Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[bytepirate]

But even so, I am again somehow left with the feeling we are debating, by analogy, the size and trajectory of the bullet that was used to assassinate President Lincoln, not the result.

well, we are looking for the shootist and his rifle. good forensic practise to examine the bullet, no?

 

[TCups]

well, we are looking for the shootist and his rifle. good forensic practise to examine the bullet, no?

The shootist was the primary containment. The rifle was the fuel transfer chute. The bullet was superheated steam and hydrogen gas with a lot of radioactive contamination. The target was the southeast corner of the upper floor of Building 3. The initial trajectory more lateral than vertical. The major explosion of the rest of the building followed, as did a large littoral explosion resulting from vaporized water. I have not been dissuaded from this theory by any evidence to the contrary posted here so far. Perhaps some may come to light that will make me reconsider. Perhaps not.

 

[razzz]

Putting a condom on a nuke building is most fascinating.

Can you imagine a still fog becoming contaminated the longer it hangs around the Units and fallout contained in the water droplets (moisture) adheres to everything?

 

[MiceAndMen]

Putting a condom on a nuke building is most fascinating.

Can you imagine a still fog becoming contaminated the longer it hangs around the Units and fallout contained in the water droplets (moisture) adheres to everything?

I hope they are planning to make the condom's skeleton strong enough to support forms for pouring concrete at a later date. I think that is what will eventually have to happen at units 1, 2 and 3.

 

[SteveElbows]

Indeed, very interesting. Thank you very much for those documents. The first one is of special interest. I think it could explain what happened to Unit 2. Maybe there are hints as to what happened to Unit 3, but I didn't found any.



March 14th, 13:25 - RCIC fails in Unit 2
March 15th, 06:00 - Explosion in Unit 4
March 15th, 06:10 - Pressure drop in torus of Unit 2
March 15th, 06:20 - Explosive sound near torus of Unit 2
March 15th, 06:51 - Radiation dose at site boundary around main entrance exceeds limit value (11,9 mSv/h are measured some time later at the main gate)
March 15th, 12:00 - Large release starts and continues into Wednesday (I'm writing this down here because I'm trying to think out of the line. Unit 4 burned 4 hours earlier. I think nearly everybody thought that the radiation originated in Unit 4. But now TEPCO's giving us an explanation that the explosions and fires weren't connected to SFP #4 - so could it've come from Unit 2? An indication of a big containment and RPV breach?)

It was reported on March 14th / 15th that the fuel rods were completely uncovered, though I don't know for how long. If we look back how fast the core meltdown occurred in Unit 1, it's possible that there was also significant meltdown in Unit 2. So here comes my theory:
Some Corium pierced the RPV and got into contact with the quoted liner. Then it failed and there was a blowdown to the torus room.

I'm not sure if that means that the torus itself is damaged. If there's a blowdown from the primary containment to the torus room (where the torus is located), one could easily mistaken that as a torus damage. Especially, if you're unable to check out the situation because of high radiation readings.

Well even TEPCOs older data for reactor 2, which has not been revised in light of the reactor 1 water level realities, shows plenty of time for the core to melt. By 10:30 (or even an hour or so before this time) on the 14th water level is starting to drop, and drops below the top of the fuel by 17:12. Reactor pressure rises during this period. One of the torus CAMS picks up rather low levels of radiation during this period, but still more than zero. By 19:03 reactor pressure has fallen dramatically. By 22:00 a drywell CAMS is registering higher levels, and by 23:44 this level shoots up further, and a torus CAMS reading also shoots up. In the hours that followed the torus CAMS tends to decrease steadily, whilst the drywell CAMS increases over this period. At 05:30 on the 15th the torus still registers some pressure, but at 06:10 the pressure is listed as 0.00. Drywell pressure decreases at some point between 07:20 and the next reading at 11:42. And it looks like something happens between 13:00 and 15:25 because the reactor pressure falls a fair bit further between these 2 times, drywell CAMS reading shoots up by almost 3 times, torus CAMS rises a bit. The CAMS readings are recorded at their highest at 16:10 and then fall pretty much ever since.

OK so if they look at the above again with unit 1 water levels in mind, then we may be looking at the core starting to be uncovered sooner than 17:12 on the 14th. But I am not sure what this will tell us, since even a 17:12 start time gave more than 12 hours till the 06:10 event.

 

[gmax137]

"Does anyone have any reliable info on the nuclear plants - the reports on the news seem garbled to me."

Weeks ago, someone mentioned the very first message in this thread (above), and how things have changed so little with Tepco that this comment is still very appropriate today.

Ringing truer than ever.

Well I never guessed when I wrote post #1 that we'd be here 2 months, 460+ pages and 7372 posts later and still know as little as we do.

 

[razzz]

The shootist was the primary containment. The rifle was the fuel transfer chute. The bullet was superheated steam and hydrogen gas with a lot of radioactive contamination. The target was the southeast corner of the upper floor of Building 3. The initial trajectory more lateral than vertical. The major explosion of the rest of the building followed, as did a large littoral explosion resulting from vaporized water. I have not been dissuaded from this theory by any evidence to the contrary posted here so far. Perhaps some may come to light that will make me reconsider. Perhaps not.

You need a source with enough water for your steam explosion. I doubt the pool was full to the brim and the reactor was venting because it was running out of coolant. Then you would need a large vacuum to draw in any water from the torus level with some heat to flash it or did the corium drop into the torus about that time? It would have had to eaten through many obstacles to get to that point. I don't think it is even designed for the corium to enter the torus.

 

[razzz]

I hope they are planning to make the condom's skeleton strong enough to support forms for pouring concrete at a later date. I think that is what will eventually have to happen at units 1, 2 and 3.

Unless they can make an encasement watertight, it seems kinda useless to dump sand and concrete on it.

 

[Atomfritz]

Interesting developments around reactor 3...

Source:http://www.spiegel.de/fotostrecke/fotostrecke-67871-8.html"
This image was published in German Spiegel magazine on May 11 and the translated picture text reads: "Photo from the SFP of Reactor 3".

Filled with rubble, not enough shown how high water level is.
Any fuel visible or completely covered with debris?


And, why are they adding huge quantities of hydrazine to the SPF cooling water now, as indicated by http://www.nisa.meti.go.jp/english/files/en20110510-1-1.pdf" ?
They didn't do (or mention) this before.

taken from image collection http://www.flickr.com/photos/xtcbz/sets/72157626687253144/with/5705937752/"
(Btw, very interesting Fukushima photo collection, many other interesting impressions there)

Constant heavy vapor emission on photo taken on May 10.
Appears to be quite more vapor than in the days immediately after the explosion. Why?
Containment slowly starting to develop more and more cracks while being flooded?

15 TEPCO, the world prevent the Second Coming of the Unit 3 reactor at Fukushima Daiichi Nuclear Power Station, the reactor cooling water, on a dissolved boric acid to absorb neutrons, the same day to the reactor announced that the injection began.

Will be the No. 1 and 2, take the same measures.

Critical re-continuous fission phenomenon again. 1 - Unit 3 reactor pressure vessel was initially injected in the history of water for cooling, TEPCO was seen as the salt will absorb neutrons. The boric acid is dissolved in water cooling, since instead of fresh water from seawater cooling down because it is seen that the salinity.

Meanwhile, the pressure vessel of Unit 3 are top of the soaring temperatures. TEPCO "There is a possibility that water is leaking irrigation pipe as a" pipe from the 12th to add another 12 tonnes of water filling the pipe with two per clock. Has increased from 14 to 15 tons per clock injection volume, temperature of the top 24 in no time at 5:00 am on July 15 rose 46.5 degrees, was 297 degrees. TEPCO said, "is still not going well injection" sees.
( 02 minutes May 15, 2011 22:00 Yomiuri Shimbun)

This temperature increase by almost 50 degrees and the reintroduction of boron sounds serious to me.
If even Tepco talks about the possibility of re-criticality, then this sounds even more serious to me.

Are neutron current measurement instruments available to exclude the possibility of re-criticality, or have they been destroyed?

 

[jim hardy]

you fellows who have studied the photos so closely
EDIT deleted , previous post shows it better and picture was too wide.

here is link to it, almost redundant to prev post.

http://cryptome.org/eyeball/daiichi-npp3/pict49.jpg

 

[Atomfritz]

Uhhhh . . . If an explosion of superheated gas blasts out a large hole in the wall and roof of a concrete building, might it be reasonable to assume a quantity of dust and particulate would result from the mechanical damage, and that that dust and particulate, in the presence of heat and air (oxygen), might form a fireball? Somehow the picture of a sawdust cannon comes to mind.



or lycopodium powder:


But even so, I am again somehow left with the feeling we are debating, by analogy, the size and trajectory of the bullet that was used to assassinate President Lincoln, not the result.

Maybe this photo, taken on May 10, could give hints?
Look at the directional damages of the foreground building and the vent building, the stairs etc...

And, from this perspective also look the damages on bldg. #4...

 

[jlduh]

Tepco does not trust the other water levels either. Will try to check on reactor 2 and 3.

TEPCO says the gauges at the No.2 and 3 reactors might not be showing the actual water levels, and that the worst case is that the rods have melted down.

http://www3.nhk.or.jp/daily/english/16_04.html

For me, just after the release of the information that N°1 core melted in the first 16 hours, this way of wording things is just a new move from Tepco towards publicly admitting the evidence: 2 and 3 also melted, and we have now 3 melted cores.

No scientific proof (yet) of this, i admit, except some experience acquired in Tepco public relations policy and strategy based on observations of the last 2 months.

 

[MiceAndMen]

Unless they can make an encasement watertight, it seems kinda useless to dump sand and concrete on it.

Indeed, a comprehensive sarcophagus would involve much more than my simplified version. If there is really bedrock below the site, then it might be possible to pour concrete down to that bedrock, forming a bathtub. Above ground, the rest of the sarcophagus would be build on top of that foundation. The structure of the condom they are going to build now could be used in the future to support sarcophagus construction. By the time that day arrives, however, the costs of building a totally new sarcophagus will be a drop in the bucket compared to the cost of everything they will do between now and then. Multiple concentric shells, like a Russian matryoshka doll, might be desirable for defense-in-depth, as they say.

On the other hand, the challenges of building a secure containment like that in an area so prone to earthquakes might be too much to overcome.

 

[ernal_student]

The full theory for #4 includes also the explanation for the fires. Now TEPCO thinks that the explosion may have caused oil to catch fire

The matter of oil as a possible source of the explosion had been reported 5 days ago (on May 11) in this forum:

https://www.physicsforums.com/showpost.php?p=3295319&postcount=6580

And was one of the causes already being considered on a speculative basis a few weeks ago in this forum.

 

[BrentLidgard]

The matter of oil as a possible source of the explosion had been reported on May 11 in this forum:

https://www.physicsforums.com/showpost.php?p=3295319&postcount=6580

And was one of the causes already being considered on a speculative basis a few weeks ago in this forum.

Wow, maybe the world should be informed of the real information, many theories have been true from people on this side of the pond...

 

[ernal_student]

For me, just after the release of the information that N°1 core melted in the first 16 hours, this way of wording things is just a new move from Tepco towards publicly admitting the evidence: 2 and 3 also melted, and we have now 3 melted cores.

No scientific proof (yet) of this, i admit, except some experience acquired in Tepco public relations policy and strategy based on observations of the last 2 months.

At least it means nobody should be surprised if that is what they find next.
I basically have the same view about TEPCO's approach to information control.

 

[jmelson]

You are surely correct, a pure hydrogen explosion or combustion is a pretty low key event, in fact the flame is invisible, at least afaik.
So the orange fireball from reactor 3 strongly indicates substantial additional combustible/explosive material was involved. Normally flames are luminous because of white or red hot particles, generally of carbon, that are carried in the heated flow. Where these came from in this case is not yet clear.

Well, we know how the human eye reacts to a hydrogen flame, ie. you can't see it, unless it is VERY intense, then you can just see a little light. But, broadcast-grade TV cameras have dichroic beamsplitters that split the light into 3 color bands (plus luminance in some systems) for the image sensors. It is possible that the orange light is due to UV from the flame getting through to the sensors, and it wasn't actually orange in reality.

Concrete dust won't burn (as another poster suggests) except in pure oxygen. But, there are probably lots of lubes all over the plant, in pumps and gearboxes, and stored for maintenance crews. Possibly also flammable hydraulic fluids to operate various actuators. The hydrogen explosion could have crushed partially filled containers or broken hydraulic lines, releasing a spray of oils. There may have been other carbon-based materials around that could be easily ignited.

Jon

 

[rowmag]

Indeed, a comprehensive sarcophagus would involve much more than my simplified version. If there is really bedrock below the site, then it might be possible to pour concrete down to that bedrock, forming a bathtub.

TEPCO has previously mentioned that they were thinking of injecting some kind of soil hardener into the ground under the reactor buildings to stop water flow through the soil. Similar to what they did to stop the #2 subdrain leak into the ocean, I guess. (The plan involved digging some tunnels underneath from which to do the injection work, which doesn't sound very pleasant...) Don't know if they have abandoned that idea -- haven't seen it mentioned again.

 

[TCups]

You need a source with enough water for your steam explosion. I doubt the pool was full to the brim and the reactor was venting because it was running out of coolant. Then you would need a large vacuum to draw in any water from the torus level with some heat to flash it or did the corium drop into the torus about that time? It would have had to eaten through many obstacles to get to that point. I don't think it is even designed for the corium to enter the torus.

Your doubt is noted. But you make several assertions or presumptions not at all needed to support the theory I attempted to outline in Occamiam razor style - sharp and simple. No water from the torus pool is needed. No melting of the corium through the RPV is needed. No sudden criticality from the SFP fuel rods is needed. No one has presented any evidence that has convinced me otherwise, least of all that post.

 

[BrendaEM]

Hi, I uploaded some enhanced videos the the explosion and spent fuel ponds:

Explosion:



Spent Fuel Pool:




I might consider doing more, if the result might be as dramatic as the first enhancment.
BTW, does anyone have have a top view plan for the GE MK1; I found the sides here, but not the top. I might do a RhinoCAD 3d Rendering for Wikipedia.

 

[razzz]

Let's hope they built directly on bedrock. The lady that stopped by saying Unit 4 was falling over and saying she heard the foundations missed bedrock by 130m or so, I hope not.
http://www.chuden.co.jp/english/initiatives/eini_nuclearpower/enuc_earthquakemeasures/eear_bedrock/index.html"

 

[razzz]

Hi, I uploaded some enhanced videos the the explosion and spent fuel ponds:

Explosion:



Spent Fuel Pool:




I might consider doing more, if the result might be as dramatic as the first enhancment.
BTW, does anyone have have a top view plan for the GE MK1; I found the sides here, but not the top. I might do a RhinoCAD 3d Rendering for Wikipedia.

Unit 1 blew the sides out and the roof collapsed as a whole almost intact.

Unit 3 looks worse every time I see it. In a longer time frame the head of the cloud is still turbulent rolling up even after the plume gets separated from it.

 

[pdObq]

By the way, have these studes already been posted here?

1) VERY INTERESTING STUFF IN IT, details and schematics including failure modes

THE IMPACT OF BWR MK I PRIMARY CONTAINMENT FAILURE
DYNAMICS ON SECONDARY CONTAINMENT INTEGRITY


http://www.osti.gov/bridge/servlets/purl/5835351-nR29Hq/5835351.pdf

2) IDENTIFICATION AND ASSESSMENT OF BWR IN-VESSEL
SEVERE ACCIDENT MITIGATION STRATEGIES

http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/24/072/24072657.pdf

Yes, the first one has been floating around this forum already, the second one has afaik only been in this forum indirectly mentioned in a link to another forum in this post by jim hardy https://www.physicsforums.com/showpost.php?p=3299953&postcount=7089 which was a reply to this post https://www.physicsforums.com/showpost.php?p=3299762&postcount=7073 (quoted again below for advertisement purposes ).

Here is the direct link to the other forum for convenience again http://tickerforum.org/akcs-www?post=182121&page=314#new , the two long posts by Analog, there are some more interesting references linked to in there.

Just to advertise the rough idea from post #7073 and #7089 again (which indeed has been considered in one of those BWR studies, see Analog's post in the other forum)...

However, what if there was recriticality in unit 3 reactor core? Would it be conceivable that after the fuel rods have been without sufficient cooling (above water level), they start heating up, melting away the control rods (borated steel, would it melt prior to the fuel pellets? [Yes, see below]), then they start injecting cooling water from outside, which cools the remains, but also acts as moderator. With control rods partly gone, the core suddenly goes critical, followed by essentially steam explosion within containment, which however, is not strong enough to destroy the drywell, but causes the spectacular explosion of unit 3 reactor building including gamma spike?

Rough melting points (from Wolfram Alpha):

Stainless Steel: 1440 degC
Zircalloy: 1850 degC
Uranium dioxide: 2180 degC (Wikipedia corium article says 2700-2800 degC for UO2, that would fit nicely with the new Tepco unit 1 data showing melting of the core)

Too bad, control roads seem to have the lowest one...

 

[pdObq]

Let's hope they built directly on bedrock. The lady that stopped by saying Unit 4 was falling over and saying she heard the foundations missed bedrock by 130m or so, I hope not.
http://www.chuden.co.jp/english/initiatives/eini_nuclearpower/enuc_earthquakemeasures/eear_bedrock/index.html"

They didn't for Fuku, it's "mudstone", bedrock is about 46m below the foundations. If it was bedrock, why would they have to permanently have groundwater pumps running to keep the local groundwater level below the lowest parts of the buildings?

EDIT: See this post for some references https://www.physicsforums.com/showpost.php?p=3291249&postcount=6263 . There was another post in response, trying to find it...
EDIT2: Ok, found it, a post by jlduh (https://www.physicsforums.com/showpost.php?p=3291411&postcount=6293) with a related article in japanese with a (not so readable) Google translation.

 

[ThomS]

TEPCO: No.4 blast due to hydrogen from No.3

From NHK.
http://www3.nhk.or.jp/daily/english/16_02.html

 

[ThomS]

Radioactivity at intake of No.3 reactor rises

Also from NHK
http://www3.nhk.or.jp/daily/english/16_06.html

 

[ThomS]

NHK is reporting that TEPCO will increase the amount of water injected into Reactor 1 from 8 to 10 tons per hour in a study of how to stabilize the reactor over the next 2 days. The belief is that if a certain level of water can be maintained, it may be possible to set up a cooling system that circulates water from the containment vessel to a heat exchanger and back to the reactor.

http://www3.nhk.or.jp/daily/english/15_14.html

----------------

Also, someone was talking about the live feed. As of 11:38 AM (local time), the feed shows local conditions at the plants to be sunny with a bit a haze. No visible steam from the plants.

 

[ThomS]

I apologize if this has been posted in another form.

TEPCO has posted this provisional data regarding Reactor 1.
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110515e10.pdf

 

[westfield]

Not sure if this has been linked but it's a reasonably in depth comparison of differences between GE BWR mark 1 designs including emergency cooling systems. I.e. RCIC systems vs isolation condensors and which designs have what.

http://pbadupws.nrc.gov/docs/ML0230/ML023010606.pdf"

 

[ThomS]

Many thanks for to the people in the forum (Astronuc: thank you for personally answering my questions!). I have been following this forum for its' grounded scientific approach and analysis. It has helped a great deal in my decision making for my family who live in Tokyo and nearer to Fukushima.

Question re: measuring radioactive materials in the environment.

Why are there only reports showing levels of Cesium and Iodine (2 kinds)? Almost all of the releases by Tepco, for instance, only show these.

Again, many thanks.

 

[pdObq]

And another question (for everybody): What's the data TEPCO used for that sheet, and where did it come from? It doesn't seem to be an estimate, since there are bumps in those graphs, indicating they are build on accurate data.

These are calculations. The timing is made to fit the measured temperatures at different places.

Oh, ok that's why it looks just like one of those severe accident calculations... Not that I have seen vary many (rather very few), but the LOCA meltdown timescale on all of them was hours AFAIK, not months, so it probably would make sense that the real "action" there already happened a long time ago.

Somewhat different topic: Regarding sudden overpressure from the RPV escaping through the main steamlines, I just read about those main steamline isolation valves (MSIV) which apparently take ~10s to close. With the EDGs and DC power those very likely have been closed immediately at the scram. But how much pressure do these things take before they fail?

Also, would it be possible that the core spray lines ruptured during the earthquake or something similar to that (i.e. replace core spray with feedwater or earthquake with hydrogen explosion), with the outcome that all that water is not actually reaching the RPV, but just dripping into the drywell or elsewhere into the building? If it only reached the outside of the RPV it probably would still generate lots of steam. One could probably tell by how radioactive the water in the basement is, whether it went through the core.

 

[etudiant]

Many thanks for to the people in the forum (Astronuc: thank you for personally answering my questions!). I have been following this forum for its' grounded scientific approach and analysis. It has helped a great deal in my decision making for my family who live in Tokyo and nearer to Fukushima.

Question re: measuring radioactive materials in the environment.

Why are there only reports showing levels of Cesium and Iodine (2 kinds)? Almost all of the releases by Tepco, for instance, only show these.

Again, many thanks.

Iodine and cesium are the most easily mobilized bioactive elements in the nuclear emissions.
Radioactive noble gasses such as xenon are emitted in even greater amounts, but are not absorbed by the human body, so they are ignored.
The other elements involved are generally less likely to become airborne, so they are pretty much a purely local problem, unless the reactor material is lofted by some explosion, conventional or otherwise. Strontium, which is absorbed as a calcium substitute by the body, is the most troublesome of those.
Thus far, the Fukushima airborne emissions have been relatively clean from these heavier elements, at least afaik. The waterborne emissions however may be messier, given the real possibility that the nuclear containments are being flushed by the cooling water injections. Sea food may be a more risky choice as a result.

 

[pdObq]

Not sure if this has been linked but it's a reasonably in depth comparison of differences between GE BWR mark 1 designs including emergency cooling systems. I.e. RCIC systems vs isolation condensors and which designs have what.

http://pbadupws.nrc.gov/docs/ML0230/ML023010606.pdf"

Nice document! I haven't seen it before, but that doesn't really mean anything. Very nice drawings and schematics of all those systems and of the RPV with all its nozzles! That should be handy in figuring out what can go where with all those pipes and valves given someone has the time to digest all that information. (Yeah, as someone mentioned here before, with all those NRC and other documents online you can almost build your own NPP in the backyard...)

 

[rowmag]

http://english.kyodonews.jp/news/2011/05/91196.html

Has it reached cold shutdown yet ?

(EDIT : yes it has ... http://search.japantimes.co.jp/cgi-bin/nn20110516a5.html )

The Nagoya-based firm said the problem in the reactor's cooling system was found Saturday evening after a gauge indicated that around 400 tons of seawater had flowed into the condenser at around 4:30 p.m., most likely because of a piping problem.

The water also found its way into the reactor, making it necessary to desalinate it, the company said.

That's kinda what you see ... One report speaks of 2 hours trouble on a Sunday , the other says the problem had been found Saturday starting at 4:30 p.m. ...Tsk Tsk

If seawater got into the reactor, wouldn't radiolysis release chlorine gas, which would start corroding things? What are the chances that Hamaoka Unit 5 just retired for good?

 

[NUCENG]

STATION BLACKOUT CALCULATIONS FOR BROWNS FERRY

http://www.osti.gov/bridge/servlets/purl/6402578-Rr9xTe/6402578.pdf


Table 2
MAJOR ACCIDENT EVENTS AFTER CORE UNCOVERY

Event Time after scram(mins)
Core uncovery 479
Structural relocation starts 572
Fuel meeting starts 604
Core plate dryout 630
Core plate failure 682
Core collapse 695
Bottom head dryout 709
Penetration failure 734
Vessel pressure equalizes with containment 743
Corium leaves vessel 797
End Hotdrop/start Corcon 800 Corcon -core concrete interaction
Containment failure 805

BWR Scenario: Extended station blackoput with ECCS injection until battery exhaustion at 6 hours. This would be similar to Units 2 and 3 at Fukushima. Unit 1 had no makeup and only the isolation condenser in operation until its pool boiled dry. So it would have been ahead of this timeline.

There are a number of other reports and analyses from DOE labs and NRC that include timelines for severe accidents either from station blackout or failure of residual heat removal. These timelines all show vessel and containment failures in less that an day.

Seems to me these timelines may be a guide to discussing the credibility of news reports from TEPCO and Japanese regulators.

 

[Gary7]

According to the Tepco site, Fukushima Daiichi is built on bedrock.
http://www.tepco.co.jp/en/challenge/energy/nuclear/plants-e.html

 

[pdObq]

Just followup. I haven't found any discussions of covering spent fuel pools. So the following points are just ideas that may be involved.

1. If they were covered at Fukushima it may have made it harder to add water to the spent fuel pools.
2. Spent fuels are warm due to decay heat. There would be a hot moist environment below a cover. That could accelerate corrosion or degradation of concrete.
3. Covering the pools may increase the demand on fuel pool cooling systems by preventing evaporation cooling at the surface of the pool. It also might result in faster heatup following a loss of Fuel pool cooling.
5. Concrete covers would be heavy loads and would have to be put on and taken off frequently. That could be a higher risk to the spent fuel that a seismic event.
6. Covering pools could allow gas buildup under the cover.
7. Currently fuel pool level is easily visible. Failure of level instrumentation while the pool is covered could be a problem.

I haven't found any discussion of design basis that would require a cover. The exclusion of debris and dirt is handled by loose parts programs, skimmers, and filtration on pool water. Obviously, if the roof caves in these systems aren't up to that task.

Thanks for looking more closely into that!

1. Yes, that might be true in this case. But another safety feature that seems to be missing are redundant SFP "core spray" lines.

2. Oh, ok, that might explain the possibility of pre-existing corrosion on the roof structure. OTOH, isn't the SFP water cooled, so that in principle it shouldn't be hot and moist there?

3. Yes, one probably would need more cooling capacity, if so far one relied on part of the cooling done by evaporation.

4. Agree, you don't want a concrete slab to fall onto your fuel (that's a somewhat recursive requirement...).

5./6. Yes, so additional venting and level sensors might be needed. But isn't the water level in the pool monitored by some sensor anyway?? E.g. that skimmer tank water level sensor?

One possibility that avoids some of those points would be to not cover it completely, but only so much that no big object can fall in.

An article on this subject of sabotage or terrorism and SFPs:
http://belfercenter.ksg.harvard.edu/publication/364/radiological_terrorism.html

Interesting, thanks for the link (Haven't had time to read it fully yet, though.). I think they should reconsider such threats in view of Fukushima. I mean it seems pretty obvious now that SFPs "on the attic" are a major possible security and safety risk.

I'm hoping my post may trigger some discussion about whether covering fuel pools would be a good idea based on what happened at Fukushima.

I would hope so to, although that might deserve a different thread, such as lessons learned or reconsidering BWR safety. And my question about SFP shield plugs was not only with regards to the roof collapsing but also to threats such as airplane crashes, as considered in the document linked to by jlduh.

No problem. I wasn't aware of anything like an equipment weight movement list.

See the attachment in this post by M&M https://www.physicsforums.com/showpost.php?p=3294820&postcount=6534 . I browsed through the whole NRC document now, but I could not find any additional details about the "Fuel Storage Pool Shield Plugs", 4x 4.5 tons, mentioned there. There is also "Fuel Transfer Shield/Cattle Chute", 2x 16.5 tons, and the "Fuel Pool gates", 2x ~1 ton. These sound more related to the shield wall and gate between the reactor well and the SFP.

I found a list of radiation monitoring equipment instead, with detector types and measuring ranges if anyone is interested in that. It's on p. 68 & 69 (one page is missing), Table 11.5-1 "Process and Effluent Radiation Monitors". CAMS seems to be a different sub-system, it is not on that list AFAIKT. There are a whole bunch of lists of other instruments and stuff in that document, as well.

 

[NUCENG]

They didn't for Fuku, it's "mudstone", bedrock is about 46m below the foundations. If it was bedrock, why would they have to permanently have groundwater pumps running to keep the local groundwater level below the lowest parts of the buildings?

EDIT: See this post for some references https://www.physicsforums.com/showpost.php?p=3291249&postcount=6263 . There was another post in response, trying to find it...
EDIT2: Ok, found it, a post by jlduh (https://www.physicsforums.com/showpost.php?p=3291411&postcount=6293) with a related article in japanese with a (not so readable) Google translation.

Mudstone:
A sedimentary rock composed of clay-size particles but lacking the stratified structure that is characteristic of a shale

Mudstone is an extremely fine-grained sedimentary rock consisting of a mixture of clay and silt-sized particles. Terms such as claystone and siltstone are often used in place of mudstone, although these refer to rocks whose grain size falls within much narrower ranges and under close examination these are often technically mudstones. Shale is often used to describe mudstones which are hard and fissile (break along bedding planes). Marl is often used to describe carbonate-rich soft mudstones.

http://sp.lyellcollection.org/content/158/1/1.full.pdf

 

[pdObq]

STATION BLACKOUT CALCULATIONS FOR BROWNS FERRY

http://www.osti.gov/bridge/servlets/purl/6402578-Rr9xTe/6402578.pdf

[...]

There are a number of other reports and analyses from DOE labs and NRC that include timelines for severe accidents either from station blackout or failure of residual heat removal. These timelines all show vessel and containment failures in less than an day.

Seems to me these timelines may be a guide to discussing the credibility of news reports from TEPCO and Japanese regulators.

So, another of those studies. Yes, as I wrote a few posts back that was also my impression, in all those simulations everything happens very quickly.

Those reactor simulation guys now have an unforeseen opportunity to validate their models...

 

[razzz]

pdObq: Thanks for going back in time and finding all those links regarding the ground and foundations at this plant site.

I am no expert but I know enough that you can build a floating foundation on poor soil conditions. Say, for a house, a shopping mall maybe even an airport where you treat the ground like it were water and you are building a concrete flat-bottom ship to sit or float on it. You wouldn't normally build a nuke plant that way, you would at least drive pilings or drill and pour columns to bedrock then start your foundation from them just for stability if nothing else.
Liquefaction caused by earthquakes is well known. Without these sub drain wells removing ground water at the plant site, the ground would saturate and then liquefy like quicksand during an earthquake. That is why you want to see your nuke foundation installed on bedrock. I guess Japan doesn't see things that way.

 

[pdObq]

According to the Tepco site, Fukushima Daiichi is built on bedrock.
http://www.tepco.co.jp/en/challenge/energy/nuclear/plants-e.html

Looking at that webpage, it says "built on solid bedrock" explicitly only for Daiichi. So, should I interpret that as Daini and Kashiwazaki Kariwa are not?

Mudstone:
A sedimentary rock composed of clay-size particles but lacking the stratified structure that is characteristic of a shale

I think it might be useful if someone could translate or summarize or find an English version of that article about the construction of Fukushima that jlduh found (see https://www.physicsforums.com/showpost.php?p=3291411&postcount=6293). The Google translation can easily be misinterpreted IMO. Maybe when TEPCO says bedrock they mean mudstone, or in other words, maybe mudstone is some type of bedrock?

PS: Funny that geologist can write an article about "Physical and fluid-flow properties" of "Muds and mudstones" without using a single graph or figure.

EDIT: Just saw your post after posting, razzz. In general, I am still somewhat confused about the ground and foundations there, so I can't really tell if things are ok there, or not so ok. If things are as they seem, and as you write, I guess that would be not so ok, which TEPCO seems to have a subscription for figuratively speaking.

 

[ernal_student]

I think it might be useful if someone could translate or summarize or find an English version of that article about the construction of Fukushima that jlduh found (see https://www.physicsforums.com/showpost.php?p=3291411&postcount=6293).

There are two links in that post and both links lead to a page with garbled english, sorry.

 

[razzz]

Bedrock begs a definition from the exact location. They didn't say solid rock. If they are using pumps and wells to constantly de-water a 100 feet of sub soil and discharge it to a concrete channel that empties into the ocean, then I'd say it is not completely bedrock. Entirely bedrock is better than sand or loose ground or a layering of all three.

 

[ernal_student]

Looking at that webpage, it says "built on solid bedrock" explicitly only for Daiichi.

I tried to locate a Japanese page with the related information on the TEPCO website, but many pages have been replaced by a note concerning the emergency since the earthquake, and I have been unable to find such information in Japanese. I would not argue about the English text until you have seen the Japanese original. That is just my opinion.

 

[pdObq]

There are two links in that post and both links lead to a page with garbled english, sorry.

Oh yes, weird. How about this one: http://www.chunichi.co.jp/s/article/2011050590094854.html ,
or this one: http://ziphilia.net/bbs.cgi/economy/1304793715/detailview#A_ja ,
or this one: http://ziphilia.net/bbs.cgi/economy/1304793715/detailview#A_DEFAULT .
I hope those are not garbled back-translations from English to Japanese. The first one looks like a link to the original article, but it looks like it does not exist anymore under that address, since there is not too much written on that page.

 

[razzz]

There are two links in that post and both links lead to a page with garbled english, sorry.

The highlight of that garbled interpretation was, before construction started they had to remove the topsoil to get to a relatively hard layering (mud-stone). And so they should, to remove beach sands and small loose rock deposits accumulated over the eons. They scraped (moved earth) down 25ft or 25m (unclear) and then started building, ignoring historical tsunami heights when they should have built back up or added new firm fill dirt to the desired height to avoid what just recently happened (Really big tsunami).

 

[NUCENG]

Thanks for looking more closely into that!

1. Yes, that might be true in this case. But another safety feature that seems to be missing are redundant SFP "core spray" lines.

2. Oh, ok, that might explain the possibility of pre-existing corrosion on the roof structure. OTOH, isn't the SFP water cooled, so that in principle it shouldn't be hot and moist there?

3. Yes, one probably would need more cooling capacity, if so far one relied on part of the cooling done by evaporation.

4. Agree, you don't want a concrete slab to fall onto your fuel (that's a somewhat recursive requirement...).

5./6. Yes, so additional venting and level sensors might be needed. But isn't the water level in the pool monitored by some sensor anyway?? E.g. that skimmer tank water level sensor?

One possibility that avoids some of those points would be to not cover it completely, but only so much that no big object can fall in.



Interesting, thanks for the link (Haven't had time to read it fully yet, though.). I think they should reconsider such threats in view of Fukushima. I mean it seems pretty obvious now that SFPs "on the attic" are a major possible security and safety risk.



I would hope so to, although that might deserve a different thread, such as lessons learned or reconsidering BWR safety. And my question about SFP shield plugs was not only with regards to the roof collapsing but also to threats such as airplane crashes, as considered in the document linked to by jlduh.



See the attachment in this post by M&M https://www.physicsforums.com/showpost.php?p=3294820&postcount=6534 . I browsed through the whole NRC document now, but I could not find any additional details about the "Fuel Storage Pool Shield Plugs", 4x 4.5 tons, mentioned there. There is also "Fuel Transfer Shield/Cattle Chute", 2x 16.5 tons, and the "Fuel Pool gates", 2x ~1 ton. These sound more related to the shield wall and gate between the reactor well and the SFP.

I found a list of radiation monitoring equipment instead, with detector types and measuring ranges if anyone is interested in that. It's on p. 68 & 69 (one page is missing), Table 11.5-1 "Process and Effluent Radiation Monitors". CAMS seems to be a different sub-system, it is not on that list AFAIKT. There are a whole bunch of lists of other instruments and stuff in that document, as well.

Covers are worth considering and the basis for a decision to cover or not should be documented. To answer new questions.

1. At least some US plants installed spray lines after 9/11.

2. Fuel pools are cooled but it may take up to all three FPC pumps to cool a pool following offload and the temperatures may be 120 to 140 degF. Evaporation keeps the refueling floor humid and indeed may be a reason for corrosion.

3. It is not just about adding cooling. If cooling is lost and the pool is covered it shortens how much time you have to restore cooling.

4. A concrete slab from the roof with a risk of 1 in 1000 years or a cover that is moved on and off at least twice a year for 60 years.

5/6. Added complexity increases possibilities for failures.

Every one of my initial problems can probably be solved. For example many of my listed issues could disappear with a cover made from carbon composites in a mesh or net. Low weight, visibility, moisture resistance, ventilation and preserves evaporative cooling, and no significant change in cooling requirements or accident response.

Terrorism threat is a serious consideration. Since we don't have a single geological storage site, we have 109 on site storage locations in the US alone. The movement of fuel from Spent Fuel Pools to Dry cask storage reduces risk, but you can't put freshly discharged fuel into dry casks until they have decayed for a few years. The elevated fuel pools at BWR seem more vulnerable than they could be. But if terrorists are looking to rival 9/11, dirty bombs or attacks on nuclear plants are much less of a risk than other targets in terms of body counts.

The idea of covers is actually the second physical change suggestion I have seen on this forum that needs to be considered seriously.

 

[Curium]

Unit 3 SFP explosion

This weekend, Gundersen reiterates the "prompt moderated criticality" hypothesis, does not back away from that concept, despite previous criticism.
He cites high levels of I-131 in the Unit 3 stored fuel pool. Since the explosion was two months ago, and given the half-life of this isotope, says it is hard to explain the current level unless there was an original fission event to produce enough I-131 for several half-lives.

Any alternative explanation for where this isotope came from?


Also he says that the fact Unit 4 SFP storage racks are intact means that physical fragments of plutonium MOX fuel, found 2 km from the reactor site, could only have come from the explosion of Unit 3 SFP. And calculates that a projectile distance two kilometers implies a supersonic launch velocity in the explosion. (Detonation in which the shock wave expanded faster than the speed of sound)

 

[~kujala~]

According to the Tepco site, Fukushima Daiichi is built on bedrock.
http://www.tepco.co.jp/en/challenge/energy/nuclear/plants-e.html

They might have steel bars going from the bottom of the buildings all the way down to bedrock. It would mean that the foundations of the buildings were built on bedrock although the bottom concrete would be much higher. Even small private houses are built using this technique if ground is loose.

If on the other hand the bottom concrete is laying on bedrock it's no surprise they are having difficulties with groundwater...

Edit: In the case #2 the problem would be that lots of groundwater could infiltrate for instance into the turbine building during normal operation. But in the case #1 groundwater could still create problems: as far as I understand the steel bar -foundations only protect the plant from going up to down. A lots of groundwater could perhaps lift the plant up, make it floating, and I am not sure if the steel bar -foundation would protect it from this kind of behaviour. It all depends if steel bars are connected to bedrock or are they just laying on bedrock.

 

[MJRacer]

Bedrock begs a definition from the exact location. They didn't say solid rock. If they are using pumps and wells to constantly de-water a 100 feet of sub soil and discharge it to a concrete channel that empties into the ocean, then I'd say it is not completely bedrock. Entirely bedrock is better than sand or loose ground or a layering of all three.

I tried to locate a Japanese page with the related information on the TEPCO website, but many pages have been replaced by a note concerning the emergency since the earthquake, and I have been unable to find such information in Japanese. I would not argue about the English text until you have seen the Japanese original. That is just my opinion.

Please see:

Manichi article about bedrock being 46 meters down http://mdn.mainichi.jp/mdnnews/news/20110427p2g00m0dm091000c.html

Study confirming the NPP is on floating mudstone base not bedrock http://www.iitk.ac.in/nicee/wcee/article/9_vol3_733.pdf