Japan Earthquake: Nuclear Plants at Fukushima Daiichi

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Discussion Overview

The discussion revolves around the technical aspects and current status of the nuclear plants at Fukushima Daiichi following the earthquake and tsunami in Japan. Participants are seeking reliable information regarding the operational conditions, safety measures, and potential risks associated with the nuclear reactors in the aftermath of the disaster.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants express skepticism about the reliability of media reports and emphasize the need for technical information from official sources like TEPCO and METI.
  • There are concerns regarding the reactor pressure levels, with reports suggesting that pressure may have exceeded safe limits, which some participants describe as a significant issue.
  • Questions are raised about the likelihood of a meltdown, with differing opinions on whether this is a realistic concern or media exaggeration.
  • One participant explains the role of coolant in a nuclear power plant, noting that it is essential for cooling the reactor and managing decay heat after shutdown.
  • There is discussion about the reactor's ability to be scrammed (shut down) and the implications of losing coolant, with some participants clarifying that decay heat continues to be produced even after shutdown.
  • Concerns are raised about the explosion of the containment building and its implications for safety, with speculation about the potential release of radioactive materials.
  • Participants discuss the wind direction at the time of the explosion and its potential impact on the dispersion of any radioactive materials released.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the likelihood of a meltdown or the implications of the current situation at Fukushima Daiichi. There are multiple competing views regarding the severity of the situation and the reliability of information being reported.

Contextual Notes

Participants note the limitations of available information, including the reliance on second-hand reports and the challenges in verifying the status of the reactors and containment structures. There are also unresolved questions regarding the operational status of safety systems and the exact nature of the explosion.

  • #11,611
I did not have a suitable BWR inventory right at hand and no time to calculate one either, so I had to do with a VVER EOC inventory and scale it according to the thermal power level. Using an EOC inventory, I probably overestimated the transuranics, thus I believe your results to be better than the quick sketch I made in order to have at least something to base the estimates on.
 
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  • #11,612
dezzert said:
The following is from
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/111104e19.pdf

If the Unit 2 fuel is in the critical state, Xe135 concentration is observed 4 orders of magnitude larger than current level. Therefore, present state is not considered critical.

OK, so on Aug 9 they found Xe-131m at 3.8 X 10¹ to 4.7 X 10¹ Bq/cm3 in the lower floors of Unit 2. This is 5 orders of magnitude greater. According to Tepco's analysis criticality has occurred. Am I missing something?

clancy688 said:
Via http://ex-skf.blogspot.com/2011/11/xenon-detection-in-reactor-2-different.html" :

Comparison between the three gas tests on October 28th, November 1st and November 2nd. Looks quite funny. With the detection limits being very funny.


fukushimareactor2xenontable.JPG


So... what the heck? No wonder they didn't detect any Xenon on October 28th.

clancy 688 - what are the units of those measurements? dezzerts values (Bq/cm^3) from Unit 2 are significantly different.
 
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  • #11,613
NUCENG said:
clancy 688 - what are the units of those measurements? dezzerts values (Bq/cm^3) from Unit 2 are significantly different.

Sorry, but what do you mean?

All of these values have the unit of Bq/cm³. http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111102_04-e.pdf" the original.
 
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  • #11,615
NUCENG said:
the effects of curium seem to control the data.

And there's my answer. Thank you.
 
  • #11,616
clancy688 said:
All of these values have the unit of Bq/cm³. http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111102_04-e.pdf" the original.

And this is the original that showed both Aug 9 readings (reported on the 10th) as well as Nov 1. Lower left box is Aug. Why they only tested for Xe-131m and not 133 or 135 is a mystery.
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111102_01-j.pdf
 
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  • #11,617
http://spectrum.ieee.org/energy/nuclear/24-hours-at-fukushima" - report by IEEE.

Probably nothing new for most of us who're following this thread regularly but it's still interesting to read.
 
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  • #11,618
TBS video showing a robot performing debris removal on unit 3's first floor under radiations up to 650 mSv/hour.
 
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  • #11,619
tsutsuji said:
TBS video showing a robot performing debris removal on unit 3's first floor under radiations up to 650 mSv/hour.


Shows removed by user.
 
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  • #11,620
  • #11,621
LabratSR said:
Shows removed by user.

New link

The original can be found on Tepco's website in the Japanese language media section : http://www.tepco.co.jp/tepconews/pressroom/110311/index-j.html

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111105_02-e.pdf "Obstacle Removal by Robot and Radiation Dose Measurement after the Removal on the First Floor of Unit 3 Reactor Building at Fukushima Daiichi Nuclear Power Station"
 
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  • #11,622
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  • #11,623
I collected some data points given in TEPCOs handouts during the autumn regarding the activity of water to be treated (see attachment). It seems the activity of the accumulated water has decreased by more than half, while its amount has been decreasing as well.

EDIT: The left Y scale should of course be Bq/cm3, not Bq.
 

Attachments

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  • #11,624
Rive said:
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111107_03-e.pdf

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111107_01-e.pdf

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111106_01-e.pdf

Can somebody please tell me why they don't just open the cooling loop and wash it through with the already treated water? With spilling the downcoming to the reactor basement?

Perhaps because the latest TEPCO Status of Countermeasures report indicates the water processing system is running at 53% capacity?
They are pretty much keeping the water level in the plant in check with cooling inflows of about 28 tons/hr.
Adding the SFP flushing water might be a tad much.
It is interesting that the presentation indicates the SFP water will be treated by discrete truck mounted water processing units, not the existing facility.
 
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  • #11,625
etudiant said:
Perhaps because the latest TEPCO Status of Countermeasures report indicates the water processing system is running at 53% capacity?
They are pretty much keeping the water level in the plant in check with cooling inflows of about 28 tons/hr.

AFAIK that is because the actual goal is to keep a ~ stable water level (a bit lower than the groundwater) instead of trying to dry the basements (which would be impossible).
 
  • #11,626
Rive said:
AFAIK that is because the actual goal is to keep a ~ stable water level (a bit lower than the groundwater) instead of trying to dry the basements (which would be impossible).

Good point.
Of course, while the level for reactors 2-4 is now around the target mark, reactor 1 is still about 4 feet above that, so I doubt they are deliberately slowing down the water processing.
 
  • #11,627
etudiant said:
... reactor 1 is still about 4 feet above that, so I doubt they are deliberately slowing down the water processing.
Check the water level changes in the Plant Status Reports!

If I'm right, U1 is waterproof, the water levels around and inside U1 are moving independently: while for U2, U3 and U4 the water levels are moving in close connection.
 
  • #11,628
Rive said:
Check the water level changes in the Plant Status Reports!

If I'm right, U1 is waterproof, the water levels around and inside U1 are moving independently: while for U2, U3 and U4 the water levels are moving in close connection.


The water level for U1 has always been much different than for 2-4. I'd assumed it was perhaps a siting difference. There was no indication that the OP + 3m water level target excluded U1 afaik.
Given the quake, waterproof seems unlikely. Objectively, the level in U1 has gone down about 60cm if memory serves.
How can you tell inside from outside? is there an indication somewhere in the JAIF report?
 
  • #11,629
what do you think about the sharp Kr-85 rise (in one day) of the famous gas sampling

I stumbled across the fact by looking at

http://enenews.com/just-in-krypton-85-up-over-14000-in-a-day-at-reactor-no-2-kr-85-used-to-detect-plutonium-separations

and do not know what to think of it...
 
  • #11,630
etudiant said:
How can you tell inside from outside? is there an indication somewhere in the JAIF report?
Afaik the 'vertical shaft of the trench' http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111107_06-e.pdf" is the water level in the sub-drain pits around the referenced building (~= local groundwater level).

etudiant said:
The water level for U1 has always been much different than for 2-4. I'd assumed it was perhaps a siting difference.
It's still possible, all what I wrote is a big 'IMHO'.

etudiant said:
Objectively, the level in U1 has gone down about 60cm if memory serves.
As the actual water level goals reached for the other buildings, they are started to work harder on the less urgent one?
 
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  • #11,633
zapperzero said:
Survey of #4 RB. TEPCO says the blast came from the aircon ducts, on 4th floor

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111110_01-e.pdf

more photos there

http://www.tepco.co.jp/en/news/110311/index-e.html


I don't think you were saying anything more than "here is the press release", and thankyou for that, but I thought someone else may take your post at face value.

What TEPCO actually said in the document is

" it was possible that the explosion occurred around the
air-conditioning ducts. "

A seemingly obvious and at the same time inconclusive statement.


Aircon ducting is very weak compared to nearly everything else in the RB. There is extensive structural damage to the building and equipment apart from the aircon is severely damaged by flying debris and\or equipment displacement. In several of the images substantial impacts to the remaining ducting are indicative of impacts and\or other forces to the outside of the ducting, deforming it inwards. It isn't beyond the realms of possibility that at least some or even all of the ducting was smashed to pieces from outside forces as opposed to from inside the ducting. The blown out vent mesh would be caused by pressure emanting from within the ducting system, no doubt, but that could in turn have been caused by the ducting being explosively crushed or explosive forces traveling via the ducting, not necesarily explosive force emanating from within it.

I don't believe this latest information gets any closer to a conclusive explanation for a source of hydrogen into RB 4 or whether the explosion emanated from inside the ducting or how\where the hydrogen may have traveled through the building.

However as TEPCO stated, the images do show good evidence that at least one part of the explosive forces that wrecked the building emanated from the fourth floor.
 
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  • #11,635
Two things I discovered by skimming through the report:

Unit 2 - If I read the section about Unit 2 correctly (and I'm not really sure I did, perhaps NUCENG could look over the sections regarding Units 1-3? There's a certain emphasis on venting valves), then Unit 2 never vented. The workers established a vent path, but a rupture disc never failed, even though the pressure was higher than the pressure needed to break it.
So when Unit 2 finally depressurized, it wasn't done through venting - but through containment failure.

Unit 3 - RCIC didn't fail on March 14th, it failed on March 12th at 11:36 local time, HPCI provided core cooling until the morning of March 14th. Was that fact known before?
 
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  • #11,637
clancy688 said:
Two things I discovered by skimming through the report:

Unit 2 - If I read the section about Unit 2 correctly (and I'm not really sure I did, perhaps NUCENG could look over the sections regarding Units 1-3? There's a certain emphasis on venting valves), then Unit 2 never vented. The workers established a vent path, but a rupture disc never failed, even though the pressure was higher than the pressure needed to break it.
So when Unit 2 finally depressurized, it wasn't done through venting - but through containment failure.

Unit 3 - RCIC didn't fail on March 14th, it failed on March 12th at 11:36 local time, HPCI provided core cooling until the morning of March 14th. Was that fact known before?

It does not seem to me like there is much in the way of new information in this report, but it is presented in a way that makes it easier to spot such details. We already knew that they had numerous problems trying to vent reactor 2, and although I am not sure we spent much time talking about it. The fact that venting never happened does not strike me as new, although prior to this latest report I am not sure it was ever specifically stated that rupture disc never failed.

Checking the info from that report with a couple of other sources such as NISA analysis of events, my brief summary of venting details for the three reactors is as follows:

Reactor 1
RPV fell to PCV pressure levels without any mention of SRV valves having been deliberately opened
PCV pressure fell somewhat, and radiation levels at plant increased, before there was any venting.
Early venting attempts were only partially successful or not successful at all for hours on the 12th.
Venting was eventually confirmed, backed up by visual evidence of venting via stack.

Reactor 2
Numerous problems when trying to get various vent paths opened.
SRV's opened on more than one occasion.
PCV pressure didn't rise significantly when RPV pressure first fell, suggesting PCV leak.
RPV pressure increased several times after initial SRV opening, requiring further SRV opening activity to be performed.
PCV pressure then went higher, but the indicated drywell pressures went much higher than the suppression chamber ones.
Venting still didn't work.
Tried to vent directly from drywell to get round the issue of lower s/c pressure compared to d/w pressure, but there was still no indication of success.
Sound near suppression chamber, pressure indication for s/c went to 0, drywell pressure fell over the next few hours.

Reactor 3
RPV pressure fell when HPCI started.
RPV pressure increased when HPCI failed.
Attempts to vent not successful.
PCV containment leaking may have occurred.
Venting succeeded, with visual confirmation of venting via stack. SRV opened at about the same time and RPV pressure fell as expected.
Problems keeping vent path open at certain times in the subsequent days, which sometimes affected ability to continuously inject enough water.
 
  • #11,638
TEPCO have released a large number of previous unpublished videos, taken over many months.

http://www.tepco.co.jp/en/news/110311/111111-e.html
 
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  • #11,639
SteveElbows said:
TEPCO have released a large number of previous unpublished videos, taken over many months.

http://www.tepco.co.jp/en/news/110311/111111-e.html

It says there
<quote>These motion pictures are available until the end of December. </quote>
so make copies
 
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  • #11,640
This was the first "extended SBO + all EDGs off" scenario, and it resulted in a total, 100% SNAFU: not a single reactor unit was saved.

It's actually worse than that: out of three active reactor units affected, FOUR blew up (counting 2nd unit's infamous "load bang in the torus area"): they managed to blow up even the unit with reactor switched off, opened and unloaded. That's quite an achievement.

Tell me how I can trust nuclear industry after this. Am I to believe French or US nuclear stations are better prepared, when more natural and conservative conclusion is 'French and US nuclear stations just didn't have their "extended SBO + all EDGs off" scenario. Yet. Just wait'?
 

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