Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[tsutsuji]

Morning of March 12, unit 1:

9:04 - Two shift personnel set out for field to perform PCV venting.
Equipment: fireproof clothing, self-contained breathing apparatus, and APD .Because of the total darkness in the field in both the reactor building and turbine building due to loss of power, they set out carrying flashlights. Because there is no means of communication, and once a team leaves for the field there is no way to get in touch, one team at a time is sent into the field and the next team sets out when the previous team returns to the Main Control Room.
・ Team No. 1 departs Main Control Room for field in order to open the PCV vent valve (MO valve). At around 9:15, 25% open is accomplished as planned and the team returned to the Main Control Room. Radiation exposure dose is about 25 mSv.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110810e21.pdf page 23

Why did they have to enter the reactor building and open the valve manually, risking radiation exposure, instead of connecting batteries inside the central control room ?

March 14 afternoon between 16:00 and 18:00, unit 2:

With no electric power, batteries would be needed to open the SR valve. Batteries were collected from vehicles and carried to the Main Control Room, and power cables were connected to the batteries, but the battery voltage was insufficient, so more batteries were added and attempts were made to open several SR valves and other efforts continued to be made toward depressurizing the reactor, and at around 18:00 reactor depressurization started.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110810e21.pdf page 33

Why did they have to use car batteries ? By that time - March 14 - had it not been possible to secure a powerful and stable DC source using power trucks ?

 

[jim hardy]

""Why did they have to use car batteries ? By that time - March 14 - had it not been possible to secure a powerful and stable DC source using power trucks ?""

the batteries are recharged by large AC powered chargers, and recall the AC distribution panels had been inundated so there was no way to power the chargers. Power trucks are typically AC so they'd have had to connect through the charger.

one might hook up an engine powered DC welding machine to charge the batteries, but i suspect those had all been inundated as well... i recall among the cryptome photos a four foot shark in middle of a plant roadway.

i'd wager that a outcome of this will be small diesel powered DC battery chargers in watertight rooms near plant batteries.

we had small diesel powered air compressors to make starting air for our big emergency diesel generators, in case of unlikely event one of them got stubborn and exhausted its main air reservoir while AC powered compressor was unavailable too.. But our battery charging power originated from redundant AC busses, as i assume did Fukushima's.

old jim

 

[Pakman]

Morning of March 12, unit 1:
Why did they have to enter the reactor building and open the valve manually, risking radiation exposure, instead of connecting batteries inside the central control room ?

Most likely, this motor operated valve was AC-motor operated, but they had only DC batterys. That's why i think.
May be the distribution board which supplies power to this MO was unaccessible or inundated
Beyond doubt, if they could avoid entering the reactor building, they surely would.

 

[tsutsuji]

http://icanps.go.jp/post-1.html Cabinet investigation committee interim report (Japanese)
http://icanps.go.jp/eng/interim-report.html (English) (summary only for now)

 

[rowmag]

http://icanps.go.jp/post-1.html Cabinet investigation committee interim report (Japanese)
http://icanps.go.jp/eng/interim-report.html (English) (summary only for now)

Thanks for the links as always, Tsutsuji.

The report was also featured on the news tonight. What a blisteringly critical report...

 

[Shinjukusam]

Thanks for the links as always, Tsutsuji.

The report was also featured on the news tonight. What a blisteringly critical report...

Oddly enough, I'm glad to see that. You can't point fingers in the midst of an ongoing critical situation, but when there's time to take a breath then you can get more political.

(which should be discussed in the more political thread...)

 

[zapperzero]

TEPCO to drill hole in Unit 2 containment for endoscope inspection:
http://www3.nhk.or.jp/daily/english/20111227_04.html

 

[clancy688]

Finally. I was waiting for such an action.

Does anyone know where that endoscope will be placed at? I don't believe that they're going to look what's going on below the RPVs, but one can still hope.

 

[zapperzero]

Does anyone know where that endoscope will be placed at? I don't believe that they're going to look what's going on below the RPVs

It just says into the PCV, coming in from the NW side of the building iirc. Given that the bottom of the PCV is below grade and the bottom of the RPV is supposed to be flooded... I don't think we will, no. But it should be good to have more data anyway.

 

[SpunkyMonkey]

Indicators of the Fukushima radioactive release in NW Romania

Levels sound pretty high for sooo far away. But it does note the levels "could be influenced by Chernobyl."

Indicators of the Fukushima radioactive release in NW Romania.

As a result of the Fukushima nuclear release, (131)I was found in different environmental media (rainwater, sheep and cow milk, herbage, sheep meat and thyroid tissue) in north-west Romania. On April 4, 2011 a maximum value of 1.40 ± 0.21 Bq/L in (131)I activity was found in rainwater obtained from the Arad region. The obtained value corresponded with the maximum of (131)I concentration in air, as measured by Toma et al. (2011) for the Piteşti area. One day later, sheep milk from the Cluj area was found to contain a maximum activity of 9.22 ± 0.95 Bq/L. A value of 0.85 ± 0.07 μSv was calculated as the total monthly effective dose received by the population as a result of the ingestion of sheep milk and sheep meat contaminated with (131)I. Only rainwater samples contained (134)Cs and (137)Cs at levels close to minimum detectable activity. Since the determined values could be influenced by Chernobyl (137)Cs, the (137)Cs concentrations are subject to uncertainty. The radioiodine transfer coefficients (Fm) and the concentration ratio (CR) from herbage to sheep milk, as well as sheep meat, from the Cluj-Apahida area are also presented.

http://www.ncbi.nlm.nih.gov/pubmed/22197532

 

[SpunkyMonkey]

J Environ Radioact. 2011 Dec 22.

Radioactive pollution in Athens, Greece due to the Fukushima nuclear accident.

As a result of the nuclear accident in Fukushima Daichi power plant, which started on March 11, 2011, radioactive pollutants were transferred by air masses to various regions of the Northern hemisphere, including Europe. Very low concentrations of (131)I, (137)Cs and (134)Cs in airborne particulate matter were measured in Athens, Greece during the period of March 24 to April 28, 2011. The maximum air concentration of (131)I was measured on April 6, 2011 and equaled 490 ± 35 μBq m(-3). The maximum values of the two cesium isotopes were measured on the same day and equaled 180 ± 40 μBq m(-3) for (137)Cs and 160 ± 30 μBq m(-3) for (134)Cs. The average activity ratio of (131)I/(137)Cs in air was 3.0 ± 0.5, while the corresponding ratio of (137)Cs/(134)Cs equaled 1.1 ± 0.3. No artificial radionuclides could be detected in air after April 28, 2011. Traces of (131)I as a result of radioactive deposition were measured in grass, soil, sheep milk and meat. The total deposition of (131)I (dry + wet) was 34 ± 4 Bq m(-2), and of (137)Cs was less than 10 Bq m(-2). The maximum concentration of (131)I in grass was 2.1 ± 0.4 Bg kg(-1), while (134)Cs was not detected. The maximum concentrations of (131)I and (137)Cs in sheep milk were 1.7 ± 0.16 Bq kg(-1) and 0.6 ± 0.12 Bq kg(-1) respectively. Concentrations of (131)I up to 1.3 ± 0.2 Bq kg(-1) were measured in sheep meat. Traces of (131)I were found in a number of soil samples. The radiological impact of the Fukushima nuclear accident in Athens region was practically negligible, especially as compared to that of the Chernobyl accident and also to that of natural radioactivity.

http://www.ncbi.nlm.nih.gov/pubmed/22197531

 

[zapperzero]

Levels sound pretty high for sooo far away. But it does note the levels "could be influenced by Chernobyl."

Yes it's not like the results of any surveys that might have been done back then ever got published.

 

[LabratSR]

Video - Tour of Fukushima Daiichi December 2011 (Japanese subtitles)

http://youtu.be/MYb7yorAarY


Video - Evaluation of Reactor Core Damage at Fukushima Daiichi No. 1, 2 and 3

http://youtu.be/tjjFrsOiQpM

 

[zapperzero]

Video - Tour of Fukushima Daiichi December 2011 (Japanese subtitles)

http://youtu.be/MYb7yorAarY

At 2:09 you can see that there is something written on the back of the worker on the left side of the picture. Later on, when he turns his back to the camera, the writing is blurred. What could be written there, I wonder? Earlier on they show images of office workers - the Toshiba stencil on the backs of their suits is not blurred out.

 

[gmax137]

I'd guess the blurred out 'words' are the workers names written in Sharpie. But that's just a guess.

 

[Bandit127]

Tepco seem to be working on a problem with temperature in the RPV of reactor 1. Below is a quote from the english update page. Tepco seem to have increased gas flow today to try to work out what is going in.

Does anyone have any thoughts on this?

-Since December 22, one of the atmospheric temperatures of Unit 1 Primary
Containment Vessel (PCV) monitored by the Containment Atmospheric
Monitoring System had risen (the atmospheric temperature of the PCV on
December 22 was approx. 38°C, at 7 pm on December 27 was approx. 49°C).
The other temperatures had not risen, so we conducted a survey from 9 am
to 10 am on December 28, and we confirmed that there are no problems.
From 11:00am to 12:15pm on the same date, to identify cause with
monitoring, we adjusted the volume of Nitrogen injection, from approx.
8 m2/h to approx.18 m2/h, and emission of the gas management system, from
approx. 23 m2/h to approx.30 m2/h, as of before December 22.

 

[Cire]

Tepco seem to be working on a problem with temperature in the RPV of reactor 1. Below is a quote from the english update page. Tepco seem to have increased gas flow today to try to work out what is going in.

Does anyone have any thoughts on this?

They're establishing if the readings are valid. Pump in more gas and the temperature should change.

 

[tsutsuji]

Concerning the IC, the cabinet investigation committee's interim report's English summary says:

Unit 1 lost its all power supplies shortly after the arrival of the Tsunami. The isolation condensers (IC) seem to have lost its functionality when its isolation valves were fully or almost fully closed by the fail-safe circuits. But at the initial stage of the Accidents, appropriate corrective action was not taken nor instruction was given. This was because it was wrongly assumed that the IC was operating normally. After a while, the shift operators on duty started to doubt the normal operation of IC from the indicators that momentarily recovered on the control panel, and switched off the IC. This judgement is not necessarily incorrect, but the decision was not properly reported to, or consulted with, the NPS emergency response headquarters.

In the meantime, the NPS emergency response headquarters and the TEPCO head office in Tokyo had the opportunities from the reports from the shift operators on duty and other sources, which could have prompted them to notice the loss of functionality of the IC. But they failed to notice and maintained their view that the IC was operating normally. These incidents in sequence indicate that not only the shift operators on duty but also the NPS emergency response headquarters as well as TEPCO head office in Tokyo did not fully understand the function of IC operation. Such situation is quite inappropriate for nuclear operators.

http://icanps.go.jp/eng/111226ExecutiveSummary.pdf page 7/22 - 8/22

Here is a selection of excerpts I translate from chapter 4 of the report:

http://icanps.go.jp/111226Honbun4Shou.pdf page 93 (17/170)

Immediately after the tsunami arrived, it became impossible to check every isolation valve of unit 1's IC as the control panel's indicator lamps indicating their open or closed status were extinguished. Moreover, although the shift operators on duty had been operating the IC by repeatedly opening and closing the return line isolation valve (MO-3A), they did not remember the open or closed status of that valve when the total loss of electric power occurred (note 22). Also, at that point of time, the shift operators on duty had not cast a thought on the possibility that the fail-safe function, coming together with the total loss of electric power, would close all the isolation valves. For that reason, the shift operators on duty could not grasp the operation status of the IC after tsunami arrival. Whatever the valve status might have been, because the indicator lamps on the control panel were extinguished, the shift operators on duty thought that, as a consequence of the loss of electric power, they could not open or close the IC's isolation valves by means of control panel operations.

Note 22: According to the plant parameters released by Tokyo Electric Power Company, immediately before the loss of electric power, the reactor pressure had turned from decline to rise, so that it can be inferred that when the tsunami arrived, the IC's return line isolation valve (MO-3A) was closed.

http://icanps.go.jp/111226Honbun4Shou.pdf page 97 (17/170)

4) Furthermore, at around 17:15 on the same day, the power plant response headquarters' technical team studied a prediction of the time it would take for unit 1's water level to reach top of active fuel (TAF), which is when fuel exposure begins. Their conclusion was that if the water level continues to decline the same way, TAF would be reached in one hour's time. It means that at that point of time, the power plant response headquarters was aware that unit 1's water level had declined by 60 cm in 14 minutes, and that fuel exposure can occur at around 18:15. Also, it can be thought that the main office response headquarters [in Tokyo], because of the teleconference transmission, was aware of the same. In that case, whatever their awareness of the IC's operation status might have been until then, at least at that point of time, the power plant response headquarters and the main office response headquarters should have easily understood that the IC's cooling function was not sufficient and that it was necessary to start implementing alternative water injection.

However, facing events beyond imagination, and with informations related to units 1, 2, 3, 4, 5, 6 coming in in a disorderly fashion, the power plant response headquarters and the main office response headquarters did not come up with the idea of inferring the IC operation status from the information on reactor water level decline.

http://icanps.go.jp/111226Honbun4Shou.pdf page 103 (27/170) to 107 (31/170)
b Judgement of IC operation status by the shift operators on duty

1) After the arrival of the tsunami, the electric power was lost and on the control panels in the units 1 and 2 central control room, the IC operation status could not be checked, and the reactor water level could not be measured either. It can be thought that, at that point of time, the IC's four isolation valves were fully closed or nearly fully closed due to the fail-safe function, but nobody among the shift operators on duty thought about the link between electric power loss and the fail-safe function.

At around 16:42 on March 11, unit 1's water level gauge (wide band) indicator became visible, indicating wide band -90 cm, and as unit 1's water level was in a declining trend, it finally indicated wide band -150 cm, but at around 16:56 on the same day, it went down scale and became unavailable again. Because the water level's declining trend indicated by the water level gauge contradicted the assumption that the IC was operating normally, the shift operators on duty thought about the possibility that the IC is not functioning normally. For that reason, the shift operators on duty considered alternative water injection means using the D/DFP, they entered the FP pump room in unit 1 turbine building basement 1st floor, and at 17:30 on the same day, they confirmed the starting of the D/DFP and put it in standby mode so that it can be started at any time.

Then, from around 17:19, the shift operators on duty, in order to check if enough water is secured in the IC condenser tank(s), decided to go to check the water level gauge(s) installed on the side of the condenser tank(s) on unit 1 reactor building's 4th floor. At that time, the shift operators on duty made preparations to check the water level gauge(s), but did not put protective masks and protective clothing on. Then, the shift operators on duty left the units 1 and 2 central control room, and as they arrived near unit 1's reactor building airlock, as the needle on their dosimeter (Geiger tube) reached the maximum value of 300 cpm (note 29) and stopped moving, they gave up their checking mission, and went back to the units 1 and 2 central control room.

Thus the shift operators on duty tried to enter unit 1 reactor building or entered into unit 1 turbine building, but as far as the operators who went on location could check, apart from what is mentioned above, no abnormal event such as steam leak and no radiation increase was found, and as many operation sounds stopped after scram, the sound of gasses and water flowing in the pipes was more clearly heard than usually (note 30).

The reason why, at that point of time, a fairly higher than normal radiation dose was detected in unit 1's reactor building and its vicinity, is hard to figure out if one excepts the possibility that radioactive substances quantities larger than normal had been released from the reactor pressure vessel and had leaked into the reactor building (note 31). Also, as already mentioned above, immediately after the tsunami arrived, the four isolation valves were fully closed or nearly fully closed, the IC's cooling function was almost lost, and more than two hours elapsed almost without cooling water injection. In that case, fuel exposure had already started at unit 1 and it is quite probable that the radiation inside unit 1 reactor building and in its vicinity became higher.

However, at that point of time, nobody among the shift operators on duty had yet clearly realized that there is a possibility that the IC's isolation valves became fully closed or nearly fully closed due to the fail-safe function, and that, at best, it almost lost its function.

note 29: The detected radiation is thought to be almost gamma rays, and assuming it is gamma rays, a 300 cpm value corresponds to about 2.5 μSv/h. However, though the probability is low, if the detected radiation is alpha, 300 cpm corresponds to about 50 μSv/h.

note 30: On the units 1 and 2 central control room white board released by Tokyo Electric Power Company, "hissing sounds are heard from corridor side" is written, but in the evening of 11 March, nobody among the several shift operators on duty who went to the corridor near unit 1's turbine building testified that they heard steam leak sound or saw white mist after a pipe was ruptured. As several kinds of missions were performed later inside unit 1 reactor building, and as there is no ground for thinking that the "hissing sound" is the sound of steam leaking from a ruptured pipe, it is thought that it was the sound of gasses and water flowing in the pipes.

note 31: If radioactive substances are generated in the reactor pressure vessel, radiations such as gamma rays are not only spread into the reactor building even if the reactor pressure vessel and the primary containment vessel are not damaged, but the shutdown of the building's air conditioning equipment due to the loss of electric power is a factor leading to the rise of radiation doses. For that reason, the rise of radiation doses alone is not sufficient to conclude that the reactor pressure vessel or the primary containment vessel (or the pipes or penetrations in their surroundings) are damaged. Moreover, it is thought that if at that point of time a large damage had occurred at some location in the reactor pressure vessel or the primary containment vessel (or the pipes or penetrations in their surroundings), this would contradict the fact that missions were conducted on location in unit 1 reactor building or turbine building such as the check of the starting of the D/DFP or the opening and closing of valves.

2) Not even one among the shift operators on duty who operated unit 1 had had a real experience of operating an IC until the March 11 tsunami occurred. Among the shift operators on duty, one of them(some of them) had heard from an older operator(s) that when the IC is working normally, the water in the condenser tank is heated and evaporated due to the heat exchange, and the steam bursts vigorously and horizontally from the two gas exhaust vents which are installed in a row on the western wall of unit 1's reactor building (the so-called "pig nose"), and that on such occasions, static electricity is generated, producing a blue light similar to a lightning, while a roaring sound resonates.

However, from the total loss of electric power to around 18:18, the shift operators on duty did not have the idea to check the IC's operation status by checking the generation of steam or the operation sound, and in practice no checking of whether steam is generated or not, or of how much steam is generated, was undertaken by observing the gas exhaust vent on the mountain side of unit 1's reactor building.

3) At around 18:18 on March 11, the shift operators on duty noticed that on the control panel in units 1 and 2 central control room, the green indicator lamps indicating that the IC (system A)'s feed line isolation valve (MO-2A) and return line isolation valve (MO-3A) are "fully closed" were lit, and they gathered in front of that control panel. The shift operators on duty thought that there is a possibility that the indicator lamps were lit after some of the batteries which had been inundated by seawater had dried.

At that time, the control panel's indicator lamps that display the open or closed status of the two primary containment vessel inner side isolation valves (MO-1A, MO-4A) were extinguished, and these valve's open or closed status could not be determined. However, finding that the feed line isolation valve (MO-2A), which is supposed to be normally open, was fully closed according to the control panel display, the shift operators on duty realized that there is a possibility that it was closed by the fail-safe function, and thought that in that case the two valves on the inner side of the primary containment vessel (MO-1A, 4A) might be fully closed too.

On the other hand, as it is not possible to go so far as ascertaining that the valves on the primary containment vessel's inner side are fully closed, and as it was certain that, regardless the status of the inner side isolation valves, the IC is completely out of function as long as the feed line isolation valve (MO-2A) and the return line isolation valve (MO-3A) are fully closed, the shift operators on duty expected that the inner side isolation valves (MO-1A, 4A) would be at least a little open, and operating from the control panel, they opened the feed line isolation valve (MO-2A) and the return line isolation valve (MO-3A).

It must be noted that the two isolation valves on the inner side of the primary containment vessel, in both A and B systems were not equipped with a mechanism that would allow to perform the valve opening operation with a manual handle while the reactor is in operation, instead of using the remote control from the control panel (note 32).

Note 32: Furthermore, as the driving motors of both A and B system's primary containment vessel inner side isolation valves were powered by AC power, when unit 1's all AC power sources were lost at around 15:57 on March 11, the valve driving power source was lost, and even if the DC power which is necessary for remote control from the control panel had been recovered, as long as AC power was not recovered the valves had fallen into a situation where opening or closing was impossible. If, as explained above, the primary containment vessel inner side isolation valves, unlike the outer side isolation valves, are not using a DC motor but an AC motor, it is because AC motors are stronger against the high temperatures and pressures inside the primary containment vessel. By the same token,Tsuruga nuclear power plant's unit 1's IC's primary containment vessel inner side isolation valves' driving power is not DC but AC. It must be noted that a manual handle is installed on the main body of the inner side isolation valves, and that by manual operation of the handle is is possible to open the valve, but as long as one cannot enter the primary containment vessel, the operation of the manual handle itself is not possible. Also, as regards the possibility that the AC power was lost during the closing operation of the inner side isolation valves due to the fail-safe function and that at that point of time the valve was not fully closed, please see the above paragraphs 2) and 3).

Furthermore, in order to check the IC's operation status by judging the quantity of generated steam, the shift operators on duty went out through the emergency door located on the north-western side of units 1 and 2 central control room, and looking beyond the reactor building, checked whether steam was generated from the IC exhaust gas vent on the western wall of unit 1's reactor building. At that time, from the place where the shift operators on duty were performing the check, only the eastern wall and the southern wall of the reactor building were directly visible, and it was a place from which a direct observation of the IC's gas exhaust vent is not possible (see figure IV-1).

At that time, looking beyond unit 1 reactor building, the shift operators on duty confirmed that a small quantity of steam was generated, but when they checked again soon afterwards, they could not confirm steam generation beyond unit 1 reactor building. Then the shift operators on duty thought that there is also a possibility that the quantity of generated steam was small because only a small quantity of coolant water remained inside the condenser tank. Furthermore, the shift operators on duty were even worried that if the quantity of coolant water inside the condenser tank is small, the high temperature, high pressure steam from the reactor would run in a loop through the IC pipes without cooling down, causing the damage of IC pipes, and that reactor steam polluted with radioactive substances would be directly released into the atmosphere.

Thinking that either way the IC is almost not functioning, at around 18:25, using control panel operations, the shift operators on duty performed valve closure operation of the return line isolation valve (MO-3A) and shut the IC down (as regards reporting to the power plant response headquarters, see e(b) below). At that time,the feed line isolation valve (MO-2A) was left fully open in accordance with the normal operation procedure.

< end of this part of translation >

The "pig nose" (IC gas exhaust vent) is visible for example on the following photograph: http://img.ibtimes.com/www/data/images/full/2011/05/25/103517-fukushima-daiichi-unit-1.jpg

My comment: I am not sure I understand how operators with no previous experience who are eventually given the first opportunity in their lives to play with a new toy can afterwards so easily forget which actions they performed with the new toy ("did not remember the open or closed status of that valve" ).

 

[steve olsen]

tsutsuji

Thanks for posting that huge translation!
Ques--maybe I am missing it, but i would assume the Pig nose to be really big, like 20 square meters or more in area...is that the right picture?

 

[tsutsuji]

tsutsuji

is that the right picture?

I can't say for sure. This is just my guessing.

 

[joewein]

Ques--maybe I am missing it, but i would assume the Pig nose to be really big, like 20 square meters or more in area...

The "pig nose" must be those short pipe stubs sticking out to the right of the http://img.ibtimes.com/www/data/images/full/2011/05/25/103517-fukushima-daiichi-unit-1.jpg , in the top centre "cloud" section of the right hand wall.

There are probably two of them because of the two IC units. It don't see why it would take much more than those pipes to release the steam from the boiling condenser water -- they look right.

 

[zapperzero]

I'd guess the blurred out 'words' are the workers names written in Sharpie. But that's just a guess.

That's a pretty long name... stretching on at least two rows, from side to side. Take a closer look.

 

[Borek]

If memory serves me well in the past blurred names were names of some agencies/organizations that wanted to stay anonymous.

For whatever reasons.

 

[clancy688]

Thanks for the translation, tsutsuji!

What's the purpose of that "fail-safe" function? Isn't closing the valves (shutting down the IC) in case of total power loss exactly the wrong thing do? This separates the reactor vessel from the only cooling function still available.

Furthermore, the shift operators on duty were even worried that if the quantity of coolant water inside the condenser tank is small, the high temperature, high pressure steam from the reactor would run in a loop through the IC pipes without cooling down, causing the damage of IC pipes, and that reactor steam polluted with radioactive substances would be directly released into the atmosphere.

That's the only probable purpose of that function I can imagine.
SBO -> reactor is doomed anyway -> so don't give it a direct path to the atmosphere

------------------

Not even one among the shift operators on duty who operated unit 1 had had a real experience of operating an IC until the March 11 tsunami occurred. Among the shift operators on duty, one of them(some of them) had heard from an older operator(s) that when the IC is working normally, the water in the condenser tank is heated and evaporated due to the heat exchange, and the steam bursts vigorously and horizontally from the two gas exhaust vents which are installed in a row on the western wall of unit 1's reactor building (the so-called "pig nose"), and that on such occasions, static electricity is generated, producing a blue light similar to a lightning, while a roaring sound resonates.

That's hilarious. The IC is their last line of defense and those guys had no idea on how to operate it. That's like sailors who don't have any idea on how to lower rescue boats to the sea.

 

[tsutsuji]

What's the purpose of that "fail-safe" function? Isn't closing the valves (shutting down the IC) in case of total power loss exactly the wrong thing do? This separates the reactor vessel from the only cooling function still available.

Tepco's internal investigation report is also questioning the suitability of the fail-safe function:

http://www3.nhk.or.jp/news/genpatsu-fukushima/20111203/0735_reikyoku.html (3 December) Tepco's internal investigation report says that the suitability of the mechanism which makes the IC's valves automatically close when battery power is lost must be investigated. The mechanism is intended to prevent radioactive substances to be released outside of the plant in case of emergency, but in this case, it prevented the emergency cooling function from being performed.

That's hilarious. The IC is their last line of defense and those guys had no idea on how to operate it. That's like sailors who don't have any idea on how to lower rescue boats to the sea.

It seems that they had been trained (on a simulator?) to use the IC from the control panel, and that they were able to run it in accordance with the operation manual between the earthquake and the tsunami. Yet I wish the investigation committee would elaborate on what they mean with "they did not remember the open or closed status of that valve". I don't think one can so easily forget this sort of things. It would seem more natural that they had in their mind the fact that the valve had been left in a closed position when the tsunami struck, and that they would be worried that under such condition the IC is shutdown and that no cooling is being performed. And even if they were not remembering and not worrying on the IC issue, should not Tepco higher-ups or the NISA have worried and asked them to remember ?

 

[jim hardy]

wow. in a so stressful event i can see priorities being muddied.

there's a certain psychological makeup needed to be a good operator. that's an ability to remain detached and aware of the "big picture".

engineers tend to be capable of focusing on one detail to exclusion of all else. that's how they get through school. just opposite makeup is needed for operations.

releasing reactor contents is a big release of radioactive stuff and i can understand how that could become a focal point, for these guys' families live just downwind.

recall that 1970's Eastern Airlines plane that got flown into the ground - all 3 guys in the cockpit were focused on the nosewheel "down" light and not aware of altitude.

having too many engineers is as bad as having too few. when i got obsessive my guys used to tell me "Go away and calculate something, we'll call you when this is working.""

i wasn't there so don't know what went on. only thing I'm sure of is everybody's sadder but wiser now.

 

[clancy688]

recall that 1970's Eastern Airlines plane that got flown into the ground - all 3 guys in the cockpit were focused on the nosewheel "down" light and not aware of altitude.

Fascinating, after reading your second line, exactly that specific accident crossed my mind. If I remember correctly, it was a turning point for the whole aircraft industry regarding security issues.
There was another accident, I don't know which one, which prompted the development of efficient checklists.
If those guys in Fukushima would've been using checklists while operating the condenser, they should've noticed the actual operation and valve status (steam discharge, etc.).

Airplanes and NPPs are not so different after all. If you screw up during a status change (landing, SCRAM), it's effectively over. So there are numerous ways to prevent screw up. The most notable probably being the checklists. In airplanes, there are checklists not only for landing and starting, but for all kinds of emergencies - engine failure, whatever. So whatever happens, they have a guideline which should lead them in NOT forgetting the crucial single one button-press-operation out of several dozens they have to perform during the emergency.

Many users posting here have experience in working in NPPs. I have not. So I ask them - is there something similar to the checklists used in aircrafts?

 

[nikkkom]

That's the only probable purpose of that function I can imagine.
SBO -> reactor is doomed anyway -> so don't give it a direct path to the atmosphere

Why dry IC should be a direct path from reactor coolant to atmosphere?
To not design IC to be able to withstand boiling dry would be a serious design mistake.

 

[clancy688]

Well, of course. But apparently, the TEPCO operators didn't think that the IC (or rather the piping) could survive boiling dry.

Furthermore, the shift operators on duty were even worried that if the quantity of coolant water inside the condenser tank is small, the high temperature, high pressure steam from the reactor would run in a loop through the IC pipes without cooling down, causing the damage of IC pipes, and that reactor steam polluted with radioactive substances would be directly released into the atmosphere.

 

[tsutsuji]

Why do nuclear power plants rely so much on electric control systems? Would not pneumatic logic systems and pneumatic motors be stronger against being flooded under several meters of seawater ? For example, instead of having IC(A) and IC(B) being both electric-controlled, couldn't we have at least one air-controlled IC(B) ?

 

[jim hardy]

""Airplanes and NPPs are not so different after all. ""

NPP operators are on instruments 100% of the time. There's no sensory feedback beyond noise of steam blowing.

yes there's checklists. operation is very procedurized.

one of the changes after Three Mile Island was a change in philosophy, from problem oriented to symptom oriented procedures...

procedures were change from "If you have (this problem) do that" approach

to

"IF you SEE this, do that."

reason is operators can't see all the pipes, they only see their instruments. So they may not be able to discern what is the problem - only that temperature and pressure are changing. That's what they were confronted with at TMI.


Some very different troubles give similar symptoms.

yes there are checklists. sadly, total loss of power may not have been bounded - again i don't know.

A procedure is like a computer program , it might crash if handed an unexpected input.

in NPPs fine tuning them to handle all possible conditions is a never ending activity. you never achieve perfection , to wit the pyramid on back of US one dollar bill is missing top brick.

 

[jim hardy]

Why do nuclear power plants rely so much on electric control systems? Would not pneumatic logic systems and pneumatic motors be stronger against being flooded under several meters of seawater ? For example, instead of having IC(A) and IC(B) being both electric-controlled, couldn't we have at least one air-controlled IC(B) ?

in 1950's pneumatic controls were the best. our plants all had them.

around 1960 solid state made electronics reliable enough to be considered for industrial controls and they got so cheap they just took over...

i too asked why do i need a box full of op-amps to replace a pressure switch.
i have long been of the opinion the best balance would be robust analog controls , perhaps pneumatic, with a fancy computer to monitor them and help you keep it in good repair.

pneumatics are absolutely impervious to lightning and walkie-talkies. power failure is gradual as the air reservoir slowly bleeds down, and you have time to start a backup compressor . when one watches them in operation, hissing and balancing, one realizes they're pretty well matched to the big clunky machines they are controlling.

but i am a luddite. computers should be allowed only to think - never trust one with anything important.
see Robert Sheckley's "Watchbirds"

old jim

 

[tsutsuji]

If a key system like the scram system is an hydraulic system, why shouldn't the IC, which is also a top level safety system, be also an hydraulic system ?

Googling a few keywords I found the following:

http://www.nrc.gov/reactors/new-reactors/design-cert/abwr/dcd/tier-2/CH_15/15_08.pdf "The ABWR, however, uses a FMCRD design with both hydraulic and electric means to achieve shutdown"

so it seems that some people have a concern for not relying on "electric only" or "hydraulic only".

 

[I_P]

Can it be definitively determined that there was no critical damage to the cooling systems from the earthquake prior to the tsunami (the workers reported broken pipes and flooding during the quake), or containment structures - based on the available sensor data? What was going on with #2 and #3? We see only the rundown on the status of #1 in this report (yes?).

Has this scenario been discussed: http://lewrockwell.com/orig4/goddard2.1.1.html ?

 

[clancy688]

Has this scenario been discussed: http://lewrockwell.com/orig4/goddard2.1.1.html ?

Yes, I think so. But it's probably in the temporarily removed "Unit 3 explosion" thread. As for containment breaches before the meltdowns:

Then, from around 17:19, the shift operators on duty, in order to check if enough water is secured in the IC condenser tank(s), decided to go to check the water level gauge(s) installed on the side of the condenser tank(s) on unit 1 reactor building's 4th floor. At that time, the shift operators on duty made preparations to check the water level gauge(s), but did not put protective masks and protective clothing on. Then, the shift operators on duty left the units 1 and 2 central control room, and as they arrived near unit 1's reactor building airlock, as the needle on their dosimeter (Geiger tube) reached the maximum value of 300 cpm (note 29) and stopped moving, they gave up their checking mission, and went back to the units 1 and 2 central control room.
note 29: The detected radiation is thought to be almost gamma rays, and assuming it is gamma rays, a 300 cpm value corresponds to about 2.5 μSv/h. However, though the probability is low, if the detected radiation is alpha, 300 cpm corresponds to about 50 μSv/h.

That's one hour before the top of the fuel even got uncovered, much less melted.

And right before the tsunami hit, a monitoring post at the vicinity border went off: http://www.bloomberg.com/news/2011-05-19/fukushima-may-have-leaked-radiation-before-quake.html

 

[tsutsuji]

Can it be definitively determined that there was no critical damage to the cooling systems from the earthquake prior to the tsunami (the workers reported broken pipes and flooding during the quake), or containment structures - based on the available sensor data?

There is a lengthy discussion in the cabinet investigation committee interim report on whether unit 1's IC was damaged by the earthquake prior the tsunami, and their conclusion is "no". I thought this is not the most interesting and I thought it would be more interesting to translate other parts of the report.

What was going on with #2 and #3? We see only the rundown on the status of #1 in this report (yes?).

The report is also talking about unit 3 (you can check by reading the "Poor handling of alternative water injection at Unit 3" section in the http://icanps.go.jp/eng/111226ExecutiveSummary.pdf ).

 

[I_P]

There is a lengthy discussion in the cabinet investigation committee interim report on whether unit 1's IC was damaged by the earthquake prior the tsunami, and their conclusion is "no". I thought this is not the most interesting and I thought it would be more interesting to translate other parts of the report.

Thanks Tsutsuji for this and all your translations/posts.

Did you find their reasoning convincing? Did they have enough evidence to support this conclusion?

I find myself wondering now how many years it will be before a definitive post-mortem can be worked up and a bit surprised at how many basic questions remain at this point.

Clancy, is that thread (about unit 3 explosion) accessible?

 

[clancy688]

Nope.

But I'm sure it'll come back soon enough. Isn't the first time it got sacked because of unnecessary speculation. Some folks sadly just can't hold their conspiracy theories back. So it's probably somewhere only moderators and administrators have access to and will come back once it's been cleaned of unnecessary speculation and related offtopic posts.

http://webcache.googleusercontent.com/search?q=cache:szk1ehUU7UQJ:www.physicsforums.com/showthread.php%3Ft%3D505630the first page in google cache.

Use this link to access the other pages. Just change the page number at the end of the URL pasted in the search window (from 1 to 47) and then access the cached version of the first search result.
That's annoying as hell, but not as annoying as not being able to read the thread. ;)


Edit:
http://webcache.googleusercontent.com/search?q=cache:tyJNyw1Flm8J:www.physicsforums.com/showthread.php%3Ft%3D505630%26page%3D39+http://lewrockwell.com/orig4/goddard2.1.1.html+physicsforums&cd=1&hl=de&ct=clnk&gl=de

 

[jim hardy]

here was another forum with a pretty decent level of discourse.

like PF, the moderator chased off the tinfoil hat types.

http://tickerforum.org/akcs-www?post=182121

but it's three hundred something pages.
around 314 was another hypothesis, about steam explosion but in-vessel.
Since you can set browser for so many posts per page, page number is unreliable.
so around may 7th is date.

 

[tsutsuji]

Follow-up of the translation started on https://www.physicsforums.com/showpost.php?p=3687263&postcount=11983

We had left on page 107 (31/170) when the operators close the MO-3A valve at around 18:25.

http://icanps.go.jp/111226Honbun4Shou.pdf translation of pages 107 (31/170) - 110 (37/170) :

At that time, the shift operators on duty thought that as the IC was not functioning normally, it was necessary to build alternative water injection means, and as a means the shift operators in duty can use in a situation of total loss of electric power, they came up with no other idea than the method of injecting water into the reactor through the FP line using the D/DFP. Then the shift operators in duty started the D/DFP at around 17:30 on the same day, and put it in standby mode, and at around 18:30 on the same day, in such places as the reactor building and the turbine building, they manually performed the valve switching operations that are necessary to enable water injection into the reactor through the FP line and the condensate feed line (MUWC line).

4) At around 21:30 on March 11, the shift operators on duty noticed that the green indicator lamp on units 1 and 2 central control room's control panel, that indicates the status of the IC's return line isolation valve (MO-3A) was beginning to fade out, and they feared that if the electric power is lost, it will be impossible to open that valve. By that time, as a result of checking the operation manual, etc. the shift operators on duty had understood that the IC can be run for several hours without needing to refill the condenser tank with cooling water.

Hence, the shift operators on duty thought that it is highly probable that the reason why from around 18:18 the quantity of steam generated by the condenser tank became small was not that the condenser tank was running out of coolant water, but that the two isolation valves on the inner side of the primary containment vessel (MO-1A, 4A) were not open due to the fail-safe function.

The shift operators on duty thought that even in that case, as long as the return line isolation valve (MO-3A) is left closed, under the hypothesis that the isolation valves on the inner side of the primary containment vessel (MO-1A, 4A) would be found slightly open, if the driving electric poser is lost, it will become definitely impossible to open the return line isolation valve (MO-3A). Furthermore, the shift operators on duty thought that notwithstanding the fact that there is no need to refill the condenser tank with coolant water even if the IC is continuously used for several hours, under the hypothesis that refilling the condenser tank with coolant water would become necessary, it is admissible to refill by operating the D/DFP and performing the valve operations that are needed to refill the condenser tank through the FP line.

At that point, the shift operators on duty thought that the probability that the IC would work is not zero, and they performed the valve opening operation of the IC's return line isolation valve (MO-3A). At that time, the shift operators on duty heard a sound sounding like a steam release, but shortly after that, they could not hear the sound any longer, and, of course, they did not think that the IC was functioning normally (note 33).

Then the shift operators on duty reported to the power plant response headquarters that the return line isolation valve (MO-3A) had been opened.

Note 33: At that time too, the shift operators on duty were not directly observing the gas exhaust vent through which the steam is discharged, but their testimony that the steam generation sound did not continue is corroborated by informations such as the about 65% water level value indicated by the IC condenser tank water level gauge more than 200 days after the accident, and it is thought that if the IC had been operating normally, this kind of steam generation situation would not have occurred.

c Judgement of IC operation status by the power plant response headquarters and by the main office response headquarters

1) After around 15:37 on March 11, total loss of AC power and DC power occurred for unit 1, and the power plant response headquarters received a report from the shift operators on duty on this situation. However, at that point of time, nobody had pointed out the possibility that the IC's four isolation valves could have been brought to a fully or nearly fully closed status by the fail-safe function.

Furthermore, at around 16:45 on the same day, the power plant response headquarters received a report from the shift operators on duty saying that unit 1's reactor level gauge became available. However, the power plant response headquarters received reports about this reactor water level gauge until around 17:07 on the same day, saying that at around 16:42 on the same day the indication was wide band -90 cm, that the later trend was a decline, that at around 16;56 on the same day the indication was -150 cm, and that finally the gauge went down scale and became unavailable again. The same information was shared with the main office response headquarters via the teleconferencing system. Then, at around 17:15 on the same day, the power plant response headquarters' technical team calculated a prediction of the time it takes until TAF is reached, and concluded that TAF would be reached in one hour's time. However, even at that point of time, nobody among the power plant response headquarters or the main office response headquarters, by linking together the observed phenomenons and estimates with the IC function, pointed out that the IC might not be operating normally.

Furthermore, at around 17:50 on the same day, the power plant response headquarters received from the shift operators on duty a report saying that a high radiation had been found when approaching unit 1's reactor building in order to check the IC's condenser tank water level, and this information was shared with the main office response headquarters via the teleconferencing system. At that point of time, nobody among the power plant response headquarters and the main office response headquarters pointed out the possibility that large quantities of radioactive substances were generated inside the reactor pressure vessel as a result of the decline of the reactor water level, because the IC was not functioning.

2) At around 18:18 on March 11, the power plant response headquarters received a report from the shift operators on duty saying that they had opened the feed line isolation valve (MO-2A) and the return line isolation valve (MO-3A) of IC (system A), and believed that the IC was working. The main office response headquarters, receiving the same information as the power plant response headquarters via the teleconferencing system, also believed that the IC was working.

No evidence can be found that at that time, the power plant response headquarters and the main office response headquarters were conscious of the problem arising from the fact that both isolation valves had been opened, meaning that until then they had been closed and that the IC had not been operating for 3 hours after the total loss of electric power, and that no water had been injected into the reactor either.

3) No sufficient mutual understanding was attempted at Fukushima Daiichi nuclear power plant between the units 1 and 2 central control room and the power plant response headquarters in the seismic-isolated building concerning the fact that the closure operation of return line isolation valve (MO-3A) had been performed at around 18:25 on March 11, and later the power plant response headquarters believed that the IC was still running.

For that reason, for example, because unit 2's RCIC's operation status could not be checked and because unit 2's reactor water level could not be measured, fearing that the water level would decline and that fuel exposure would lead to meltdown, until between 21:00 and 22:00 the power plant response headquarters had a stronger feeling of danger regarding unit 2 than regarding unit 1, and later the measures that are necessary to control each plant unit were studied, based on the prejudice that unit 1's IC was working normally and that the cooling function was obtained.

Nevertheless, according to the power plant response headquarters' members' notebooks and other records, there is evidence that the power plant response headquarters grasped the information that the shift operators on duty were fearing that the IC's condenser tank was running out of water. However, the condenser tank water replenishment was eventually not performed, and also, no evidence whatsoever was found that any preparation for an alternative water injection task using fire trucks or for reactor depressurization had been started on the same day concerning unit 1.

Also, via the teleconferencing system, the main office response headquarters thought the same as the nuclear plant response headquarters, which is that unit 1's IC was under operation, and that for the time being, the cooling function could be maintained for several hours. The ministry of economy and industry's emergency response center (ERC) was also reporting that unit 1's IC was under operation.

4) At around 21:30 on March 11, the power plant response headquarters received a report from the shift operators on duty saying that they had opened the IC's return line isolation valve (MO-3A). However, at that time, nobody among the power plant response headquarters and the main office response headquarters, including plant manager Yoshida was conscious of the problem arising from the fact that this report implied that the IC's return line isolation valve (MO-3A) had been in a closed status until then, and nobody asked the shift operators on duty whether they had previously closed that valve.

At that time, the main office response headquarters and the power plant response headquarters were not grasping that at around 18:25 on the same day the shift operators on duty had closed the IC's return line isolation valve (MO-3A) and they were both believing that the IC was operating normally.

d Response of the safety inspectors

According to the Nuclear Industry Safety Agency (NISA), from the off-the-Tohoku-Pacific-coast-earthquake occurrence at around 14:46 on March 11 until the early morning of March 12, the safety inspectors were present on the second floor of the seismic-isolated building, and staying in the conference room on the side of the emergency response room, they received the plant parameters made available by the power plant response headquarters, and using mobile telephones or satellite telephones, they only reported these contents to the offsite center or to the ERC.

However, the safety inspectors being in a position where informations similar as those of the power plant response headquarters and the main office response headquarters can be easily obtained, instead of simply and entirely focusing on the retrieval of information provided by the power plant response headquarters, they should have asked questions to the power plant response headquarters concerning the IC operation status, they should have strived to grasp a more accurate account of the situation, and when necessary, they should have given instructions or provided advice.

In fact, no evidence could be found that the safety inspectors provided necessary instructions or advice to the power plant response headquarters. There is no apparent sign of a situation where the safety inspectors in the seismic-isolated building contributed in some way to the response to the accident.

 

[tsutsuji]

Did you find their reasoning convincing? Did they have enough evidence to support this conclusion?

Basically, the IC worked quite well between the earthquake and the tsunami, and if any major damage had been caused by the earthquake alone, it would have been obvious during that early phase.

 

[Joffan]

Thanks once again tsutsuji for another superb translation job.

My earlier thought that the explosion of R/B#1 could have been averted through earlier venting and injection, although still possible, has faded into the background with these revelations about the failure to use the IC properly. The operators appear less heroic when the tools were almost certainly at hand to control the plant.

The other point I've taken notice of is that the workers going to investigate valves retreated at doses that, in the emergency circumstances, should not have stopped them.

 

[clancy688]

The other point I've taken notice of is that the workers going to investigate valves retreated at doses that, in the emergency circumstances, should not have stopped them.

Well, it was "over the scale". Since the scale was 300 cpm / 2.5 uSv/h Gamma, you can't hardly blame them. That can be everything from "temporary nuisance" to "lifethreatening double digit Sv values".
I remember a (BBC - Surviving Disaster - Chernobyl) docu drama about Chernobyl. The workers reported that they measured 3.6 R/h - but with 3.6 being the top of the scale, and the readings being off the scale. The plant director didn't believe in a big emergency and reported that value to Moscow. Turned out the real readings were 15'000 R/h.

 

[jim hardy]

yes that's a fundamental rule

never go anyplace in a rad area where you don't know what's the radiation field
if your meter tops out you don't know how much over the top it is
so you go back and get a bigger one

clancy's example shows that.
it's part of good design - a good meter should tell you it's topped out.

russian electronics of the 80's that i encountered was regarded, well, primitive.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20111229/0545_3goki.html Did unit 3's explosion result from a backward flow of hydrogen ? Checking one pipe that forks from the venting pipe and connects to the reactor building, Tepco recently found traces of the vented gas that contained hydrogen. This pipe is equipped with a valve and a device that prevents backflow, but the valve is designed to automatically open if electric power is lost, and the backflow preventing device has a low airtightness, so that it is possible that hydrogen flowed backwards into the reactor building and caused an hydrogen explosion. So far it was thought that the hydrogen would have leaked through interstices such as those of the containment vessel cover. The NISA is studying the reinforcement of backflow preventing devices in other nuclear plants.

http://www.asahi.com/national/update/1226/TKY201112260188.html [with http://www.asahi.com/national/update/1226/images/TKY201112260191.jpg] finding that the radiation decreases from the outer site to the inner side, Tepco concluded that radioactive substances had flowed backwards in the pipe. This was found at unit 3, but the same kind of backflow might have happened at unit 1 too.

http://www.nikkei.com/news/category...39180EAE2E2E2;at=DGXZZO0195583008122009000000 During a hearing of specialists organised on 27 December, the NISA publicly released the results of an analysis saying that there is a possibility that hydrogen backflow is one of the causes of the hydrogen explosions in unit 1 and unit 3.

http://www.news24.jp/articles/2011/12/27/07197167.html At the 27 December meeting, the NISA said that one of the causes of hydrogen explosions could be the degradation of the silicone gum in the joining parts of the primary containment vessel. Concerning the backflow from unit 3 into unit 4, there was no backflow preventing device, and there was no instruction to close [unit 4's] valves in the operation manual.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111226_01-e.pdf "Fukushima Daiichi Nuclear Power Station: Unit 3 Measurement of Radiation Dose of Emergency Gas Treatment System and the Result of the Status of Valves"

 

[Most Curious]

I would think getting a large butterfly valve to be "hydrogen tight" would be a big challenge! The stuff is "slippery" due to small molecule and is hard to contain.

IOW, I would expect LOTS of hydrogen leaks in that plant!

 

[Joffan]

Fair enough if their meters were maxed out. I didn't read it that way, but that would be a good reason for stopping for sure.

 

[NUCENG]

Thanks Tsutsuji for this and all your translations/posts.

Did you find their reasoning convincing? Did they have enough evidence to support this conclusion?

I find myself wondering now how many years it will be before a definitive post-mortem can be worked up and a bit surprised at how many basic questions remain at this point.

Clancy, is that thread (about unit 3 explosion) accessible?

Thinking about a Definitive Post-Mortem, what do you expect it to answer?

I will be years before health actual impacts can be determined.

It may be several years befor vessel disassembly and determination of in-vessel damage.

It will probably be a year before initial investigations can be completed. (We are starting to see preliminary information and interim reports, but a lot of it is based on best guess and analysis, not physical evidence.

Right now there are some important preliminries that are priorities including:

• Stabilizing and cooling the fuel debris and corium.
• Clearing debris and controlling radiation on site.
• Eliminating off-site releases.
• Cleaning up water and reducing inventory in buildings.
• Dealing with radiation sources in populated areas.
• Clearing debris and stabilizing buildings to provide safe work area for disassembly.

It took years to complete the "final" story on TMI2 - a single reactor with an intact contailmentm and all fuel remaining in the RPV.

 

[Pakman]

Thank you,Tsutsuji for great job!

I have a quastion. In your translation there is no even a word about IC B as if there was no such an equipment at unit 1. Is there any explanation in the report on why IC B had been never used since the time of shutting it down at 15:03 by operator? Once operators tried to restore cooling of the reactor and failed with IC A, why they did not resort to [STRIKE]plan[/STRIKE] IC B?

 

[jim hardy]

please pardon me if this report has already been linked...

http://www.power-eng.com/content/dam/pe/online-articles/documents/2011/november/fukushima report.pdf