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Japan Earthquake: nuclear plants

by gmax137
Tags: earthquake, japan, nuclear
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SpunkyMonkey
#10855
Aug8-11, 05:55 PM
P: 65
Quote Quote by joewein View Post
I'm sorry, that stuff still looks like rust to me. The horizontal pipe running right below the brown pipe elbow looks clean closest to the most stained portion of the elbow. That does not look like a high pressure cesium leak to me.
Perhaps, but to me it looks like a water-carried distribution of the similar-colored dark stuff splattered around and heaped at the base of the same pipe. And because that heap of red-brown gunk is extremely radioactive and associated with a ventilation/filtration system, it may well be (largely) cesium-vapor residue, which is also dark red-brown.

If you look at a higher res picture of that pipe, it looks like it was wrapped with some kind of tape, perhaps to protect it against corrosion. The brown stuff seems to have leaked out from underneath the tape. Perhaps the tape trapped moisture, allowing rust to fester underneath. The vertical brown lines are consistent with rust getting washed down by rain.
What we can say for sure is that the stain lines are consistent with some red-brown substance washed down with rain. But that does not entail that it's rust.

Yes I see the tape, it's obvious, but what kind of tape allows rust to fester as you suggest? I don't see why the tape increases the likelihood of the staining being rust. Maybe it's to stop corrosion as you suggest, or then maybe to reduce the escape of cesium-vapor residue in the event of a filtration-system rupture. It might be there for a number of reasons. I doubt we can infer much from the tape being there.
swl
#10856
Aug8-11, 07:32 PM
P: 108
When it rains hard, as it has recently in the Fukushima area, what happens to all the water that falls down the ventilation stack? After rinsing down the inner walls of the stack, it then hits the bottom, and what? Does anyone know if there is an automatic drain mechanism? Knowing that heavy rain is common here, I'm certain that something has been done to address this issue, but I don't remember reading about it. I'm curious where rain water and condensate goes after reaching the bottom of the stack.
AtomicWombat
#10857
Aug8-11, 07:39 PM
P: 150
Quote Quote by etudiant View Post
Certainly the current designs do not appear to fail at all gracefully if the emergency venting is just flushed through the stack. That just maximizes the problem. What is the rationale for such a design?
Quote Quote by joewein View Post
I think the rationale is the mistaken assumption that extended station blackouts do not happen in the first place. It's a "beyond design base" condition.

However, venting from the wet well air space as in unit 1 does still seem the lesser evil compared to an uncontrolled containment failure from over-pressure as may have happened in unit 2, which is assumed to have released a lot more contamination than unit 1 (think Iitate-mura). At least the vented gas has been scrubbed to some extent by first bubbling it through the pool water in the torus. With a cracked containment all bets are off what gets released.
I agree with joewein.

As I take it, the rationale behind the hardened wet well vents is as a last ditch attempt to prevent a hydrogen explosion or primary containment over-pressurisation, on the basis that either event would release more radioactivity (due to catastrophic failure of the containment) than direct venting of the torus to the environment.

See:
http://www.gereports.com/venting-sys...rk-i-reactors/
http://www.nrc.gov/reading-rm/doc-co...9/gl89016.html

Ironically all 3 operating units experienced hydrogen explosions and the hardened vents did nothing to prevent these. It appears that in at least one case (unit 1) the hardened vent was operated as well, created the worst of both worlds.
AtomicWombat
#10858
Aug8-11, 07:43 PM
P: 150
Quote Quote by swl View Post
When it rains hard, as it has recently in the Fukushima area, what happens to all the water that falls down the ventilation stack? After rinsing down the inner walls of the stack, it then hits the bottom, and what? Does anyone know if there is an automatic drain mechanism? Knowing that heavy rain is common here, I'm certain that something has been done to address this issue, but I don't remember reading about it. I'm curious where rain water and condensate goes after reaching the bottom of the stack.
I have a nasty suspicion that the rain water simply is passed to the normal storm water system and then to the ocean and/or ground water. The rationale being that on the "design basis" only filtered gases are exhausted through the stack. Remember that the hardened vent was a retrofit.
westfield
#10859
Aug8-11, 10:34 PM
P: 145
Quote Quote by joewein View Post
snip >


. At least the vented gas has been scrubbed to some extent by first bubbling it through the pool water in the torus.

<snip.
This document appears to indicate the operators aligned the venting from both drywell AND S\C. No scrubbing from the drywell venting.

The document also indicates very high dose rates in the buildings and onsite well before the venting even took place. To my laybrain that seems odd - was there containment failure before they even got to vent?

source : TEPCO


On the SGTS\HVS contamination - why the high dose rates in the Unit 1 Turbine building early on? And why does SGTS even go into the turbine building? Why does the SGTS appear to be HEAVILY contaminated, it shouldn't have even been possible for it to be working after loss of power. So SGTS just opens itself up on loss of power? WTF. The more I read about the design of these systems the less I want to know, kind of.
SpunkyMonkey
#10860
Aug9-11, 12:23 AM
P: 65
Let me suggest these possible flow patterns that seem to be both logico-physically intuitive and empirically observed:


By stalagmatic accumulation I refer to the process slow water-carrier driven stalagmite formation. The rust-color residue has accumulated to a few inches in height at the base of the feed-in pipe's interface with the main vent, and that heap of gunk is the highest-dose spot.

Moreover, the same rust-colored stain (that I propose is cesium-vapor residue) is also seen emanating from the interface seam. This constitutes a second unique source of rust-color staining and flow pattern versus that coming down the pipe, and both pathways would logically converge at the accumulation point. The rust-colored staining clearly appears to be associated with the highest-dose accumulation of dark-red gunk.
joewein
#10861
Aug9-11, 01:19 AM
joewein's Avatar
P: 192
Quote Quote by westfield View Post
This document appears to indicate the operators aligned the venting from both drywell AND S\C. No scrubbing from the drywell venting.
If the RPV steam from the pressure release valves is always released into the wetwell, the air space there should be much more contaminated than the nitrogen in the drywell. The drywell would get more severely contaminated later on, once the RPV melts through or the seals around it start leaking, but initially all the good stuff ends up in the torus.

There may be some exchange of pressure via the downcomer tubes between the two if there is a large pressure differential (will water get pushed up the tubes if pressure gets too high in the torus, opening a path for contaminated gas to leak from the torus into the drywell?), but my understanding is that until the RPV gets damaged by excessive temperatures the wetwell would be the more contaminated of the two spaces.

Quote Quote by westfield View Post
The document also indicates very high dose rates in the buildings and onsite well before the venting even took place. To my laybrain that seems odd - was there containment failure before they even got to vent?

source : TEPCO
It says they prohibited entry to R/B 1 at 21:51 on 2011-03-11 because of radiation (about seven hours after the quake). Tepco estimates that fuel was exposed five hours after the quake because the water level had fallen too far. So by the time they prohibited entrance, the meltdown had been in progress for about two hours. I don't know what the containment pressure was like by then, but 4 hours later, at 02:00 JST it was 0.6 MPa and at 05:30 it was at 0.82 MPa. The containment may already have been near or at design pressure (0.42 MPa = 4.2 bar) when the radiation went up.

For radiation levels inside the building to go up without venting there must have been some leaks. But in a way it is not surprising that the unit 1 containment was leaking in 2011 (when it was 40 years old and stressed to the max by a melting core) when it had already leaked unacceptably in 1992 during routine inspections when tested at 3 bar:

Faked pressure test

Yet in the most serious case of all, Tepco officials are alleged to have faked a pressure test designed to test the integrity of the containment building. The test involves pumping nitrogen gas into the building to increase the pressure to about three times atmospheric pressure, then taking pressure readings to measure the leak rate.

Regulations state that the leak rate must be less than 0.45% per day. However, at Fukushima I-1 in 1992, the company conducted its own tests before the government inspectors turned up, and discovered that the building might not pass the test. One source quoted in the Daily Yomiuri said that leak rates fluctuated from 0.3% to 2.5% per day.

Documents found at Hitachi by Tepco’s own investigative team describe a method to fake the test by secretly pumping in extra air from the main steam isolation valve. At the time, Hitachi had a contract to check Tepco equipment. It is alleged that Tepco officials followed this procedure when the government inspectors were checking the leak rate.

http://www.klimaatkeuze.nl/wise/monitor/574/5441
2.5% of several thousand cubic meters of nitrogen at 3 bar is several hundred cubic meters that would have leaked per day.

Quote Quote by westfield View Post
On the SGTS\HVS contamination - why the high dose rates in the Unit 1 Turbine building early on? And why does SGTS even go into the turbine building?
Probably because most of the pipes coming out or going into the containment go next door to the turbine building. It's like the belly button of the reactor. The turbine hall is also more spacious.
joewein
#10862
Aug9-11, 01:28 AM
joewein's Avatar
P: 192
Quote Quote by AtomicWombat View Post
Quote Quote by swl View Post
When it rains hard, as it has recently in the Fukushima area, what happens to all the water that falls down the ventilation stack? After rinsing down the inner walls of the stack, it then hits the bottom, and what? Does anyone know if there is an automatic drain mechanism? Knowing that heavy rain is common here, I'm certain that something has been done to address this issue, but I don't remember reading about it. I'm curious where rain water and condensate goes after reaching the bottom of the stack.
I have a nasty suspicion that the rain water simply is passed to the normal storm water system and then to the ocean and/or ground water. The rationale being that on the "design basis" only filtered gases are exhausted through the stack. Remember that the hardened vent was a retrofit.
That is a very interesting question. Note that the guy who measured the radiation with a 3 meter long pole (and took a 40 mSv hit) is standing next to what looks like a sewer lid inside the structural frame of the stack pipe.
tsutsuji
#10863
Aug9-11, 07:38 AM
PF Gold
P: 1,220
Quote Quote by joewein View Post
For radiation levels inside the building to go up without venting there must have been some leaks. But in a way it is not surprising that the unit 1 containment was leaking in 2011 (when it was 40 years old and stressed to the max by a melting core) when it had already leaked unacceptably in 1992 during routine inspections when tested at 3 bar:

Faked pressure test

Yet in the most serious case of all, Tepco officials are alleged to have faked a pressure test designed to test the integrity of the containment building. The test involves pumping nitrogen gas into the building to increase the pressure to about three times atmospheric pressure, then taking pressure readings to measure the leak rate.

Regulations state that the leak rate must be less than 0.45% per day. However, at Fukushima I-1 in 1992, the company conducted its own tests before the government inspectors turned up, and discovered that the building might not pass the test. One source quoted in the Daily Yomiuri said that leak rates fluctuated from 0.3% to 2.5% per day.

Documents found at Hitachi by Tepco’s own investigative team describe a method to fake the test by secretly pumping in extra air from the main steam isolation valve. At the time, Hitachi had a contract to check Tepco equipment. It is alleged that Tepco officials followed this procedure when the government inspectors were checking the leak rate.

http://www.klimaatkeuze.nl/wise/monitor/574/5441
2.5% of several thousand cubic meters of nitrogen at 3 bar is several hundred cubic meters that would have leaked per day.

The following NISA report, written in December 2002, contains a time-line. Here are a few translated excerpts :
September 25 (Wednesday). The Yomiuri Shimbun evening edition reports that fraud took place, during leak rate tests conducted in 1992.
[...]
November 06 (Wednesday). Start of legally required on-site inspection regarding the leak rate of the concerned unit.

November 29 (Friday). A one-year shut-down of the concerned unit is ordered.
[...]
December 05 (Thursday). Tepco announces that, regarding the concerned unit, it obtained a leak rate measurement result of 0.092% / day which satisfies the standard criteria.

http://www.meti.go.jp/report/downloa...1224d0122j.pdf p. 15-16
The 28 May 2004 Tepco press release announces the following :
28 May (Friday) 10:00~16:00 : 0.122% / day (below the 0.348% / day standard criteria)

27 May (Thursday) 10:00~16:00 : 0.123% / day (below the 0.348% / day standard criteria)

http://www.tepco.co.jp/fukushima1-np/bi4509-j.html
The 15 December 2010 press release about regular inspection No. 26 (March 2010 -December 2010) says :
13 July 08:00~14:00 : 0.166% / day※ (below the 0.4% / day standard criteria) (※ 95% confidence limit - upper limit)
http://www.tepco.co.jp/nu/f1-np/pres...a/bi0c06-j.pdf page 5 (pdf page number 7)
http://www.tepco.co.jp/nu/f1-np/pres...a/bi9714-j.pdf (page 5) 17 February 2009 : 0.176%
http://www.tepco.co.jp/nu/f1-np/pres...a/bi8116-j.pdf (page 7) 12-13 September 2007 (24 hour test) : 0.101%
tsutsuji
#10864
Aug9-11, 09:37 AM
PF Gold
P: 1,220
An interesting (1) theory is proposed to explain the March 20~24 radiation peak in the Kanto area:

A second meltdown likely occurred in the No. 3 reactor at the Fukushima No. 1 nuclear power plant, a scenario that could hinder the current strategy to end the crisis, a scientist said.
[...]
One factor used by Tanabe in speculating that a second meltdown occurred is the increase in radiation levels from the morning of March 21 in areas downwind from the Fukushima No. 1 plant, such as the Fukushima No. 2 nuclear power plant as well as the Kanto region municipalities of Kita-Ibaraki, Takahagi and Mito.

Initially, officials of the Nuclear and Industrial Safety Agency explained that the higher radiation levels were caused by radioactive materials falling to the ground with the rain.

But there is also the possibility that additional radioactive materials emitted from the second meltdown may have been blown by the wind.

Between 1 a.m. and 3 a.m. on March 21, the pressure within the pressure vessel of the No. 3 reactor core increased sharply to about 110 atmospheres, likely caused by an explosion within the pressure vessel due to a lack of cooling of the fuel. That was probably the start of the second meltdown, Tanabe said.

http://www.asahi.com/english/TKY201108080276.html "Report suggests second meltdown at reactor at Fukushima plant" by Tomooki Yasuda staff writer
See also the diagrams on the Japanese language article page : http://www.asahi.com/national/update...108070330.html

(1) I discussed the 21 March radiation peak in Mito City in April on http://www.physicsforums.com/showthr...to#post3258064 and again in May in relation with the 21 March 8~12 MPa unit 3 pressure data on http://www.physicsforums.com/showthr...to#post3308800

http://www.nikkei.com/news/category/...08122009000000 The unit 1 SFP cooling system will be launched on 10 August. The remote-controlled construction of the steel frame of unit 1's cover structure will be achieved by mid-September. SARRY will be launched next week.
joewein
#10865
Aug9-11, 09:53 AM
joewein's Avatar
P: 192
Thank you, tsutsuji!

From 0.101% to 2.5% leakage per day seems like a huge spread. I wonder what measures they took to reduce the leakage and if this is tested while the reactor is in cold shutdown or powered up. Temperatures could hugely alter tolerances due to thermal expansion and contraction.

I checked the operating records and for example the 2007 figure for unit 1 was measured more than 6 weeks before the reactor went on the grid again and after 9 months of shutdown.

The Mark I containment in unit 1 seems to have a free volume (dry+wet) of 5800 m3, of which 2100 m3 is water in the suppression chamber and 3700 m3 is space for nitrogen. A permitted leak of 0.4% per day of 3700 m3 is 14,800 liters of containment gas per bar of internal pressure. In a station blackout the SGTS could not take care of cleaning up any contamination from that.
tsutsuji
#10866
Aug9-11, 10:33 AM
PF Gold
P: 1,220
Quote Quote by joewein View Post
Thank you, tsutsuji!

From 0.101% to 2.5% leakage per day seems like a huge spread.
You're welcome, Joewein. Note also the 0.092% rate I mentioned above, measured by Tepco 15 days after the 20 November 2002 shutdown.

Quote Quote by joewein View Post
I wonder [...] if this is tested while the reactor is in cold shutdown or powered up.
Sealing tests are usually carried out at the last phase of government inspections
http://www.thefreelibrary.com/Agency...se.-a093437939
Which perhaps leaves plenty of time if the company wants to perform its own informal tests beforehand. So It seems that the tests are usually performed during cold shutdown. Wouldn't it be dangerous to perform tests while the plant is in full operation ?
HowlerMonkey
#10867
Aug9-11, 09:49 PM
P: 276
I think the brown/red stuff is from rainwater that gets between the insulation and the outside of the pipe itself that is flowing to the bottom and out the gaps as rust.

You can see similar deposits near that railing and this facility is bordering the ocean which causes things to rust at unbelievable rates.
westfield
#10868
Aug9-11, 11:06 PM
P: 145
Quote Quote by AtomicWombat View Post
I have a nasty suspicion that the rain water simply is passed to the normal storm water system and then to the ocean and/or ground water. The rationale being that on the "design basis" only filtered gases are exhausted through the stack. Remember that the hardened vent was a retrofit.
or you could go and look at some drawings of say Oyster Creek as an example that show the sump pumps in the base of their stack are indeed fed to rad waste treatment.

dwg here


Even when things are normal at these plants the stack emissions are still not 100% clean by any measure so it would be a given any fluid in the stack sump\s should be sent to treatment not to normal stormwater.
tsutsuji
#10869
Aug10-11, 07:29 AM
PF Gold
P: 1,220
http://mainichi.jp/select/today/news...40046000c.html Struck by a lightning at 8:20 PM on 8 August, the water treatment facility was shut down for two hours as a wrong signal was emitted by some storage tank's water level gauge and a fuse was blown at another tank. The facility is not equipped with lightening countermeasures. Junichi Matsumoto said "if long term use is considered, countermeasures are needed".

http://www.nikkei.com/news/category/...08122009000000 The utilization rate for the 3 August - 9 August week is 77%. This is short of the 90% goal for August. Tepco admits that the plan to treat all the accumulated water by the end of the year will be "a little delayed". On the one hand, the bypass lines which have been used since 4 August have enabled to greatly recover from the flow rate decline, but on the other hand, the facility stopped for 7 and a half hours on 7 August. A gas sample from unit 2 containment vessel was analysed, finding a radiation level lower than expected, and Xe and Kr among the radioactive substances.

http://www.tepco.co.jp/cc/press/betu...es/110810g.pdf 3 August - 9 August water treatment weekly report (Japanese)

http://www.tepco.co.jp/en/nu/fukushi...10810_03-e.pdf "Results of Gas Sampling inside the Primary Containment Vessel of Unit 2 Fukushima Daiichi Nuclear Power Station"

http://www.tepco.co.jp/en/press/corp...1081003-e.html [unit 1] "At 9:00 am on August 10, we started to assemble steel frame for the Reactor Building Cover"

http://www.tepco.co.jp/cc/press/betu...es/110810l.pdf Update of the worker radiation exposure statistics (Japanese)

http://www.tepco.co.jp/en/nu/fukushi...10810_02-e.pdf Water level gauge problem at the desalination facility, causing a shutdown from 1:50 to 9:35 AM.
rmattila
#10870
Aug10-11, 08:32 AM
P: 242
Quote Quote by tsutsuji View Post
http://www.tepco.co.jp/en/nu/fukushi...10810_03-e.pdf "Results of Gas Sampling inside the Primary Containment Vessel of Unit 2 Fukushima Daiichi Nuclear Power Station"
The detection of Kr-85 (if the results are correct) is interesting. As far as I am aware, Kr-85 is not produced in the long decay chains, so all of it has been around ever since the fissions stopped. If it is still found in the containment, my first impression is that either

(a) the containment has somehow been able to contain the noble gas Kr-85 ever since the fuel failures occurred in spite of the leaks and the suspected hydrogen explosion early on during the accident
(b) Kr-85 has been released to the containment atmosphere more recently, which means that some fuel rod claddings have lost their integrity only recently
zapperzero
#10871
Aug10-11, 11:59 AM
P: 1,044
c) corium is still outgassing
rmattila
#10872
Aug10-11, 12:24 PM
P: 242
Quote Quote by zapperzero View Post
c) corium is still outgassing
As far as I am aware, noble gas releases from fuel would have reached 100 % before it even starts to melt. Therefore, the only way I see new release of Kr possible is that part of the fuel would have not overheated to 100 % release levels (=would possible have maintained their cladding integrity and would continue to slowly release noble gases). This is exactly the point I found interesting about the results: to me it seems that either the containment is able to contain noble gases for a long period of time or part of the core must have remained unmelted.


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