Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[rmattila]

Once the fuel reaches melting point, iodine, Cs and noble gases have already been boiled out and what remains, does not migrate as easily. So emission-wise, a re-melt would not constitute a comparable risk to what already occurred, even if it would theoretically be possible (which is not necessarily the case, if the molten material has mixed with sufficient amount of structural materials).

 

[clancy688]

@It is too bad that TEPCO is not removing every rod they can to yet another location so as to minimize the number of "rods" that remain in the pool itself; the fewer rods the slower the remaining rods would tend to boil the volume of water they are in...

Um, we are all talking about removing the fuel from the SFPs, but is this even possible? It's my understanding that most of the fuel there is still "young", generating much radiation and therefore heat. Which's exactly the point why it's somewhere near the reactor - easy transfer.
So if you'd take a "young" fuel element out, you probably have to provide massive shielding and considerable cooling. And then there's the point of safe storage. Where to put those things? They just lost 10 of 17 SFPs (reactors) and 2 of 3 NPPs and as far as I'm informed there is no other storage site for used fuel elements in Japan than on top of or next to the reactors. Putting them into an unused swimming pool wouldn't make us any happier... ;)

 

[tsutsuji]

The latest video on http://www.fairewinds.com/content/tepco-believes-mission-accomplished-regulators-allow-radioactive-dumping-tokyo-bay , about the situation of the plant going into 2012, managed to surprise me, however, when it claimed that an aftershock in Fukushima could knock out the piping installed since the accident (which is easily believable) and would cause another meltdown within 40 hours.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20111013/0500_kunren.html The drill assumed that tanks and pumps had been broken by an earthquake. 40 people installed fire trucks and 300 m of hoses, so that cooling was restored to one reactor in 1 hour 10 minutes. In the future Tepco will perform other drills assuming a tsunami with debris spread on roads, and occurrences at times when gathering people is more difficult, such as on holidays and during the night.

So if they can be as quick as in the drill, the water injection is restored before the 40 hours elapse.

There was another drill during the night on 7 December : http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111208_02-e.pdf

 

[Rive]

@ kaworu1986
The Spent Fuel Rod (SFR) pool MUST be cooled constantly ...

On the early days (as the site was hardly reachable) it was a real problem, but for now they would be able to refill them and maintain a stable water level even if the cooling is lost. The fuel pools would run dry only after a week or so.

The PCVs/RPVs are more of a concern, but as they are at low pressure even pumps of fire trucks would be able to provide enough cooling to prevent really serious problems.

@Clancy688 (Say Hi to smilin' Tom)
Nine months is a long time, with a crash program TEPCO could easily build another "hardened" SPR POOL and start transferring PFR's ASAP into it; even if the transferring was done one at a time with the MOX rods having priority...

To start transferring the fuel rods they would need
- a fully functional and reliable crane system which is able to access the pools with high accuracy and able to lift even full transfer casks: the original crane systems are gone, not reliable or not accessible now
- free access to the pools (U1 pool has the whole roof on its top: U2 pool level is not accessible due the high radiation, U3 pool is a mess, U4 pool is not accessible due the debris of the roof. )

And there are no MOX rods in any of the pools AFAIK. U3 had some MOX rods loaded.

 

[Joffan]

And there are no MOX rods in any of the pools AFAIK. U3 had some MOX rods loaded.

... and even if there were, they wouldn't be significantly different from any other spent fuel rods. There is no magic excessive hazard to MOX rods.

 

[Yamanote]

Many things could go wrong. Does this mean that they will?

When it comes to nuclear engineering, it is quite useful to expect also the unexpected and to be prepared as good as possible, when something goes wrong. At F1 they were not and we can see now the outcome with all the consequences.

Even today - nine months later - there are still many questions unanswered how to cope with an accident, that was obviously beyond imagination. And as there is no book with answers available, they have to go the painful way finding answers on a trial and error basis.

So talking about answers and plans - what could be the plan for a massive water leak in one of the SFP? How to recover, when the water is dropping rapidly? Or is the only solution to pray, that this will never happen?

 

[zapperzero]

So talking about answers and plans - what could be the plan for a massive water leak in one of the SFP? How to recover, when the water is dropping rapidly?

"thinking aloud" here, for lack of time, sorry.

I think first you would put some more water in, using a fire engine or maybe one of those big concrete pumps. Even if you do not succeed in re-filling immediately, spraying the fuel may be enough to keep it cool. Of course, you would have a big problem with radioactivity if the pool actually empties.

Then, you could drop some filler material into the gap, or maybe patch it up from outside. It would be a very bad situation, for sure, but not, I think, unrecoverable.

How this could happen, I am not so sure. Perhaps the seal around the gate failing with age and lack of maintenance? The pools seem to have endured at least one major quake just fine and then explosions above three of them. I don't think they will suddenly crack like eggs. Maybe the steel lining could be corroded away? But that by itself is not enough to cause a major leak. The concrete would have to be eaten away too but this would take months, I believe.

 

[al2207]

In reactor 3 there was quite large explosion some people think of weak nuclear explosion originated from SFP after water was evaporated and rod were melting creating all necessary conditions to dissociate water, have uranium plutonium concentrated at bottom and first hydrogen and OX exploding with shock wave concentrating curium and starting nuclear explosion process .
just curious to have your comments

 

[Pakman]

The Chernobyl operators knew they were receiving large doses and they died without making any difference in the outcome. In any case according to repports I've read they stuck around for only two reasons - to make sure no one was trapped, and to try to see what the could toppass on to the responders. I don't think any mitigation actions were attempted by the operators. That was heroic but futile.

Well, let me tell you about a couple of such an action.
The first instruction was given immediately after the sound of explosion is to cool down the reactor with emergency rate. The next instruction was to start up the emergency cooling system and to open its valves, which was set to local mode before testing, so operator had to go to the valves location. Next instruction was for operators to go to reactor hall to manually insert the control rods.
Since there was no reactor any more, this actions could be called futile. But they didn't know for sure what's happened to reactor and they acted
The staff of the turbine hall also didn't sit without work. The debris of the destroyed #4 reactor building fell through the roof directly to the turbine and to the feedwater pumps. Fires broke out. The main objective for the operators was to save from fire each flammable material in turbine hall.
Operators removed hydrogen from damaged generator to prevent the explosion inside the turbine hall which is also the turbine hall for unit 3.
They drained oil from turbine oil tanks (100 m3 of extremely flammable oil) into the underground storage. They operated manually, since the power cable to drain valve was broken. There two operators had got their lethal doses of radiation, because there was a nuclear fuel fragment near this place outside the building.
They did many other usefull things saving #3 unit from fire. Here’s the difference in outcome.

 

[zapperzero]

Superhot "corium" will find the rebars and eat away through those little molten steel highways. Fuel Pool 4 did apparently crack/leak

It was the skimmer surge tank that leaked for some reason, not the pool. Also, I meant water would "eat" the concrete, not corium, as I don't believe even TEPCO is incompetent enough that they can't keep a damned pool filled with water, given the needed pumps (which are on-site anyway).

 

[tsutsuji]

Cabinet investigation committee interim report translation (part 3)

part 1 : https://www.physicsforums.com/showpost.php?p=3687263&postcount=11983
part 2 : https://www.physicsforums.com/showpost.php?p=3688404&postcount=12005

What follows is mostly a restatement of already mentioned events with some comments and, I am afraid, quite few new details :

http://icanps.go.jp/111226Honbun4Shou.pdf translation of pages 111 (35/170) - 114 (38/170)

e Indication of problem items (concerning the judgement of the IC's operation status and the response to it)

(a) judgement by the shift operators on duty

1) At the point of time after around 15:37 on March 11 when all of unit 1's AC electric power and DC electric power were lost, nobody among the shift operators on duty had an awareness of the problem posed by the possibility that the IC's isolation valves might be closed due to the fail-safe function.

At that time, the shift operators on duty were in an ongoing situation where one cannot determine clearly whether the IC is operating or not, but after around 16:42 on the same day, the reactor water level gauge became available and it was confirmed that the reactor water level was decreasing. Furthermore, after the reactor water level gauge went down scale and became unclear again, the shift operators on duty decided to go inside unit 1's reactor building to check the amount of water in the IC's condenser tank, but they renounced because the radiation dose was high.

Although this sequence of events had taken place, at that time, the shift operators on duty did not come up with the idea to verify the IC's operation status by checking whether steam is released from the IC's exhaust vent on the western wall of unit 1's reactor building. It can be thought that one of the main reasons for this is that the shifts operators on duty had no previous experience of operating unit 1's IC, and had received no training or education enabling them to take countermeasures based on a suitable judgement in real operation conditions.

2) Although the shift operators on duty were not able to think about a suitable method to check the IC's operation status, because the reactor water level was in a decreasing trend, at around 17:30 the possibility that the IC was not operating sufficiently had already entered their mental horizon, and in order to secure alternative water injection means, they started the D/DFP and put it in standby mode.

Furthermore, despite the fact that after the tsunami arrival they had left the three other isolation valves in an open status and were controlling the IC's operation by opening and closing the sole return line isolation valve (MO-3A), at around 18:18 on the same day, as it was confirmed that the green lamps indicating the full closure of not only the return line isolation valve (MO-3A) but also of the feed line isolation valve (MO-2A), were lit (note 34), the shift operators on duty came up with the idea that there was a possibility that the fail-safe function had been operated, and thought that there was a high probability that the other isolation valves on the inner side of the primary containment vessel (MO-1A, 4A) had also been fully closed by the fail-safe function.

Note 34: At that time, the lamps on the control panel indicating the status of the isolation valves on the inner side of the primary containment vessel were extinguished and it was impossible to check their open or closed status.

Also, at that time, at long last, the shift operators on duty came up with the idea to check the IC's operation status by observing the status of the steam released from the IC's exhaust vent, but they only looked beyond unit 1's reactor building, and although one cannot be sure that this was the steam released from the IC's exhaust vent, they did not attempt a direct visual observation.

Anyway, at that time, judging that the quantity of steam released by the IC's exhaust vent is small and thinking that the quantity of water remaining in the IC's condenser tank might have become small, in order to prevent pipe damage, at around 18:25 on the same day, the shift operators on duty decided to fully close the return line isolation valve (MO-3A).

Then, as the IC was not functioning, and as other water injection means could not be used due to the loss of electric power, thinking that there is no other solution than injecting water through the FP line with the D/DFP, at around 18:30 on the same day, in order to enable water injection into the reactor through the FP line, the shift operators on duty started to manually operate the valves.

It can be said that such judgement by the shift operators on duty, though late as it was, was rational as regards its content.

Also, as it can be thought that at around 18:25 on the same day the IC was already almost not functioning, it can be thought that the impact on the reactor status of the decision by the shift operators on duty to shutdown the IC, was low.

3) However, as a result of the difference between the D/DFP output pressure and the reactor pressure, it is physically impossible to perform water injection into the reactor with the D/DFP without depressurizing the reactor by opening the SR valve, and the shift operators on duty were well aware of this.

Then, as it was impossible, as a consequence of the loss of electric power, to remotely open the SR valve from the units 1 and 2 central control room, the shift operators on duty should have clearly indicated the problem concerning the IC's operating status to the power plant response headquarters, and they should have requested their help so that the batteries that are necessary to open the SR valve, as part of the construction of an alternative water injection means, are delivered and connected to the contacts on the rear side of the control panels.

However, at that time, the power plant response headquarters was mistakenly believing that the IC was operating normally, and was not aware that the above mentioned help was needed. Also, no traces whatsoever were found that, from the evening to the night on the same day, batteries had been gathered on the power plant premises for a total amount of 120 V as needed for a depressurizing operation performed with the SR valve.

Hence, it can be thought that, at least, the shift operators on duty did not sufficiently report to the power plant response headquarters the IC's operation status or the necessity to urgently deliver and connect the batteries that are needed to perform the SR valve opening operation.

(b) Reporting of the opening operation of return line isolation valve (MO-3A)

1) It is clear from the hand-written mentions on the memos of the electric power group who was receiving the reports at the power plant response headquarters, that the shift operators on duty reported to the power plant response headquarters the opening operations of the feed line isolation valve (MO-2A) and of the return line isolation valve (MO-3A) at around 18:18 on March 11 and of the return line isolation valve (MO-3A) at around 21:30 on the same day.

However, the closure operation of the return line isolation valve (MO-3A) by the shift operators on duty at around 18:25 on the same day is not mentioned in the hand-written memos of the electric power group of the power plant response headquarters or in any other record. Furthermore, among the members of the electric power group of the power plant response headquarters who were receiving unit 1's reports or among the persons who wrote the above mentioned hand-written memos or among other members of the power plant response headquarters or of the main office response headquarters, nobody testified anything purporting that "I was aware at that time that the return line isolation valve (MO-3A) had been closed". Actually, plant manager Yoshida to begin with, as well as the other members of the power plant response headquarters and of the main office response headquarters, testified purporting that "at that time I thought the IC was under operation".

2) The head of the shift operators on duty at that time testified purporting that "I phoned to the electric power group of the power plant response headquarters by fixed phone, and reported the problem concerning the IC's operation status saying something like "As, when we started the IC, the quantity of generated steam was small, there is a possibility that the quantity of water in the IC's condenser tank is not sufficient, and I wonder if we should not suspect that the IC is not functioning "". However, the head of the shift operators does not remember clearly reporting that the IC had been shutdown by closing the return line isolation valve (MO-3A).

About this, the person at the electric power group of the power plant response headquarters who was receiving the reports about unit 1 testified purporting that "I received a report from the head of the shift operators on duty saying something like "We started the IC, and as the quantity of generated steam is small, there is a possibility that the quantity of water in the condenser tank is small", and at that time, I thought that it was possible to operate the IC. Also, if the quantity of water in the condenser tank is not sufficient, it would be enough to refill the cooling water by using the FP line, and I thought that the shift operators on duty could respond to this sort of problem all by themselves". Actually, according to the head of the shift operators on duty, when the report receiving person received the report about the construction of a line injecting water into the reactor through the FP line and using the D/DFP, his reply suggested that he mistakenly believed that it was a line aimed at refilling the [IC's] condenser tank with cooling water, and no matter how many times the head of the shift operators on duty tried to correct him, it seemed that he did not sufficiently understand.

Under such circumstances, in view of the importance of information, the head of the shift operators on duty should have sufficiently explained so that the misunderstanding of the power plant response headquarters' electric power group's person in charge clears up. It can be thought that the misunderstanding would have been easily cleared up if it had been clearly explained that "As the isolation valve was closed, the IC is shutdown, and it is necessary to inject water into the reactor by using the D/DFP, and we would like the power plant response headquarters to help because we don't have the batteries that must be used to open the SR valve as needed for the depressurization operation". However, the member of the power plant response headquarters' electric power group who was receiving the reports about unit 1 testified that he did not receive the needed clear explanation, and, as a matter of fact, no trace was found at the power plant response headquarters of any concrete preparation for unit 1's alternative water injection at that time.

3) Anyway, the shift operators on duty did not accurately communicate to the power plant response headquarters and to the main office response headquarters the information about the IC's operation status, which was at that time one of the most important informations concerning unit 1, and it is clear that a large awareness gap was generated between the power plant response headquarters and the shift operators on duty, and it is acknowledged that no sufficient mutual understanding took place between the shift operators on duty and the power plant response headquarters.

(c) Judgement by the power plant response headquarters and by the main office response headquarters

(to be continued)

 

[steve olsen]

Do you have any good diagram of the fuel pool, surge tank, and how that connects to the reactor...I have seen some, but they don't really make sense. I never really "got" how they all work together.

I mean the used rods must always be submerged once taken out, or do they do this 100% by remote control with no human within 100 yards.

 

[tsutsuji]

Do you have any good diagram of the fuel pool, surge tank, and how that connects to the reactor...

there is a diagram about the pool, the reactor well and the gate called ""water inflow mechanism through pool gate" on the second report to IAEA on page II-165 : http://www.meti.go.jp/english/earthquake/nuclear/iaea/pdf/20110911/chapter2.pdf

there is diagram about the pool and the surge tank at http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110823_04-e.pdf

 

[Astronuc]

Do you have any good diagram of the fuel pool, surge tank, and how that connects to the reactor...I have seen some, but they don't really make sense. I never really "got" how they all work together.

I mean the used rods must always be submerged once taken out, or do they do this 100% by remote control with no human within 100 yards.

The reactor cavity is flooded to the height of the spent fuel pool, and the gate between the reactor cavity and spent fuel pool is removed. This allows transfer of the fuel from the reactor to the spent fuel pool while the fuel is maintained under water. There is typically a seal ring at the top reactor vessel that keeps the water from flooding lower containment.

http://www.westinghousenuclear.com/Products_&_Services/docs/flysheets/NS-ES-0044.pdf

 

[zapperzero]

Cabinet investigation committee interim report translation (part 3)
(a) judgement by the shift operators on duty

It is rather unclear from this report if the operators were aware or not of the status of the IC themselves. It would appear they were not. Interestingly enough, neither was Yoshida's group, yet the question went unasked and unanswered.

Also, I do not understand the decision-making process involved. Who was in charge?

What was the status of this line, at 18.30? How come the operators did not try to open a vent path, fail and report their failure?

So many questions, still.

 

[tsutsuji]

Also, I do not understand the decision-making process involved. Who was in charge?

Though not providing an answer to your question, even if you don't read Japanese the diagrams on the top of attachment IV http://icanps.go.jp/111226Siryo4.pdf might be helpful:

IV-1 Layout of the emergency response room p. 103 (the red dot on the 発電班 (electric power group) top right table is the "units 1 & 2 hotline")
IV-2 Layout of the headquarters seats p.104 (the red dot at the table is the president seat (I guess it is Yoshida's seat) and on his right the head of units 1,2,3,4 is sitting)
IV-3 Organisation of shift operators on duty (the number of operators in the units 1 & 2 central control room is 1+1+2+1+2+4=11 people). p. 105
IV-4 Layout of units 1 & 2 central control room

 

[Yamanote]

Also, I do not understand the decision-making process involved. Who was in charge?

I suppose that actually confusions, panic and desperation were in charge, after the tsunami knocked out the Fukuichi plant. A natural human reaction.

Considering the circumstances (damage/flooding of a plant with 3+2 reactors and 6 spent fuel pools, loss of power/lighting/control room equipment/communication facilities, very limited time to respond and to take the right actions), there might have been only a small chance to save the plant. But taking this small chance would have required a perfect emergency preparedness. The operators were not well prepared and also out of luck, so they failed.

I would like to turn back the time to that black day last March, in order to take the right actions to save the plant and the day. But in this case there is no second chance and we can only look ahead and try to learn and make things better in the future.

 

[zapperzero]

I would like to turn back the time to that black day last March, in order to take the right actions to save the plant and the day.

It is not clear that anything COULD have saved the plant on that day. This report does not convince me of the contrary so far, anyway.

 

[zapperzero]

Though not providing an answer to your question, even if you don't read Japanese the diagrams on the top of attachment IV http://icanps.go.jp/111226Siryo4.pdf might be helpful:

IV-1 Layout of the emergency response room p. 103 (the red dot on the 発電班 (electric power group) top right table is the "units 1 & 2 hotline")
IV-2 Layout of the headquarters seats p.104 (the red dot at the table is the president seat (I guess it is Yoshida's seat) and on his right the head of units 1,2,3,4 is sitting)
IV-3 Organisation of shift operators on duty (the number of operators in the units 1 & 2 central control room is 1+1+2+1+2+4=11 people). p. 105
IV-4 Layout of units 1 & 2 central control room

Thank you. Would people actually remain seated in such a situation? I mean, the people in the meeting room, not the operators.

 

[tsutsuji]

Cabinet investigation committee interim report translation (part 4)

part 1 : https://www.physicsforums.com/showpost.php?p=3687263&postcount=11983
part 2 : https://www.physicsforums.com/showpost.php?p=3688404&postcount=12005
part 3 : https://www.physicsforums.com/showpost.php?p=3696394&postcount=12082
( A full official translation will be available some day at http://icanps.go.jp/eng/interim-report.html )http://icanps.go.jp/111226Honbun4Shou.pdf translation of pages 114 (38/170) - 119 (43/170)

(c) Judgement by the power plant response headquarters and by the main office response headquarters

1) While from their location they could not measure the parameters that are needed to control unit 1 such as reactor pressure and reactor water level, while performing various controlling operations toward cold shutdown in a bad environment, without lighting, etc., as mentioned below, the shift operators on duty basically reported to the power plant response headquarters the important information pertaining the judgement of the IC's operation status, except the fact that the return line isolation valve (MO-3A) had been closed at around 18:25 on March 11.

2) Knowing that when electric power is lost, the IC's fail-safe function is activated and the four isolation valves installed on the pipes are closed is a basic knowledge concerning the design and the function of the IC, an equipment fulfilling an emergency cooling function.

During their hearing by this investigation committee, many Tokyo Electric related people said something like: "The IC is something special installed on unit 1 only", and while explaining at great length the specificity of the IC, when this investigation committee asked: "When electric power is lost and it becomes impossible to perform the necessary operations, are the isolation valves closed as a result of the activation of the primary containment vessel's containment function, or are they kept open?", all of them answered the same way: "I think they are closed". In other words, it can be thought that, let alone the specificity of the IC and of unit 1, if they had had a basic knowledge about the containment function, they would have easily become aware of the possibility that the IC's isolation valves are closed during a loss of electric power, even if they did not know the details about the pipe rupture detection circuit and the fail-safe function.

It is therefore recognized that - as the full loss of electric power occurred at around 15:37 on March 11, and as it became known that unit 1's DC power had also been fully lost - at least at that point of time, both at the power plant response headquarters and at the main office response headquarters, there were sufficient opportunities to develop an awareness of the problem regarding the possibility that the IC's four isolation valves were closed and the IC was not functioning.

In reality, however, among the power plant response headquarters or the main office response headquarters, not even a single person did develop a questioning attitude and point out the problem. Furthermore, no trace has been found that the preparation for reactor depressurization and alternative water injection was started, and instead, even at around 21:00 on the same day, they were still mistakenly believing that the IC was under operation.

3) Next point: the power plant response headquarters received reports from the shift operators on duty concerning the fact that during the lapse of time from 16:42 to 16:56 on the same day when unit 1's water level (wide band) was measurable, the reactor water level was displaying a decreasing trend, concerning the fact that the water level went down scale and became unavailable, or concerning the fact that at around 17:50 on the same day, they could not check the IC's condenser tank water level because the radiation dose in the vicinity of unit 1's reactor building was high. Furthermore, at a point of time around 17:15 on the same day, the power plant response headquarters' technical group had already predicted, based on unit 1's water level's declining trend, that TAF would be reached within one hour.

Then, the main office response headquarters was sharing these informations via the teleconferencing system.

If they had accurately evaluated these informations, the power plant response headquarters and the main office response headquarters should have become aware that the IC was clearly not operating normally. If the IC had been operating in a suitable manner, the cooling function should have been fulfilled for at least 6 hours, that is until around 21:30 on the same day and it can be thought that probably, by observing the symptoms from the 16:00 - 17:00 hour to the 17:00 - 18:00 hour, they could have easily realized that the IC was not functioning normally and could not be expected to perform the cooling function. However, while recognizing those symptoms, they were still relying on the IC for water injection, and they did not immediately start to prepare reactor depressurization and alternative water injection. It cannot be thought that this was an appropriate judgement of the situation.

4) Normally, Fukushima Daiichi's unit 1's IC is started, controlled and shut down by operating - among the four isolation valves - only the return line operation valve (MO-3A) which is located on the outer side of the primary containment vessel, and the three other valves are maintained open, without performing opening or closure operations. It is hard to believe that, among the power plant response headquarters or the main office response headquarters who are in a position to assist the shift operators on duty, not even a single person knew about this. Under the hypothesis that it is so, we have to say that this fact alone is a problem, and that a radical reform of education and training is indispensable.

Then, at least the fact that at around 18:18 the shift operators on duty had opened not only the return line isolation valve (MO-3A) but also the feed line isolation valve (MO-2A) was reported by them to the power plant response headquarters.

Hence, upon receiving this report, the power plant response headquarters should have realized that at least until that time, the feed line isolation valve (MO-2A) and the return line isolation valve (MO-3A) were closed, and that the IC was shut down. Then, although fuel exposure and fuel damage, depending on how long the IC was shut down, must be suspected, instead of duly checking with the shift operators on duty how long the IC had been shut down, the power plant response headquarters did not become aware of this issue and did not check anything.

Furthermore, if at a point of time around 18:18 on the same day the power plant response headquarters had known the basic facts about the normal operations of the IC's isolation valves and the fail safe function, they would have noticed that the shift operators on duty had opened the normally open feed line isolation valve (MO-2A) because it was closed. Furthermore, it should have been easy to realize that there was a possibility that that valve had been closed by the fail-safe function. Then, it is thought that if they had realized these basic facts, they would have questioned whether the isolation valves on the inner side of the primary containment vessel (MO-1A, 4A) (note 35) had been fully or nearly fully closed the same way as the feed line isolation valve (MO-2A) as the closure signal was emitted by the fail-safe function as a consequence of the earthquake and tsunami. As a matter of fact, the shift operators on duty were questioning what was happening and taking countermeasures on location.

Note 35 :the isolation valves on the inner side of the primary containment vessel cannot be manually operated when electric power is lost, and in order to open them, there was no other solution to open them than performing a remote controlled operation from the control panel depending on a recovery of electric power

About this, the same can be said about the main office response headquarters who was grasping the same informations through the conferencing system.

Notwithstanding the above, the power plant response headquarters and the main office response headquarters were not aware of the problems and did not study the IC's operation status, and did not provide necessary assistance or give instructions to the shift operators on duty about the following :

a) about why the normally open valves were in closed status;
b) about the possibility that, as a consequence of the earthquake and tsunami, the closure signal could have been emitted by the fail-safe function, and the isolation valves on the inner side of the primary containment vessel (MO-1A, 4A) could be closed too;
c) about the possibility that under such conditions the IC's cooling function is not sufficiently fulfilled and alternative water injection means have to be implemented soon.

Furthermore, at around 21:19 on the same day, the power plant response headquarters and the main office response headquarters received a report saying that unit 1's water level was TAF + 200 mm, and based on the fact that the water level was in the TAF + something domain, they still mistakenly believed that the IC was functioning. However, as unit 1 had undergone a total loss of AC power at around 15:37 on the same day and at about the same time a total loss of DC power too, and while more than 5 and a half hours had already elapsed, the IC had fallen into a situation of near loss of function, adding to the fact that no alternative water injection was being performed, so that it is difficult to believe that the water level was in the TAF + something domain, and the value indicated by the reactor water level gauge should not have been blindly trusted. Then, although the reactor water level gauge was indicating TAF + 200 mm, if the power plant response headquarters and the main office response headquarters had accurately understood the action of the fail-safe function and the open or closed status of the IC's isolation valves, and if they had accurately evaluated the informations about the reactor water level decline between 16:42 and 16:56 on the same day, after which the water level gauge went down scale, and about the high radiation dose in the vicinity of unit 1's reactor building at around 17:50 on the same day, they would not have been misguided by the reactor water level gauge's indicated value and they would not have mistakenly believed that the IC was under operation.

5) At around 18:25 on 11 March, when the shift operators on duty closed the IC's return line isolation valve (MO-3A), the power plant response headquarters, far from receiving no report at all concerning the IC, received a report from the operators saying that the quantity of steam generated when the IC was started was small, and that they were considering the IC's operation status as a problem.

In that case, let alone the question whether the real reason why the IC was not sufficiently functioning was that the condenser tank was running out of water, it can be said that the power plant response headquarters naturally recognized at that time that there was a possibility that there was some functional problem affecting the IC.

Even under the hypothesis that they did not receive a clear report of the closure of the IC's return line isolation valve (MO-3A) at around 18:25 on the same day, if there was no report from the shift operators on duty about the IC status after that, instead of leaving the issue, they should have requested a sufficient report from the shift operators on duty.

If they had requested such a report from the shift operators on duty, the power plant response headquarters could have accurately and early grasped the fact of the closure of the return line isolation valve (MO-3A) at around 18:25 on the same day.

In reality, however, until they received the report about the opening of the return line isolation valve (MO-3A) at around 21:30 on the same day, the power plant response headquarters did not sufficiently check with the shift operators on duty the IC's operation status including that valve's open or closed status, and they believed that the IC was running.

6) At around 21:30 on the same day, the shift operators on duty reported to the power plant response headquarters the fact that they had opened the return line isolation valve (MO-3A).

Even if we closely investigate Tokyo Electric's internal records, we conclude that the power plant response headquarters received no report whatsoever about the return line isolation valve (MO-3A) during the more than 3 hours between the reception of the report about the opening operation at around 18:18 on the same day and 21:30 on the same day.

In that case, after receiving the report from the shift operators on duty saying that they had opened the return line isolation valve (MO-3A), as it means that they are suddenly opening the valve again after more than 3 hours have elapsed, the power plant response headquarters should have questioned the following:

a) when did return line isolation valve (MO-3A) become closed ?
b) wasn't the IC under operation ?

and they should have been able to check this with the shift operators on duty. However, they did not develop such questions and they did not inquire with the shift operators on duty who were in the units 1 and 2 central control room.

7) As a result of the above, even if they did not clearly grasp the information about the fact that the return line isolation valve (MO-3A) had been closed at around 18:25 on the same day, it is recognized that if they had appropriately evaluated the important information mentioned above from 2) to 6), the power plant response headquarters and the main office response headquarters at least would have had sufficient opportunities to develop questions about the IC's operation status.

(d) The expected role of the power plant response headquarters and of the main office response headquarters

(to be continued)

 

[zapperzero]

Cabinet investigation committee interim report translation (part 4)

part 1 : https://www.physicsforums.com/showpost.php?p=3687263&postcount=11983
part 2 : https://www.physicsforums.com/showpost.php?p=3688404&postcount=12005
part 3 : https://www.physicsforums.com/showpost.php?p=3696394&postcount=12082
( A full official translation will be available some day at http://icanps.go.jp/eng/interim-report.html )


http://icanps.go.jp/111226Honbun4Shou.pdf translation of pages 114 (38/170) - 119 (43/170)

(c) Judgement by the power plant response headquarters and by the main office response headquarters

3) Next point: the power plant response headquarters received reports from the shift operators on duty concerning the fact that during the lapse of time from 16:42 to 16:56 on the same day when unit 1's water level (wide band) was measurable, the reactor water level was displaying a decreasing trend, concerning the fact that the water level went down scale and became unavailable, or concerning the fact that at around 17:50 on the same day, they could not check the IC's condenser tank water level because the radiation dose in the vicinity of unit 1's reactor building was high. Furthermore, at a point of time around 17:15 on the same day, the power plant response headquarters' technical group had already predicted, based on unit 1's water level's declining trend, that TAF would be reached within one hour.

[...]

Furthermore, at around 21:19 on the same day, the power plant response headquarters and the main office response headquarters received a report saying that unit 1's water level was TAF + 200 mm, and based on the fact that the water level was in the TAF + something domain, they still mistakenly believed that the IC was functioning. However, as unit 1 had undergone a total loss of AC power at around 15:37 on the same day and at about the same time a total loss of DC power too, and while more than 5 and a half hours had already elapsed, the IC had fallen into a situation of near loss of function, adding to the fact that no alternative water injection was being performed, so that it is difficult to believe that the water level was in the TAF + something domain, and the value indicated by the reactor water level gauge should not have been blindly trusted. Then, although the reactor water level gauge was indicating TAF + 200 mm, if the power plant response headquarters and the main office response headquarters had accurately understood the action of the fail-safe function and the open or closed status of the IC's isolation valves, and if they had accurately evaluated the informations about the reactor water level decline between 16:42 and 16:56 on the same day, after which the water level gauge went down scale, and about the high radiation dose in the vicinity of unit 1's reactor building at around 17:50 on the same day, they would not have been misguided by the reactor water level gauge's indicated value and they would not have mistakenly believed that the IC was under operation.

I take this to mean that the commission believes water level was not TAF+200 at 21:19.

There is an apparent contradiction here, too. If power plant response headquarters thought at 17:15 that TAF would be reached at 18:15, does this not already mean that they assumed loss of cooling function?

On an unrelated note, two levels of operational management dealing with one crisis from different locations seems... a bit dysfunctional.

 

[nikkkom]

It is not clear that anything COULD have saved the plant on that day.

ICs were capable to cool Unit 1 reactor for about six hours. In fact, they were *more than capable* - apparently, they were doing it too well, scaring operators into worrying that they cool it too quickly.

Six hours might have been enough to organize pumping of replacement water into boiling shell side of ICs. This could render Unit 1 essentially stable.

And without having Unit 1 explode in their faces, operators could do a much better job dealing with Units 2 and 3.

 

[tsutsuji]

Thank you. Would people actually remain seated in such a situation? I mean, the people in the meeting room, not the operators.

As they are using a teleconferencing system, they probably have to remain in the field of view of the camera.

 

[matthewdb]

What's the purpose of that "fail-safe" function?

The IC is under reactor pressure all the time. If the exchanger or any associated piping were to spring a leak the only thing to stop the flow of reactor steam would be the isolation valves.

The inside set of valves is only closed in case of a leak. There is a mass balance calculator that is measuring steam out and water in. If there is a mass imbalance, then the internal isolation valves are commanded shut.

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.

If power was lost in the order of AC gone and then DC then the valves would remain open. On a power loss the valves remain where they were. The only way for the valves to close is if the close command was issued prior to AC power loss.

I would speculate that the designers of the system never considered the loss of DC power with AC still supplied and / or the gradual collapse of the DC voltage resulted in a malfunction.

This is a very serious issue for ALL BWR plants. The IC was replaced by RCIC (reactor core isolation cooling, a small steam turbine driven pump). RCIC supply pipes have the same possibility of a leak so they are also fitted with the same type of isolation system, hence RCIC could fail just the same way. In addition, BWR2 though BWR4 have HPCI, a large steam driven pump used to backup RCIC and fill the RPV in the case of a large leak. It too has this type of isolation system.

 

[NUCENG]

Well, let me tell you about a couple of such an action.
The first instruction was given immediately after the sound of explosion is to cool down the reactor with emergency rate. The next instruction was to start up the emergency cooling system and to open its valves, which was set to local mode before testing, so operator had to go to the valves location. Next instruction was for operators to go to reactor hall to manually insert the control rods.
Since there was no reactor any more, this actions could be called futile. But they didn't know for sure what's happened to reactor and they acted
The staff of the turbine hall also didn't sit without work. The debris of the destroyed #4 reactor building fell through the roof directly to the turbine and to the feedwater pumps. Fires broke out. The main objective for the operators was to save from fire each flammable material in turbine hall.
Operators removed hydrogen from damaged generator to prevent the explosion inside the turbine hall which is also the turbine hall for unit 3.
They drained oil from turbine oil tanks (100 m3 of extremely flammable oil) into the underground storage. They operated manually, since the power cable to drain valve was broken. There two operators had got their lethal doses of radiation, because there was a nuclear fuel fragment near this place outside the building.
They did many other usefull things saving #3 unit from fire. Here’s the difference in outcome.

Thank you for the information. One of the big problems at TMI2 in the early hours was that there were too many people in the control room. It must be a characteristic of nuclear operators to try to stick around and do what they can even if it fails. I believe that is corage.

 

[NUCENG]

In reactor 3 there was quite large explosion some people think of weak nuclear explosion originated from SFP after water was evaporated and rod were melting creating all necessary conditions to dissociate water, have uranium plutonium concentrated at bottom and first hydrogen and OX exploding with shock wave concentrating curium and starting nuclear explosion process .
just curious to have your comments

that is highly speculative and may be part of the reason the mentors pulled the Unit 3 Explosion thread. There is no evidence of a nuclear explosion.

 

[rmattila]

I updated the plot on the reported Cs activities of the water accumulated in the CW and HTI basements.

For some reason, the Cs content in the water at the centralized water treatment building basement appears to have increased between Nov 29 and Dec 20, and was somewhat higher than that measured in the RB/TB basements around mid-December,

NOTE: for keeping the table simple, I plotted the latest figures for both the CW and HTI at Dec 29, even though the first one was reportedly measured on Dec 20.

 

[zapperzero]

ICs were capable to cool Unit 1 reactor for about six hours. In fact, they were *more than capable* - apparently, they were doing it too well, scaring operators into worrying that they cool it too quickly.

Six hours might have been enough to organize pumping of replacement water into boiling shell side of ICs. This could render Unit 1 essentially stable.

And without having Unit 1 explode in their faces, operators could do a much better job dealing with Units 2 and 3.

The famous MO-3A valve was only closed for about four hours, starting at 18:18. The reason given in the committee report is that the operators did this because they thought cooling water in the IC had been exhausted or almost exhausted and the water tank was inaccessible due to high radiation field. Surely there would have been an attempt to replace that water, had it been found possible?

Instead, the operators decided to attempt spraying the core through the fire lines.

That is, if i am reading this convoluted narrative right.

 

[tsutsuji]

I have received a private message from a from a journalist from The Economist, who said he mentioned Physics Forums in his article, and gave a link: http://www.economist.com/node/21542437 . He also said he wants to interview me, but I replied he'd have more valuable answers if he interviews someone with experience in nuclear engineering such as the people marked with "Recognitions:Science Advisor".

The inside set of valves is only closed in case of a leak. There is a mass balance calculator that is measuring steam out and water in. If there is a mass imbalance, then the internal isolation valves are commanded shut.

The investigation committee provides diagram IV-10 http://icanps.go.jp/111226Siryo4.pdf page 114 (12/52) showing an elbow differencial pressure flowmeter.

This is a very serious issue for ALL BWR plants. The IC was replaced by RCIC (reactor core isolation cooling, a small steam turbine driven pump). RCIC supply pipes have the same possibility of a leak so they are also fitted with the same type of isolation system, hence RCIC could fail just the same way. In addition, BWR2 though BWR4 have HPCI, a large steam driven pump used to backup RCIC and fill the RPV in the case of a large leak. It too has this type of isolation system.

By the way do you know why the same problem didn't happen with Fukushima Daiichi unit 2's RCIC or HPCI ?

 

[zapperzero]

I have received a private message from a from a journalist from The Economist, who said he mentioned Physics Forums in his article, and gave a link: http://www.economist.com/node/21542437 . He also said he wants to interview me, but I replied he'd have more valuable answers if he interviews someone with experience in nuclear engineering such as the people marked with "Recognitions:Science Advisor".

check your private messages

 

[jim hardy]

ZZ:

""Operators placed the A IC back in service at about 2130 (T plus 6.7 hours), when once
again the indications began to work. By this point, no cooling or injection had been
provided to the reactor for almost 6 hours, and core damage was most likely occurring.
While steam was observed coming from the condenser vent, it is not clear that the IC
went into service as expected. Inspections performed in September 2011 revealed that
the A IC valves did open but the water level in the secondary side remained at 65 percent,
indicating that the system may not have functioned as designed. ""

i'd guess, repeat guess, they suspected it was gas-bound ...
now that'd be a pickle - high pressure in vessel, no natural circulation, and only low pressure fire pumps to inject water

pretty good narrative here pages 12 to 37.http://www.power-eng.com/content/dam/pe/online-articles/documents/2011/november/fukushima report.pdf above from p15

 

[clancy688]

The reason given in the committee report is that the operators did this because they thought cooling water in the IC had been exhausted or almost exhausted and the water tank was inaccessible due to high radiation field.

Uh, wait a moment. Why was the water tank inaccessible? Isn't it on the shell side, outside the primary containment? Why is there radiation so early into the accident?

I always thought that the operator who tried to check the valves and came back because of radiation wanted to enter the primary containment.

 

[zapperzero]

Uh, wait a moment. Why was the water tank inaccessible? Isn't it on the shell side, outside the primary containment? Why is there radiation so early into the accident?

It says so right in the report:

they could not check the IC's condenser tank water level because the radiation dose in the vicinity of unit 1's reactor building was high

and in another place:

the shift operators on duty decided to go inside unit 1's reactor building to check the amount of water in the IC's condenser tank, but they renounced because the radiation dose was high.

Note it says "reactor building" not "containment". It struck me as very odd, too.

Seems to lend credence to the idea that some damage to piping took place very early on. I doubt fuel uncovery alone could increase doses as much, but then, what do I know?

Elsewhere in the report, there is an odd passage about checking the status of the IC by observing the steam that came out.

Also, at that time, at long last, the shift operators on duty came up with the idea to check the IC's operation status by observing the status of the steam released from the IC's exhaust vent, but they only looked beyond unit 1's reactor building, and although one cannot be sure that this was the steam released from the IC's exhaust vent, they did not attempt a direct visual observation.

In my mind's eye, this plays out as operators peeking beyond a corner and seeing a wisp of steam, too concerned by what the dosimeter was showing to actually walk up to those pipes. I dunno... maybe I watched too much Hollywood.

 

[zapperzero]

ZZ:

""Operators placed the A IC back in service at about 2130 (T plus 6.7 hours), when once
again the indications began to work. By this point, no cooling or injection had been
provided to the reactor for almost 6 hours, and core damage was most likely occurring.
While steam was observed coming from the condenser vent, it is not clear that the IC
went into service as expected. Inspections performed in September 2011 revealed that
the A IC valves did open but the water level in the secondary side remained at 65 percent,
indicating that the system may not have functioned as designed. ""

i'd guess, repeat guess, they suspected it was gas-bound ...
now that'd be a pickle - high pressure in vessel, no natural circulation, and only low pressure fire pumps to inject water

pretty good narrative here pages 12 to 37.http://www.power-eng.com/content/dam/pe/online-articles/documents/2011/november/fukushima report.pdf above from p15

The timelines do not coincide between the two reports. Neither do the conclusions. I do not know what to think.

As regards the pickle, maybe the "right" answer would have been to vent (ideally through SC) into atmosphere, pump water through fire line, rinse, repeat.

 

[tsutsuji]

pretty good narrative here pages 12 to 37.
http://www.power-eng.com/content/dam/pe/online-articles/documents/2011/november/fukushima report.pdf

Thanks for the link. I think these narratives are really clear and easy to read.

Looking at "Figure 7.4-1 Isolation Condensers on Unit 1" on page 54 (58/104), it seems that the water condensed in the IC has to run through the RR pump (B) to go back to the RPV. Is it really so ? Would that mean that the IC cannot operate if the RR pump (B) is not running ? And I don't see how it could when all AC or DC power is lost.

 

[rmattila]

Looking at "Figure 7.4-1 Isolation Condensers on Unit 1" on page 54 (58/104), it seems that the water condensed in the IC has to run through the RR pump (B) to go back to the RPV. Is it really so ? Would that mean that the IC cannot operate if the RR pump (B) is not running ? And I don't see how it could when all AC or DC power is lost.

The water can flow backwards through the recirculation loop into the reactor.

 

[jim hardy]

Thanks for the link. I think these narratives are really clear and easy to read.

Looking at "Figure 7.4-1 Isolation Condensers on Unit 1" on page 54 (58/104), it seems that the water condensed in the IC has to run through the RR pump (B) to go back to the RPV. Is it really so ? Would that mean that the IC cannot operate if the RR pump (B) is not running ? And I don't see how it could when all AC or DC power is lost.

well we need a BWR guy to say for sure. i am a PWR guy..
here's how i was thinking -

If the pipes are arranged physically so that steam could rise into IC , condense and run back downhill as water into the vessel,
perhaps through RR pump suction line

then the IC could move a respectable amount of heat by that mechanism.
that'd be a mighty nice feature to design in.
i assumed since they were valving it in and out that they were using natural circulation
and it quit working after hydrogen largely filled the system.
but i don't know BWR systems at all well enough to assert that as a fact.

if you ever lived in an old house with steam heat you know about having to vent the radiators when they become air-bound.

so above made sense to me. but I'm no BWR expert.EDIT thanks Rmatilla, while i was typing

 

[Pakman]

Well, I could be a BWR guy. After all, RBMK is some kind of a boiling water reactor, isn't it?

it seems that the water condensed in the IC has to run through the RR pump (B) to go back to the RPV. Is it really so ?

Not nesessary. In fact, IC operates only under reactor isolation condition. RP aren't running in this case. The IC condencate flaws through RP's suction pipe in backward direction towards the reactor vessel. There's no check valve on RP's suction pipe.

Would that mean that the IC cannot operate if the RR pump (B) is not running?

Actually, slight flow can run thruogh the pump's impeller even if the pump is stopped.

 

[tsutsuji]

The water can flow backwards through the recirculation loop into the reactor.

There's no check valve on RP's suction pipe.

Actually, slight flow can run thruogh the pump's impeller even if the pump is stopped.

Thanks. I was unsure how to interpret the arrows on the diagram.

 

[tsutsuji]

Cabinet investigation committee interim report translation (part 5) [IV 3 (1) e (d)]

part 1 : https://www.physicsforums.com/showpost.php?p=3687263&postcount=11983 [IV 3 (1) b]
part 2 : https://www.physicsforums.com/showpost.php?p=3688404&postcount=12005 [IV 3 (1) b - IV 3 (1) c - IV 3 (1) d]
part 3 : https://www.physicsforums.com/showpost.php?p=3696394&postcount=12082 [IV 3 (1) e (a) - IV 3 (1) e (b)]
part 4 : https://www.physicsforums.com/showpost.php?p=3697961&postcount=12085 [IV 3 (1) e (c)]
( A full official translation will be available some day at http://icanps.go.jp/eng/interim-report.html )

This will be the last part of IV 3 (1):

IV Accident response at Tokyo Electric Power Company Fukushima Daiichi nuclear power plant
...3 Situation and response from the notification of special event occurrence pursuant of nuclear disaster law article 15 paragraph 1 to the explosion of unit 1's reactor building (from around 17:12 March 11 to around 15:36 the 12th of the same month)
...(1) Operation status of unit 1's IC and judgements about it

As I started translating on page 103 with IV 3 (1) b , for the time being IV 3 (1) a (pages 98-102), remains untranslated.

http://icanps.go.jp/111226Honbun4Shou.pdf translation of pages 119 (43/170) - 121 (45/170)

(d) The expected role of the power plant response headquarters and of the main office response headquarters

1) Tokyo Electric's own "Report on Preparation for Accident Management" notes that "Against more complex events, the degree of importance of the technical assessment pertaining to grasping the accident situation and to choosing accident management measures, is high, and a variety of information is needed. For that reason, the assistance organization performs such technical assessment and assists decision making."

At that time, plenty of information was coming about the situations of units 1 to 6, and the power plant response headquarters (the assistance organization is composed of some of the functional groups such as the electric power group, the recovery group, etc.) had to respond to them, but if we think about the role of the assistance organization, we cannot agree that the mistaken assumptions concerning the most fundamental and important information that is the one concerning unit 1's IC's operation status, are admissible for the reason that the assistance organization was in such a severe situation.

First, that a plurality of information comes as an intricate mass is the name of the game under an emergency situation, and based on the circumstances of the moment, one has to appropriately assess and choose which is the important information.

As regards unit 1, in the situation, immediately after the tsunami arrival, where almost none of the plant parameters could be measured, the information about the operation status of the IC, the unique equipment expected to fulfil the cooling function, qualified as fundamental and most important information pertaining to the study of response measures toward cold shutdown. If that information is overlooked, it is clear that the response is forestalled and it can even be feared that it leads to an irreversible mistaken response.

The power plant response headquarters worked out each response based on its division into 12 functional groups such as the electric power group, the recovery group, the technical group and the safety group (note 36), themselves dividing the roles into a units 1 and 2 response subgroup, and a units 3 and 4 response subgroup inside each functional group. Even if plenty of information arrived at the power plant response headquarters concerning units 1 to 6, the organization was prepared so that the whole information does not have to be digested by a single person, and so that, instead, each person in charge in each functional group sorts information in accordance with his role and in function of its importance, so that the necessary response measures can be worked out based on relevant information.

Note 36: In the disaster prevention organization, the firefighting group (self defense fire brigade) belongs to the recovery group, so it is not included into the 12 functional groups.

Hence, we have to say that it is largely possible and necessary that the power plant response headquarters assesses the IC's operation status based on the information about the IC's operation status provided by the shift operators on duty, and that otherwise if such information is not provided, it is also largely possible and necessary to actively get in touch with the shift operators on duty and collect such information. As part of the accident management policy, as an assistance organization, the power plant response headquarters' information group, technical group, safety group, recovery group and electric power group must advise and give instructions to the head of the shift operators on duty, as well as provide technical assessments for such purposes, etc. and it can be thought that it was necessary for these groups to sufficiently grasp the necessary information as a precondition.

2) Moreover, at the main office response headquarters too, functional groups are organised, whose basic task is to respond to the power plant response headquarters. Grasping important information via the teleconferencing system in accordance with each role, each group in charge was expected to assist the power plant response headquarters by evaluating this information from a calmer point of view, as they are located at a greater distance from the accident than the power plant response headquarters who is under the pressure of the response tasks. This way, it can be thought that in order to provide sufficient assistance in a timely manner, it was largely possible to provide appropriate advice to the power plant response headquarters, by striving to grasp information about the IC's operation status, by evaluating the IC's operation status without letting information go in at one ear and out at the other when it comes, or if it does not come, by collecting information.

3) However, it cannot be thought that the power plant response headquarters and the main office response headquarters judged the IC's operation status by appropriately sorting and assessing information.

About this, plant manager Yoshida testified purporting that: "Encountering a situation that had never been thought until then, under the pressure of the informations that arrived one after another, there was no more margin left to judge globally in a rational manner the links between important pieces of information among those that had been coming in sequentially until then".

It can be thought that it was very difficult to appropriately sort and assess the information necessary for the control of each plant unit from the mass of intricate information, while the SPDS is not functioning, for people who until then had been educated and trained only on the basis of the prerequisite that the information pertaining to the status of every plant unit can be quickly retrieved via the SPDS, and who are facing a situation where several plant units suffer a simultaneous total loss of electric power due to an extremely severe natural disaster. Also, even if at that time there were inappropriate things in the assessment and sorting of important information, it does not mean that the people who responded to the real events were lacking enthusiasm and energy. Still, even if everyone devoted all his energy, in retrospect, the above problem items are being discovered and we think that they must be pointed out as problem items.

Finally, there is no alternative but to say that no sufficient education and training had been done in prevision of a situation where several plant units suffer a simultaneous total loss of electric power due to an extremely severe natural disaster. For that reason, it can be thought that, unable to accurately sort and evaluate important information, the power plant response headquarters and the main office response headquarters consequently could not obtain an appropriate judgement about the IC's operation status, and it can be thought that such training and education is extremely important.

(2) situation of the preparation for alternative water injection into unit 1 and unit 2's reactors
a Plant manager Yoshida's alternative water injection instruction
(to be continued)

 

[NUCENG]

It says so right in the report:

and in another place:


Note it says "reactor building" not "containment". It struck me as very odd, too.

Seems to lend credence to the idea that some damage to piping took place very early on. I doubt fuel uncovery alone could increase doses as much, but then, what do I know?

Elsewhere in the report, there is an odd passage about checking the status of the IC by observing the steam that came out.



In my mind's eye, this plays out as operators peeking beyond a corner and seeing a wisp of steam, too concerned by what the dosimeter was showing to actually walk up to those pipes. I dunno... maybe I watched too much Hollywood.

The IC condensers are in the reactor building outside of primary containment (Drywell) The tubes inside the ICs contain steam from the RPV, condensing and returning to the RPV driven by natural circulation. After the operators stopped IC operation and fuel damage occured, the first thing released was the so-called "gap release source term" nobel gases and other volatiles that escaped from fuel pellets and collected in the gap inside a fuel rod. As damage progressed massive amounts of hydrogen and further gas releases from fuel pellets gave more non-condensible releases into the RPV. Those non-condensible raqdioisotopes would have been in the steam in the pipes to the ICs. In addition, pressure rose inside the containment, leakage would have released more radiation into secondary containment. (Remember, pressure was more that twice the design limit for containment.)

The indications on the instruments for the IC before the tsunami hit showed that the IC was working until it was turned off. Based on that and the explanation of the radiation above I don't see a need to assume IC damage occurred during the earthquake.

 

[clancy688]

But the operator checked sometime before 1800. zapperzero said here that the valve was closed at 1818. According to the TEPCO analysis, fuel didn't get uncovered before 1800.
The timing doesn't fit. Why a gap release when the core is still covered?

concerning the fact that at around 17:50 on the same day, they could not check the IC's condenser tank water level because the radiation dose in the vicinity of unit 1's reactor building was high.

 

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20120107/0500_osensui.html 140 tons of low contaminated water (most likely rain water) were found in a different tunnel. This tunnel is not connected to the sea. Tepco has a plan to check about 100 locations among the underground tunnels that connect to the waste treatment facility buildings where the high contaminated water is stored.

But the operator checked sometime before 1800. zapperzero said here that the valve was closed at 1818. According to the TEPCO analysis, fuel didn't get uncovered before 1800.
The timing doesn't fit. Why a gap release when the core is still covered?

I think the valve was closed at 18:25. And Tepco's simulation said fuel uncovering started at 17:46 :

From your text, we can place this detection at somewhere between 17:19 and 17:50.
So we can suppose containment breach? Is it coincidence that the simulation says 17:46 is when water level reached TAF?

 

[clancy688]

I think the valve was closed at 18:25. And Tepco's simulation said fuel uncovering started at 17:46 :

I think they said that fuel uncovering started around 3 hours after SCRAM. Which was at 14:46.

I'm using this TEPCO-analysis for all of my statements. But I don't know if it's the most recent one.

Anyway, it states that fuel unovering started around 3 hours after SCRAM, but the depicted graphs show that TAF was reached at or a couple of minutes after 18:00.
Moreover, on page 4 there's a depiction of the core support plate 4.8 hours (19:30) after SCRAM with only 2% core damage in the lower middle of the core.

So now I have one question - when do cladding damage / gap releases occur (state of the core: ~3 hours after SCRAM)? In the moment the core is uncovered? Or later? 30 minutes? 1 hour?

So even if the core was uncovered moments or several minutes before the operator checked for the shell side IC pools, is it still possible for the fuel to rupture and for the fission elements to reach the shell side? Especially when the IC was effectively out of action, with the inner side valves (nearly) fully closed?

I still don't see any way for fission products to reach THAT specific place in such a short amount of time and over nearly fully closed piping with no or only minor natural circulation.

So my conclusion would be that those fission products reached the shell side before the IC shut down, hence before the Tsunami hit. And that leads to the assumption that the fuel may've been damaged during the earthquake.
Little fissures in the fuel rod cladding should be enough to let radioactive noble gases escape.

 

[Pakman]

When talking about how could high radiation appear in the reactor building, I think we miss the true matter: how do we know there was high radiation?

As we know from the report the dosimeters that were used by operators has full scale of 2,5 mkrSv/h of gamma radiation. It's only in 25 times more than natural background radiation. To imagine how insignificant it is, realize that it will take take for 5 years to achieve the emergency doze limit of 100 mSv. In Sophie, Bulgaria, natural radiation level is more than 1,5 mkrSv/h and people lives there.

Is it supposed to be so low radiation in the reactor building rooms behind the airlock even under normal operation? Really so? It's hard to believe in it. So there's the question what is the purpose of using such detectors when entering the building? Could it show another result but being overscaled? By myself, I use quite the same detectors when I go to market. Did they go to market? Or may be they thought they are working in the flower garden?

Coming back to Chernobyl, there were used dosimeters with top of 10 mSv/s (per second! not hour) and it was not enough. That is the suitable size of measurement, because the track of time in severe accident is determined by the time remaining to onset of melting. And it is hours, not years. Exactly such a dosimeter should be used to figure out whether or not you achieve doze limit being working for an hour or a half in the reactor building.

 

[clancy688]

Is it supposed to be so low radiation in the reactor building rooms behind the airlock even under normal operation?

Are the IC pools behind an airlock? I really don't know. But they are not in the primary containment. Are there airlocks for secondary containments?

You may be right regarding the actual doses. But that doesn't change the fact that there was radiation where it was not supposed to be at a time when the core still should've been undamaged.

And if the operators were equipped with dosimeters with a top scale of 2.5 uSv/h, then normal radiation levels must be well below that. What's the point in wearing a dosimeter if it goes off at radiation doses considered to be normal every five minutes?

 

[rmattila]

Would anybody by a chance happen to have information, how much the water level in the reactor normally sinks after closure of the MO-3 valves? According to the transient recorder data published by TEPCO, the measured level in the reactor dropped by 400 mm after the 15:04 closure of the valves. Since the main circulation pumps were already stopped at that time, and there should not have been any transients affecting the level measurement impulse tubes, it seems that about 8 cubic meters of water really did exit the reactor before the level stabilized, which feels rather a large amount to fill the IC tubes.

I have no experience on the isolation condensers and have so far been unable to verify if level drop of this magnitude is a normal phenomenon or not.

 

[tsutsuji]

Have you read Note 31:

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,

What do you think they mean ? I thought they mean that if there are high radiations in the RPV or in the PCV, such as during a meltdown, the PCV's wall is not thick enough to stop all the gamma rays. Is that correct ? If this is correct, then the next question is: are the doors thick enough to stop the gamma rays that come from inside the reactor building ?

 

[Pakman]

So now I have one question - when do cladding damage / gap releases occur (state of the core: ~3 hours after SCRAM)? In the moment the core is uncovered? Or later? 30 minutes? 1 hour?

As I understand this, at 17:20 it was the attempt to enter the reactor building, which was immediately renounced due to "high" radiation. At 17:50 it was reported to the headquarter. So, most likely the actual time of radiation mesurement is 17:20. By all means the core was covered at this time.

The quake could damage the cladding, yes. It could easely be checked by viewing the alarm list if there is high radiation alarm to the main steam (it flows towards turbine for 40 sec after SCRAM). I don't have this list under my hand righ now.

The reason for increased radiation at the reactor building airlock could be the SVR's operation. It drains inventory from RPV, which is in the drywell, to suppression pool which is out in the room with less thicker concreate walls than drywell has. So the radiation from the thorus inventory could affect the measurement at the airlock.

 

[tsutsuji]

Are there airlocks for secondary containments?

As Tepco wrote (about unit 1 on March 11) :

Government and other authorities were notified at 23:40 of survey results showing rising radiation dose levels inside turbine building (1.2mSv/h in front of turbine 1st floor north-side airlock and 0.5mSv/h in front of turbine 1st floor south-side airlock).
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110810e21.pdf page 9

23:00 - Radiation dose levels rise inside the turbine building (1.2 mSv/h in front of turbine 1st floor north side airlock, 0.5 mSv/h in front of 1st floor south side airlock) due to the influence of rising radiation in the reactor building.
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110810e21.pdf page 21

I guess the answer to your question is "yes". But I would be glad that Tepco provides a map showing where all these airlocks are located. What do they mean by "turbine building airlock" ? Is it an airlock between the turbine building and the outside, or between the turbine building and the reactor building ?