Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[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

 

[Rive]

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?

Radiolysis applies only on molecules with covalent bonds. NaCl has ionic bonds - as it solved it becomes a mix of separated Na+ and Cl- ions immediately.

 

[PietKuip]

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.

In the beginning of March, they had many other isotopes. Some of which were short-lived, like chlorine-38 and iodine-134. Those were in error. Tepco had to apologize, and say that they would never publish inaccurate data ever again. Since then they have limited themselves to iodine-131 and cesium.

http://www.tepco.co.jp/en/press/corp-com/release/11040408-e.html
"Three nuclides (Iodine-131, Cesium-134 and Cesium-137) that affect more for radioactivity and easy to identified are to be published as fixed figures. Other nuclides figures are to be released as soon as identified."

We have not seen much of those other nuclides.

 

[Dmytry]

Covering the pools to protect them from roof falling down?
Come on, the pool is on the top floor! The cover that has no risk of failing in, combined with instruments to ensure that cooling water level is correct, etc... it'd quickly be much cheaper not to have the spent fuel pool be on top floor next to the reactor in first place, eliminating entirely the risk of cascading failure from reactor to spent fuel pool. But the cascading failures were never considered in the risk assessments (which is imo a case of utter incompetence), hence the pool is found next to reactor, on top floor.

 

[zapperzero]

Speaking of cesium. Apparently an article was pulled from yesterday's (May 15) online edition of the Asahi Shimbun.

It contained, according to readers on the ex-skf blog, a table of results from a study of radioactive contamination in Kanto province (in and around Tokyo that is).
http://ameblo.jp/renatarojp/entry-10892684176.html
google translate link, so English-only readers like me can understand what I am babbling about
http://translate.google.com/transla...//ameblo.jp/renatarojp/entry-10892684176.html

Also from there, an alleged photo of the table of results from the paper's print edition:
http://2ch-ita.net/upfiles/file7582.jpg

Could someone here who reads Japanese confirm?

 

[jlduh]

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.

Nice work Brenda

Just a small mistake in a title i think: this is spent fuel of N°4 reactor, not N°2 (which can not be accessed anyway).

http://www.youtube.com/watch?v=tGuUuGRHlhI&feature=related

 

[PietKuip]

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.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110514e10.pdf is about the ground water at the different units. Some data points are clearly in error, like I-131 on May 10 at Unit 1 has an error in the exponent.

But the graph of Unit 3 is weirdest. It is very difficult to make sense of the ratios of iodine-131 to the cesium activities. Unless one assumes errors in exponents at several dates.

 

[Dmytry]

Speaking of cesium. Apparently an article was pulled from yesterday's (May 15) online edition of the Asahi Shimbun.

It contained, according to readers on the ex-skf blog, a table of results from a study of radioactive contamination in Kanto province (in and around Tokyo that is).
http://ameblo.jp/renatarojp/entry-10892684176.html
google translate link, so English-only readers like me can understand what I am babbling about
http://translate.google.com/transla...//ameblo.jp/renatarojp/entry-10892684176.html

Also from there, an alleged photo of the table of results from the paper's print edition:
http://2ch-ita.net/upfiles/file7582.jpg

Could someone here who reads Japanese confirm?

nothing outstanding or surprising. the clueless are promptly learning that a: the radioactivity is distributed in spots, and VERY much in spots (several orders of magnitude difference between hotspot and area around it) and b: the poorly done monitoring misses those spots. Then they will learn that c: even good monitoring will miss many of those spots.
On to food testing when they will 'discover' that a good chunk of radioactivity is in samples hundreds times above limit, which are rare, and aren't stopped effectively by traditional random sampling.

 

[MadderDoc]

<..>Do you believe that the images you added conclusively refute the contention that "fireball" conflagration of the gas cloud occurred mostly or entirely after the gas was ejected?

No, certainly not. I am just saying that the simplest explanation that is consistent with the evidence is not consistent with the claim of anyones seeing the ignition. You can uphold the claim only by adding more assumptions to the explanation, however these assumptions would seem to be added, not to make the explanation consistent with the evidence, but to make it consistent with this extraneous claim.

 

[NUCENG]

Please see:

Is it possible that the mudstone is considered bedrock? The seismic sensors discussed in the scientific article are down to 143 m and show consistent accelerations with those at 40m and 17 m. The site discussion says that the new unit is partially embedded in mudstone.

When the news article says "There is bedrock 46 meters underground." does that mean there is no bedrock until you go down 46m or does it mean there is at least 46 m of bedrock in which to put a storage tank?

Look at those old pictures of the construction of Brown's Ferry. They show extensive excavation. In the midwest there was a second plant at Callaway that was cancelled. The foundations had been excavated down to limestone bedrock. In an area as earthquake prone as Japan is it even conceivable that they wouldn't make the foundations as firm as possible?

 

[Rive]

Any alternative explanation for where this isotope came from?

There is that stem flow from under the top cover of the reactor...

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)

The only source about all this 'MOX fuel piece found far away' thing is Gundersen himself. Or at least I could not find anything else, and please inform me if anybody could.

 

[razzz]

Please see:

Those articles are between unclear to confusing.

One discusses Unit 6 and how it is partially imbedded in mudstone down at 17m. What is the other part sitting on?

The other article says a holding tank location has waterproof bedrock down below at 46m. Where do any leaks spread from the bottom of the tanks while traveling down 46 meters?

Might drill a big hole 46m deep and put some metal casing in it to make a holding well. Could get lucky and strike oil.

 

[jlduh]

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

And according to this seismic study, reactor N°6 which is founded 17m below ground level is embedded in MUDSTONE as we already mentioned it here... (see page 1 and 2)

http://www.iitk.ac.in/nicee/wcee/article/9_vol3_733.pdf (oops, sorry some were quicker to post!)

The reactors 1 to 4 are not so deep underground i think, but this confirms that they are not on bedrocks but on mudstone. And mudstone (which is dryied mud basically) is not bedrock. Except for Tepco maybe.

An other example of lies in communication strategy IMO.

To RAZZ and NUCENG:

One discusses Unit 6 and how it is partially imbedded in mudstone down at 17m. What is the other part sitting on

Re-read the exact sentence in the study linked above: "The reactor is partially embedded and is founded on mudstone", which is different than your wording! It doesn't say it is PARTIALLY FOUNDED on mudstone, it says it is partially embedded!

 

[razzz]

Mudstone is a second class bedrock. If exposed, it would erode rather rapidly compared to say, granite.

 

[MadderDoc]

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.

There is no need for an assumption of the presence of any additional combustible/explosive material. While in a testtube with pure hydrogen you can well produce a near colorless flame, in a Fukushima reactor you can hardly have a hydrogen explosion without producing concrete dust, and concrete dust in the heat zone will glow white, yellow or red depending on its temperature just as good as carbon particles. The blasts in unit 1 and unit 3 glowed just like they would be expected to do when a hydrogen combustion heats concrete dust.

 

[NUCENG]

Mudstone is a second class bedrock. If exposed, it would erode rather rapidly compared to say, granite.

Once the foundations are in place the site would be backfilled around the foundations to reach current levels, In the US there are extensive provisions for controlled runoff and draining to ensure potential released of ground water are not contaminated or if contamination exists, that it is monitored and reported. Would that help stabilize the mudstone so it wouldn't erode?

 

[Gary7]

Regarding the article discussing cesium found in Tokyo:

Although I didn't sight the actual Asahi article myself, I read the article that was copy & pasted onto the Japanese website, as well as the newspaper clipping that was linked, and they both look to be legitimate. The samplings were apparently taken at various locations in Tokyo, Chiba, Saitama, Ibaraki, and Fukushima. The earliest sample is from March 19th (Fukushima, 27650 becquerels/kilo). The most recent sample was taken on April 20th from the city of Tateyama in Chiba (127 becquerels/kilo) and the city of Kamisu in Ibaraki (455 becquerels/kilo). Tokyo's highest reading was from Kameido in the suburb of Koto-ku　(3201 becquerels/kilo) sampled on April 16th.

 

[yakiniku]

Regarding the article discussing cesium found in Tokyo:

Yes, the article is real. I obtained a copy of yesterday's Asahi Shimbum from a neighbor.

The article is on page 5 from the 15th May. I've scanned the full article for those who are interested.

 

[zapperzero]

Yes, the article is real. I obtained a copy of yesterday's Asahi Shimbum from a neighbor.

The article is on page 5 from the 15th May. I've scanned the full article for those who are interested.

Thank you very much indeed.

 

[MadderDoc]

Just can't remember the Hindenberg mushroom cloud and that was a big hydrogen sucker.<..>

source http://www.aerospaceweb.org/question/investigations/q0277.shtml

 

[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.

OK, the pool shield plugs referenced are interlocking stacked shield blocks that fill in the area where the fuel transfer chute connects to the reactor cavity. They aren't part of the fuel pool per se. They just fill in the area aroung the drywell cap to provide biological shielding during normal operation. Once these plugs are in place the hemispheric shield plugs are added to top off the reactor cavity above the drywell cap up to ffloor level.