29 and 30 June. So as a whole the 80% goal is not achieved. While Tepco wants to achieve an 80% goal, the 90% goal is abandoned.

http://mainichi.jp/select/today/news/20110706k0000e040049000c.html From 16 June to 5 July, 46 adsorption towers have been replaced at the Kurion facility. The maximum radiation at the surface of the vessel was 6.1 mSv/h. The maximum worker exposure was 1.13 mSv. Tepco is studying improvements, including changes in replacement frequency, in order to diminish worker exposure.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110705_01-e.pdf and http://mainichi.jp/select/weathernews/news/20110706ddm001040018000c.html Tepco announced on 5 July the completion of the work to seal the water intake at units 1,2,3,4. An amount of 109 concrete plates (32 cm thick, 4560 kg heavy) were installed as shown in the Tepco handout pdf.

http://www.mbs.jp/news/jnn_4769268_zen.shtml a video made last week on the plant site, independently acquired by JNN.　It shows an automated machine performing debris removal near unit 3, the open doors at unit 2 reactor building, the fallen crane near unit 5 sea water intake, the blue tanks used for storing decontaminated water, and the arrival of the cover parts at the harbour.

http://www.tudou.com/programs/view/Cw5FeFIJxeI/ the video released by Tepco on 14 June showing the Meccano-toy-like construction of the cover structure. I guess the music is not from Tepco, though.

A 1 minute long accelerated version of 24 hours of Fukushima Daiichi Nuclear Power Plant　Live Camera. 2011-07-05

 

[zapperzero]

http://www.mbs.jp/news/jnn_4769268_zen.shtml a video made last week on the plant site, independently acquired by JNN.　It shows an automated machine performing debris removal near unit 3, the open doors at unit 2 reactor building, the fallen crane near unit 5 sea water intake, the blue tanks used for storing decontaminated water, and the arrival of the cover parts at the harbour.

Thanks for all these informative links. I was not aware there was a fallen crane? Also, it will be interesting to see how much contamination TEPCO thinks is going on.

 

[jim hardy]

Bandit observed "This gives rise to frustration and the opinion in some minds that TEPCO are witholding information. In fact, TEPCO are only witholding interpolation and opinion. Rightly in my mind.""

I hope they will make public in what condition they find the reactor vessels.

I believe they are withholding information.
Perhaps it's rightly withheld, for it would be leapt on by sensationalists in the irresponsible sector of press. ... maybe product liability lawyers too.

Reason i say that is from observing the scarcity of hi res photos of unit 3, as was noted by Atlantic Monthly back in April:
"Unfortunately, Welch couldn't share the specifics of the missions his team flew. The cone of secrecy around Fukushima extends far and wide. We don't get to know where they launched from or what their camera targets were. He couldn't discuss whether their operations center had a roof over it or not, or whether it was a tent. We don't even know how many flights they made, though he confirmed it was "a bunch."
http://www.theatlantic.com/technolo...he-drone-missions-to-fukushima/237981/#slide6

the plastic covers will keep away roving eyes in the sky.

but were they my reactors i just might do the same thing.

 

[tsutsuji]

Thanks for all these informative links. I was not aware there was a fallen crane?

We talked about it in May :

I add a picture showing how they look like -these are from N°5 reactor and got hit by this big blue structure, but they look similar to the others:

http://www.netimago.com/image_202944.html

The trajectory of the big blue structure, a gantry crane, is shown on page 40 of http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110525_01-j.pdf. (...)
English version is now available at http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf

 

[robinson]

I'm not sure anymore where to even post at times, too many threads.

After some investigation, we can now confirm that the Kauai Monitoring Station in Hawaii broadcast yet another Radiation Alert recently (see graph at right), commencing toward midnight of June 29th and continuing into the early morning hours of June 30th.

This is becoming somewhat of a routine event for the Kauai station, considering elevated radiation detections twice before, on June 10th and June 22nd.

This most recent Alert was triggered by a detection of over 100 CPM (Counts per Minute) for a sustained period of almost 15 minutes, followed by lower, yet elevated radiation levels for another half hour, making this the longest detection period yet for the Kauai station (clear sky this time – no rain). Background radiation for that station approximates 37 CPM, so these sustained levels were 2 to 3 times normal. Again, our best judgment is that the source of this radiation is probably Fukushima, perhaps from recent “releases” – we will try to correlate.

http://hawaiinewsdaily.com/2011/07/kauai-station-suspects-new-traces-of-fukushima-radiation/

 

[Caniche]

Cook em Dano

 

[RealWing]

If memory serves, the Besse Davis reactor vessel had the head almost corroded through, as no one asked where the copious rust in the water was coming from. Is there an industry mechanism to help bring such generic problems to the foreground?

The Davis Besse reactor vessel corrosion event was another significant wake-up-call for the whole industry. One or more long standing reactor coolant system leaks resulted in boric acid completely eating through ~6.5" of the vessel pressure boundary. All the was preventing a Loss of Coolant Acident was the thin S/S liner inside the vessel.

So - what are the "industry mechanisms to help bring such generic issues to the foreground"??

First - what failed?
1. The utility who has primary responsibility for the safety of the plant - failed to act on clear evidence of a leak. This included all levels of management as well as their internal oversight group
2. The regulator (NRC) failed to adequately communicate indications of a leak and assess the safety consequences
3. The industry oversight organization (INPO) failed to adequately assess the safety culture and outage programs in the utility.

In my view - a failure of the whole industry.

Like NUCENG - who knows the US industry very well, I can only comment with some knowledge on the Canadian industry. I know that this event had a significant effect on me personally because we, as nuclear plant managers must always keep a strong questionning attitude and strive to never become complacent. We do this by having a relentless focus on safety and by learning from other's mistakes. This was a major learning.
This event had many parallel's to the Columbia and Challenger events where management became complacent about O-ring leakages and foam detachments. The issue eventually faded into the background because of a poor management safety culture.
Even though Canadian reactors do not have a reactor pressure vessel or boric acid, this event resulted in an in-depth review of our safety culture as well as ensuring there are no "hidden" long term safety issues lurking in the plants.

My $0.02.

 

[robinson]

Big new crane on the live cam

http://www.tepco.co.jp/nu/f1-np/camera/index-j.html

 

[Joe Neubarth]

It may be too early for Tepco to even know exactly what went wrong and when. It does seem obvious that even a 30 meter wall wouldn't have prevented the immense pressure to the intake/outflow areas, the pipes that actually have to be directly connected to the ocean for cooling.

The turbine rooms and other areas may still have failed even if somehow they had a wall high enough to stop the ocean. From careful observation of the tsunami waves, it isn't just a matter of stopping the waves. The intakes have to be connected to the ocean. A wall would have stopped the damage to the buildings, but not to the intakes and where they connect to.

Loss of cooling may still have happened, both to the diesels and the reactors. It's an issue that probably wasn't planned for at all.

An increase in pressure to the intake and discharge points would have no effect on the operation of the Nuclear Reactor Plant for any short term interval...

 

[joewein]

I have never seen this mentioned, but may have missed if it was discussed early in the thread: Unit 3 had the biggest explosion of the three blocks that blew their tops, but when you look at shots of the unit 3 building, you can see that the truck bay, a tunnel-like entrance on the west side is largely intact. In unit 4, the walls of the truck bay are cracked and have almost blown away (probably only held by some reinforcement bars inside the concrete).

See for example on these Cryptome pictures:
http://cryptome.org/eyeball/daiichi-npp15/daiichi-photos15.htm

This suggests that hydrogen filled the ground floor (1F) of unit 4, but perhaps not unit 3.

 

[joewein]

Units 5 and 6 survived because one of the diesels at unit 6 was air cooled, so losing the sea water pumps didn't kill it. Other than that single diesel, units 5 and 6 still depend on either the grid or truck-mounted generators. I have not heard anything about moves to replace the dead diesels.

That has in fact already happened, I missed the news. Two new emergency diesels were installed and tested in unit 5 on June 27/28, mentioned towards the end of this document:
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110629_02-e.pdf

As a result, units 5 and 6 should now have 3 EDGs between them. No word on whether the replacement units are water-cooled or air-cooled...

 

[tsutsuji]

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110706e11.pdf is a 6 July update of the "storing and treatment of accumulated water including highly concentrated
radioactive materials at Fukushima Daiichi Nuclear Power Station". You can compare it with the first release http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110629e13.pdf published on 29 June.

http://www.jiji.com/jc/c?g=soc_30&k=2011070600860 from 29 June to 5 July 6380 tons have been produced from the 8400 capacity. This gives a 76% utilization rate, which is an improvement from the 55% rate a week earlier. The 96,980 ton accumulated in the plant on 5 June is 1830 ton less than at the end of June. Tepco initially planned to achieve an 80% utilization rate by 5 July, and a 90% rate henceforth. Instead, it is now planning an 80% rate by the end of July and 90% from August. This could cause delay to the goal of treating 200,000 tons within this year. The Areva system has already produced 109 tons of highly radioactive sludge, which is more than planned. Tepco is studying the possibility to undertake purification again with the top layer in order to reduce the volume of the sludge.

http://www.jiji.com/jc/c?g=soc_30&k=2011070700396 In a reply to Yukishige Okubo at the Upper House Budget Committee on 7 July, minister Goshi Hosono said there was a plan to introduce Japanese technology led by Toshiba in August to supplement the French/US, Areva/Kurion technology currently used at Fukushima Daiichi. He also insisted that the current facility was a temporary one, while a permanent facility using Japanese technology was being studied in combination with the temporary one.

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110707_03-j.pdf (not yet translated into English) the Decontamination Factor at the Kurion facility has greatly improved. As a result the radiation at the end of the Areva facility is below the detection limit for cesium.

http://www.jiji.com/jc/c?g=soc_30&k=2011070500852 In order to reduce worker exposure, flushing with low contaminated water has been performed since some time ago before replacing the adsorption towers at the Kurion facility, which is done using a crane. To further reduce worker exposure, what is planned is to change the policy to change 2~4 towers every day into 4 towers or so every other day. This has already been tried on 5 July with the replacement of 4 towers at the same time.

http://www.nikkei.com/news/category...3E2E2E2E2E2E2;at=DGXZZO0195165008122009000000 0.13 Bq/cm³ of Cs-134 and Cs-137 is detected again in ground water South East of the Process Main Building, after a number of days below the detection limit. This is thought to be either a consequence of the rain or of moving debris nearby.

http://japanfocus.org/-Sakai-Yasuyuki/3546 (English article) Sakai Yasuyuki, Japan’s Decline as a Robotics Superpower: Lessons From Fukushima, The Asia-Pacific Journal, Volume 9, Issue 24, No. 2, June 13, 2011.

 

[tsutsuji]

Fukushima One's first four reactors were just one tsunami away from destruction from the first day they put number One in operation about 40 years ago.

Consider this:

1. When they lost one Utility Power Line leading to the plant, there was no backup source of commercial electricity. (Was this the case for 40 years and nobody realized what a serious error it was in site design?)

Tepco has always said that there were 6 or 7 lines : see http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e17.pdf which is one of the attachments from the 16 May press release on the damage of electric facilities ( http://www.tepco.co.jp/en/press/corp-com/release/11051613-e.html ). If this is what you mean, could you explain your view that losing only one line was enough to cause a black out of the whole plant ?

By the way, there is a fresh new press release concerning the reliability of the power supply to the neighbouring Fukushima Daini power plant published today : http://www.tepco.co.jp/cc/press/11070704-j.html (not yet translated into English).

 

[joewein]

http://en.wikipedia.org/wiki/Fukushima_Daiichi_Nuclear_Power_Plant#Electrical_connections" also lists multiple grid connections (pre-tsunami):

Electrical connections

The Fukushima Daiichi plant is connected to the power grid by four lines, the 500 kV Futaba Line (双葉線), the two 275 kV Ōkuma Lines (大熊線) and the 66 kV Yonomori line (夜の森線) to the Shin-Fukushima (New Fukushima) substation.

The Shin-Fukushima substation also connects to the Fukushima Daini plant by the Tomioka Line (富岡線). Its major connection to the north is the Iwaki Line (いわき幹線), which is owned by Tohoku Electric Power. It has two connections to the south-west that connect it to the Shin-Iwaki substation (新いわき).

TEPCO seems to have managed to lower radioactivity levels in one corner of unit 3 to 1/3-1/4 of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110703_01-e.pdf" in preparation for nitrogen injection, after robot-cleaning and laying steel plates for shielding:
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110707_02-e.pdf

Units 1 and 2 are already receiving N₂ injections.

 

[robinson]

An increase in pressure to the intake and discharge points would have no effect on the operation of the Nuclear Reactor Plant for any short term interval...

I don't know. If the outflow from the turbine room, the hot water discharge, is designed to operate at atmospheric pressure, and suddenly the water being pumped out is facing water at a depth of 20 meters, that's a lot of pressure to be forcing water against. In fact the pressure of the water forcing itself in when the pumps want the water to be going out, that might damage the pumps. It's the sort of thing that could be tested of course.

There are a lot of unknowns involved. Did anyone ever do any testing to see what would happen?

If the force of the water was enough to rip strong metal objects from their moorings, smash sturdy objects and in general just destroy, I can see it doing some serious damage to a pump motor trying to pump 10,000 gallons a second against the flow.

 

[Joe Neubarth]

I don't know. If the outflow from the turbine room, the hot water discharge, is designed to operate at atmospheric pressure, and suddenly the water being pumped out is facing water at a depth of 20 meters, that's a lot of pressure to be forcing water against. In fact the pressure of the water forcing itself in when the pumps want the water to be going out, that might damage the pumps. It's the sort of thing that could be tested of course.

There are a lot of unknowns involved. Did anyone ever do any testing to see what would happen?

If the force of the water was enough to rip strong metal objects from their moorings, smash sturdy objects and in general just destroy, I can see it doing some serious damage to a pump motor trying to pump 10,000 gallons a second against the flow.

Robinson, there is video footage of the Tsunami striking the plant complex. You can see the 4.2 meter swell out in the harbor rolling in. You can see the Run Up effects as it reaches shallower water. You can see the Big Splash at it hits the quay wall and water shoots up thirty or more meters. (Now, that was impressive!) You see that happen and you run like 'ell up the nearest hill. There are many reports of people having done just that at the site. A couple of technicians inside the turbine room complex were killed and mutilated by the wave as they did not have the presence of mind to get out of that area before the wave struck. As you can see along the coast in that immediate area, there are sea cliffs. Like any wave the water runs up against the cliff and then runs back out as a wave going in the opposite direction. There is video and still photos of the wave washing back out from Fukushima just a few seconds later. The sea water injection pumps would not have been effected by that momentary surge and increase in pressure at the inlet. They might have sped up a little, but the amount of sea water coolant running through the condenser tubing probably would not have increased that much simply because of capacity limitation. Any effluent flow might have been held up by the increase in pressure, but being of short duration it was not an issue of major importance considering that most of the Emergency Diesel Generators were under water and their controlling panels were water logged and inoperable

 

[Joe Neubarth]

Tepco has always said that there were 6 or 7 lines : see http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e17.pdf which is one of the attachments from the 16 May press release on the damage of electric facilities ( http://www.tepco.co.jp/en/press/corp-com/release/11051613-e.html ). If this is what you mean, could you explain your view that losing only one line was enough to cause a black out of the whole plant ?

.

TEPCO admitted that they had one electrical tower go down on the mainland.

When they lost that one tower, they lost all commercial power to the Fukushima Plant. That is the reason why right after the earthquake all of the Emergency Diesel Generators that were operable were running when the tsunami hit forty some minutes later.

A loss of electrical power to a nuclear plant is considered to be the Worst Case Scenario. Because of that, Nuclear Plants are designed to have multiple redundancy in commercial power sources. TEPCO lost one source (One Line Source) and the plants were in the dark. THERE IS NO ABSOLUTELY EXCUSE FOR THAT!

When the emergency diesel generators were submerged (again a serious site engineering design flaw), the reactors were left with no power for the coolant pumps and the meltdowns started within a couple of hours and were quite well advanced within 24 hours.

 

[nikkkom]

I don't know. If the outflow from the turbine room, the hot water discharge, is designed to operate at atmospheric pressure

No. Reactors were already scrammed ~40 minutes ago when tsunami arrived. IOW, turbine was not working, and even if F1 used regular turbine hall condensers for post-scram cooling, the required sea water flow was about fifty times smaller than one needed at 100% rated power operation.

 

[robinson]

The same problem could have effected the cooling pumps for the EDGs

 

[Atomfritz]

Is there an industry mechanism to help bring such generic problems to the foreground?

At least in Germany, this is not the case. Here the operating companies try to hide all that could undermine trust in the nuclear industry.

Here is just one such example:
Biblis NPP operators in the course of ten years repeatedly made dangerous maneuvers not covered by the procedure manuals to avoid shutdowns of the reactor. With these maneuvers (venting primary circuit coolant to outside the containment, into the machine building) they risked uncontrollable LOCAs.
This incident was not told to german nuclear authorities until almost half a year later, and then the violations were omitted in the report.
German government and public media got alarmed by an article in "Nucleonics Week" that made them start investigations and so uncover the coverup.

Technical description of this "top-level" incident: http://www.oecd-nea.org/nsd/docs/1990/csni90-180.pdf
Description of the cover up by the NPP operators in: http://www.greenpeace.org/raw/content/international/press/reports/the-greenpeace-book-of-the-nuc.pdf (Sorry for this source, it was the only one in English. All other detailed articles about this I found are in German)

It galls me to the core that this accident could have been prevented. I am trying hard not to let my anger and embarrassment prevent me from seeing that opponents like Arnie may have some valid points.

Maybe even stupid people like me sometimes have valid points.
And yes, it's so sad that they now build a higher tsunami wall... only after that lovely NPP has been destroyed.

This suggests that hydrogen filled the ground floor (1F) of unit 4, but perhaps not unit 3.

I always thought that in normal operation (#1-#3) the transport shaft zone is sealed by a sort of door.
Maybe this seal was open in RB4 due to core shroud material transport and other maintenance, so the damage?

http://en.wikipedia.org/wiki/Fukushima_Daiichi_Nuclear_Power_Plant#Electrical_connections" also lists multiple grid connections (pre-tsunami)

If this is what you mean, could you explain your view that losing only one line was enough to cause a black out of the whole plant ?

On Google Earth images I can see at least three grid connections (rough directions: SW, SWW, W). Maybe some masts carry more than one connection, ripping them all open when masts fall? There were reports of several fallen masts.
If six or even seven grid connections fail at once this shows clearly that complete station blackouts may be not that rare and hypothetical as postulated. Especially if all grid connections lead to the same grid node station, as Wikipedia article could be interpreted. This is no real redundancy to rely upon imho.

If the force of the water was enough to rip strong metal objects from their moorings, smash sturdy objects and in general just destroy, I can see it doing some serious damage to a pump motor trying to pump 10,000 gallons a second against the flow.

I think they will have backflow prevention, though designed only for 5.7m tsunami.
Some kind of valve (in German: "Rückschlagklappe", don't know in english) that is common in flood areas, like those that avoid the drain flowing over into your basement at heavy rains.

 

[joewein]

TEPCO admitted that they had one electrical tower go down on the mainland.

When they lost that one tower, they lost all commercial power to the Fukushima Plant. That is the reason why right after the earthquake all of the Emergency Diesel Generators that were operable were running when the tsunami hit forty some minutes later.

But according to this diagram there were multiple, simultaneous points of failure in the grid connections:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e17.pdf

From that diagram, it doesn't look like it was a single tower going down that triggered it all.

 

[zapperzero]

But according to this diagram there were multiple, simultaneous points of failure in the grid connections:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e17.pdf

From that diagram, it doesn't look like it was a single tower going down that triggered it all.

Yet another example of fake redundancy - a common failure mode exists for the assumed redundant elements, and moreover a common-cause failure is possible. So it happens, naturally, sooner or later.

 

[tsutsuji]

The collapse of Yonomori tower No. 27 is mentioned on http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e17.pdf : it is responsible for the collapse of two lines because both lines are using the same towers. Yet this event does not account for the failure of the other 5 lines.

As I wrote in June ( https://www.physicsforums.com/showpost.php?p=3356083&postcount=9758 ) I think the Japanese government's view expressed in the report to IAEA that more should have been done to ensure that the power lines are able to withstand earthquakes is interesting. I would be glad to learn more about the feasibility and the cost of earthquake resistant power lines, which sounds to my ears better than multiple, redundant lines, if they are not designed to withstand earthquakes in the first place. Conversely, if they were thought and designed to withstand earthquakes, an investigation should tell what was wrong in that design.

Also I was wondering whether it would not be possible to use the high voltage power lines backwards to supply power back to the plant in case of emergency if they are still safe while all other lines have collapsed.

 

[Atomfritz]

But according to this diagram there were multiple, simultaneous points of failure in the grid connections:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e17.pdf

From that diagram, it doesn't look like it was a single tower going down that triggered it all.

Yet another example of fake redundancy - a common failure mode exists for the assumed redundant elements, and moreover a common-cause failure is possible. So it happens, naturally, sooner or later.

Thanks for the link.
If I interpret the pdf correctly then each reactor has one 275kV line.
Each mast carries two lines. So mast cave-ins, mast collapses, shorts due wires tied together always put out out two reactors.
The 66kV Tohoku line (maybe Earth cable) backup also was damaged.
The only functional lines (Okuma 1+2) could not be utilized because line switch and circuit breaker damage on unit 1/2 switchyard.

So sad that there has been no redundancy switch so that unit 3/4 switchyard could have been supplied via Okuma 1 line, the only one whose connection to the Daiichi plant was not broken.
If it had, at least reactors 3+4 possibly could have been saved.

 

[Bandit127]

Quite a substantial piece of framework to hang the plastic curtains from. It is good to see that they are having a trial run too.

Trial fitting of the cover for Unit 1, Fukushima Daiichi Nuclear Power Station at Onahama port
[URL]http://www.tepco.co.jp/en/news/110311/images/110707_1.jpg

[/URL]

 

[Luca Bevil]

Also I was wondering whether it would not be possible to use the high voltage power lines backwards to supply power back to the plant in case of emergency if they are still safe while all other lines have collapsed.

What do you mean exactly ?

 

[ElliotLake]

I wondered that too; my house has a switch box so I can use generator power in winter outages (without endangering linesmen trying to make repairs). And there's a power line near me with "caution, reversing voltage" warning or some such. So--lines distributing electricity from Fukushima, could they not have been reversed to bring power in? Or were they all swept away?

 

[Atomfritz]

Also I was wondering whether it would not be possible to use the high voltage power lines backwards to supply power back to the plant in case of emergency if they are still safe while all other lines have collapsed.

What do you mean exactly ?

As the grid is synchronized, you can (very simplified) think of it as a grid where all power plants are connected in parallel.
So there is no reversing in the sense of "re-plugging" the lines.

I wondered that too; my house has a switch box so I can use generator power in winter outages (without endangering linesmen trying to make repairs). And there's a power line near me with "caution, reversing voltage" warning or some such. So--lines distributing electricity from Fukushima, could they not have been reversed to bring power in? Or were they all swept away?

Just imagine you are connected to several lines, which can fail individually.

Look at the schematic http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e17.pdf".
Just imagine a switch so you can conduct the Okuma-1 supply (cut off after switch at circuit breaker O-1) to circuit breaker O-84.

If such a switch had been there, then the Okuma-1 line that delivered 275kV to the damaged, defunct switchyard 1/2 could have been connected to the switchyard 3/4.
So it could have provided power to at least unit 3 and 4, saving them.

This was no "real" blackout.
Power was there on the Daiichi plant all the time.
It just could not be used due to lacking switches.
So the redundant grid connections were rendered useless.

 

[Joe Neubarth]

The collapse of Yonomori tower No. 27 is mentioned on http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e17.pdf : it is responsible for the collapse of two lines because both lines are using the same towers. Yet this event does not account for the failure of the other 5 lines.

As I wrote in June ( https://www.physicsforums.com/showpost.php?p=3356083&postcount=9758 ) I think the Japanese government's view expressed in the report to IAEA that more should have been done to ensure that the power lines are able to withstand earthquakes is interesting. I would be glad to learn more about the feasibility and the cost of earthquake resistant power lines, which sounds to my ears better than multiple, redundant lines, if they are not designed to withstand earthquakes in the first place. Conversely, if they were thought and designed to withstand earthquakes, an investigation should tell what was wrong in that design.

Also I was wondering whether it would not be possible to use the high voltage power lines backwards to supply power back to the plant in case of emergency if they are still safe while all other lines have collapsed.

They did not do their homework and they had all power to Fukushima 1 going through that tower. Thus, they created a single point of failure. If they were trying to design in double and triple redundancy, they failed miserably. I was a data communications manager with Pacific Bell. They put millions and millions of dollars into a new data communications system for company business offices. It was the most modern state of the art system we were all told and had multiple redundancy with 32 data switches all over the state, and 128 trunk lines connecting the data switches, so the communications links would absolutely have 100 percent reliability.

I was not at that time associated with that new system, but from the beginning it constantly had unexplained outages when just one link would go down. Just one link failing could cause outages in northern California, Nevada and southern California at the same time. It seemed like they never could solve that problem.

Three years later I took over the network and I flowcharted all of the communication paths drawing them out by hand on brown wrapping paper. I created scenarios "That if Line A went down how was I certain that the data traffic went to Line B? And, if Line B went down, how was I certain that it switched to Line C, and so on for lines D, E, F, G, H, and all the rest."

I found to my amazement that the original configurations that had been put in the switches years earlier had failure paths switching back to the same physical failure path in the configurations. I found 26 instances where the backup path was the same as the path that had failed. AMAZING! Those configurations had been in that system for years and nobody caught it. (Just like the Hubbell Telescope having that refraction error and nobody caught it until after it was launched. Or, like that Mars lander mission that had been calculated in meters but adjusted in feet, so the drogue parachute opened after the lander was fifty feet under the Martian soil. The Japanese do not have exclusive ownership of intelligent people doing stupid things. That can happen anywhere, but in the case of Nuclear Power Plants where meltdowns can result in millions dying of cancer, this electrical circuitry screwup -- EVERYTHING ROUTED THROUGH ONE TOWER. -- should have been caught and corrected years ago.)

I informed my superior of the configuration screwups and corrected the problem. We had 100 percent reliability on that network for the next year and then the top company bosses decided to replace it because it had such a bad long term performance history. It appeared that the screwup that I had discovered had never made it to the top bosses because nobody wanted it known that it was a problem that was easily corrected with people doing their jobs in an attentive fashion.

 

[robinson]

The Japanese do not have exclusive ownership of intelligent people doing stupid things. That can happen anywhere, but in the case of Nuclear Power Plants where meltdowns can result in millions dying of cancer, this electrical circuitry screwup -- EVERYTHING ROUTED THROUGH ONE TOWER. -- should have been caught and corrected years ago.)

It is this human nature issuer you describe that makes me question the safety and wisdom of nuclear reactors, situated close to population centers and valuable real estate.

 

[Joe Neubarth]

I wondered that too; my house has a switch box so I can use generator power in winter outages (without endangering linesmen trying to make repairs). And there's a power line near me with "caution, reversing voltage" warning or some such. So--lines distributing electricity from Fukushima, could they not have been reversed to bring power in? Or were they all swept away?

Electricity that is generated for transmission on high power lines has stepup transformers in the system. Not only that, but the actual wires are designed for high voltage. Trying to use those lines to build an emergency power supply back to Fukushima would be totally impractical. It could not have been reengineered in time to prevent the total melt down of the three plants that are now belching radioactive gases over Japan and the Pacific Ocean.

 

[Atomfritz]

Joe, thank you for the illustrative explanation of "routing affairs".

...they had all power to Fukushima 1 going through that tower. Thus, they created a single point of failure. If they were trying to design in double and triple redundancy, they failed miserably.

As I explained above, according the schematic each reactor had it single grid line.
Reactors 1+2 had no redundant supply transformers, so have to shutdown when line fails.
Reactors 3+4 share two redundant supply transformers, one was unavailable due to maintenance.
There is no power input/output switching capability to make use of any other than their fixed assigned line.

The Japanese do not have exclusive ownership of intelligent people doing stupid things. That can happen anywhere, but in the case of Nuclear Power Plants where meltdowns can result in millions dying of cancer, this electrical circuitry screwup -- EVERYTHING ROUTED THROUGH ONE TOWER. -- should have been caught and corrected years ago.)

Indeed.
In the given scenario, line Okuma-1, the only line that still delivered electricity to the plant could not be used because it was connected to reactor 1, whose circuit breaker was damaged.
Sadly there had been no possibility to switch line Okuma-1 onto reactor 4 (Okuma-4).

In Germany usually 2 to 3 different lines (not fake redundancies like 2-line-masts etc) are connected to a NPP, so that shutdowns due to line failure are very rare. Usually it's just a matter of re-routing at line failures and maintenance, preventing outages and worse things.

Electricity that is generated for transmission on high power lines has stepup transformers in the system. Not only that, but the actual wires are designed for high voltage. Trying to use those lines to build an emergency power supply back to Fukushima would be totally impractical.

They just repaired the switchyard damage to get back to grid power, as was done quite early and shown in photos.

 

[joewein]

Also I was wondering whether it would not be possible to use the high voltage power lines backwards to supply power back to the plant in case of emergency if they are still safe while all other lines have collapsed.

That's the status that Fukushima-II (which kept its grid connection) is in right now.

 

[jim hardy]

""Look at the schematic here mentioned by joewein.
Just imagine a switch so you can conduct the Okuma-1 supply (cut off after switch at circuit breaker O-1) to circuit breaker O-84.""

that lateral tie appears to exist at the "M/C" (motor control center?) level, observe the horizontal lines connecting the three 'normal M/C' 's.

I see five lines coming into plant which seems enough.
but it's a moot point because all the M/C's are shown "Out of order because of inflowed or inundated.." except a lone one on unit 6.Loss of the complete electric grid is considered a single failure so should cause no trouble.
But there should be no single failure that'll take out both of a plant's diesels (or their respective switchgears) at once.
We're back to electrical switchgear in a basement that got filled with seawater.

Some poor soul is really kicking himself right now for not acting on those mid-nineties warnings about tidal waves. And somebody else is proud of #6.

 

[elektrownik]

They should use cable underground lines... Air lines are not quake-resistant...

 

[maddog1964]

They should use cable underground lines... Air lines are not quake-resistant...

Overhead lines vs underground lines would be not be a simple decision... there are many engineering factors that would have to be addressed... remember the pictures of how much the land (shown mostly) on the road pictures shifted. Then you also have to engineer the water intrusion issues (this would be all the time, not just when a EQ or storm happens, as you have water table). Last but definately not least when you have a disruption, not if, it is very combersom and time consuming to repair as fast. You can see a down wire or tower.

It would come down to a risk assesment issue and there would probably be places that underground might be better.. and some that overhead would be better...

but I don't believe we have the information necessay to make a logic choice.. remember the dicharge to the sea has been through the "mechanical tunnels (in part)...

Possibly a good ideal in some locations, but not in others

 

[zapperzero]

Meanwhile, three more workers got doses in excess of 250 mSv.

http://www.bloomberg.com/news/2011-07-07/tepco-says-3-more-workers-exposed-to-radiation-exceeding-limit.html

Must be the guys who went exploring in reactor three.

 

[tsutsuji]

What do you mean exactly ?

On http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e20.pdf we can see the 500 kv Futaba line located next to the collapsed Yonomori line. I don't know the status of the Futaba line, but if it was safe, Tepco could have found convenient to use that Futaba line to bring power.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e25.pdf shows that Tepco used Futaba line tower No.2 as a replacement of the collapsed Yonomori tower No. 27 (1). My idea is to use the whole Futaba line : all its towers and all its conductors, with switching equipment on both ends enabling to connect quickly in case of emergency.

(1) Tepco also released this picture : http://www.tepco.co.jp/en/news/110311/images/110323_denngen_4.jpeg showing workers working on Futaba tower No. 2, and this one http://www.tepco.co.jp/en/news/110311/images/110323_denngen_3.jpeg showing the work on Yonomori tower No. 28.

 

[Susudake]

They should use cable underground lines... Air lines are not quake-resistant...

My understanding of this as a non-technical expert is that the above-ground power lines in Japan is because of the earthquake situation--both diagnosis and repair are greatly expedited. Ugly but practical.

More knowledgeable folks--is that not the case?

 

[NUCENG]

My understanding of this as a non-technical expert is that the above-ground power lines in Japan is because of the earthquake situation--both diagnosis and repair are greatly expedited. Ugly but practical.

More knowledgeable folks--is that not the case?

You are correct. If an underground cable is faulted it must first be excavated for repair. In high earthquake areas the biggest concern is a slip or thrust fault that can shear a cable just as it does to roads.

In the case of the tower that collapsed, I think the investigation will reveal that the foundation was either eroded or disrupted by the earthquake.
I heard something about a landslide, but can't remember if that was what collapsed the tower.

 

[NUCENG]

Electricity that is generated for transmission on high power lines has stepup transformers in the system. Not only that, but the actual wires are designed for high voltage. Trying to use those lines to build an emergency power supply back to Fukushima would be totally impractical. It could not have been reengineered in time to prevent the total melt down of the three plants that are now belching radioactive gases over Japan and the Pacific Ocean.

Joe I need to clarify this. In normal power operation the license requires at least two independent feeds of offsite power to the plant switchyard. TEPCO reports have claimed six, but at least one other line was in close proximity to the failed tower, apparently running parallel in the same right-of-way. The two would really only count as one due to the potential for one failure to take them both out.

The plant generator feeds the grid through the Main transformer which raises voltage from the generator to grid voltages. An auxiliary transformer taps off power for the plant to run non-essential (non-safety) loads. The essential switchgear receives input s from the grid through another transformer. All house loads are thus already supplied with step down transformers to permit them to run from the grid. Depending on the damage to switchyard breakers and transformers, this would have been the fastest way to restore power to the plants. If anyone has seen a detailed list of failures in the switchyards, I would appreciate a link.

In an accident, the generator trips off , but the plant busses should automatically transfer to the grid. That didn't happen at Fukushima Daiichi due to failure of all offsite power at the time of the earthquake.

The best information I have seen from the NISA report to the CNS was that the switchgear to connect the diesels to the essential busses was also located in the turbine building basement and was flooded. so only one air cooled EDG was able to carry essential loads at units 5,6. That led to the extended SBO at units 1-4 and to core damage after batteries were exhausted and the IC on unit 1 was isolated.

Non-essential loads are not supplied from the diesels so they were all off. The SFP Cooling system pumps were thus lost with the offsite power. However, there is a backup mode of SFP cooling using the RHR system which is powered from the diesels. At Fukushima that was disabled along with the diesels.

There should never be a case where all the offsite power depends on a single tower. And I believe that is true with Fukushima. I will keep looking to clarify how many offsite feeds were lost and the actual causes for each one. I expect to find that the tsunami destroyed a number of switchyards both north and south of the plant. The grid diagraqm of japan i saw earlier that I will be looking for did not have many east-west links across the island, probably because of the mountains. To be continued.

The quality of backup power for SFP cooling is one of the big lessons learned, and that should require modifications at most BWRs.

 

[tsutsuji]

I heard something about a landslide, but can't remember if that was what collapsed the tower.

The landslide is mentioned in http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e20.pdf

If an underground cable is faulted it must first be excavated for repair. In high earthquake areas the biggest concern is a slip or thrust fault that can shear a cable just as it does to roads.

Perhaps the cable should not be buried, but installed in a trench or a tunnel where it is easily accessible. That tunnel, in turn, would be compliant with the relevant earthquake resistance standard, using whatever earthquake engineering technology is needed. The system should allow enough flexibility to prevent the cable from breaking if pulled. The following does not concern electric cables, but the general idea is perhaps relevant :

In a question about the reliability of the 4 km water pipes at the water treatment facility this morning, Junichi Matsumoto said : "The hoses are not attached to the ground, so (in case of earthquake or typhoon) they can absorb even if they vibrate. As long as they are not stretched by a crack in the ground, it is OK. The risk that highly contaminated water leaks over a large area is low" http://sankei.jp.msn.com/life/news/110708/trd11070813220012-n1.htm

 

[Atomfritz]

that lateral tie appears to exist at the "M/C" (motor control center?) level, observe the horizontal lines connecting the three 'normal M/C' 's.

I see five lines coming into plant which seems enough.
but it's a moot point because all the M/C's are shown "Out of order because of inflowed or inundated.." except a lone one on unit 6.

[...] We're back to electrical switchgear in a basement that got filled with seawater.

Hmm, I do not know if the station transformers also have been flooded and rendered unusable. They are outside of the parts enclosed with the red dotted line (flooded or submerged components).
But the fact that they are not being used (except at #5/#6) indicates that you are probably right.

(opinion)
BTW, I disagree somewhat with the opinion that one line is sufficient.
I really prefer the german approach of at least two redundant line transformers/lines. So in case of line problems (could be just due to lightning and such minor causes), transformer fires etc usually no shut down is necessary, just some instant re-routing.
(/opinion)

On http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e20.pdf we can see the 500 kv Futaba line located next to the collapsed Yonomori line. I don't know the status of the Futaba line, but if it was safe, Tepco could have found convenient to use that Futaba line to bring power.

As the Futaba line is not shown in the schematic, I suppose it is normally used to transport unit #5/#6 power to the grid. 66kV (Yonomori) really is a bit little for roughly 2GWe.
On the other hand, 500kV is not easy to handle in emergency situation when you have to improvise. You cannot handle this with portable equipment.
If the 500kV transformer has also been damaged, it will take some time to repair the 500kV connection.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e25.pdf shows that Tepco used Futaba line tower No.2 as a replacement of the collapsed Yonomori tower No. 27 (1). My idea is to use the whole Futaba line : all its towers and all its conductors, with switching equipment on both ends enabling to connect quickly in case of emergency.

They just hung the conductors of Yonomori line to Futaba line tower in a temporary makeshift way, without altering anything on the Futaba line.
If they'd like, they could easily use the Futaba line at 66kV using a mobile transformer, but probably they feel to have sufficient redundancy now.

Edit:
They operate part of Yonomori 1 line at 6kV, using a portable transformer (see Work 3,4,9) to transform from 66 to 6.
Maybe because in March the roads were in no shape to transport a big transformer on a truck convoy?
I am still guessing why they did this. Maybe it was the fastest way to get a handy low voltage to operate with?

Thanks Tsutsuji for the links! This schematic and the pictures really help to get some insight.

 

[NUCENG]

...

Additional Information:

Applicable drawings in the NISA report to the Convention on Nuclear Safety are Figures 3.2-8a, and b. Explanation was as follows:

"The earthquake caused damage to the breakers of the switchyards of Units 1 and 2. As to TEPCO nuclear line (66 kV) from Tohoku Electric Power, although it’s not possible to estimate the cause, cables were damaged. Concerning Units 3 and 4, in addition to the Okuma No. 3 transmission line under construction, the breakers of Nos. 3 and 4 transmission lines on the side of Shin Fukushima Power Substation failed. In addition, about Units 5and 6, one transmission line tower (No. 27 tower) connecting to the switchyards of Units 5 and 6 was collapsed. So, as a result, although damage caused by tsunami was not clear, all external power supplies of Units 1 to 6 were lost." page III-33.

That explanation leaves me with more questions than answers.

The two independent offsite feeds I discussed above are apparently a 275 kV supply and a 66 kV supply. Th 66 kV supply was lost due to cable failures.

For the 275 kV supply there were the following problems and failures:

• It appears there were breaker failures in the site switchyard for units 1 and 2 that took out all offsite power to those units.
  
• Units 3 and 4 had breaker failures at the Shin Fukushima switchyard, plus there was a line that was under construction.
  
• The tower colloapse took out supplies to Units 5 and 6.

There was a common cause failure here - the earthquake, but the tower failure was only one of several failures. Cables and breakers failed in the Shin Fukushima switchyard and on site in the 66 kV swichyard and supplies to units 1 to 4.

I earlier quoted reports that TEPCO had initiated a seismic upgrade of the Fukushima plants under direction from NISA. They had not completed reanalysis and upgrades to the new SS2 limit of 600 gal for seismic events off the coast. Based on the number of failures above, I wonder whether they even looked at their offsite power supplies and the Shin Fukushima switchyard. Even more important, some of the failures in the on-site switchyard may have been in safety related cables or breakers. The description above isn't detailed enough to tell.

 

[NUCENG]

The landslide is mentioned in http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e20.pdf



Perhaps the cable should not be buried, but installed in a trench or a tunnel where it is easily accessible. That tunnel, in turn, would be compliant with the relevant earthquake resistance standard, using whatever earthquake engineering technology is needed. The system should allow enough flexibility to prevent the cable from breaking if pulled. The following does not concern electric cables, but the general idea is perhaps relevant :

In a question about the reliability of the 4 km water pipes at the water treatment facility this morning, Junichi Matsumoto said : "The hoses are not attached to the ground, so (in case of earthquake or typhoon) they can absorb even if they vibrate. As long as they are not stretched by a crack in the ground, it is OK. The risk that highly contaminated water leaks over a large area is low" http://sankei.jp.msn.com/life/news/110708/trd11070813220012-n1.htm

Thanks, I had just seen the landslide drawing that almost took out the second line as well.

I just looked up the insulation standards for a 300 kv (close to the 275 kV at Fukushima. The standard ceramic stacked insulators used on transmission towers at that voltage are about 10 feet long (about 3 m). That tunnel would have to be pretty big to prevent ground faults and moisture intrusion is a huge threat for shorts. I have never seen buried applications of high energy transmission lines, but I'm not rejecting your idea. I'm thinking it may be a lot better to really amp up backup supplies,on site or close by, that can be done at 480 or 1600 VAC which covers the onsite voltages for the big loads.

Edit: Just talked to a transmission engineer. Apparently another reason not to bury or have high voltage lines close to the ground is that it skews power factor by adding a lot of capacitance between the cables and ground. Also he reminded me that three phase power lines have to be separated from each other as well as from ground so a tunnel or trench would bave to be on the order of 9 m or larger to keep the lines separated from each other and from ground.

 

[Atomfritz]

Thanks NUCENG for hinting to the convention report!

Now I have three different pictures to compare: http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e25.pdf":

Looking at the image above you hinted at, I learn that the Futaba line apparently cannot be used for supplying power to the plant, as it is marked with the text "let-off only".

And, it still remains unclear where the #5/#6 switchboard can draw its supply from. From Tohoku line only, or from the other reactor's switchyards also?

It is really confusing that one document talks of "under construction", and the other talks of "under maintenance". Looking closely at the schematics, I suppose there is has in fact been only maintenance, and not construction of a new line.

BTW, I read in the report "In addition, the normal high voltage switchboard of Unit 1, the normal high voltage switchboard of Unit 2, and the normal high voltage switchboard of Units 3 and 4 were connected mutually, and electric power interchange was possible."
So I possibly was wrong in my assumption that each reactor was fixed to one single line. The above sounds like that it was possible, for example. to have reactor 2 and line 1 in maintenance, using line 2 to let off reactor 1's electric output.

Based on the number of failures above, I wonder whether they even looked at their offsite power supplies and the Shin Fukushima switchyard. Even more important, some of the failures in the on-site switchyard may have been in safety related cables or breakers. The description above isn't detailed enough to tell.

Indeed.
I think we can excuse the on-site breakers and switches for failing when submerged in seawater. Maybe just nothing special would have happened without this flooding.

But, look at the second link above. You could think of the breakers at Shin-Fukushima grid station just tripped (these marked with blue cross). This would be completely normal when the line got shorted as happened.
Really, for me it is somehow hard to believe that 5 out of 6 breakers being destroyed by the earthquake only. This is sturdy stuff designed to withstand heavy blows. Just look at youtube and watch such a breaker trip.
So we do not even know enough to do more than speculate if the breakers tripped or failed. And this makes quite a difference.
I really hope it was only a translation problem and nothing worse.

Edit:
I fear I might be too optimistic.
On p. III-36, regarding Daini:

"The transmission network of external power supply of Fukushima Dai-ni NPS contain four lines including two lines of the extra high voltage switchyard on the site used in combination among Units 1 to 4 and the Tomioka Nos. 1. and 2 transmission lines outside the site (500 kV), and two line of the Iwaido Nos.1 and 2 transmission line (66 kV), and they connect to Shin Fukushima Power Substation, 8km upper, and in addition, connect to Shin Iwaki Switchyard, approximate 40 km upper. Out of transmission lines, Iwaido No.1 had been stopped power supply for maintenance.

The seismic intensity in the area around Shin Fukushima Power Substation is estimated to be 6 upper. The Tomioka No. 2 transmission line (500 kV) and the Iwaido No. 2 transmission line (66 kV) to Units 1 to 4 of Fukushima Dai-ni NPS stopped transmission due to failure restoration of devices on the side of the switchboard, etc. The Tomioka No. 2 transmission line (500 kV) and the Iwaido No. 2 transmission line (66 kV) to Units 1 to 4 of Fukushima Dai-ni NPS stopped transmission due to failure restoration of devices on the side of the switchboard, etc. caused by strong ground motion in this earthquake."

This report is somewhat clearer - massive damage on Shin-Fukushima substation...