Japan Earthquake: nuclear plants
|Mar30-12, 12:16 PM||#12785|
Japan Earthquake: nuclear plants
In regards to similar USA BWR plants (Oyster Creek \ Duane) - The buildings have "normal" HVAC systems, then the SGTS, then the hardened vent systems (There are other ventilation systems as well but they are minor\ are more plant specific). SGTS is not related to normal building ventilation or the "hardened" vent system. SGTS is a standby system only for purging containment for startup\shutdown or (minor) emergency use.
We know for sure the hardened vent system is a totally seperate system all the way to the stack. Early on (but post construction of this type of reactor unbelievably) it was found the SGTS would be inadequate and fail inside the RB during a high pressure venting scenario, filling it with steam and gases. So the hardened vent system was a retrofit to address this issue.
For others, some good insights on those systems and the accident in general in these two docs:
Role of BWR secondary containments in severe accident mitigation
Joseph Shephard - CalTech - The Crisis at Fukushima NPP (Sept 2011, some of it might be out of date but it's still worth a read
Re - pipes diving underground at base of stacks - without TEPCO drawings who knows. There are sump pumps in the base of the stacks so there would be some outlets for those to send to waste treatment although those ones look a bit large for that purpose. This is a drawing for the stack at Oyster Creek which indicates there are lots of connections to their plant stack.
( Who knows, there may be seperate lines to the stack for the "wet" & "dry" hardened vent lines although I've only seen drawings that contradict that.)
Re - exhausts on NW corners of Units 2,3,4 & 5 ("boxed in" on NW corner of U5 RB),
Unit 1 & 6 dont have it there but they but have a similar stack on the northside of their TB's. "Normal" building vent stacks (non SGTS) or are they steam exhausts?
Maybe someone can clarify which. US plant drawings show seperate (from the large stack) "normal" building stacks with their own filter train.
@ ZZero - The EDG's exhausts are right over on the eastern sides of the TB's on units 1-5 as the EDG's are in the TB's of units 1-5 (Apart from the retrofitted two air cooled EDG's for units 2 & 4 over in the common spent fuel building which were added in the '90's. For a few million more they could have put those two air cooled EDG's and their switchgear on the hill.......so much for SAM) , on unit 6 only you can see the EDG exhausts up the north side of the RB , the EDG's are in a building attached to the side RB 6 (however in another drawing they appear in the bridge building between RB 6 & it's TB but thats more the US style I believe) . Then to finish this for others benefit, U6 is unique at fukuichi in that it has three EDG's, one of the DG's is dedicated to powering HPCS, there is the seperate air cooled EDG north of Unit 6 which likely saved units 5 & 6 (from exploding at least))
|Mar30-12, 04:30 PM||#12786|
Technically Tepco tries isolating both basements.
Making two separate not-interconnected non-interacting water circuits makes sense.
Effects easily obtained:
Contaminants from R/B won't reach T/B anymore.
Possibility to prioritize on leaks in R/B.
Less groundwater contamination.
R/B protection from T/B salt water inflow.
P.S.: Thank you Mr. Tsutsuji-san! Excellent informative posts!
|Mar30-12, 04:42 PM||#12787|
Interesting scenes from TEPCO's video related to ocean monitoring of sea life in 20 km
|Mar30-12, 05:49 PM||#12788|
|Mar31-12, 02:17 AM||#12789|
Yikes :-), now you've got me wondering how the contamination of the water in the R/B basements compares to that of the T/B basements and further downhill.
|Mar31-12, 03:36 AM||#12790|
Every TEPCO Daiichi plant status report contains this passage:
However this doesn't exclude other water or additives (boron) potentially being added to cooling water.
(see Tsutsuji's posts on previous page).
|Mar31-12, 04:55 AM||#12791|
A) The leakage point is located lower than the present torus room water level
The leakage rate would depend on the difference of height between the drywell water level and the torus room water level. In this case, lowering the torus room water level would be a bad idea, because the leakage flow rate would increase, and this would affect the water level in the drywell (if the injection rate into RPV is kept constant).
B) The leakage point is located higher than the present torus room water level
The leakage rate would depend on the difference of height between the drywell water level and the leakage point. In this case, lowering the torus room water level would not affect the leakage rate nor the drywell water level.
So I think it would be good to install a water level gauge in the drywell, and perform the torus room drainage with an eye on the water level gauge. If the drywell water level starts decreasing, you know that you are in the wrong case and you must stop what you are doing. At least you learnt something : you learnt that you are in case A).
You may want to consider the present 60 cm above PCV bottom as a minimum that must be kept. To create a margin, you could increase the RPV injection rate until the drywell water level rises to 70 cm above PCV bottom.
If this water was not badly contaminated, you may have wanted to try to do the opposite: to raise the torus room water level, and see if it affects the drywell water level.
|Mar31-12, 05:42 AM||#12792|
I am not sure the hardened vent is a totally separate system at these plants. From what Tepco has said, such retrofits were indeed made to the plants. Also it would seem implied by what Tepco has said, that these vent lines were used for the PCV ventings. However, Tepco has speculated that the Unit 1 PCV vent might have back-flowed into the Unit 1 R/B through its SGTS piping, causing the explosion. And Tepco has more than speculated that Unit3 PCV vent back-flowed into the Unit4 SGTS system. Either of these theories by Tepco implies that the PCV vent lines and the SGTS lines are not separate all the way to the stack, and it would be implied that the SGTS lines were either not protected by back-flow valves (seems to be the case of Unit 1) or the back-flow valve had failed open when power was lost (units 2-4). (All the SGTS systems were presumably operating per automation from shortly after the earthquake, and until power was lost.)
|Mar31-12, 06:24 AM||#12793|
http://www.meti.go.jp/earthquake/nuc...120328_02m.pdf Scattered debris survey plan (28 March 2012 mid-long term steering committee meeting)
To perform a survey, checking whether debris spread by the hydrogen explosions are staying in the electric power plant premises.
Explore regions of the premises starting at the center where units 1~4 are located, and going toward monitoring posts MP1~MP8. (As the first 500 m closest from center have already been explored and the debris there have been collected, they are excluded)
Definition of the debris that are the object of the survey
* Shape: solids (building rubble) like small stones or bigger that can be checked by visual observation
* Radioactivity, radiation dose: high radioactivity, high radiation dose objects that depart from background (BG)
Scattered debris determination standard
* When a debris is discovered, it is measured with a surveymeter (Geiger tube, ionization chamber). BG is also measured.
* If the measured value is higher than BG, the object is judged to be a scattered debris.
* Leader : 1 person, survey: 4 groups of 3 people (total 13 people)
* 26 March 2012 ~30 March 2012 (2 April ~ 6 April is reserved in case of rain)
* Below 1 mSv/person.day
Fukushima Daiichi premises general layout map
In case building debris scattered material is discovered, the discovery location is marked on a map. [Computing] the distance from units 2 and 3 reactor buildings with the premises layout map CAD system, the maximum scattering distance is measured and a map of the scattering area is generated.
[see also the map on page 4:]
yellow=scattered object survey directions
red dots=500 m range where scattering was confirmed
|Mar31-12, 09:26 AM||#12794|
http://www.meti.go.jp/earthquake/nuc...120328_02x.pdf Results of survey of debris distribution in spent fuel pool, unit 4 (28 March 2012 mid-long term steering committee meeting)
1. Survey of debris distribution in unit 4 spent fuel pool
same as http://www.tepco.co.jp/en/nu/fukushi...20312_01-e.pdf page 1
2. Outline of survey of debris distribution in unit 4 spent fuel pool
same as http://www.tepco.co.jp/en/nu/fukushi...20312_01-e.pdf page 2
3. Result of survey of debris distribution in unit 4 spent fuel pool (19 ~ 21 March)
4. Outline of survey of debris at the bottom of unit 4's reactor
same as http://www.tepco.co.jp/en/nu/fukushi...20312_01-e.pdf page 2 except "(if
necessary, we will use ROV)" which was deleted.
5. Result of the survey of debris at the bottom of unit 4's reactor
The diagram is the same as the one on http://www.tepco.co.jp/en/nu/fukushi...20312_01-e.pdf page 4
6. New transparency check inside unit 4 spent fuel pool (20 March)
1. Checking method
At almost the same location as the last time (9 February), using the same camera, the same wire and marks, the visibility distance is measured.
Visibility was comparable with that of February 9. Therefore, we conclude that there
has been no change in the degree of transparency.
[The diagram does not require a translation as it is almost the same as the one on http://www.tepco.co.jp/en/nu/fukushi...20210_03-e.pdf except that the man is now standing on the float, the fuel handling machine is not shown, and the spent fuel is not shown.]
7. Result of the transparency check inside unit 4 spent fuel pool (20 March)
same as http://www.tepco.co.jp/en/nu/fukushi...20322_02-e.pdf
|Mar31-12, 10:49 AM||#12795|
http://www.meti.go.jp/earthquake/nuc...120328_02d.pdf plant status (28 March 2012 mid-long term steering committee meeting) [only partial translation]
[A table displaying the plant parameters on 26 February and 27 March]
As unit 1, unit 2 and unit 3's PCV temperatures and RPV temperatures are around 25°C ~ 55°C (as of 27 March), there is no significant variation of RPV and PCV parameters such as the released radiation doses, and we judge that the cold shut down status is comprehensively maintained.
In order to maintain the measuring instruments' soundness in the future, while the surveillance with measuring instruments is continuing, a study toward diversification and implementation of alternative temperature surveillance means is under way.
|Apr1-12, 10:36 AM||#12796|
http://weather.goo.ne.jp/earthquake/12040123040.html There was a magnitude 5.9 earthquake off the Fukushima coast on 1 April 2012 at 23:04 JST. JMA seismic intensity scale "5 minus" was recorded at Tomioka and Naraha, Fukushima prefecture. There is no tsunami risk.
http://www3.nhk.or.jp/news/html/2012...131781000.html The NISA said that no problem was reported from Fukushima Daiichi or Daini (in consequence of this earthquake). Monitoring post radiations are stable.
|Apr1-12, 11:02 AM||#12797|
Dark smoke looks quite normal so Doom is off ;)
|Apr1-12, 01:43 PM||#12798|
The implementation of the common pipe to the stack from the SGTS and the hardened vent system includes a diving section just before the vent pipe enters the stack. It can be seen as a foo or a feature to have what is essentially a a water trap incorporated in such a system. On one hand it might provide additional scrubbing during a hardened vent procedure -- otoh it might also provide increased back-pressure, and increase the risk of diverting the flow of the vented gases back into the buildings through the SGTS system.
|Apr2-12, 04:32 AM||#12799|
http://www.tepco.co.jp/cc/press/betu...20402j0101.pdf Report to NISA on units 1 ~ 3 thermometer reliability. (the NISA requested Tepco to write a report once a month) : some of the thermometers not previously evaluated were found to be usable, and some were found to be broken. Some thermometers that were not connected to a digital recorder have been connnected to a digital recorder.
According to the plot on page 126, unit 2's 69 TE-16-114L#2 RPV BELLOWS SEAL AREA, newly connected to a digital recorder (on 8 March 2012) reached 100°C on 19 March 2012. (but it is not marked as "broken"). TE-16-114L#1 is having a similar rising trend, reaching 83°C on 19 March 2012. I will be curious to see if those two are marked "broken" in next month's report.
|Apr3-12, 05:07 AM||#12800|
http://www3.nhk.or.jp/news/html/2012...177241000.html Because strong winds of 18 metres [per second] are expected, outdoor work with cranes is suspended at Fukushima Daiichi on 3 April afternoon. Crane arms have been made shorter. Sheets covering debris have been reinforced with weights and ropes.
|Apr3-12, 06:55 PM||#12801|
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