Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[jim hardy]

fwiw - regarding switchyard breaker failures

the breakers are mostly out in the yard someplace. They are controlled remotely and the ones that affect the plant have a lot of small wires going into the plant. These wires are part of the relay logic that controls the breakers. Some relays are in the plant switchgear, some are in the switchyard.

This brings up two failure scenarios:
1. Earthquake can displace the Earth shearing buried conduits and cutting those wires, or more likely stretching them to point their insulation gets scraped away and they 'ground out' . I suspect this is one of the things Nuceng meant when he said (to effect) 'safety related cables may have failed'.
2. Relays in the plant switchgear panels likely got submerged in seawater and ceased working. Certainly they wouldn't work after station batteries ran down.

Indeed the breakers themselves are very robust devices and the term "breaker fail" only means it is unusable for whatever reason - very likely a flimsy #12 control wire scraped bare in a broken conduit, or a relay full of seawater.

hope this helps clear thought path for your continued analysis.

 

[NUCENG]

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.

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...

You may be forgetting that offsite power was lost prior to the tsunami. I'm not sure whether some of the failures I discussed were only a result of the tsunami and which were there at the earthquake itself. It is fact however that offsite power was gone prior to the tsunami, so there were enough faillures from the earthquake alone to do the job.

I agree they probably meant that the line was down for maintenance, but either way it was not available.

 

[NUCENG]

fwiw - regarding switchyard breaker failures

the breakers are mostly out in the yard someplace. They are controlled remotely and the ones that affect the plant have a lot of small wires going into the plant. These wires are part of the relay logic that controls the breakers. Some relays are in the plant switchgear, some are in the switchyard.

This brings up two failure scenarios:
1. Earthquake can displace the Earth shearing buried conduits and cutting those wires, or more likely stretching them to point their insulation gets scraped away and they 'ground out' . I suspect this is one of the things Nuceng meant when he said (to effect) 'safety related cables may have failed'.
2. Relays in the plant switchgear panels likely got submerged in seawater and ceased working. Certainly they wouldn't work after station batteries ran down.

Indeed the breakers themselves are very robust devices and the term "breaker fail" only means it is unusable for whatever reason - very likely a flimsy #12 control wire scraped bare in a broken conduit, or a relay full of seawater.

hope this helps clear thought path for your continued analysis.

Thanks, Jim, that is correct. Once the wires come down into the onsite switchyard from the last transmission tower, the power busses use rigid conductors instead of cables. They no longer have enough ground clearance to allow the use of cables that would be drooping and blowing in wind. The only cables within the swichyard are as you pointed out, instrumentation and control wiring and power cables to station battery chargers, and cooling systems on transformers. Much of this instrumentation cabling provides lockout functions that trip breakers and can prevent repowering the lines. A good portion of the control circuitry is for automatic transfer functions to transfer essential power to whateve source of offsite power is available.

 

[Atomfritz]

Thanks Jim and Nuceng for the info!

So probably indeed the "failure" is not the breakers', but rather something other in their control circuitry.

I'm not sure whether some of the failures I discussed were only a result of the tsunami and which were there at the earthquake itself.

Me neither. I really need to re-read the infos about the first hour after the earthquake again.
I especially do not understand what was failing around Okuma line 1. Probably it could not be utilized due to sorts of damage Jim explained. But I ask myself, why exactly?

http://www.tepco.co.jp/cc/press/betu11_j/images/110524d.pdf". Does anybody know of an english translation?
Logs of unit #1 and #6 are in English and so quite understandable.


(semi-offtopic)

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.

Hm, maybe this is one of the reasons why the major international submarine power cables seem to run on DC.
No worries with capacitance.

https://www.physicsforums.com/attachment.php?attachmentid=37019&stc=1&d=1310162658

Either HVAC or HVDC, the articles linked below say usual trench size is about 3x5 ft.
Some further reading:

• http://www.sjbenergyconnect.com/involvement/documents/SJ-Overhead_Underground_Feb-2011.pdf"
• "[URL cable company page, some basic information about long range underground/submarine
  high-power transmission, some informative pics[/URL]
• http://www.guardian.co.uk/environment/2011/apr/11/uk-netherlands-power-cable-britned"

(/semi-offtopic)

 

[Most Curious]

The rigid conductors in substations (welded aluminum pipe in most cases) would not fare well with a lot of Earth movement! Broken support insulators and transformer / breaker bushings would be likely, IMHO.

The control wiring would be subject to shearing or stretching and the control devices (relays in the power trade terminology) do not respond well to shaking.

Any of the above problems, not to mention towers collapsing, insulators failing or conductor failure, particularly if the natural resonant frequency of anything happened to be excited by the earthquake could cause massive damage. Not all of these potential problems are likely to have been predicted accurately, even if the system were carefully designed. I am actually surprised there was not more damage than has been reported.


As for buried high voltage lines, I remember a buried 138 KV line at my former employer. Thing was paper insulated in a 5" steel pipe. The pipe was mastic coated with a DC protective charge on the pipe with high pressure oil inside the pipe. Pot heads / risers for the thing were large and potentially earthquake sensitive. When our guys inquired of the installing contractor about locating faults in the line, his reply was "look for the large crater from the explosion"! I do not remember how deep it was buried but the thing always gave me the creeps to be around it. Fortunately, we never had a failure in the line other than dig-ins that damaged the protective coating. Technology has no doubt changed from that period but not THAT much. Bump up to 500 KV and the problems in building a reliable underground circuit would multiply as well.

 

[westfield]

In case its not been linked - http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110615e11.pdf"-

 

[jmelson]

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.

It is done, in special cases, like running under bays and such. They pump oil through the conduit to cool the cable, and provide insulation as well. It is a huge complication, and it has to be insanely expensive to do it any other way before it becomes affordable to use underground HT mains.

Jon

 

[tsutsuji]

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.

On a road sign, the same Japanese word means "work ahead", be it a new work or a repair work.

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

The list of damages at Shinfukushima substation is provided at http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e18.pdf . The referred pictures are at http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e19.pdf .

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?

I wonder what the meaning of the dots on this image from convention report page III-42 is. If I follow http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e25.pdf, the Yonomori line should be shown going all the way to the Shinfukushima substation. The repair work connecting Yonomori line No. 1 and Ookuma line No.3 is mentioned as "work 6" on http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e25.pdf and it is clearly outside the plant, while the dots on page page III-42 of the report are inside.

According to http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e25.pdf , Work 6 seems to consist in connecting Ookuma tower No.7 with Yonomori tower No.8 (or the other way round Ookuma tower No. 8 with Yonomori tower No. 7 : the "Tower(s) No. 7.8 (No. 7.8 鉄塔)" wording is ambiguous).

Edit : Work 6 is also mentioned on page 3 of http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e26.pdf where they say "Transmission Tower №7 and 8 of Okuma Transmission Line 3 and 4L: Connection of Okuma Transmission Line 3L and Yonomori Transmission Ligne 1L started.【Work⑥】".

Page III-42 says the image is based on http://info.nicovideo.jp/pdf/2011-03-18_1930_touden_genpatsu.pdf where only one tower is shown and the connection is made between two lines on the same tower. See image below :

I have no idea if he is correct, but according to Martin Gugino who tried to map the power lines using satellite views on http://commons.wikimedia.org/wiki/File:FukushimaGrid.JPG , the Yonomori line is "a shared tower with the second Okuma towers". What adds to the mystery is that Yonomori is a village located South from the plant and one wonders why the power line is called with that name if it does not actually run through that village. See also what Martin Gugino says after "I speculate that" on http://commons.wikimedia.org/wiki/File_talk:FukushimaGrid.JPG .

The 1/25000 map at http://watchizu.gsi.go.jp/watchizu25.html?longitude=141.030889&latitude=37.429553 shows only 3 lines going from the plant to Shinfukushima substation, not making the distinction between Futaba line and Yonomori line and does not locate the towers, but perhaps it could help.

Page III-42 of the report aslo refers to http://www.tepco.co.jp/nu/kk-np/info/tohoku/pdf/23032202.pdf (this is a report from Kashiwazaki-Kariwa, not translated into English, as far as I know) where the figure page 3 shows 4 pairs of lines, with 4 rows of towers depicted with "☒" boxes and named from left to right Ookuma 4, Ookuma 3, Ookuma 2, Ookuma 1, Yonomori 2, Yonomori 1, Futaba 1, Futaba 2. That figure marks tsunami damages with red crosses and ignores earthquake damages such as the collapse of Yonomori tower No. 27.

 

[NUCENG]

On a road sign, the same Japanese word means "work ahead", be it a new work or a repair work.



The list of damages at Shinfukushima substation is provided at http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e18.pdf . The referred pictures are at http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e19.pdf .



I wonder what the meaning of the dots on this image from convention report page III-42 is. If I follow http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e25.pdf, the Yonomori line should be shown going all the way to the Shinfukushima substation. The repair work connecting Yonomori line No. 1 and Ookuma line No.3 is mentioned as "work 6" on http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e25.pdf and it is clearly outside the plant, while the dots on page page III-42 of the report are inside.

According to http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e25.pdf , Work 6 seems to consist in connecting Ookuma tower No.7 with Yonomori tower No.8 (or the other way round Ookuma tower No. 8 with Yonomori tower No. 7 : the "Tower(s) No. 7.8 (No. 7.8 鉄塔)" wording is ambiguous).

Page III-42 says the image is based on http://info.nicovideo.jp/pdf/2011-03-18_1930_touden_genpatsu.pdf where only one tower is shown and the connection is made between two lines on the same tower. See image below :

I have no idea if he is correct, but according to Martin Gugino who tried to map the power lines using satellite views on http://commons.wikimedia.org/wiki/File:FukushimaGrid.JPG , the Yonomori line is "a shared tower with the second Okuma towers". What adds to the mystery is that Yonomori is a village located South from the plant and one wonders why the power line is called with that name if it does not actually run through that village. See also what Martin Gugino says after "I speculate that" on http://commons.wikimedia.org/wiki/File_talk:FukushimaGrid.JPG .

The 1/25000 map at http://watchizu.gsi.go.jp/watchizu25.html?longitude=141.030889&latitude=37.429553 shows only 3 lines going from the plant to Shinfukushima substation, not making the distinction between Futaba line and Yonomori line and does not locate the towers, but perhaps it could help.

Page III-42 of the report aslo refers to http://www.tepco.co.jp/nu/kk-np/info/tohoku/pdf/23032202.pdf (this is a report from Kashiwazaki-Kariwa, not translated into English, as far as I know) where the figure page 3 shows 4 pairs of lines, with 4 rows of towers depicted with "☒" boxes and named from left to right Ookuma 4, Ookuma 3, Ookuma 2, Ookuma 1, Yonomori 2, Yonomori 1, Futaba 1, Futaba 2. That figure marks tsunami damages with red crosses and ignores earthquake damages such as the collapse of Yonomori tower No. 27.

I think the doublr slash is a cable failure and the dots show repair connections.

 

[tsutsuji]

I think the doublr slash is a cable failure and the dots show repair connections.

According to the key on the top right corner of the page (http://info.nicovideo.jp/pdf/2011-03-18_1930_touden_genpatsu.pdf page 4), straight red lines mean "completed work" and red dotted lines mean "work to be performed in the future". The handwritten note adds "as of 17 March". I guess the double slash mean "disconnected jumpers" as the key in http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e25.pdf mentions.

The only instances of cable failures I have heard of are those mentioned on http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e17.pdf :

* "cable damage" between the Tohoku electric 66 V line and unit 1
* Okuma 3L "overhead line broken" inside shinfukushima substation, referred to as "ground wire disconnected" on page 1 of http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e19.pdf
* The Yonomori tower No. 27 collapse

Pages 8 and 9 of http://www.tepco.co.jp/cc/press/betu11_j/images/110524d.pdf explain why the breakers tripped :

Okuma 1L : breaker O-1 trips because of the damage of breaker O-81
Okuma 2L : breaker O-32 trips because of the damages of breaker O-82 and disconnector O-82
Okuma 3L : breaker O-33 trips because of the arc at tower No. 7 (arc traces were observed, showing a conductor touched or came close to the tower)
Okuma 4L : breaker O-34 trips because of the arc at tower No. 11 (arc traces were observed, showing a conductor touched or came close to the tower)
Yonomori 1L : breaker O-93 trips because conductors touched or came close to each other. Also, Yonomori tower No. 27 collapsed.
Yonomori 2L : breaker O-94 trips because conductors touched or came close to each other. Also, Yonomori tower No. 27 collapsed.

 

[tsutsuji]

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?

On pages 64 and 65 of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf , there are a few explanations on the different power voltages used at the plant. The diesel generators supply 6.9 kV, and some equipments can use this 6.9 kV directly. Then the voltage is lowered to 480 V for some other equipments. Some yet other equipments use DC 125 V.

I wonder if they actually mean 6.9 kV when they write 6 kV or if they mean exactly 6.0 kV.

 

[Atomfritz]

I think the doublr slash is a cable failure and the dots show repair connections.

In electrical engineering the double slash means "line cut". Didn't ever find an other meaning, even though schematics are drawn differently around the world.

No matter whether for revision, modification etc.
Just my 2 ct, as my profession is electronics engineering and when dealing with apparatuses you always have to keep in mind what version they are of.

@ tsustsuji-san:
Thank you for the links!
I have to admit that I didn't see these detailed pics before. This damage on Shin-Fukushima really shocks me. (Please don't misunderstand me, in Germany we know such damage only from former foreign bomb raids...) I really have to sleep over all this information before I can digest it and get clear thoughts about the whole thing.

Edit:

The diesel generators supply 6.9 kV, and some equipments can use this 6.9 kV directly. Then the voltage is lowered to 480 V for some other equipments. Some yet other equipments use DC 125 V.

I wonder if they actually mean 6.9 kV when they write 6 kV or if they mean exactly 6.0 kV.

In fact this is not very important due to the tolerances. Under-overvoltages of +-20% are usually of no problem. So you usually can supply a 6kV transformer primary with 7kV without noticing an adverse effect on the secondary (except higher consumption and wear), and vice versa.

 

[jim hardy]

this is more trivia, but it helps one's thought processes to not let these little questions pile up unanswered for they chip away at our confidence.

so i'll cast a little light on this one:
"I wonder if they actually mean 6.9 kV when they write 6 kV or if they mean exactly 6.0 kV. "


4160 and 6900 volts are two very common standard voltages. With higher voltage you need less copper but better insulation. As plant designs require ever bigger motors the wire sizes required become unmanageably big. Biggest motor in my plant was 7,000 hp and we were 4160, those wires looked like firehoses. They are difficult to install and copper is today ~ $4 a pound.It's almost certain they are referring to nominal 6.9kv equipment. We tend to name things colloquially, 4kv and 6kv is how we referred to ours though 7kv would have been more accurate.

The tolerance Atomfritz mentioned is important to the plant. We have to float up and down a few percent according to system load.
Power company tries to deliver constant voltage to the customer. On days with high demand the plants will raise their voltage a bit to overcome voltage loss in the transmission wires & transformers, and on easy days lower voltage somewhat. That's all directed from a central system control office.

We always said "Our in-plant power is not nearly so stable as what the customer sees".

old jim

http://www.resourcesaver.com/file/toolmanager/O105UF493.pdf

 

[Lambert]

oh oh

http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/usc0004sg6.php

http://www.vancouversun.com/news/Quake+jolts+northeast+Japan+nuclear+workers+evacaute/5079075/story.html

 

[Gary7]

Was about a magnitude 4 (Japanese scale) in Fukushima. Fukushima Daiichi reported no damage as a result of this quake. Tsunami was about 10 centimeters in Fukushima.
Tsunami alert has been lifted.

 

[joewein]

Was about a magnitude 4 (Japanese scale) in Fukushima.

The Japanese "shindo" scale is usually translated as "intensity" or "seismic intensity" in English (you don't say "magnitude" unless you mean the Western scale that measures energy released, which is sometimes incorrectly referred to as "Richter scale").

It's listed as M7.1 here:
http://www.jma.go.jp/en/quake/20110710100736491-100957.html

That's almost 1000 times less energy than the M9.0 quake on March 11. I still felt it here in Tokyo and it was fairly long but quite weak here, unlike 3/11. Only half of my family noticed it at all.

 

[tsutsuji]

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?

So this 6kV is another name for the 6.9 kV which they need at the plant. You need to lower that 66 kV into this 6 or 6.9 kV some way or other. My guess is that they wanted to work as far away from the plant as possible, rather than risk the workers' lives in a contaminated plant where hydrogen explosions occur every couple of days.

Was about a magnitude 4 (Japanese scale) in Fukushima. Fukushima Daiichi reported no damage as a result of this quake. Tsunami was about 10 centimeters in Fukushima.
Tsunami alert has been lifted.

http://mainichi.jp/select/jiken/news/20110710k0000e040029000c.html During the tsunami alert, workers evacuated the area close to the sea and the megafloat filling operation was stopped.

[URL]http://www.tepco.co.jp/en/news/110311/images/110710_1t.jpg[/URL]
http://www.tepco.co.jp/en/news/110311/images/110710_1.jpg

It had been a long time since they last had a trouble at the water treatment facility.

http://www.jiji.com/jc/c?g=soc_30&k=2011071000054 : It had to stop at 4:50 AM because of a chemical leak at the Areva facility. A green coloured chemical burst out at the junction of the chemical hose and the (contaminated water?) pipe. The amount leaked is 50 l. The chemical is not poisonous but some contaminated water could have leaked too. It is the first trouble since 30 June.

http://mainichi.jp/select/jiken/news/20110711k0000m040021000c.html the leak was viewed on a surveillance camera at 4:53 AM. The facility was started again at 5 PM after the junction was changed for a cast iron one. The leaked liquid's radiation was 5500 Bq/cm³ of Cs-137 which is a normal radiation at the entrance of the Areva system and a hint that contaminated water flowed backwards through the leak. Tepco is studying what to do with another similar junction located elsewhere in the facility, beyond a visual inspection showing it is not leaking. The megafloat filling will start again on 11 July.

http://www.asahi.com/national/update/0708/OSK201107080148.html In a symposium in Tokyo, Kyoto university reseachers presented a water decontamination method they claim is cheaper and faster, and produces less waste than the one used at Fukushima Daiichi. It is based on the flotation method used in the mining industry. You add Fe or Ni, and chemicals that help separate Cs from water and precipitate the Cs. Then you add bubbles from the bottom, and the Cs rises to the surface with the bubbles. Then you skim the foam. Their tests with 5 different contaminants show that more than 99% can be removed.

 

[Bioengineer01]

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.

Joe, I have been in several situations similar to what describe but in the pacemaker/defibrillator industry of medical devices. And always the screw-ups got to the top the bosses, but never in writing (so that they could deny knowing), but never to the board of Directors, because it would have made them look bad. It is possible that your fix was known by your top brass, but that they had already told the board that it was a system problem and had already requested approval for the expenditure for the new system.

 

[Bioengineer01]

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.

I did a back of the envelope reliability analysis similar to those we do for medical devices and calculated what is the reliability level that the worst Nuclear Power Plant (and associated systems, like power lines) should have to have a 99% probability level that NO nuclear plant will have a catastrophic failure in the next 30 years. The number is scarely close to 100%. I am not a reliability person, but if you know of anybody, please invite him/her to destroy my guestimates here. When I brought that system reliability number down, it very quickly trended to 100% probability of one catastrophic failure every thirty years...

 

[Bioengineer01]

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.

I completely agree with Nikkom perspective. It is unbelievable how close the analogy is to implantable medical devices too. Where the shuttle accident reports were evaluated in detail and lessons learned. Sadly the reality always was that before the money was invested, every lesson was used correctly and the burden of proof was on the engineers to prove it was safe, but after the product was launched commercially, then the burden of proof was shifted to "prove to me it is unsafe". Most recalls in the implantable medical device industry have been made a lot worse by this behavior. NPPs are in the post commercial launch situation and thus the mentality is prove it is unsafe before I do something. That is not the mentality of the patient that has the device or the public that will suffer the consequences of failure.

 

[NUCENG]

I completely agree with Nikkom perspective. It is unbelievable how close the analogy is to implantable medical devices too. Where the shuttle accident reports were evaluated in detail and lessons learned. Sadly the reality always was that before the money was invested, every lesson was used correctly and the burden of proof was on the engineers to prove it was safe, but after the product was launched commercially, then the burden of proof was shifted to "prove to me it is unsafe". Most recalls in the implantable medical device industry have been made a lot worse by this behavior. NPPs are in the post commercial launch situation and thus the mentality is prove it is unsafe before I do something. That is not the mentality of the patient that has the device or the public that will suffer the consequences of failure.

I do not understand how any progress can be made without some risk. What do you want? It would be wonderful if new technologies like medical implants, or space exploration, or nuclear power, or anything else you care to name could be born without any potential for errors or flaws, or unconceived risks, but can you name one development that has? The logical consequence of what you just wrote is that we can never do anything new. Doctors should tell people they are going to die because we never could risk reactions to vaccines or medications, or surgery or any of the thousands of medical developments that came before implants.

The Black Plague did not end urbanization. The Titanic did not end shipbuilding. The Hindenberg did not stop commercial aviation. The Tacoma Narrows did not end bridge building. Louis Washkansky's death did not stop medical science from trying to correct heart disease. The Challenger has not ended Space exploration.

The burden on engineers (and doctors) is to find solutions to problems. It is impossible to prove that anything is "safe." In solving problems they have to balance benefits and risks. Society has to agree with that assessment of benefit and risks or the engineers work will never be built. The job doesn't stop there. A technology must be proved over time, and adapted, updated, and improved.

Your analogy is inappropriate, your logic is absent, and your conclusion is dead wrong. The standard you are trying to demand would halt all progress, including development of solar and wind power generation. (Electricity has risks all by itself, whatever the source.)

 

[zapperzero]

The Black Plague did not end urbanization.

Gentlemen, methinks it's time to take this to the political thread?

 

[NUCENG]

Gentlemen, methinks it's time to take this to the political thread?

I agree.

 

[Gary7]

Another layman's question: Assuming meltdown of a portion of the fuel (or most/all of the fuel) in the reactors of Fukushima Daiichi #1, #2, and #3, what condition could we expect the corium to be in after 2+ months of cooling. Is there a possibility that the various fuel masses have completely solidified by now, or would the center still be liquid/molten?

Clarification: Let me say that I understand the heat comes from decay of the fission products, and that even if water is continually poured onto it, it will continue to generate heat for years. I suppose what I am asking is whether or not the addition of steel, concrete, zirconium, etc... will enable the corium to solidify (or to form a crust that is sufficiently deep that it ceases to pose a problem with regard to moving around the underside of what is left of the reactors).

 

[Caniche]

60 ton lumps enriched to 5%,

 

[Bioengineer01]

I think there's been some interest, just not many comments. I, for one, haven't yet found the time to do much more than a quick skim-through.

EDIT: the idea of printing out e-mails, then collating them in a scanned PDF? Who came up with that one? There's zero excuse here - while I can understand why rules and regulations would have treeware master copies, this is just stupid, verging on willfully incompetent.

If I sound frustrated, it's 'cause I am. I have good text processing, indexing and search tools at my disposal - and none of them work!

In the past (10 years ago +) I have used very successfully OCR programs that can read pdf files and output a pdf file with a built-in searchable text layer. Extremely useful when building a database with pdf files.

 

[etudiant]

Another layman's question: Assuming meltdown of a portion of the fuel (or most/all of the fuel) in the reactors of Fukushima Daiichi #1, #2, and #3, what condition could we expect the corium to be in after 2+ months of cooling. Is there a possibility that the various fuel masses have completely solidified by now, or would the center still be liquid/molten?

Clarification: Let me say that I understand the heat comes from decay of the fission products, and that even if water is continually poured onto it, it will continue to generate heat for years. I suppose what I am asking is whether or not the addition of steel, concrete, zirconium, etc... will enable the corium to solidify (or to form a crust that is sufficiently deep that it ceases to pose a problem with regard to moving around the underside of what is left of the reactors).

If we assume that all of the core is neatly collected into one lump, we have a blob that needs to dissipate somewhere around 5 megawatts continuously to stay in a steady state. Water has a latent heat of vaporization of about 2000 joules/gm, so we need to vaporize about 2.5 kg of water every second, or about 9 tons/hr. Do note that this is boil off, although it may re condense in the water flooding the plant.
That is about the rate at which the reactors are getting fed, so we have a measure of stability.

However, that says nothing about the state of the fuel, except that if it were still a superhot melt the vapors given off from the reactors would show some of the chemical dissociation products. However, TEPCO has been only modestly informative about the reactor airborne emissions and I've no competence to assess that which they have released. Because no one expert has raised any alarm, I assume the fuel is largely immobile, while still in dire need of continuous cooling.

 

[robinson]

Wouldn't any melted spent fuel also be an issue? Seems like at least one fuel pool is steaming away as well.

 

[etudiant]

Wouldn't any melted spent fuel also be an issue? Seems like at least one fuel pool is steaming away as well.

The spent fuel does need cooling as well, but normally a cooling circuit keeps the refrigeration going.
Afaik, that has been restored at the SFPs for reactors 1-3, but is still not there for reactor 4, because the explosion blew out part of the cooling pipes. They have been able to access an essential valverecently and expect to be able to restore cooling to SFP 4 as well. TEPCO hopes to wrap up that work this month.

 

[joewein]

If we assume that all of the core is neatly collected into one lump, we have a blob that needs to dissipate somewhere around 5 megawatts continuously to stay in a steady state. Water has a latent heat of vaporization of about 2000 joules/gm, so we need to vaporize about 2.5 kg of water every second, or about 9 tons/hr. Do note that this is boil off, although it may re condense in the water flooding the plant.
That is about the rate at which the reactors are getting fed, so we have a measure of stability.

On June 1 the remain decay heat output in unit 1 was 3.7 MW while in units 2 and 3 it was 6.3 MW, which is 0.26% of thermal output at shutdown. Over the next 8 months that will go down to 0.21% of thermal output at shutdown, so it's essentially steady now (http://mitnse.com/2011/03/16/what-is-decay-heat/" ), since most of the iodine-131 and other shortlived isotopes are largely gone.

Water injection in units 1 and 2 is currently running at 3.5 t/h, while unit 3 is receiving 9 t/h, even though unit 2 and 3 should have the same decay heat output. If all the heat was being dissipated by boiling they would consume the same amount of water. Unit 3 is receiving more water because measured temperatures at the lower end of the RPV were higher.

If temperatures in unit 2 are lower despite only receiving 1/3 of the amount of water, perhaps most of the fuel there has already left the RPV and has splashed onto the containment concrete floor. Alternatively, the shape of the corium may obstruct water flow in the RPV of unit 3, so water boils on top of it but doesn't flow past it.

Units 2 and 3 should be largely identical, except that unit 3 was more recently refueled and therefore the average burn-up rate of its fuel should be lower, hence there should be marginally *less* decay heat output in unit 3 than unit 2.

60 ton lumps enriched to 5%,

Unit 1 had 68 t fuel enriched to 3.4% while unit 2 and 3 had 94 t enriched to 3.6%.

 

[joewein]

Wouldn't any melted spent fuel also be an issue? Seems like at least one fuel pool is steaming away as well.

The fact the pool is steaming shows that it has water in it, which is good. If they got the heat exchanger hooked up, it would be even better of course.

The spent fuel pool with the most active fuel and cause for the biggest worries was unit 4, but radioactivity levels there are much lower than in the reactor building (R/B) basement water:

Unit 4 SFP: 123 Bq/cm3 (Cs-134 + Cs-137)

Unit 1 R/B: 250,000 Bq/cm3 (Cs-134 + Cs-137)
Unit 2 R/B: 6,100,000 Bq/cm3 (Cs-134 + Cs-137)
Unit 3 R/B: 3,100,000 Bq/cm3 (Cs-134 + Cs-137)

This is why TEPCO doesn't believe in major fuel damage in the #4 SFP.

Its radioactivity levels are also orders of magnitudes lower than in the #1 through #3 SFPs.

Unit 1 SFP: 26,000 Bq/cm3 (Cs-134 + Cs-137)
Unit 2 SFP: 191,000 Bq/cm3 (Cs-134 + Cs-137)
Unit 3 SFP: 290,000 Bq/cm3 (Cs-134 + Cs-137)

Number three has the worst numbers, perhaps because it had that big blast. It is the one with lots of concrete and steel on top of the fuel assemblies seen in http://www.youtube.com/watch?v=KugIrnThul0" (you don't actually see the fuel, except for a single handle sticking out).

 

[tsutsuji]

Under the timeline, nuclear fuel will be removed from the pools for spent fuel at the No. 1 to 4 reactors starting in fiscal 2014. Officials hope to finish removing such fuel from the first reactor by fiscal 2016.
http://mdn.mainichi.jp/mdnnews/news/20110711p2a00m0na003000c.html

http://www.tv-asahi.co.jp/ann/news/web/html/210710029.html Picture of the repaired hose fitting at the water treatment facility.

http://www.nikkei.com/news/category...39797E3E2E2E2;at=DGXZZO0195165008122009000000 Tepco is going to repair the damages caused by the tsunami in the walls of the water inlet by planting steel tubes in the water. This requires opening the fence, and allowing some radioactive materials from the inlet to flow into the harbor. 14 m³/h of nitrogen will be injected into unit 3 starting 12 July. The robot found 50 mSv/h near the heat exchanger on the second floor of unit 2, which hampers the work that has to be done there. 6 people among the 9 initially feared have been confirmed to have exceeded 250 mSv.

 

[etudiant]

On June 1 the remain decay heat output in unit 1 was 3.7 MW while in units 2 and 3 it was 6.3 MW, which is 0.26% of thermal output at shutdown. Over the next 8 months that will go down to 0.21% of thermal output at shutdown, so it's essentially steady now (http://mitnse.com/2011/03/16/what-is-decay-heat/" ), since most of the iodine-131 and other shortlived isotopes are largely gone.

Water injection in units 1 and 2 is currently running at 3.5 t/h, while unit 3 is receiving 9 t/h, even though unit 2 and 3 should have the same decay heat output. If all the heat was being dissipated by boiling they would consume the same amount of water. Unit 3 is receiving more water because measured temperatures at the lower end of the RPV were higher.

If temperatures in unit 2 are lower despite only receiving 1/3 of the amount of water, perhaps most of the fuel there has already left the RPV and has splashed onto the containment concrete floor. Alternatively, the shape of the corium may obstruct water flow in the RPV of unit 3, so water boils on top of it but doesn't flow past it.

Units 2 and 3 should be largely identical, except that unit 3 was more recently refueled and therefore the average burn-up rate of its fuel should be lower, hence there should be marginally *less* decay heat output in unit 3 than unit 2.



Unit 1 had 68 t fuel enriched to 3.4% while unit 2 and 3 had 94 t enriched to 3.6%.

It is interesting that the temperatures are being stabilized with these low levels of water injection. The decay energy created must go somewhere, so if it is not taken up by the injected water, it must be heating up the water in the plant. Given that there are about 100,000 tons of water in the plant and that we are apparently dissipating about two thirds of the energy ( about 10 megawatts) into the existing pool. The specific heat of water is about 4 joules/gram, so the conversion would be roughly:
10x10**6j/sec / 4 j/gm =2.5 x10**6 gm/s heated 1 degree. There are 10**11 grams (10**5x10**6) of water in the plant, so the hourly heating of the plant pool should be 10**11 gm / 9x10**9 gm/hr (3.6x10**3s/hr x2.5x10**6gm/sec), which rounds out to one degree every 10 hours.
This is clearly too high, as the plant would be swimming in boiling water after a few weeks, which it is not. So where has the energy gone?

 

[robinson]

I'm just going by what I see happening in the rare video. #3 seems to have a boiling fuel pond.

 

[hellbet]

So where has the energy gone?

Tepco only cares of the "inside" part of the melted fuel that is the main part of so-called "corium" has probably escaped out the containment. How would you possibly care of something that is out of range? Frankly, I'm afraid we're now facing at some possible "melt-out" event taking place after all sort of barely admitted "melt-something".

 

[joewein]

I'm just going by what I see happening in the rare video. #3 seems to have a boiling fuel pond.

No it doesn't. That video is not exactly new.

According to status updates, an "alternative cooling system" for the spent fuel pool of unit 3 has been in place since July 1:

<Cooling by the alternative cooling system for the Spent Fuel Pool>
July 1 11:00 ～ July 8 08:20, July 8 14:24 ～
(Source: http://www.nisa.meti.go.jp/english/press/2011/07/en20110711-1-2.pdf" )

Furthermore they are working on one for unit 4 too:

The alternative cooling system for the Spent Fuel Pool of Unit 3 was
temporarily suspended due to the installation works of the alternative
cooling system for the Spent Fuel Pool of Unit 4. (from 08:20 till 14:24 July 8)
(Source: http://www.nisa.meti.go.jp/english/press/2011/07/en20110710-1-1.pdf"

 

[joewein]

Tepco only cares of the "inside" part of the melted fuel that is the main part of so-called "corium" has probably escaped out the containment.

What makes you think the melted fuel has left the containment? Where do you think it is now located and why do you think so?

Of course a lot of the more volatile substances in the core have left the containment, as one can see from the radiation levels in the basement of the reactor building and turbine hall, but the less soluble substances are likely to be either inside the RPV or on the containment floor.

If all of it had left the RPV, the RPV bottom temperatures would not respond to the water flow because there would be no heat source to interact with the water flow, even more so if all of it had not only left the RPV but also the containment.

 

[tsutsuji]

No it doesn't. That video is not exactly new.

According to status updates, an "alternative cooling system" for the spent fuel pool of unit 3 has been in place since July 1:Furthermore they are working on one for unit 4 too:

Concerning unit 4 they said that they could restore a vital pipe called "FPC-68" for that purpose : http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110709_02-e.pdf. Details explaining why they had to stop unit 3 SFP cooling equipment to allow starting the construction of the cover structure at unit 4 are provided in http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110708_01-e.pdf .

The spent fuel does need cooling as well, but normally a cooling circuit keeps the refrigeration going.
Afaik, that has been restored at the SFPs for reactors 1-3, but is still not there for reactor 4, because the explosion blew out part of the cooling pipes.

As Joewein says above, the cooling has been restored for the SFP at unit 3. What is making you think it has been restored for unit 1 as well ?

On http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/11071106_table_summary-e.pdf the SFP temperature at unit 1 is still marked today with "instrument failure" which makes me doubt much equipment has been restored there.

Concerning unit 2, the SFP circulating cooling system has been running since 31 May, according to http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110711_05-e.pdf page 3. It is also marked as "May 31 17:21 Started full-fledged operation of the alternative cooling system for the Spent Fuel Pool" on http://www.nisa.meti.go.jp/english/press/2011/07/en20110711-1-2.pdf page 5.

 

[etudiant]

Concerning unit 4 they said that they could restore a vital pipe called "FPC-68" for that purpose : http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110709_02-e.pdf. Details explaining why they had to stop unit 3 SFP cooling equipment to allow starting the construction of the cover structure at unit 4 are provided in http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110708_01-e.pdf .



As Joewein says above, the cooling has been restored for the SFP at unit 3. What is making you think it has been restored for unit 1 and unit 2 as well ?

On http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/11071106_table_summary-e.pdf the SFP temperature at unit 1 is still marked today with "instrument failure" which makes me doubt much equipment has been restored there. The news I summarized above about unit 2 says that the radiation hampers the work, so I also doubt a lot of work has been performed at unit 2. See also http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110711_04-e.pdf concerning the radiation measurements in unit 2 reactor building.

The JAIF status report summary here:

http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1310358115P.pdf

states that the SFP cooling function for reactors 2 and 3 have been restored and that SFP for reactor 1 is now receiving water from the SFP coolant clean up line ( not sure what that represents).
I was mistaken to believe that the reactor 1 SFP was already getting circulation cooling.

 

[tsutsuji]

The JAIF status report summary here:

http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1310358115P.pdf

states that the SFP cooling function for reactors 2 and 3 have been restored and that SFP for reactor 1 is now receiving water from the SFP coolant clean up line ( not sure what that represents).
I was mistaken to believe that the reactor 1 SFP was already getting circulation cooling.

And I was mistaken concerning unit 2. I edited my previous post concerning that unit.

If I try to gather information concerning unit 1 SFP :

NISA press conference 2011.06.24 11:10 http://www.ustream.tv/recorded/15577343 : it is expected that the original primary circuit at the unit 1 SFP cooling system can be reused instead of creating a new one as was previously thought.

http://www.nisa.meti.go.jp/english/press/2011/07/en20110711-1-2.pdf page 3 : "<Fresh water injection to SFP via FPC (using the temporary motor-driven pump) > May 29 11:10～15:35, June 5 10:16～10:48, July 5 15:10～17:30" (compare with unit 2 SFP on page 6, saying the last water injection was performed on May 30)

http://www.meti.go.jp/press/2011/07/20110711006/20110711006-1.pdf page 8 : the amount injected into SFP on July 5 was about 75 tons.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110711_05-e.pdf page 3 : "status of cooling" marked with "no plan on 7/11". ( http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1310358115P.pdf translates　http://www.jaif.or.jp/ja/news/2011/110711status_of_countermeasures-j-188.pdf's 検討中 as "planned", but a more accurate translation would be "under study" ; conversely, unit 4's 作業中 should translate as "under work" rather than "Construction to be prepared").

from the SFP coolant clean up line ( not sure what that represents).

They mean that they no longer pour water using a concrete pump truck, using instead the original pipes of the Fuel Pool Cooling and Purification System, sometimes shortened as "FPC". Apparently the pump (according to http://www.ustream.tv/recorded/15577343 ) and the pipes in the primary system are OK, but the secondary system (the pipes and pump(s) bringing sea water for cooling) has collapsed. I am not sure about the status of the heat exchanger.

By the way, concerning unit 4, there is a big translation mistake. 20A/B弁閉操作完了　on http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110709_02-j.pdf means "finished the closure operation of valve 20A/B", not "opened 20 A/B valve" as translated in http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110709_02-e.pdf

 

[Bandit127]

What a surprise (or more precisely - Quelle suprise!)

Removal of reactor fuel won't start until 2021
http://www.yomiuri.co.jp/dy/national/T110711004878.htm"

I hope this forum (and this thread) are still open when they finally get into the reactors and work out what happened. But that day is a long way away yet.

 

[etudiant]

What a surprise (or more precisely - Quelle suprise!)
I hope this forum (and this thread) are still open when they finally get into the reactors and work out what happened. But that day is a long way away yet.

If anything, that schedule seems very ambitious. Seen that it took a decade for the TMI reactor fuel to be removed, it would be surprising if this much larger and more complicated accident took a similar amount of time. Afaik, there is no effective way to decontaminate concrete, simply because the radioactive material will have infiltrated deep beyond the surface, helped by the natural aging of the concrete as well as the fissures created by the earthquake and the explosions. So just approaching the lower levels of the reactors to start that part of the cleanup will be a major challenge. Imho, the site will take decades to remediate.
More to the point, once the emissions from the site have been capped, further cleanup work will be very expensive, not only in financial but even more so in human terms, with zero economic reward. Japan is saddled with a massive dead weight loss project because of this disaster.
These costs may be so large that industry is forced to shift to smaller reactors that fail somewhat more gracefully, because no country can afford these consequences.

 

[Cire]

If all of it had left the RPV, the RPV bottom temperatures would not respond to the water flow because there would be no heat source to interact with the water flow, even more so if all of it had not only left the RPV but also the containment.

I've argued this several times. You don't have RPV bottom temperatures if corium melted out the bottom of the RPV. You don't have temperatures at all if the bottom of the RPV ever reached or exceeded 1000C. The thermocouples and their leads would have melted off long before the RPV failed.

 

[etudiant]

I've argued this several times. You don't have RPV bottom temperatures if corium melted out the bottom of the RPV. You don't have temperatures at all if the bottom of the RPV ever reached or exceeded 1000C. The thermocouples and their leads would have melted off long before the RPV failed.

True, but if that were the case, there would not be readings that fluctuate with the volume of water injected.

 

[NUCENG]

I've argued this several times. You don't have RPV bottom temperatures if corium melted out the bottom of the RPV. You don't have temperatures at all if the bottom of the RPV ever reached or exceeded 1000C. The thermocouples and their leads would have melted off long before the RPV failed.

You may be assuming a complete failure of the vessel bottom which may not have happened. The instrument and CRDM penetrations of the vessel are more likely to have failed first allowing corium to exit the vessel. The thermocouples in US plants are qualified to at least 2300 degrees F per USNRC Regulatory Guide 1.97.

 

[joewein]

I've argued this several times. You don't have RPV bottom temperatures if corium melted out the bottom of the RPV. You don't have temperatures at all if the bottom of the RPV ever reached or exceeded 1000C. The thermocouples and their leads would have melted off long before the RPV failed.

Perhaps you are thinking that if the corium melted its way out of the RPV, all of the bottom would have been heated to 1500 deg C (melting point of steel) to create an exit path. I don't think that's necessarily the case. In a BWR the control rods are inserted through the bottom of the RPV. If the core melts inside the RPV, corium could flow into the control rod channels and escape from below there without having to take out the entire bottom of the RPV. Therefore in my opinion corium outside the RPV is entirely consistent with the thermocouples still functioning.

The fact that temperatures at the core bottom went up in unit 3 when they cut back on cooling water flow to stem the flooding of the basements and trenches, and dropped back again when they stepped it up again suggests that those thermocouple readings are not totally phantom readings.

Furthermore, dry well and RPV temperature readings (4 sensors in total) broadly went up and down together during those periods, which gives me some confidence that RPV readings are not totally bogus like the core water level readings turned out to be. See http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/out/plot-un3-t-T-full.png" .

What I don't have a clear picture of is how many MW of heat could have been conducted away by the 160 mm (BWR3) / 138 mm (BWR4) of steel of the RPV and of the (unknown) m2 of concrete floor inside the containment bulb.

The containment would eventually be pierced by a melted core if less heat is conducted away from the surface of the corium than is generated as decay heat inside, leading to a rise of temperature beyond the melting point of concrete. How realistic is that at this stage? We would need to understand the heat flow, which depends on conduction and convection.

If the RPVs are pierced at the bottom from a meltdown then water injected through the feed water pipe at the top of the RPV should leak out through the bottom, unless it all boils off inside the RPV from decay heat of any portion of the corium still left inside.

If cooling water leaks out of the RPV it may create a shallow pool inside the containment, at the bottom of which the corium will cause continuous boiling. Steam should be rising and perhaps recondensating inside the containment steel wall that carries heat away into the building. In that case the containment floor is not the only surface area removing heat from the corium.

If steam condensates on the containment walls and trickles down into the corium pool again, it could boil multiple times before eventually leaking out through damaged seals. That would explain why the apparently sufficient amount of cooling water in units 1 and 2 is less than the theoretical amount boiled away per hour by the predicted decay heat output.

That makes me wonder if the 5 cm gap between the steel and concrete portion of the containment could somehow be used for air-cooling the containment.

 

[Joe Neubarth]

Concerning unit 4 they said that they could restore a vital pipe called "FPC-68" for that purpose : http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110709_02-e.pdf. Details explaining why they had to stop unit 3 SFP cooling equipment to allow starting the construction of the cover structure at unit 4 are provided in http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110708_01-e.pdf .



As Joewein says above, the cooling has been restored for the SFP at unit 3. What is making you think it has been restored for unit 1 as well ?

On http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/11071106_table_summary-e.pdf the SFP temperature at unit 1 is still marked today with "instrument failure" which makes me doubt much equipment has been restored there.

Concerning unit 2, the SFP circulating cooling system has been running since 31 May, according to http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110711_05-e.pdf page 3. It is also marked as "May 31 17:21 Started full-fledged operation of the alternative cooling system for the Spent Fuel Pool" on http://www.nisa.meti.go.jp/english/press/2011/07/en20110711-1-2.pdf page 5.

Considering the degree of site contamination, my hat if off to the Japanese. They have accomplished a lot.

 

[tsutsuji]

http://www.asahi.com/national/jiji/JJT201107120052.html At 8:40 AM on 12 July, a leak was observed on a surveillance camera, and the water treatment facility was manually stopped 10 minutes later. The leak location is in the Areva system, in the close proximity of the leak that occurred and was repaired on 10 July. The desalination facility is still running.　Repairs are shown on http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110712_02-j.pdf (top picture is before repair, bottom picture is after repair).

http://www.nikkei.com/news/headline...1949EE3E0E291838DE3E0E2E5E0E2E3E3E2E2E2E2E2E2 The leaked volume was 10 l. The leak location was exactly the same as two days ago. The facility was started again at 4:58 PM after changing the fitting for a stainless steel one. It is thought that the zinc-coated cast iron one installed two days ago was corroded by the ferric sulfate flowing in the hose.

http://www.asahi.com/national/update/0711/TKY201107110485.html For the purpose of breakwater reinforcement work repairing the tsunami damages at the south of the water inlet, the silt fence will be opened 36 times for two hours each time in the upcoming 3 months to let the steel sheet pile driving boat to come and go. This rises the fear that some of the 1.2 terabecquerels in the water inlet could flow into the sea. The silt fence opening time being limited, Tepco says the consequence on the periphery is limited. Radiation measurements in the sea will be intensified. Local governments have been notified.

http://news.tbs.co.jp/newseye/tbs_newseye4773907.html the nitrogen hose will be connected on unit 3 on 12 July afternoon. The nitrogen injection will start at unit 3 this week (nitrogen injection is already being performed at units 1 & 2).

http://www.yomiuri.co.jp/science/news/20110712-OYT1T00502.htm 　Minister Goshi Hosono said the details on a new middle to long term study team whose purpose is to study the decommissioning of Fukushima Daiichi will be announced on 19 July. They will have to find a solution so that the final disposal is located elsewhere than in Fukushima prefecture.

http://www.ustream.tv/recorded/15943265 NISA press conference, 12 July : The original heat exchanger at unit 1 SFP can be reused. Tepco hopes the SFP cooling system can be started at the end of July or within the first decade of August.

Operation of the diesel generators was carried out as follows due to the
preparatory construction of Yonomori line for duplication of line (July 11);
D/G 5A started (03:03), connected to the grid (03:19) and stopped
(09:07).
D/G 5B started (03:37) and connected to the grid (03:44).
D/G 6A started (04:17) and connected to the grid (04:21).
D/G 6B started (04:31) and connected to the grid (04:36).
・The power supply from Yonomori line was suspended due to the preparatory
construction for Yonomori line for duplication of line. (05:01, July 11)
http://www.nisa.meti.go.jp/english/press/2011/07/en20110712-1-1.pdf

http://www.meti.go.jp/press/2011/07/20110712005/20110712005-1.pdf page 23 : white smoke observed at unit 4 on 12 July 6:30 AM.

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110712_01-j.pdf page 2 : water injection into unit 4 reactor well and dryer storage pool started at 11:22 AM on 12 July. It had to stop at 12:03 because of a leak in the connection of the injection line.

 

[Cire]

You may be assuming a complete failure of the vessel bottom which may not have happened. The instrument and CRDM penetrations of the vessel are more likely to have failed first allowing corium to exit the vessel. The thermocouples in US plants are qualified to at least 2300 degrees F per USNRC Regulatory Guide 1.97.

According to GE they are actually a Type T Thermocouples with a 350C upper limit. They are magnetically attached which is another big problem. Does anyone know of a magnet that still works when heated over 1000C? Only the thermocouples on the RPV head are attached mechanically.

[PLAIN]http://img89.imageshack.us/img89/7498/thermo.jpg

 

[NUCENG]

According to GE they are actually a Type T Thermocouples with a 350C upper limit. They are magnetically attached which is another big problem. Does anyone know of a magnet that still works when heated over 1000C? Only the thermocouples on the RPV head are attached mechanically.

[PLAIN]http://img89.imageshack.us/img89/7498/thermo.jpg[/QUOTE]

My bad, thermocouples were dropped for RG 1.97 per
http://pbadupws.nrc.gov/docs/ML1109/ML11098A049.pdf

You are correct about type T range. Thanks for the correction.