Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[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 ?

 

[Pakman]

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]

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.

 

[Pakman]

What's the point in wearing a dosimeter if it goes off at radiation doses considered to be normal every five minutes?

Who knows how far is our knowledge? What's the point in fail-saving the emergency cooling system due to DC power loss, which most likely means something unexpected is happened?

 

[rmattila]

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?

As both trains were operating until 15:03-15:04 and then both of them were closed by shutting the MO-3 valve, I suppose both of them would continue taking steam until they fill up to a stable level. But I have no idea of the amount of space available for the steam to get condensed into water.

 

[rmattila]

However, I bet nobody else here even know what tubes you are talking about.

Well, theoretically (=if the level measurement reference line is very close to the reactor temperature) it would be possible that while the IC is operating and the reactor pressure is dropping, the hot condensate at the top of the level measurement reference tube would flash to steam, causing the level measurement to show too high a value, and after the IC is closed and the pressure rises again, the reference tube would fill up and the level measurement would drop to the correct value.

But i doubt it, since the pressure transients caused by operation of the IC were not very large. However, as I said, I have never seen an IC operating, so I can't say for sure.

 

[Gary7]

Interesting story about a plan to use muons to take a virtual x-ray of the reactor cores.

http://www.yomiuri.co.jp/dy/national/T120107003539.htm

 

[jim hardy]

"" the hot condensate at the top of the level measurement reference tube would flash to steam, causing the level measurement to show too high a value, and after the IC is closed and the pressure rises again, the reference tube would fill up and the level measurement would drop to the correct value. ""

that's one reason it's recommended to depressurize quickly in station blackout.
depressurizing reduces reactor temperature
which reduces heatflow from vessel to containment, ( which has no cooling in blackout, )
where the 'reference legs' are located.
the containment temperaturre needs to be kept low
both for sake of electronics in there and you don't want the containment's metal wall to expand from the heat, buckle and crack
not to mention reference legs.

reference legs depend on steam moving into condensate pot, condensing and running back out the sloped sense pipe toward vessel, to keep condensate pot full.
so the condensate pot will be at saturation temperature.
that's how you check them - feel and if they're not scalding hot they're "gas bound", ie filled with noncondensables that keep the steam out.
we had vents atop ours to let out the noncondensibles.

the cooler water in reference leg can carry dissolved noncondensibles, just like carbonated soda does.
If the reference legs got hot enough to boil out some of the water or drive out dissolved noncondensibles
at a time when there was significant noncondensibles in the vessel (hydrogen? )

i believe the reference legs would become gas-bound and not refill.

just an old instrument guy's estimate.

 

[Pakman]

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.

Without denying written above, as a simpler explanation may be the lack of ventilation in the reactor building. Did you know if you shut the vent hole in the bathroom and turn on the shower, radiation inside rapidly increases up to 2 mkSv due to Radon? Such was certainly here but in a more rigid form.

Everything about the attempt to enter the reactor building rests on the fact that the dosimeters were not suitable for this job, even there wasn't any damage to the equipment inside the building, and certainly if there was. Why then the report does not blame operators for this? This is a real bug, unlike the lack of knowledge of the fail-safe automatic functioning imposed by the report.

 

[jim hardy]

we might be over-focused on dosimeters. i don't know what they had.

surely they had survey meters good for a few R/hr?

the Inpo report mentions water deeper than their boots, i'd have turned back too.
water can carry reeally nasty stuff, recall the electrical workers who got radiation burns from walking through water. presumably dissolved beta emitters because field above water wasn't too bad.

decisions have to be judged by the facts they were based on, ie what was known at that time & place.

i'd wager too much credence was put on the reactor level instrument.

 

[rmattila]

i'd wager too much credence was put on the reactor level instrument.

I've been wondering about the level measurement systems since the very beginning, even started a thread in March to get some justification for the trust that seemed to be put on the level instrumentation.

A rule of thumb is that 10 kg/s decay heat evaporation rate (typical about 1 hour after shutdown) will cause the level in the tank to drop about 3 cm per minute (=about two meters per hour), and as there was no cooling for several hours, it should have been obvious that the core will have been uncovered during the evening of March 11.

(And, by the way, I am still somewhat uncertain whether the GE level instrumentation will work at all, when the level drops below -1200 mm).

Diversification of the low level instrumentation with a binary signal based on floats is one way to improve reliability of data concerning the level drop in situations where impulse pipes might not work properly (rapid depressurisation etc.) My understanding is that such plant modifications/improvements have already been implemented at some European BWRs, and are currently being carried out at least in the Finnish plants.