Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Dmytry]

1. We may experience a China Syndrone as written by Time.com. Core will explode when hitting ground water soon. Or burns deep into Earth's crust triggering a volcano (wtf! I cannot believe this could happen).

1. 
   this could not. absolutely impossible. When core melts through stuff, it dilutes. This is case of stupid abstract thinking by media. Reactor core. A core, something hard, that stays itself.
   Reality: molten corium, of low thermal conductivity, mixes up with stuff, dilutes, the heat output decays, etc. Hitting ground water, another dumb abstraction. Water content in the soil increases gradually, the material in question (corium lava) has low thermal conductivity, and freezes on contact. The giant steam explosion is a concern if a lot of it falls literally into a body of water at once. Otherwise you simply do not get heat transmission rate enough to explode anything. Even if it literally falls into water it might not explode. Indeed it did fall into water once, when the water ran below the fuel level - and remained there, corium falling into it.

 

[MadderDoc]

<..>the data that showed huge pressure spike from one sensor at 01:25, 01:45 and 02:30 had certainly been seen before by some people on this forum, because someone found old version of this data on the internet and posted about it here a while back, but again I am not sure if anyone noticed the pressure spike early on 21st march.

Perhaps you can dig up a link to the data to which you make reference. It would be interesting to correlate it with this present dataset.

The problem I still have with this event is that there are no interesting changes to CAMS readings around this period, and simply because there was so much going on during the week of the 20th march that it is hard to know what to rule out.

Well, not all events in a wrecked NPP would affect CAMS readings, I reckon.

I have already talked about weather, and I believe tepco webcam archive images from around 20th will show that it rained on site.

Not really. Neither the evening shots of the webcam from March 20th nor the morning shots on March 21st indicate any rain. At the time of the event itself it was of course dark night, and there is no data from the webcam.

They had been connecting power up to various things at various reactors. When they got temperature sensors working at reactor 3 around 19th march, they saw scary temperatures and I think they implemented additional cooling within a few days.

During this period it appears several hefty and dangerous missions to control unit 3 was done by first the Japanese Defence Force, then the Hyper Rescue Unit of the Tokyo Fire Department using firetrucks and fire hoses.

At the time of the apparent event in unit 3 around 2 am on March 21st, according to Tepco press releases, the Hyper Rescue Unit would have been in action at unit 3:
"At approximately 9:30 pm, March 20th, spraying water was started with the
cooperation of Fire Rescue Task Forces of Tokyo Fire Department. At
approximately 4 am, March 21st, they finished the operation."

 

[NUCENG]

This link shows a basic layout of the level circuit. 2 taps into the vessel connected to a differential pressure (DP) cell and transmitter. http://www.pbnc2010.org.mx/pdfs/technical/tuesday/14.00_ModelingLevelInstrumentation.pdf

The released TEPCO photo shows the techs at a whole panel of DP cells.
I don't think anyone knows for sure where these taps actually sense level in the RPV. Is the bottom tap in the shroud region or acually in the vessel itself (ie below the downcomer)??
It is also not clear if they blew back the sensing lines to make sure they were clear of any obstruction. They also should have pumped water back up to the upper condensate pot to ensure the reference leg was full. Without doing these 2 steps - the readings may still be wrong!

See RG 1.97 for requirements for Post-Accident Monitoring Instrumentation at US Nuclear plants (Rev 3 is the latest version that included the required ranges):
http://adamswebsearch2.nrc.gov/idmws/DocContent.dll?library=PU_ADAMS^pbntad01&LogonID=104a5533b05307c56d262f6d365c76e8&id=003957314

Table 2 BWR Variables
Coolant Level in Reactor Vessel
Required Range.
Bottom of core support plate to lesser of top of vessel or centerline of main steam line.

For post- accident monitoring instrumentation, I checked one BWR3 and one BWR 4 in the US. Both of these plants have instrument taps about 150 cm below the steam nozzle centerlines and a lower tap near the bottom of the core shroud well below the core support plate. The fact that the highest tap is below the nozzle centerline is of no consequence in a Fukushima-type event.

These water level instruments are Category 1 per RG 1.97 and are qualified seismically and environmentally for design basis accidents. Both plants have keep-fill systems that will maintain the reference legs filled. Every US plant has made submittals of the design , qualification, and quality controls for their Post-Accident Monitoring Programs. These submittals have been reviewed and approved by NRC and are subject to periodic inspections by NRC inspections.

Again, I cannot say for certain whether Japan has similar requirements, however, this all came out of TMI2 and Japan did implement many of the Post-TMI Lessens Learned.

 

[jim hardy]

But: How can the core melt holes into the RPV without falling out afterwards at least partially?

there's a Oak Ridge study about that at
http://www.osti.gov/bridge/servlets/purl/6124656-R8y05j/6124656.pdf

it's linked someplace earlier in this long, long thread I'm not first.

basically the rods and instrument tubes penetrate the vessel bottom through stub tubes to which they are in turn welded. The rod stub tubes stick up a ways, instruments are welded right at inside bottom.

there's sketches around page six.

I remember hearing in a press release that some of (which unit? i forget)'s rod mechanisms were observed down against their mechanical stop, meaning they are detached on the inside as expected. The mechanical stop is there to keep them from falling all the way out in case they do detach..

 

[SteveElbows]

Please, can I ask of your source of this information?

Official english TEPCO documents that contain history of things says:

Since 6:15am, March 17th, the pressure of the Suppression Chamber temporarily increased, on March 20th, we were preparing for implementing measures to reduce the pressure of the reactor containment vessel (partial discharge of air
containing radioactive material to outside) in order to fully secure safety. However, at present, it is not a situation to immediately implement such measures and discharge air containing radioactive material to outside. We will continue monitoring the status of the pressure of the reactor containment vessel.

Sorry I don't have link to document handy right now. But it also says things about spraying operations you just mentioned,with more detailed timing. These come from the section dealing with spraying of seawater into spent fuel pool at reactor 3.

From approx. 9:30am to past 10:00am, March 17th, water was sprayed by helicopters upon our request for the cooperation to Self-Defense Forces.
- From approx. 12:30am to 1:10am, March 19th, water was sprayed with the cooperation of Fire Rescue Task Forces of Tokyo Fire Department. They resumed the operation from approx. 2:10pm to 3:40am, March 20th.
- From approx. 9:30pm, March 20th to 3:58am, March 21st, water was sprayed with the cooperation of Fire Rescue Task Forces of Tokyo Fire Department.
- From approx. 3:10pm to 3:59pm, March 22nd, water was sprayed with the cooperation of Fire Rescue Task Forces of Tokyo Fire Department.
- Sea water was injected through Fuel Pool Cooling and Filtering System; From approx. 11:03am to 1:20pm on March 23rd From approx.5:35am to 4:05pm on March 24th

 

[ernal_student]

Sorry I don't have link to document handy right now.

Maybe this one? It has an odd URL, though - not original TEPCO

http://www.tepco.co.jp.cache.yimg.jp/en/press/corp-com/release/betu11_e/images/110506e2.pdf

 

[SteveElbows]

Perhaps you can dig up a link to the data to which you make reference. It would be interesting to correlate it with this present dataset.

I found the post on this thread where these older documents were rediscovered:

https://www.physicsforums.com/showthread.php?p=3291191&highlight=google#post3291191

As for comparing it with new version of data, one version of the data released just the other day showed which entries were new by putting them in blue. These were what I quickly skimmed over in order to conclude that most pertinent new info was about a certain key time at reactor 2, but that I may have missed other important new aspects. Do have to be careful in a few places though because for at least one reactor not all the reactor pressure readings that are in blue are really new, rather they seem to have swapped round the A and B readings that were previously published, and so that's why the data is classed as new.

Well, not all events in a wrecked NPP would affect CAMS readings, I reckon.

True, its just in particular at 01:25 on 21st I would have liked to see even more data that could lead us neatly to a theory, and the CAMS does not help in this case, especially as much like the temperature data they only started getting it again a few days before the 21st so can't see moment that CAMS levels first shot up, there is a gap.

Not really. Neither the evening shots of the webcam from March 20th nor the morning shots on March 21st indicate any rain. At the time of the event itself it was of course dark night, and there is no data from the webcam.

Well bear in mind that I have indicated that I am looking at a wider period of time, not just restricting myself to 01:25 on that day. But even so I am not sure what webcam images you are looking at, because I look at the archive for March 21st and very quickly it shows what looks like raindrops on camera lens cover.

http://gyldengrisgaard.dk/tepcowebcam/tepweb20110321.html

During this period it appears several hefty and dangerous missions to control unit 3 was done by first the Japanese Defence Force, then the Hyper Rescue Unit of the Tokyo Fire Department using firetrucks and fire hoses.

As hinted at in my previous post, its not safe to characterise these JDF missions as being about the reactor, but rather the fuel pool. In theory its possible that it was to do with reactor and they never told anyone, but we would need better evidence to lead us in that direction.

 

[NUCENG]

Interesting, thanks for sharing. That seems like very solid data, I mean it comes from the official "Japanse Geospatial Information Authority of Japan (GSI)" site after all (link from ex-skf's blog entry: http://www.gsi.go.jp/chibankansi/chikakukansi40005.html ).

And it comfirms what some people have mentioned on this forum based on the TEPCO webcam pictures.

Thinking of those pictures of that road and the pictures from the New Zealand quake, it's good that at least there was no crack and horizontal offset in the ground right through the site of the power plant.

At lunch today I spoke with a college geology professor who tried to explain this to me. Hopefully I won't confuse everybody further. The area just off the Japanese east coast is a subduction zone where the pacific geological plate is diving down underneath the asian plate. As the pacific plate tries to move to the west over time it builds up pressure which tries to move Japan to the west and also pushes it upward. When the quake hit the two plates slipped and the result was that Japan moved to the east as the pressure was relieved and also dropped vertically.

Japan is riding on top of two plates. As the Pacific plate gets deeper and melts beneath Japan some of it rises through cracks above to fuel Japan's volcanos. Japan is apparently not in any danger of sinking, but it is likely to get shaken up periodically and may experience further problems from volcanos.

 

[MadderDoc]

Maybe this one? It has an odd URL, though - not original TEPCO

http://www.tepco.co.jp.cache.yimg.jp/en/press/corp-com/release/betu11_e/images/110506e2.pdf

"Since 6:15am, March 17th, the pressure of the Suppression Chamber temporarily
increased, on March 20th, we were preparing for implementing measures to
reduce the pressure of the reactor containment vessel (partial discharge of air
containing radioactive material to outside) in order to fully secure safety. However,
at present, it is not a situation to immediately implement such measures and
discharge air containing radioactive material to outside."

It is clear this is a poor translation of a text in Japanese, which I am sure originally made perfect sense.

As it stands, it appears to be saying that S/C pressure was seen as a problem due to pressure readings on March 17th. (D/W and S/C pressure readings on March 17th at our present state of knowledge do not clearly show which S/C readings could have caused this concern. The DW/SC readings for this period appear incomplete, confusingly unstable, and/or implausible.

Anyhow, due to this concern, it appears, Tepco would have liked to vent, and had anticipated that such a measure could be implemented on March 20th. It may be implied here that conditions at the reactor did not allow this to be done earlier, and from what else we know that may very well have been the case, whatwith all the douching with helicopters and firetrucks and hoses to the top of the wrecked reactor building.

The last statement, I do read it as saying that the present conditions at unit 3 on March 20th doesn't allow venting to be done (one would have to wait a bit longer than anticipated) -- however alternatively it seems to me the statement can perfectly well be read as saying that present conditions at unit 3 on March 20th no longer makes the measure necessary to implement immediately.

 

[Astronuc]

At lunch today I spoke with a college geology professor who tried to explain this to me. Hopefully I won't confuse everybody further. The area just off the Japanese east coast is a subduction zone where the pacific geological plate is diving down underneath the asian plate. As the pacific plate tries to move to the west over time it builds up pressure which tries to move Japan to the west and also pushes it upward. When the quake hit the two plates slipped and the result was that Japan moved to the east as the pressure was relieved and also dropped vertically.

Japan is riding on top of two plates. As the Pacific plate gets deeper and melts beneath Japan some of it rises through cracks above to fuel Japan's volcanos. Japan is apparently not in any danger of sinking, but it is likely to get shaken up periodically and may experience further problems from volcanos.

Japan and Indonesia are somewhat unique, which has to do with a convergent boundary and the smaller plates involved.

http://pubs.usgs.gov/gip/dynamic/zones.html
http://earthquake.usgs.gov/learn/topics/plate_tectonics/plates.php

http://en.wikipedia.org/wiki/Plate_tectonics

The western side of the Pacific Ring of Fire (Pacific and Asia plate intersection and Australia and Pacific plate intersection) and the Sunda extension (Australia and Asia plate intersection) have become particularly active in the last decade.

 

[jlduh]

Some informations that you know already maybe about the flaws of the Mark I design, from an article that summarizes the history of mark I containment and some old studies (not sure they are available on the net anyway) which made this design very controversial:

http://www.nytimes.com/2011/03/16/world/asia/16contain.html

Several utilities and plant operators also threatened to sue G.E. in the late 1980s after the disclosure of internal company documents dating back to 1975 that suggested that the containment vessel designs were either insufficiently tested or had flaws that could compromise safety.

See also this document hyperlinked in the article, which criticizes the technology used by GE in order to reduce size of containment and ultimately cost:

http://graphics8.nytimes.com/images/blogs/greeninc/hanauer.pdf

And you have also an interesting page, PAGE 63, in this document, where are compared with curves the abilities of different containments to absorb a sudden Hydrogen production from Zr oxydation, and Mark I is far behind the other ones (high percents of H2 inside the containment are reached much quicker, increasing risks of explosion...)

http://www.galcit.caltech.edu/~jeshep/fukushima/ShepherdFukushima30April2011.pdf

These reactors have been through some retrofit to improve the flaws but it is unclear right now which ones are implemented at Daichi (the hardened venting seems part of this, also some deflectors in the torus?)

But still retrofit has its limits of course...

 

[MadderDoc]

I found the post on this thread where these older documents were rediscovered:

https://www.physicsforums.com/showthread.php?p=3291191&highlight=google#post3291191

Disappointingly this dataset does not appear to include data for the pressure peak during the early hours of March 21st. (I inferred from your previous words that it did.)

<..> in particular at 01:25 on 21st I would have liked to see even more data that could lead us neatly to a theory, and the CAMS does not help in this case <..>

Well, one would always like to have more data

Well bear in mind that I have indicated that I am looking at a wider period of time, not just restricting myself to 01:25 on that day. But even so I am not sure what webcam images you are looking at, because I look at the archive for March 21st and very quickly it shows what looks like raindrops on camera lens cover.

http://gyldengrisgaard.dk/tepcowebcam/tepweb20110321.html

I think it risks confusing things for everybody to take observations over several days in one stew. The whimpering demise of unit 3 after the explosion might be describable as a series of events that could better be approached independently, than as included in a 'grand unified theory' of 'what happened'.

As hinted at in my previous post, its not safe to characterise these JDF missions as being about the reactor, but rather the fuel pool. In theory its possible that it was to do with reactor and they never told anyone, but we would need better evidence to lead us in that direction.

I do apologize if I have used such sloppy language and characterised any JDF missions as being about the reactors.

It is clear from video evidence, that the building was douched with water from the sky using helicopters, and was douched from the ground at its north, west, and south side, and that some of that douching neither targeted nor significantly hit the spent fuel pool.

 

[Astronuc]

It is clear from video evidence, that the building was douched with water from the sky using helicopters, and was douched from the ground at its north, west, and south side, and that some of that douching neither targeted nor significantly hit the spent fuel pool.

The spray from the helicopters and ground was directed at the SFPs. The spray from the helicopter was ineffective with respect to the SFP, although it might have suppressed any fire.

Before the top of Unit 4 came off, the helicopter spray would have been useless inside containment. Hence the concrete pump truck on the south side of the building.

 

[jlduh]

This shows that things are more complex in real life than on paper...

Generator trucks proved useless at Fukushima plant

http://www3.nhk.or.jp/daily/english/17_11.html

The operator of the stricken Fukushima Daiichi nuclear plant says dozens of power-generating trucks brought to the plant just after the March 11th disaster mostly proved to be useless.About 70 generator trucks from the Self-Defense Forces and other entities headed to the plant after the quake knocked out external power and the tsunami disabled the facility's backup generators.

But plant operator TEPCO says debris strewn across the compound and flooded switchboards hampered the trucks' set up.The utility says a switchboard for the No.2 reactor was finally wired to one of the generator trucks about 24 hours after the disaster.
But moments later, a hydrogen explosion at the neighboring No.1 reactor fried the wiring and cut off the power supply from the truck.

Another hydrogen explosion 2 days later at the No.3 reactor damaged generator vehicles with chunks of flying concrete.Electricity was finally restored to the plant through the regular power grid on March 21st -10 days after the quake and tsunami.

 

[Astronuc]

These reactors have been through some retrofit to improve the flaws but it is unclear right now which ones are implemented at Daichi (the hardened venting seems part of this, also some deflectors in the torus?)

But still retrofit has its limits of course...

It is my understanding with information provided by others, that the FK units with MkI containment did not have the various retrofits applied in the US.

 

[jlduh]

It is my understanding with information provided by others, that the FK units with MkI containment did not have the various retrofits applied in the US.

Ok thanks. I think the list of these retrofits in US is like described in this document, right?

http://www.nrc.gov/reading-rm/doc-collections/gen-comm/gen-letters/1989/gl89016.html

I'm still trying to find an accurate description and drawing of what this hardened venting (enabling it seems direct venting from primary containment to environment) looks like. I read somewhere that some venting -like the illustration below- was placed in the Torus, but this is secondary containment.

http://www.netimago.com/image_201117.html Does hardened venting means direct venting from primary (so with pressures much higher)?

 

[MadderDoc]

The spray from the helicopters and ground was directed at the SFPs.

Yes, largely speaking. However, in the case of unit 3, we do have videos showing firetrucks targeting the north end of the building, while the SFP is situated in the south end of it.

The spray from the helicopter was ineffective with respect to the SFP, although it might have suppressed any fire.

It probably did not have much effect, no, but in the context of the situation, it is quite understandable that the attempt was made. There was not much else to do either. It came at a time, when unit 3 had most recently acted out in such obnoxious fashion that it must have looked as prohibitively risky business to get close to it.

 

[jlduh]

Also, of interest, i put this article on "passive cooling" (no external power required to cool the reactor).

http://motherjones.com/blue-marble/...chnology-safer-not-always-japans-crisis-shows

BWR3 reactors are of this type, and number 1 unit is a BWR3 (that's why it has a different cooling principle than the others, that we just learned Tepco workers have possibly volountarily turned off after Tsunami and shutdown, in a procedure to "protect" the reactor).http://www3.nhk.or.jp/daily/english/17_22.html

The operator of the Fukushima Daiichi nuclear power plant says workers may have manually shut down the No.1 reactor's emergency cooling system in order to prevent damage to the reactor. It says pressure inside the reactor had dropped sharply after the earthquake struck the plant on March 11th.

The system is designed to cool the reactor even if all external sources of power are lost, but the move to shut it down temporarily means that it did not fully function.TEPCO says the decision may have been made based on a manual to prevent damage to the reactor. It says if the system had worked, it may have had more time until the meltdown, so it will investigate developments leading up to the decision to turn it off and whether the move was correct.

 

[ThomS]

I have been watching the Live cam some this morning here and noticed that there is some smoke or steam coming from Plant 2. Not much, but still...

Edit: First noticed (saw) at 09:29am Local time. Now at 10:38 am, it is sporadic with occasional small plumes.

 

[Astronuc]

Ok thanks. I think the list of these retrofits in US is like described in this document, right?

http://www.nrc.gov/reading-rm/doc-collections/gen-comm/gen-letters/1989/gl89016.html

I'm still trying to find an accurate description and drawing of what this hardened venting (enabling it seems direct venting from primary containment to environment) looks like. I read somewhere that some venting -like the illustration below- was placed in the Torus, but this is secondary containment.

http://www.netimago.com/image_201117.html


Does hardened venting means direct venting from primary (so with pressures much higher)?

These are the major mods in the US.
http://resources.nei.org/documents/japan/major_mod_usbwr_4511.pdf

It's not clear if they were implemented in Japan.

 

[NUCENG]

Ok thanks. I think the list of these retrofits in US is like described in this document, right?

http://www.nrc.gov/reading-rm/doc-collections/gen-comm/gen-letters/1989/gl89016.html

I'm still trying to find an accurate description and drawing of what this hardened venting (enabling it seems direct venting from primary containment to environment) looks like. I read somewhere that some venting -like the illustration below- was placed in the Torus, but this is secondary containment.

http://www.netimago.com/image_201117.html


Does hardened venting means direct venting from primary (so with pressures much higher)?

That is a drawing of the hardened wetwell vent. The torus is part of primary containment.

 

[mscharisma]

...

These reactors have been through some retrofit to improve the flaws but it is unclear right now which ones are implemented at Daichi (the hardened venting seems part of this, also some deflectors in the torus?)

But still retrofit has its limits of course...

In another NYT article, it is claimed that hardened vents were installed at Fukushima:

"American officials had said early on that reactors in the United States would be safe from such disasters because they were equipped with new, stronger venting systems. But Tokyo Electric Power Company, which runs the plant, now says that Fukushima Daiichi had installed the same vents years ago. "

http://www.nytimes.com/2011/05/18/w...son8.nytimes.com/pages/world/asia/index.jsonp

 

[SteveElbows]

Disappointingly this dataset does not appear to include data for the pressure peak during the early hours of March 21st. (I inferred from your previous words that it did.)

Yes it does. That post links to multiple documents, one of which is this one:

http://k.min.us/ilnMjk.pdf

The pressure peak is right there, in the tables of data.

 

[MiceAndMen]

These are the major mods in the US.
http://resources.nei.org/documents/japan/major_mod_usbwr_4511.pdf

It's not clear if they were implemented in Japan.

This 17 May article in the New York Times says the hardened vents were implemented in Japan.

http://www.nytimes.com/2011/05/18/world/asia/18japan.html?_r=1&pagewanted=all

In early April, Massachusetts Congressman Markey asked the NRC whether the Fukushima Daiichi Mark I reactors had the "hardened vents" installed. The NRC also says they were implemented in Japan.

http://markey.house.gov/docs/4-6-11markey_e-mail_2_-nrc_question_regarding_fukushima_unit_2.pdf

This could wind up being another black eye for the industry, GE in particular, and the NRC. A 10-year study and safetly modification program (apparently designed to address precisely some of the conditions encountered at the Fukushima Daiichi reactors) came up with critical modifications that failed when most needed. This assumes, of course, that the hardened vent system did fail there.

There are also potentially significant implications here for Mark I operators in the US.

 

[jlduh]

This 17 May article in the New York Times says they did.

http://www.nytimes.com/2011/05/18/world/asia/18japan.html?_r=1&pagewanted=all

Massachusetts Congressman Markey asked the NRC whether the Fukushima Daiichi Mark I reactors had the "hardened vents" installed. The NRC says they did.

http://markey.house.gov/docs/4-6-11markey_e-mail_2_-nrc_question_regarding_fukushima_unit_2.pdf

This won't be good for General Electric if they spearheaded an industry working group for a decade and one of the outcomes of that group's work was the "hardened vent", and when most needed those vents did not work as planned.

So, hardened vent or not hardened vent, that is the question!

Let's assume that Fukushima has the hardened vent implemented since several years, then, my next question is: what kind of "non hardened" vent was in place before?

As you can see, on this 1975 picture of Daichi (N°6 is still under construction), the stacks are already there with the tubings coming from 1/2 and 3/4 reactors...

http://www.netimago.com/image_201119.html

So if hardened vent is a vent from the torus towards the stack (according to the little sketch i posted), what is a "not hardened" vent?

I don't know if I'm the only one to get lost with these vents, but really the infos are very contradictory!

And apart from the little sketch hand written, i couldn't find one clear official drawing explaining the difference between the "before and after" modification.

 

[MiceAndMen]

I'm still trying to find an accurate description and drawing of what this hardened venting (enabling it seems direct venting from primary containment to environment) looks like. I read somewhere that some venting -like the illustration below- was placed in the Torus, but this is secondary containment.

http://www.netimago.com/image_201117.html Does hardened venting means direct venting from primary (so with pressures much higher)?

The torus is part of the primary containment.

The hardened vent provides a manual way for an operator to vent from the torus directly to the stack, bypassing the normal gas treatment system. The diagram shows this "new pipe", connected to a manual valve, pretty clearly.

Venting from the RPV is normally done, as far as I understand it, through the torus so that radioactivity can be "scrubbed" to a degree by the water in the suppression chamber before being released to the outside atmosphere.

 

[rowmag]

Yes, largely speaking. However, in the case of unit 3, we do have videos showing firetrucks targeting the north end of the building, while the SFP is situated in the south end of it.

I'm not sure they were targeting the north end of the building. I only remember hearing that they were targeting the SFP. I think the area to the north side of Unit 3 was more approachable (lower radiation levels), so they may have tried to shoot over the top from there. I do recall that the first attempt was reported as a failure, with the water not going far enough. This may look like they were targeting something they weren't.

 

[MiceAndMen]

So, hardened vent or not hardened vent, that is the question!

Let's assume that Fukushima has the hardened vent implemented since several years, then, my next question is: what kind of "non hardened" vent was in place before?

As you can see, on this 1975 picture of Daichi (N°6 is still under construction), the stacks are already there with the tubings coming from 1/2 and 3/4 reactors...

http://www.netimago.com/image_201119.html

So if hardened vent is a vent from the torus towards the stack (according to the little sketch i posted), what is a "not hardened" vent?

I don't know if I'm the only one to get lost with these vents, but really the infos are very contradictory!

And apart from the little sketch hand written, i couldn't find one clear official drawing explaining the difference between the "before and after" modification.

I've read several documents regarding the Mark I Owners Group modifications, and the little drawing you posted is the only sketch I've seen depicting the hardened vent. The tall stacks do indeed pre-date any discussion of hardened vents.

Each reactor building also has a vent pipe attached directly to it (looks to be approximately 1 meter in diameter). I haven't seen anything that indicates what they are for. Perhaps they're for regular non-power-plant-related building services, e.g. plumbing, HVAC, etc.

 

[jlduh]

This 17 May article in the New York Times says the hardened vents were implemented in Japan.

http://www.nytimes.com/2011/05/18/world/asia/18japan.html?_r=1&pagewanted=all

In early April, Massachusetts Congressman Markey asked the NRC whether the Fukushima Daiichi Mark I reactors had the "hardened vents" installed. The NRC also says they were implemented in Japan.

http://markey.house.gov/docs/4-6-11markey_e-mail_2_-nrc_question_regarding_fukushima_unit_2.pdf

This could wind up being another black eye for the industry, GE in particular, and the NRC. A 10-year study and safetly modification program (apparently designed to address precisely some of the conditions encountered at the Fukushima Daiichi reactors) came up with critical modifications that failed when most needed. This assumes, of course, that the hardened vent system did fail there.

There are also potentially significant implications here for Mark I operators in the US.

From http://www.nytimes.com/2011/05/18/world/asia/18japan.html?_r=1&pagewanted=all

One reason the venting system at the plant, which was built by General Electric, did not work is that it relied on the same sources of electricity as the rest of the plant: backup generators that were in basements at the plant and vulnerable to tsunamis. But the earthquake may also have damaged the valves that are part of the venting system, preventing them from working even when operators tried to manually open them, Tokyo Electric officials said.

In either case, regulators in the United States and Japan will now need to determine if such systems at similar plants designed by G.E. need to undergo expensive and time-consuming retrofitting or redesign to allow them to function even in severe accidents.

Hummm, if confirmed, this will be called retro-retrofitting, right?

As workers scrambled to comply with their new directive, they faced a cascading series of complications.

The venting system is designed to be operated from the control room, but operators’ attempts to turn it on failed, most likely because the power to open a critical valve was out. The valves are designed so they can also be opened manually, but by that time, workers found radiation levels near the venting system at Reactor No. 1 were already too high to approach, according to Tokyo Electric’s records.

At Reactor No. 2, workers tried to manually open the safety valves, but pressure did not fall inside the reactor, making it unclear whether venting was successful, the records show. At Reactor No. 3, workers tried seven times to manually open the valve, but it kept closing, the records say.

The results of the failed venting were disastrous.

Reactor No. 1 exploded first, on Saturday, the day after the earthquake. Reactor No. 3 came next, on Monday. And No. 2 exploded early Tuesday morning.

With each explosion, radioactive materials surged into the air, forcing the evacuation of tens of thousands of earthquake survivors living near the plant, contaminating crops and sending a faint plume of radioactive isotopes as far as the United States within days

Humm, that's a nice serie of failures.

Something is strange though as we saw several times on Tepco webcam some steam plume exiting the stacks, right?

 

[MiceAndMen]

From http://www.nytimes.com/2011/05/18/world/asia/18japan.html?_r=1&pagewanted=all

Hummm, if confirmed, this will be retro-retrofitting, right?

Yes, until the next unforseen accident scenario unfolds that exceeds the ability of the retro-retrofit to cope, at which time they'll need to develop a retro-retro-retrofit.

In all seriousness, however, the program that resulted in the "hardened vent" modification was a long drawn-out affair that lasted well over 10 years. The hard vent was only 1 of the "critical modifications" that came out of that process. I don't know for sure, but I suspect that the reason the hard vent system was not designed to operate during a station blackout, was based on economics. Existing Mark I operators now face the prospect of having the entire rationale behind their calculated safety margins called into question, and that will happen regardless of whether or not it's justified.

If you notice in those recent NYT articles, General Electric would not comment. GE was the technical leader of the working group that came up with the retrofit plan that started in 1974 and lasted well into the 1990s.

A good summary of the process can be found in this report:

http://www.nei.org/filefolder/Report_-_BWR_Mark_I_Containment_03192011_2.pdf

The last 2 pages list the important modifications that have been made to the Mark I design over the years, including the hardened vent.

Ok thanks. I think the list of these retrofits in US is like described in this document, right?

http://www.nrc.gov/reading-rm/doc-collections/gen-comm/gen-letters/1989/gl89016.html

Also it's interesting that GL 89-06 from the NRC says the hardened vent modification is an optional requirement. If an operator thought it was too expensive to implement, they didn't have to do it. They were required only to submit a cost estimate.

 

[razzz]

While reading the electronic reams of papers trying to satisfy my curiosity with this event, the latest and greatest idea was to vent any hydrogen directly to the outside atmosphere plus flare it (burn it off, radioactive or not) hence the term 'hardened' for the plumbing involved. If I ever find the article again, I'll post it.

 

[razzz]

I wonder what prompted a late Level 7 call after Units 1,2 and 3 had already spewed their poisons?

 

[mscharisma]

Don't know if this document is of any use in the discussions about what Japan may or may not have implemented in terms of retrofitting, but I thought I'd share.

 

[mscharisma]

... I don't know for sure, but I suspect that the reason the hard vent system was not designed to operate during a station blackout, was based on economics. Existing Mark I operators now face the prospect of having the entire rationale behind their calculated safety margins called into question, and that will happen regardless of whether or not it's justified.
...

The operability of hardened vents during station blackout was certainly a known problem (bolding added by me):

... "A hard pipe vent and vent valves capable of withstanding the anticipated severe accident pressure loadings would eliminate the problems with operating the vent system during a severe accident. The vent isolation valves should be remotely operable from the control room and should be provided with a power supply independent of normal or emergency AC power. Other changes, such as raising the RCIC turbine back-pressure setpoint, may also be desirable and could be considered. Venting capability, in conjunction with proper operating procedures and other improvements discussed in this item, would greatly reduce the probability of core-melt due to TW and station blackout sequences." ...

http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr0933/sec3/157r1.html

Edit: oops, looks like this is a very recent document ...

 

[MiceAndMen]

The operability of hardened vents during station blackout was certainly a known problem (bolding added by me):

... "A hard pipe vent and vent valves capable of withstanding the anticipated severe accident pressure loadings would eliminate the problems with operating the vent system during a severe accident. The vent isolation valves should be remotely operable from the control room and should be provided with a power supply independent of normal or emergency AC power. Other changes, such as raising the RCIC turbine back-pressure setpoint, may also be desirable and could be considered. Venting capability, in conjunction with proper operating procedures and other improvements discussed in this item, would greatly reduce the probability of core-melt due to TW and station blackout sequences." ...

http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr0933/sec3/157r1.html

Edit: oops, looks like this is a very recent document ...

That's true, but it still calls for a power supply, which they didn't have once the batteries gave out. From reading the news accounts it sounds like TEPCO wasn't sure whether they should vent or not at first. When the government ordered them to vent, they still did not do so for some hours. When they finally decided to vent - and this is not 100% clear to me yet - they were unable to do so because either the valves had no power or had malfunctioned.

Edit: ... or the reactors had already self-vented making the whole exercise moot.

Did any of the venting go completely according to plan? The explosions suggest not.