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Japan Earthquake: nuclear plants

by gmax137
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tsutsuji
#12097
Jan6-12, 09:39 AM
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Quote Quote by jim hardy View Post
pretty good narrative here pages 12 to 37.
http://www.power-eng.com/content/dam...a%20report.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
#12098
Jan6-12, 09:51 AM
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Quote Quote by tsutsuji View Post
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
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Jan6-12, 09:58 AM
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Quote Quote by tsutsuji View Post
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
#12100
Jan6-12, 01:13 PM
P: 28
Well, I could be a BWR guy. After all, RBMK is some kind of a boiling water reactor, isn't it?
Quote Quote by tsutsuji View Post
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.
Quote Quote by tsutsuji View Post
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
#12101
Jan6-12, 05:46 PM
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Quote Quote by rmattila View Post
The water can flow backwards through the recirculation loop into the reactor.
Quote Quote by Pakman View Post
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
#12102
Jan6-12, 06:00 PM
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Cabinet investigation committee interim report translation (part 5) [IV 3 (1) e (d)]

part 1 : http://www.physicsforums.com/showpos...ostcount=11983 [IV 3 (1) b]
part 2 : http://www.physicsforums.com/showpos...ostcount=12005 [IV 3 (1) b - IV 3 (1) c - IV 3 (1) d]
part 3 : http://www.physicsforums.com/showpos...ostcount=12082 [IV 3 (1) e (a) - IV 3 (1) e (b)]
part 4 : http://www.physicsforums.com/showpos...ostcount=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
#12103
Jan7-12, 04:16 AM
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Quote Quote by zapperzero View Post
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
#12104
Jan7-12, 04:46 AM
P: 546
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?

Quote Quote by tsutsuji View Post
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
#12105
Jan7-12, 08:53 AM
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http://www3.nhk.or.jp/news/genpatsu-...0_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.

Quote Quote by clancy688 View Post
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 :

Quote Quote by zapperzero View Post
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
#12106
Jan7-12, 10:34 AM
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Quote Quote by tsutsuji View Post
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
#12107
Jan7-12, 12:19 PM
P: 28
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, realise 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
#12108
Jan7-12, 12:49 PM
P: 546
Quote Quote by Pakman View Post
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
#12109
Jan7-12, 01:00 PM
P: 242
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
#12110
Jan7-12, 01:05 PM
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Have you read Note 31:

Quote Quote by tsutsuji View Post
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
#12111
Jan7-12, 01:11 PM
P: 28
Quote Quote by clancy688 View Post
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, wich 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
#12112
Jan7-12, 01:34 PM
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Quote Quote by clancy688 View Post
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.../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.../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 ?
Pakman
#12113
Jan7-12, 01:51 PM
P: 28
Quote Quote by rmattila View Post
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?
I see you're tightly in subject, neighbor! I counted 10 cubic meters. About. You think this is for both IC or only for B?

However, I bet nobody else here even know what tubes you are talking about.
Pakman
#12114
Jan7-12, 02:23 PM
P: 28
Quote Quote by tsutsuji View Post
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 ?
BWR has quite contaminated steam-water circuit loop, including the turbine flow, so the turbine set in maintenance-free room with airlock to outside. Almost like secondary containment of the reactor building. Therefore one doesn't simply walk into turbine hall.


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