Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[tsutsuji]

Does anyone have a clue about what happened to the diesel generators in the common pool building first floor (unit 2 DG B and unit 4 DG B) which are marked "unusable" although they are also marked as "not inundated" in table II-2-14 of the second report to IAEA : http://www.meti.go.jp/english/earthquake/nuclear/iaea/pdf/20110911/chapter2.pdf page 72 ? The diesel generators of unit 5 are also both "unusable" and "not inundated", which can mean that only their seawater cooling system was unusable because of damaged seawater pumps. But aren't unit 2 DG B and unit 4 DG B air-cooled ?

The internal investigation interim report tells a few additional remarks about the diesel generators, like diesel generator inundation was generally caused by a tsunami water route via the air intake louver, generally located on the first floor ( http://www.tepco.co.jp/cc/press/betu11_j/images/111202f.pdf page 24/140 ), or that in the USA diesel generators are often not in basements because there are no basements in turbine buildings in the USA, while in Japan anti-seismic rules imply to build buildings on the base rock layer (page 23/140). But I still do not understand what they mean with the diesel generators that are not inundated yet unusable.

 

[Joffan]

The sizing of the IC is also intended to remove heat in events where the reactor remains at higher powers due to ATWS. One of the problems of simple solutions is that it may overlook impact on other types of accidents or transients.

Thanks for the response. You'll notice though I did say an extra loop - I was thinking of smaller piping, not a smaller IC, that could be simply left open once activated. There may of course be good reasons why this is not feasible, and there is always the danger that extra loops bring extra complexity with the potential for additional problems.

 

[etudiant]

Separate topic.
There are reports on Energy News, a generally alarmist website, claiming the NRC believes there was a sustained fire in reactor 2 after the accident sustained by reaction products of the zirconium cladding reacting with the water.
The source appears to be this video:
http://www.youtube.com/watch?v=vSfaJTjvmHo&feature=relmfu
The video, which looks to be an NRC product dating from end Nov, features Frederick (Rick) Hasselberg. who is identified as a reactor engineer and incident response coordinator in NRC’s Office of Nuclear Security and Incident Response (NSIR).

He notes, among other items

At Units 1, 2 and 3, a huge amount of hydrogen was generated as the fuel rods were violently consumed by the self-sustaining zirconium-water reaction.
Core temperatures continued to rise.
You could hardly call them fuel rods anymore, but some of the materials that used to be inside the fuel rods were reaching 3000, 4000, 5000 degrees.

and then goes on to say that the hydrogen produced burned for several days at unit 2, unlike the explosions at 1 and 3.
I've heard nothing of a prolonged fire at reactor 2, although that might help explain why so much of the emissions came from that unit.

Has anyone any comment on the NRC video that is the source for these claims? It seems a fairly well produced piece of work but does not appear to have made much splash.

 

[swl]

But I still do not understand what they mean with the diesel generators that are not inundated yet unusable.

Interesting question. I wonder if the transfer switches could have been inundated, thus rendering the generators unusable?

 

[rmattila]

Does anyone have a clue about what happened to the diesel generators in the common pool building first floor (unit 2 DG B and unit 4 DG B) which are marked "unusable" although they are also marked as "not inundated" in table II-2-14 of the second report to IAEA : http://www.meti.go.jp/english/earthquake/nuclear/iaea/pdf/20110911/chapter2.pdf page 72 ? The diesel generators of unit 5 are also both "unusable" and "not inundated", which can mean that only their seawater cooling system was unusable because of damaged seawater pumps. But aren't unit 2 DG B and unit 4 DG B air-cooled ?

This is just a random guess, but e.g. loss of the fuel supply system, starting system (I don't know if it uses compressed air or battery power), or damage to the outgoing power supply system (switchboards, busbars, cables) would make the EDG unusable even if the engine itself would have survived the tsunami.

 

[zapperzero]

Interesting question. I wonder if the transfer switches could have been inundated, thus rendering the generators unusable?

Well if the design is similar to that of units 1-4, the switching boards are in the basements.

 

[tsutsuji]

This is just a random guess, but e.g. loss of the fuel supply system, starting system (I don't know if it uses compressed air or battery power), or damage to the outgoing power supply system (switchboards, busbars, cables) would make the EDG unusable even if the engine itself would have survived the tsunami.

Thanks for the random guess. I was wondering if there was a way to quickly fix those generators, more quickly than waiting for the power trucks to come. Especially after it was understood that "the [power] trucks exceeded the [helicopter] weight capacity, and neither the JASDF nor the American military could perform the airlift and the plan was abandoned" : http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110810e21.pdf page 4.

5. possible failure to properly install, maintain and/or operate safety-critical equipment such as hydrogen recombiners and ICs (TEPCO, NISA)

This Yomiuri article : http://www.yomiuri.co.jp/dy/national/T111215006237.htm suggests that Japan might have been slower and less effective than European nations in implementing lessons from Chernobyl. On the other hand Japan is not as close to Chernobyl as Western Europe, so perhaps the feeling of danger was less, and the public opinion pressure could have been lower.

 

[zapperzero]

4/5/6. This can't be fixed. The only way to REALLY test emergency procedures and equipment is to have a REAL emergency. Anything less (such as drills) can be - and was! - successfully cheated. It (cheating) will happen again.

I am sorry, but no. Air travel industry is the example to hold up here. It IS possible to build a simulator that handles exactly like the real thing. Of course, it's not the real thing but it builds confidence and skills just fine.

Operating manuals for aircraft get amended all the time, and not just based on black-box data. Speaking of which, I cannot understand why NPPs do not have black boxes. I am sure that much more could have been learned from almost-accidents than the NRC's half-page incident reports would let one suppose.

It is relatively easy to mitigate cheating on simulations - introduce the concept of certified operators/crews, have (re-)certifications dependent on both theoretical tests and randomized simulator runs, make it so that anyone person or crew COULD be up for re-cert at any time and that the regulator is responsible for certification, while the plant operators are responsible for ongoing training.

It is not interesting to find out if some jumper can, indeed, go into a 0.5 Sv/h field and operate some stuck vane. It IS interesting to know that an operator would not do stupid things like relying on a jumper to save his plant...

 

[nikkkom]

I am sorry, but no. Air travel industry is the example to hold up here. It IS possible to build a simulator that handles exactly like the real thing. Of course, it's not the real thing but it builds confidence and skills just fine.

While virtual piece of equipment (such as IC) would work fine in simulator, how do you know that REAL one is in working shape? How do you know that plant owner (think "TEPCO") did not fake its inspections? How would you test that in real emergency something unexpected (think "valve 1A closure commanded by bogus pipe rupture sensor trip") would not render it useless?

 

[tsutsuji]

I found the answer to my question concerning the status of D/G 2B and D/G 4B after tsunami in http://www.nisa.meti.go.jp/earthquake/houkoku6/main.pdf (the 9 September report on the impact of the earthquake on Fukushima Daiichi - Japanese only) page 10: "(11) Operation Auxiliary Common Facility (common pool and diesel generators 2B and 4B): the Operation Auxiliary Common Facility's ground floor was inundated through aeration louver(s) or entrance door(s). Inundation was also confirmed in the basement first floor, the inundation route being via the ground floor, or through cable penetrations, etc. In the area where the D/G 2B and 4B equipments are installed, inundation was not confirmed." And page 11: "Unit 2's D/G 2B, unit 4's D/G 4B and unit 6's D/G 6B are air-cooled diesel generators. Because they are not equipped with seawater pumps, there is no damage caused by the tsunami to their cooling systems. D/G 2B and D/G 4B are installed in the Operation Auxiliary Common Facility, which is located at the south-west of unit 4's reactor building. The diesel generator main bodies did not suffer inundation damage, but the electric room in the basement of the Operation Auxiliary Common Facility suffered inundation damage, the diesel generators' power panels were submerged and lost function."

 

[dezzert]

The other day I was watching the following NHK video about manhole covers being ejected　by the tsunami and the new type of covers being designed to remain assembled with the hole even in case of a tsunami : http://www.dailymotion.com/video/xmsci6_3-11-yyyyyyyyyyyy_news

Perhaps this is not off-topic in a nuclear power plant thread as http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110810e21.pdf says "the work was made very difficult due to the darkness, pools of standing water from the tsunami, scattered debris obstructing the roads, missing manhole covers on the roads" (page 5) and "the severe working environment (darkness, scattered obstacles, missing manholes on roads)(...) prevented the work from progressing as expected" (page 44).

Looking a schematics of the tunnels at Fukushima, and comparing this to early overflight photos, the manholes that were blown off were covering electrical and piping ducts that didn't have a path for inundation like the sewage treatment plant shown in the video posted above. How did the tsunami water get into these closed systems and blow the manholes, some of which were many times the size of the average street manhole covers. For me the above is not a plausible explanation.

 

[tsutsuji]

Looking a schematics of the tunnels at Fukushima, and comparing this to early overflight photos, the manholes that were blown off were covering electrical and piping ducts that didn't have a path for inundation like the sewage treatment plant shown in the video posted above. How did the tsunami water get into these closed systems and blow the manholes, some of which were many times the size of the average street manhole covers. For me the above is not a plausible explanation.

You might be correct. http://gendai.ismedia.jp/articles/print/2350 (April 4) quotes a worker, "Mr A", who was in unit 5 and 6 turbine buildings when the earthquake occurred, and then walked back to his company's office in an office building located nearby. He remembers the documents fallen on the floor in the office, and looking through the window, he saw an iron manhole cover that had moved 3 m away from the hole. He waited with other workers in the office "for about one hour" for Tecpo's instructions. When they received "10 m tsunami is coming" warning messages on their mobile phones, as there was no tsunami evacuation plan other than "take refuge in an elevated place distant from the coast", he and a colleague decided to run away by car to the outside of the plant premises (however, there was a traffic jam at the gate). That manhole cover must have been moved by the earthquake.

 

[zapperzero]

While virtual piece of equipment (such as IC) would work fine in simulator, how do you know that REAL one is in working shape? How do you know that plant owner (think "TEPCO") did not fake its inspections? How would you test that in real emergency something unexpected (think "valve 1A closure commanded by bogus pipe rupture sensor trip") would not render it useless?

You test exactly like that. You announce to your trainees: "ICs A and B are not operational". That is, if you want to coddle them. If not, you just stick to manipulating what the instruments show and say nothing, let them figure out by themselves that there are stuck valves, or hydrogen or whatever. Failing is how we all learn.

EDIT: to clarify, simulator training is about the operators, not about the actual system. Which is why in aviation you get sadistic scenarios like "oh btw your rudder just fell off". There is no telling what the actual system might fail like.

 

[nikkkom]

You test exactly like that. You announce to your trainees: "ICs A and B are not operational". That is, if you want to coddle them. If not, you just stick to manipulating what the instruments show and say nothing, let them figure out by themselves that there are stuck valves, or hydrogen or whatever. Failing is how we all learn.

Thanks. I do understand this.

I am splitting F1 lesson regarding IC into three points

(1) There should be plans how to use IC in the total SBO. Looks like on F1 they thought they will always have at least some power.

(2) Not only plans should be made, but operators should be trained to follow them. I agree that it is possible to do this right, as you described

(3) And finally, IC hardware should be in good order and operate according to plan. In F1, it looks like inaccessible valves 1 and 4 inside containment on strings A and B were wrongly closed, and then powered down. No amount of planning and training would help in this situation.

Judging by past performance of TEPCO, I'd say the worry that they wouldn't do point 3 correctly is real.

 

[Most Curious]

Thanks. I do understand this.

I am splitting F1 lesson regarding IC into three points

(1) There should be plans how to use IC in the total SBO. Looks like on F1 they thought they will always have at least some power.

Well, that IS the design basis! DC power reliability is assumed to be even higher than AC. No doubt further examination of that assumption will be made!

(2) Not only plans should be made, but operators should be trained to follow them. I agree that it is possible to do this right, as you described

(3) And finally, IC hardware should be in good order and operate according to plan. In F1, it looks like inaccessible valves 1 and 4 inside containment on strings A and B were wrongly closed, and then powered down. No amount of planning and training would help in this situation.

Judging by past performance of TEPCO, I'd say the worry that they wouldn't do point 3 correctly is real.

It appears the situation with the AC powered valves inside the PCV is still not clearly determined. VERY unlikely they were closed AFTER the tsunami as they are AC powered and AC was gone after the flood. At some point they had been open as evidenced by steam generation in the IC and as shown by less than 100% full water level well after the tsunami. Water would have been boiled away in proper operation and apparently was.

It seems to me that additional information will be required to determine a few critical facts concerning the IC.

 

[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.