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Japan Earthquake: nuclear plants

by gmax137
Tags: earthquake, japan, nuclear
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radio_guy
#10765
Aug3-11, 01:16 PM
P: 24
that 4 Sv/h source is really making the camera struggle.. I wonder what it looked like when they got closer? snow?
etudiant
#10766
Aug3-11, 01:37 PM
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P: 866
Quote Quote by rmattila View Post
Regarding the Finnish/Swedish BWR:s referred to previously:

With the exception of the already-closed Barsebäck units, the Swedish BWR:s (and their two sister plants here in Finland) were backfitted with two separate severe-accident systems: the containment overpressure protection system (system 361 in ASEA coding) and the filtered venting system (system 362). 362 is filtered with so called SAM scrubbers, whereas 361 is unfiltered.


So the venting after fuel damages are to be expected is always done through the filtered-venting line (system 362). Since it has frangible plates, human decision will not be needed to initiate the first venting, but after the venting begins and the manual valves are closed for the first time, re-opening them will require manual action. Both lines are "hardened" in the sense that they are dimensioned for the severe accident conditions, and are separated from the normal containment venting lines used for atmosphere change etc. And as said earlier, they were installed in the late 80's following the TMI accident (which initiated the SAM system projects) and ultimately Chernobyl (which gave it more urgency).

Would the venting still work if the power was out?
Presumably there need to be blowers to force the vented gasses through the filter media.

Separately, if the vent pipe is internally coated with enough material to provide a 10+ Sievert/hr dose, as suggested by the probes, does that not imply the stacks were a very large contributor to the wide dissemination of airborne contamination? Other than the initial blast at reactor 3, pretty much all of the site emissions were fumes from the SFPs and reactors, stuff that would be expected to redeposit locally. It is the plumes from the 200+ ft stacks that really disseminate emissions.
Joewein's reference to Sellafield seems quite apposite, that design did have filters on the stacks, which saved the country when the reactor graphite core burned. Would seem logical to re institute that precaution more broadly.
SpunkyMonkey
#10767
Aug3-11, 01:55 PM
P: 65
Quote Quote by etudiant View Post
Would the venting still work if the power was out?
The vents did work. Units 1 and 3 containment vessels were vented by way of the stacks several times before they exploded. The exact time of each venting was recorded and can be found online. There are also Tepco-Camera stills showing stack emissions, one was just posted in this thread.

Separately, if the vent pipe is internally coated with enough material to provide a 10+ Sievert/hr dose, as suggested by the probes, does that not imply the stacks were a very large contributor to the wide dissemination of airborne contamination? Other than the initial blast at reactor 3, pretty much all of the site emissions were fumes from the SFPs and reactors, stuff that would be expected to redeposit locally. It is the plumes from the 200+ ft stacks that really disseminate emissions.
There's not much visible stack emissions at the time of the explosions. A faint wisp can be seen from the unit 3/4 stack when unit 3 blew.

What I wonder is why it's being said this new high reading is from residual emissions from the March 12 explosion. But it's not like the unit 1 stack was just discovered after months of looking for it. They've been all around unit 1 but only recently did this super-high reading arise. So imo it seems to reflect something new happening.
rmattila
#10768
Aug3-11, 02:01 PM
P: 242
Quote Quote by etudiant View Post
Would the venting still work if the power was out?
Presumably there need to be blowers to force the vented gasses through the filter media.
Still regarding the ASEA plants in Finland:

Valves are manual (with a long shaft running through one room and a concrete wall to reduce dose rate), so no power is needed for venting. The running force is the overpressure in the containment, and only very small pressure difference is needed to force the gases through scrubbers, so the system has no blowers either.

So loss of power should not incapacitate the filtered venting system - since total loss of power is one of the most probable causes for a severe accident, it would not make much sense to make severe accident management systems depend on electricity. However, even though the system is equipped with the mechanical remote operation handles, it was not included in the plants' original design basis, and therefore is not quite optimally located within the plant. Thus the valve operations cause some burden to the workers in the severe accident conditions (climbing of several stairs etc.)

The operation philosophy is that the operators won't initiate the venting, but rather wait for the frangible plate to give in and start the venting by itself. After the pressure has been reduced to a given value, the operators will then close the valve manually. Thereafter, if the pressure would rise again to require venting, further ventings are done manually. For these later ventings the preferable route is from the wet well (the initial release being from the drywell) in order to take advantage of the scrubbing capabilities of the containment blowdown and spray systems.
etudiant
#10769
Aug3-11, 03:59 PM
PF Gold
P: 866
Quote Quote by rmattila View Post
Still regarding the ASEA plants in Finland:

Valves are manual (with a long shaft running through one room and a concrete wall to reduce dose rate), so no power is needed for venting. The running force is the overpressure in the containment, and only very small pressure difference is needed to force the gases through scrubbers, so the system has no blowers either.

So loss of power should not incapacitate the filtered venting system - since total loss of power is one of the most probable causes for a severe accident, it would not make much sense to make severe accident management systems depend on electricity. However, even though the system is equipped with the mechanical remote operation handles, it was not included in the plants' original design basis, and therefore is not quite optimally located within the plant. Thus the valve operations cause some burden to the workers in the severe accident conditions (climbing of several stairs etc.)

The operation philosophy is that the operators won't initiate the venting, but rather wait for the frangible plate to give in and start the venting by itself. After the pressure has been reduced to a given value, the operators will then close the valve manually. Thereafter, if the pressure would rise again to require venting, further ventings are done manually. For these later ventings the preferable route is from the wet well (the initial release being from the drywell) in order to take advantage of the scrubbing capabilities of the containment blowdown and spray systems.

That seems like a well engineered design to reduce the impact of an accident.
It would be helpful to have some idea of the size of the installation needed, to ghet a sense of how easily it can be retrofitted.
Certainly it does give one pause, the idea that the hardened vents might in fact be the instrument for spreading the impact of a disaster over a much wider area. I am surprised that this design feature has not been discussed at all afaik in the US licensing program. What am I missing?
NUCENG
#10770
Aug3-11, 04:18 PM
Sci Advisor
P: 916
Quote Quote by zapperzero View Post
Any idea where they got their 10E-6/reactor-year probability for an accident?
See section 2.4 in the main report. Note that the Peach Bottom and Surry PRAs have been peer reviewed so this is really "state of the art."

Also note that seismic risk was already being reevaluated as described here:
http://www.nrc.gov/reading-rm/doc-co...ic-issues.html.

The unmitigated Long Term SBO is the closest case to Fukushima Daiichi Units 2 and 3.
The effects of RCIC blackstart and black run and B.5.b capabilities added agfter 9/11 in the mitigated cases are significant.
joewein
#10771
Aug3-11, 08:09 PM
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P: 192
Quote Quote by SpunkyMonkey View Post
What I wonder is why it's being said this new high reading is from residual emissions from the March 12 explosion. But it's not like the unit 1 stack was just discovered after months of looking for it. They've been all around unit 1 but only recently did this super-high reading arise. So imo it seems to reflect something new happening.
One thing that is different and that therefore comes to mind is that construction of the plastic cover around unit 1 started recently, meaning there is a lot more activity around the building and more chances to notice what was overlooked before.

Quote Quote by Jim Lagerfeld View Post
Here is a link to nikkei

- the story says that the radiation was recorded on the outside surface of some external 'ventilation' plumbing near to the ground between reactors 1 & 2 by a worker clearing rubble. The upper limit of his meter is 10 Sv/hr and it maxed out, so the true figure is possibly higher. They speculate that radioactive materials released / leaked during the initial venting (pre-explosion) may have adhered to the pipe.
The "worker clearing rubble" quote to me suggests a connection to the cover construction.

Also, is it possible that recent rains could have washed condensate down the inside walls of the stack, concentrating them at the lower end, including the "elbow" joining it at the bottom?

SteveElbows
#10772
Aug3-11, 08:12 PM
P: 630
Quote Quote by etudiant View Post
Does this not mean that the stack emissions were the primary source of the contamination plumes that Japan is now starting to focus on? It seems to indicate that the explosions may have played second fiddle to the stack emissions in propagating the radioactivity beyond the plant boundaries.
The picture that emerged from a variety of official data points to quite a collection of significant releases over a number of days early on. The releases that seem to be responsible for the plumes that caused significant land pollution were probably from reactor 1 and then later a much more significant one from reactor 2, which is blamed for around 90% of the total radioactive release into the air.

What I cannot say with any certainty is how much of this stuff came from vent stack rather than more directly from the reactor, turbine or waste processing buildings of each reactor after containment damage and explosions. Early contamination data from before reactor 1 explosion certainly points to some radioactive material having travelled off-site before the explosion, so I think its probably reasonable to expect that venting had a notable impact in this regard.

As for reactor 2, they had a lot of trouble trying to get venting procedures to work, so the picture as to whether venting happened successfully, to what extent, and at what time, is less than complete. And despite the official estimations for radioactive release putting so much blame on reactor 2, we never really got much more detail from company, government or media about this. But if we recall how the news of the suspected explosion near the suppression chamber was treated when it happened, it was considered a big deal and so it would be reasonable to think that this event, rather than venting via stack, caused a lot of the reactor 2 release. But I cannot rule out a large amount coming from the stack via venting either, not enough information & visual evidence to be sure.

I think Reactor 3 explosion stuff was lately carried away from land due to wind direction at the time, and I have not studied venting activity for reactor 3 or tried to connect it to times when site radiation levels rose.

Official data also shows that significant releases (albeit several orders of magnitude less than the peak release rate) continued for much of March, and it is possible that some of this was due to further venting.

The chart of estimated release rates over time may be of help when trying to get our heads round this stuff, or quite the opposite as it kills the simplified version of events:

clancy688
#10773
Aug3-11, 09:28 PM
P: 546
Quote Quote by SteveElbows View Post
Official data also shows that significant releases (albeit several orders of magnitude less than the peak release rate) continued for much of March, and it is possible that some of this was due to further venting.
I think "albeit several orders of magnitude less" is correct but misleading. Actually, between March 30th and 31st 1900 TBq C-137 was released. That's 10-15% of the total number.
The discharge on March 30th was magnitudes smaller than the maximum discharge rate right after the tsunami, but it went on for a whole day. So it highly contributed to the total release.

http://physicsforums.com/showpost.ph...ostcount=10418
etudiant
#10774
Aug3-11, 10:12 PM
PF Gold
P: 866
Quote Quote by SteveElbows View Post
The picture that emerged from a variety of official data points to quite a collection of significant releases over a number of days early on. The releases that seem to be responsible for the plumes that caused significant land pollution were probably from reactor 1 and then later a much more significant one from reactor 2, which is blamed for around 90% of the total radioactive release into the air.

What I cannot say with any certainty is how much of this stuff came from vent stack rather than more directly from the reactor, turbine or waste processing buildings of each reactor after containment damage and explosions. Early contamination data from before reactor 1 explosion certainly points to some radioactive material having travelled off-site before the explosion, so I think its probably reasonable to expect that venting had a notable impact in this regard.

As for reactor 2, they had a lot of trouble trying to get venting procedures to work, so the picture as to whether venting happened successfully, to what extent, and at what time, is less than complete. And despite the official estimations for radioactive release putting so much blame on reactor 2, we never really got much more detail from company, government or media about this. But if we recall how the news of the suspected explosion near the suppression chamber was treated when it happened, it was considered a big deal and so it would be reasonable to think that this event, rather than venting via stack, caused a lot of the reactor 2 release. But I cannot rule out a large amount coming from the stack via venting either, not enough information & visual evidence to be sure.

I think Reactor 3 explosion stuff was lately carried away from land due to wind direction at the time, and I have not studied venting activity for reactor 3 or tried to connect it to times when site radiation levels rose.

Official data also shows that significant releases (albeit several orders of magnitude less than the peak release rate) continued for much of March, and it is possible that some of this was due to further venting.

The chart of estimated release rates over time may be of help when trying to get our heads round this stuff, or quite the opposite as it kills the simplified version of events:

Thank you again for this excellent graphical summary of the initial releases.
My focus on the stack emissions comes from a background in air pollution. When standards were first set, it became rapidly clear to industry that tall stacks were a great way to meet standards by polluting a much larger area less intensively. Normally, emissions tend to redeposit within a few miles, but a multi hundred foot stack will lift the plume enough to diffuse through tens of miles. Unfortunately, this accident was so bad the dilution was entirely too little. That seems a serious weakness in the design, that it potentially magnifies the geographic scale of the damage considerably.
tsutsuji
#10775
Aug4-11, 01:41 AM
PF Gold
P: 1,220
Quote Quote by tsutsuji View Post
http://www.tepco.co.jp/nu/fukushima-...10803_04-j.pdf Water treatment facility bypass line No. 1 and bypass line No. 2 diagram (not yet translated into English)
http://www3.nhk.or.jp/news/genpatsu-...tsu_ho-su.html The hoses are being connected today, which requires shutting down the facility for half a day. SARRY will be launched on 8 August. With the increase of water treatment capacity, Tepco thinks they can achieve to bring the basement water levels to "safe levels" in unit 1 & 2 in the first decade of September, instead of the last decade of September as originally planned.

Quote Quote by tsutsuji View Post
http://www.tepco.co.jp/cc/press/betu...es/110803l.pdf This is the Japanese language press release version of Tepco's report to NISA about the stability of securing cooling to units 1,2,3. According to http://mainichi.jp/select/weathernew...40042000c.html it contains details such as the earthquake safety of the system, or how much time it would take to recover from a blackout. I have begun to read some pages. Page 11-1 (pdf page number 33) tells how much time it would take to reach 1200°C if cooling stops : 15,14,13 hours respectively for units 1,2,3.
http://www3.nhk.or.jp/news/genpatsu-...00_saikai.html Tepco says they can recover from a blackout in 3 hours. If backup pumps and generators are available, they can recover in 30 minutes. If fire engines need to be brought, it takes 3 hours. When recovering from a loss of coolant the injection rate would be brought to a maximum to minimize the risk of hydrogen explosion.

http://www3.nhk.or.jp/news/genpatsu-...803/index.html The middle-long term special committee had its first meeting yesterday. They listened to the explanations of Mr Yuichi Hayase who worked in a joint US-Japan research team on Three Mile Island. The committee president said he expects the work to remove the fuel from Fukushima Daiichi will take longer than at TMI, because the fuel damage is worse.

http://www3.nhk.or.jp/news/genpatsu-...804/index.html He said it could be something like 20 years. According to Mr Hayase, it took one year until workers could enter TMI's containment vessel, and 3 and a half years until cameras could enter TMI's RPV. It took 3 years to complete water treatment at TMI. Then the work was delayed because of a growth of micro-organisms in the water. The fuel removal started 6 and a half years after the accident and was completed 11 years after the accident. However, with broken containment vessels and not only one but three reactors, the situation at Fukushima is worse than TMI.

Quote Quote by tsutsuji View Post
http://www.meti.go.jp/press/2011/08/...10803004-2.pdf The water treatment facility treated 6190 m³ during the 27 July-2 August week. Utilization rate 6190/(50*24*7) = 74%.
http://news.tbs.co.jp/newseye/tbs_newseye4792695.html It is a dramatic increase from the previous week's 58%, but the quantity accumulated in turbine buildings basements decreased by 60 tons only! This is due to either rainfalls or ground water seeping in.

http://www.tepco.co.jp/en/press/corp...s/110803e2.pdf (English version of the above). Aren't they forgetting the extra 700 tons recently found in the Site Bunker Building ?

http://www.tepco.co.jp/en/press/corp...s/110803e4.pdf This press release version of a Tepco report to NISA shows the various switching possibilities between the SARRY, KURION and AREVA systems.

On 28 July, Tepco reported to NISA the following SFP cooling systems design changes:

Unit 1
In order to maintain spent fuel pool water level and manage leakage, we have reported to monitor the water level of skimmer surge tank by existing skimmer surge tank water gauge. However, we will alter this method as the corresponding water gauge is broken.(ref. Figure 1)

Unit 2
We will alter the layout of weirs etc to prevent leakage of contaminated water outside building, as a result of consideration to reducing workers' exposures. We will partly amend the evaluation result of estimated leakage amount, in cases leakage occur. We will add method to treat accumulated water containing radioactive materials within buildings, in cases leakage occur (ref. Figure 2)

Unit 3
We will add method to treat accumulated water containing radioactive materials within buildings, in cases leakage occur

Unit 4
We will alter the area to install weirs, and alter method to drain leakage water, as a result of consideration to site conditions, working environment safety and constructing conditions (ref. Figure 3).
http://www.tepco.co.jp/en/press/corp.../110728e17.pdf
rmattila
#10776
Aug4-11, 01:58 AM
P: 242
Quote Quote by etudiant View Post
It would be helpful to have some idea of the size of the installation needed, to ghet a sense of how easily it can be retrofitted.
Some idea of the design bases can be found in this presentation, pages 8 and 9. (Not the actual dimensions of the tanks, though.)
nikkkom
#10777
Aug4-11, 02:49 AM
P: 611
Quote Quote by rmattila View Post
Still regarding the ASEA plants in Finland:

Valves are manual (with a long shaft running through one room and a concrete wall to reduce dose rate), so no power is needed for venting. The running force is the overpressure in the containment, and only very small pressure difference is needed to force the gases through scrubbers, so the system has no blowers either.

So loss of power should not incapacitate the filtered venting system - since total loss of power is one of the most probable causes for a severe accident, it would not make much sense to make severe accident management systems depend on electricity. However, even though the system is equipped with the mechanical remote operation handles, it was not included in the plants' original design basis, and therefore is not quite optimally located within the plant. Thus the valve operations cause some burden to the workers in the severe accident conditions (climbing of several stairs etc.)

The operation philosophy is that the operators won't initiate the venting, but rather wait for the frangible plate to give in and start the venting by itself. After the pressure has been reduced to a given value, the operators will then close the valve manually. Thereafter, if the pressure would rise again to require venting, further ventings are done manually. For these later ventings the preferable route is from the wet well (the initial release being from the drywell) in order to take advantage of the scrubbing capabilities of the containment blowdown and spray systems.
I imagine than if you are in SBO and all cooling is lost, it is actually better to vent (depressurize) early, while temperature in the reactor is not much higher than ~300 C - this will deprive Zr from the water to react with when/if temperature will rise later. Additional benefit is that in many cases, the vented steam will not be strongly radioactive yet, since fuel did not yet melt.

IOW: "dry" (waterless) meltdown is better than "wet" one. If you think you are heading towards one, try to at least make it "dry".

However, I do not know if (1) I am correct in my reasoning, and (2) whether current accident manuals and operator training include guidelines for such a severe accident case.

Can someone from industry comment on this?
nikkkom
#10778
Aug4-11, 02:56 AM
P: 611
Quote Quote by tsutsuji View Post
http://www3.nhk.or.jp/news/genpatsu-...804/index.html He said it could be something like 20 years. According to Mr Hayase, it took one year until workers could enter TMI's containment vessel, and 3 and a half years until cameras could enter TMI's RPV. It took 3 years to complete water treatment at TMI. Then the work was delayed because of a growth of micro-organisms in the water. The fuel removal started 6 and a half years after the accident and was completed 11 years after the accident. However, with broken containment vessels and not only one but three reactors, the situation at Fukushima is worse than TMI.
The understatement of the year?
tsutsuji
#10779
Aug4-11, 03:18 AM
PF Gold
P: 1,220
Quote Quote by nikkkom View Post
The understatement of the year?
This is not a quote. It is my summarized translation. A more literal translation of the NHK article would be "It will take more time at Fukushima as the situation is deemed more serious/severe, compared with TMI" (instead of "worse than").
rmattila
#10780
Aug4-11, 03:25 AM
P: 242
Quote Quote by nikkkom View Post
IOW: "dry" (waterless) meltdown is better than "wet" one. If you think you are heading towards one, try to at least make it "dry".

However, I do not know if (1) I am correct in my reasoning, and (2) whether current accident manuals and operator training include guidelines for such a severe accident case.

Can someone from industry comment on this?
I'd say there is no such thing as a "wet meltdown": as long as at least half of the core is covered, the steam will provide some cooling to the top of the fuel to slow down the heat buildup, and cladding integrity is lost only after water will fall to -2m or so.

In the particular Finnish case, SAM procedures are entered when water level has been below +0.7 m for more than 30 minutes. At that time, the reactor pressure vessel is depressurized (to prevent high-pressure melt through, which the containment would not endure, and also to enable low-pressure core injection, if it would happen to be available) and the lower drywell is flooded in preparation for a melt-through. However, there's no point in venting the containment at that time, since there's a relatively high probability that no venting will be needed at all - venting will only be needed, if the power outage lasts for several hours after the core has melted, and the decay heat removal from the wet well can not be started.

In other words, venting is not a standard procedure to be applied in core melt situations, but rather an additional backup in case the containment heat removal has not been started after about 8 hours after the meltdown. If this can be done, then no venting will be needed to contain the core remains.
Dmytry
#10781
Aug4-11, 04:42 AM
P: 505
Regarding the filtered venting - just as Fukushima struck, NRC was in the final stage of preparation of a much lower impact estimate for core meltdowns:
http://www.physorg.com/news/2011-08-...-meltdown.html
, most interestingly, downsizing the Cs-137 release in a core melt from 60% of the inventory to 2% of the inventory.
My understanding is that it is the 60% estimate which justified Finnish/Swedish implementation of filtered high volume venting.
This reminds of Cockcroft's Folly...
SteveElbows
#10782
Aug4-11, 05:57 AM
P: 630
Quote Quote by clancy688 View Post
I think "albeit several orders of magnitude less" is correct but misleading. Actually, between March 30th and 31st 1900 TBq C-137 was released. That's 10-15% of the total number.
The discharge on March 30th was magnitudes smaller than the maximum discharge rate right after the tsunami, but it went on for a whole day. So it highly contributed to the total release.

http://physicsforums.com/showpost.ph...ostcount=10418
Yeah thats a fair point. Do we have any idea what happened on the 30th-31st? I don't remember hearing of anything specific in the past, is venting a possibility?


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