Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[SteveElbows]

Excellent, finally a document that sheds some significant light on timing of certain things.

This part of the report to IAEA deals with radioactive release into the environment:

http://www.kantei.go.jp/foreign/kan/topics/201106/pdf/chapter_vi.pdf

Within just a page or two it starts to make sense of some of the increases in radiation detected in various places, and attributes events at specific reactors to them. Just a small taster below, check out the document for more.

After earthquake, the discharge of radioactive materials became evident early on the morning of March 12 when the air dose rate measured by a monitoring car near MP-6(monitoring post No. 6 in the site of Fukushima Dai-ichi NPS) increased. It can be estimated that there was a leakage of radioactive materials from the PCV and a discharge of such materials to the air, as a slight decrease in the PCV pressure was observed in Unit 1 after an abnormal rise at this point. According to an analytical result, that fuel meltdown had already started.

And at the other end of the time range covered by this stuff:

In addition, an increase in the air dose rate was observed near MP-6 at 23:00 on March 15 and at 12:00 on March 16. D/W pressure decreases were observed in Unit 3 and Unit 2 at respective times. It is estimated, therefore, that discharges occurred from Unit 3 and Unit 2 at these respective times.

Dont get me wrong, its not perfect, it doesn't cover everything in great detail but its way better than the complete lack of narrative we've previously had on this subject from official sources. Dont think there's anything for those fascinated by reactor 3 march 20th-23rd events though.

 

[Quim]

From a physics point of view, how long would it take for a meltdown in #1 if the earthquake damaged the reactor while it was going full bore? Hypothetically. If the quake damaged both the control rods, preventing them from being inserted, and broke a main pipe, leading to loss of water, how long would it take for a reactor of that design to fail in a catastrophic way?

Here is a good place to look for that kind of information:
http://www.ornl.gov/info/reports/1981/3445600211884.pdf The NRC had a study done to examine the probable failure sequence of a Mark I reactor.
Read that and you will know as much as anyone else here.

 

[clancy688]

Here is a good place to look for that kind of information:
http://www.ornl.gov/info/reports/1981/3445600211884.pdf

But that doesn't include a meltdown scenario with the core being still at full power, does it? He asked how long a meltdown would need if the control rods weren't inserted.
I'd say it would be a matter of minutes.
If coolant flow is cut off and control rods are not inserted, there's an accumulation of 1,4 Gigajoule thermal energy every second. I don't think the RPV will withstand such stress for more than a few minutes... but the thermal energy production will probably decrease as soon as the fuel melts.
Still I don't think that something like this happened. It was told that all reactors scrammed successfully.

 

[joewein]

Which once again points out how unfortunate it is that we are lacking a poster knowledgeable of the subject of geology.

It simply can't be true that the underground rock formations, water tables and streams at the Fukushima site are an unknown.

Somebody did the engineering for that dam.

Google Earth shows several lakes in hilly woodlands to the west of the power station, within 1-2 km. When TEPCO started switching from sea water cooling to fresh water cooling around march 22 they once listed the name of the dam on a diagram.

 

[joewein]

Can anyone explain me this graph at page 3, there is big jump in I-131 level between 5/27 and 5/31: http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110607e8.pdf

What's so interesting in that "Radioactivity Density of Sub-drain at Unit 3 (Bq/cm3)" graph is not so much the increase but the change in isotope ratios.

If we look at corresponding graphs for units 1 and 2 we see them start off with I-131 activity more than an order of a magnitude higher than cesium activity, but due to the 8 day half life, iodine drops off against longer lived Cs-134 (2 yr) and Cs-137 (30 yr) until it ends about an order of a magnitude *below* cesium.

We saw the same picture here in Tokyo, in published fallout numbers. From 3/20-23, I-131 levels in fallout in Tokyo were 1-2 orders of magnitutes higher than Cs-134 and Cs-137. About 4 weeks ago, the last detected iodine level was one order of a magnitude lower than the last detected cesium level.

That's how it should be. Adding water (rainwater or groundwater) might change absolute concentrations, but should dilute all isotopes equally.

What happens on the unit 3 chart between about 5/27 and 6/2 is iodine coming back up again to the level of cesium. That means some inflow of water in which iodine was at least as prevalent as cesium. About 10 half-lives after the SCRAM (i.e. a 3 order of magnitude drop in iodine) there shouldn't be any such water in Fukushima 1, unless limited re-criticality occurred at some point.

 

[Jorge Stolfi]

Report of Japanese Government
to the IAEA Ministerial Conference on Nuclear Safety
June 2011
http://www.kantei.go.jp/foreign/kan/topics/201106/iaea_houkokusho_e.html

For convenience, I have combined all of the PDFs on that page into one 385-page document that can be downloaded from here: http://min.us/mvoVGLP
... there are 2 pages numbered IV-37 and there may be other oddities in there as well.

Thanks for the work!

Another possible error: in the section that describes the status of each unit, "cooled at the bottom of the RPV" perhaps should have been "pooled at the bottom of the RPV". Or perhaps not.

 

[jim hardy]

@nuceng

thanks for the pointer.

i too have considered recriticality. I decided it was not credible in the pools, on basis it would have steam cleaned and left them in disarray.
4's pool looks orderly.
3's pool looks to me like rubble is on top of fuel, stuff was blown into not out of pool.
i feel foolish admitting this but i even looked into fast criticality in a dry pool with NaCl moderator. Decided physics rules that out.

-----

regarding your transport of H2 from 3 to 4 :

do i recall that being dismissed because the stack has four separate vent lines going all the way to top? Or am i having a senior moment?

looking closely at the aerial photos.
The stack showing 4 pipes at top is the one at extreme south end of plant and looks like it serves that common building south of unit 4.

The stack between units 3 and 4 shows just one round hole at top and pipes entering at bottom from both units 3&4. Stack between 1&2 looks similar.

someplace i saw posted drawing of a stack with 4 pipes going all the way up but that's not what the photos show for two of the three stacks.

So fwiw i think your H2 communication between 3&4 via the vent lines is plausible.


old jim

 

[Quim]

3's pool looks to me like rubble is on top of fuel, stuff was blown into not out of pool.

You dismiss the possibility of a criticality because of the way the rubble on the top of the pool looks?

On the basis of the way the rubble from the blast arranged itself I could not dismiss the possibility of the Loch Ness monster being in there.

Was it Ifred or TCups that postulated that there was an eyeball looking out of that pond back in April?

Or was it March?

Or am I having a senior moment?

 

[MiceAndMen]

Another possible error: in the section that describes the status of each unit, "cooled at the bottom of the RPV" perhaps should have been "pooled at the bottom of the RPV". Or perhaps not.

This article in the Los Angeles Times says the report to the IAEA is 750 pages long. So either the LA Times story is wrong or there's a lot more to it than what's posted on the Japanese government's website.

http://www.latimes.com/news/nationworld/world/la-fg-japan-nuclear-report-20110608,0,7481490.story

 

[StrangeBeauty]

Edit: I think I am a bit behind on the discussion, but I will leave this up as a possible reference for others. Here is a recent post from NUCENG on the topic:

My reasoning that the Hydrogen...

I think lack of accurate plans for this specific site is hindering the analysis of the plausibility of tepco's idea that the SGTS was used as the conduit for the hydrogen traveling from #3 to #4. Hence my confusion about the identification of the gas treatment line. I am still not clear on which lines are being discussed (what photo/where it is).

=================================================

@nuceng
...
regarding your transport of H2 from 3 to 4 :

do i recall that being dismissed because the stack has four separate vent lines going all the way to top? Or am i having a senior moment?

looking closely at the aerial photos.
The stack showing 4 pipes at top is the one at extreme south end of plant and looks like it serves that common building south of unit 4.

The stack between units 3 and 4 shows just one round hole at top and pipes entering at bottom from both units 3&4. Stack between 1&2 looks similar.

someplace i saw posted drawing of a stack with 4 pipes going all the way up but that's not what the photos show for two of the three stacks.

So fwiw i think your H2 communication between 3&4 via the vent lines is plausible. old jim

Pardon my interjection, but it seems we're covering at least some old ground here. My recollection is that the venting stack piping was previously shown to be broken prior to #4 exploding (via the same image iirc). TEPCO then postulated a different avenue for the hydrogen to travel by. I questioned that here:

Agreed. That pipe was definitely broken after the #3 explosion. Also it can be seen on this page (about half way down):
http://www.houseoffoust.com/fukushima/april15.html

However, I thought Tepco was claiming that the hydrogen went from #3 to #4 via a different piping system? Here's the quote:

According to Tepco, hyrogen produced in the overheating of the reactor core at unit 3 flowed through a gas-treatment line and entered unit No. 4 because of a breakdown of valves.

Where is this gas-treatment line?

There was some discussion of this, but I'm not convinced it was resolved about what and where this 'gas-treatment line' might be and if that was a plausible way for the hydrogen to travel. For example:

I agree, we can leave the theory that the exhaust stack pipes between unit 3 and 4 after the explosion in unit 3 would have been able to lead hydrogen from unit 3 to unit 4.

If I remember correctly Tepco's original idea was that the leak of hydrogen to unit 4 went through the 'gas treatment lines'. I suggest what could be meant there is the large pipe system running along the turbine buildings, leading to a minor building at the Centralized Radiation Waste Treatment Facility, and from there to the big south exhaust stack SW of unit 4.

and here, recently:

The non-hardened vent system is the Standby Gas Treatment System. In an emergency it takes a suction on the secondary containment and discharges to the stack through particulate HEPA filters and activated charcoal filters to remove radiation from the vented air. The system maintains secondary containment at a small negative pressure so any leakage of the building is from the atmosphere to the building. Later in an accident the system can be used to take a suction on containment to clean up radiation inside a depressurized containment. Again it would discharge through the filters to minimize the release.

The whole purpose of the hardened vent is to allow a high pressure vent path from the torus air space to save containment integrity. The only motive force is containment pressure. The drywell will releve through the downcomers to the torus water pool which will also hold up soluble contaminants. As torus pressure drops whole containment is being vented.

Trying to summarize this for further analysis. Hope this is helpful.

Perhaps I am just not seeing this gas treatment line? I don't remember it being pointed out on an image.

 

[robinson]

Plutonium that is believed to have come from the crippled Fukushima No. 1 power plant has been detected in the town of Okuma about 1.7 km away from the plant's front gate, a Kanazawa University researcher said Sunday.

It is the first time plutonium ejected by the stricken facility has been found in soil beyond its premises since the March 11 megaquake and tsunami led to a core meltdown there.

http://search.japantimes.co.jp/cgi-bin/nn20110606x2.html

Of course the next thing you will hear after any mention of plutonium is that it is lower than the amount from bomb tests, and probably came from old bomb testing.

If only there was some way to find out.

By analyzing the ratio of three types of isotopes in the plutonium, Yamamoto was able to determine that it was emitted by Fukushima No. 1 and not past bomb tests.

The soil samples were collected by a team of researchers from Hokkaido University before April 22.

Oh my. From reactor one. Science, it doesn't care about what you believe.

 

[robinson]

So how does plutonium get out of a nuclear reactor? Or spent fuel pond? It's not like the airborne isotopes, wafting about in the air, the steam, the smoke. Right?

It doesn't float or escape in a cloud of steam. Does it?

 

[MiceAndMen]

Perhaps I am just not seeing this gas treatment line? I don't remember it being pointed out on an image.

Page IV-96 in the "Japanese Government report to the IAEA" shows an image that labels the large pipes that converge at the vent stack between Units 3 and 4, the "SGTS exhaust pipe junction".

http://www.kantei.go.jp/foreign/kan/topics/201106/iaea_houkokusho_e.html

Perhaps they are thinking that maybe the hydrogen flowed through the connecting pipe (about 200m of pipe all told) while the hydrogen was being produced and accumulating in Unit 3, and before Unit 3 exploded. Agree that it would be impossible for any hydrogen to travel through broken pipe after the explosion.

 

[ThomS]

The pressure vessel of reactor 3 was is measuring 181 degrees Celsius at 5:00 am (JST).

Here is the link as reported by TBS News (Japanese): http://news.tbs.co.jp/newseye/tbs_newseye4745702.html

 

[dh87]

So how does plutonium get out of a nuclear reactor? Or spent fuel pond? It's not like the airborne isotopes, wafting about in the air, the steam, the smoke. Right?

It doesn't float or escape in a cloud of steam. Does it?

PuO₂ boils at 2800 °C. That's slightly below the melting point for uranium oxide (2865 °C). (Wikipedia.)

I think that the reference to Fukushima No. 1 means Fukushima Daiichi, not reactor #1.

 

[swl]

Thank you!

Now for some small measure of consensus, it would be great if one (or more) other experts replied to this with an "I agree. 100 Sv/h is a reasonable estimate." or...not! :)

Yes, thanks, MadderDoc.

The 100 Sv/h number you give is for spent fuel that has been stored for ten years. In regard to reactor #3 fuel, I would be more interested in leaning about the radiation estimate for partially spent fuel a couple days after scram.

TIA

 

[razzz]

Again from http://ex-skf.blogspot.com/2011/06/fukushima-i-nuke-accident-tellurium-132.html#comments" June 6 and 3 he is already translating Japanese reports to English...

TEPCO thinks that tellurium came from the Reactor 1 whose fuel core was most damaged, and explains, "As the pressure inside the Containment Vessel rose, tellurium, along with hydrogen, may have escaped from the joints [on the Containment Vessel]. The pressure inside the reactor building also rose, and then tellurium leaked outside the building and was carried by the wind and spread wide."

　ただ、拡散しやすい揮発性のヨウ素１３１の検出量はテルルの半分程度。テルルと同じ金属性のセシウム１３７は浪江町の一カ所でテルルを上回った以外、微量しか検出されなかった。

However, volatile and therefore more easily dispersed iodine-131 was detected at half the amount of tellurium. Cesium-137 was detected in one location in Namie-machi in the amount exceeding that of tellurium; however, at other locations, it was detected in only minute amount.

　京都大原子炉実験所の山本俊弘准教授（原子炉物理）は「現在分かっている状況では、テルルが遠方に飛散することは考えにくい」と述べた。

Associate Professor Toshihiro Yamamoto of Kyoto University Research Reactor Institute (reactor physics) says "Under the circumstance that we have understood so far, it is hard to believe that tellurium would spread far."

Also on his site he posts wind patterns calculated for TEPCO for the Unit 3 blast blown offshore but some fallout hooked backed around and floated directly over Tokyo that day. http://ex-skf.blogspot.com/2011/06/fukushima-nuke-accident-wspeedi-shows.html"

After reading the links, click on 'Home' at the top of the page to see his current posts where is tracking other Nuke sites and conditions in Japan.

 

[Quim]

So how does plutonium get out of a nuclear reactor? Or spent fuel pond? It's not like the airborne isotopes, wafting about in the air, the steam, the smoke. Right? It doesn't float or escape in a cloud of steam. Does it?

My non-expert opinion:

I believe the industry guys are right, the amount of plutonium is trivial.
On the level of a very slight rise in one localized area. The bomb test stuff is everywhere, that's what makes it so undesirable.

However you are on the trail of something interesting.

Assuming that they have found a quantity of plutonium that is larger than what could be from the bomb tests, the odds are about 99.999% that it came from SFP3.
Maybe it's 100%, if one of the the experts chimes in we'll find out.

And finding absolute proof that the contents of the #3 fuel pond were ejected as far away as this would be positive proof that the mushroom cloud blast from #3 came from the fuel pond and would make it hard to understand how such a force could have been caused by a hydrogen/oxygen reaction.

 

[elektrownik]

Interesting why they are installing this not in center of SFP, sfp is weakest there ?, the point where they are installing it is strongest I think (because of drywell thick): http://www.tepco.co.jp/en/news/110311/images/110607_1f_2.pdf

 

[Jim Lagerfeld]

The pressure vessel of reactor 3 was is measuring 181 degrees Celsius at 5:00 am (JST).

Here is the link as reported by TBS News (Japanese): http://news.tbs.co.jp/newseye/tbs_newseye4745702.html

Apparently they reduced the flow of water from 18 to 11.5 tons per hour in the hope of delaying the trenches from overflowing, as they are running out of options until the water treatment plant is up and running, but the temperature in the reactor appeared to rise as a result.

It also says that they are facing a difficult judgement as to how much cooling water to pump as they try to balance the risk of overheating the reactor vs overflowing the basements - "燃料を冷やすための注水量について難しい判断を迫られることになります".

The article does not say which way TEPCO are leaning, except to point out that to let the reactor get too hot would be a 'dangerous state of affairs'.

If you were TEPCO, what would you do?

 

[razzz]

If you were TEPCO, what would you do?

Send the least contaminated water out to sea and hope it doesn't rain again until after some storage space is constructed and keep flooding to cool the corium, wherever it is.

 

[biffvernon]

The geologist would bring the information, and point to sources of information, both raw and compiled.

Information on the geology and underground water exists for that location.

I am convinced of that.

What we need is not just a geologist (like me) but a geologist that reads Japanese and can find the data.

A quick scan through the Report of Japanese Government to the IAEA Ministerial Conference on Nuclear Safety June 2011 http://min.us/mvoVGLP appears silent on the matter of site geology. Maybe I missed it but a search on 'geology' got only one inconsequential result and there were no results on 'mudstone'.

 

[Quim]

If you were TEPCO, what would you do?

If it were up to me, they would start injecting sand into the cooling water, as much sand as the water can carry.

That would entomb the upper facet of the corium.

That's half the battle.

Then you could keep the sand wet and dissipating heat, it would steam off, but the H2O would have less contact with corium.

If the lower half of the puddle (which might be sitting in the middle of the torus) can also be surrounded by either the same sand or in some other way shielded from contact with air there would be no more need for water. It would become inert.

I would also have the guys with the slide rules working overtime to tell me when it had cooled enough to stop watering it (it is only producing about a megawatt or less of heat right now.)

 

[MadderDoc]

<..>
The 100 Sv/h number you give is for spent fuel that has been stored for ten years.

The source says it exceeds 100 Sv/h at that stage, so the number is >100 Sv/h.

In regard to reactor #3 fuel, I would be more interested in leaning about the radiation estimate for partially spent fuel a couple days after scram.
TIA

I suppose an expert could do a better job than I, otoh since in the context it is more a question of producing a rough order of magnitude estimation.. :-)

If the spent fuel after ten years in the pool is at >100 Sv/h, I'd expect it to be at >1000 Sv/h after one year in the pool, and plausibly at >10000 Sv/h at the time of removal from the core, i.e when the fuel has been fully spent. So, doing simple interpolation I'd find it plausible that half spent fuel could have an activity of >5000 Sv/h, give or take one order of magnitude.

 

[thewild]

Hello all. I've been following this very interesting thread for some time now. I don't have your scientific expertise and English is not my mother tongue, so I stick to reading and not participating, but I have just a remark about this post :

From a physics point of view, how long would it take for a meltdown in #1 if the earthquake damaged the reactor while it was going full bore? Hypothetically. If the quake damaged both the control rods, preventing them from being inserted, and broke a main pipe, leading to loss of water, how long would it take for a reactor of that design to fail in a catastrophic way?

If that is not a theoretical question but an assumption that this could have happened, I believe that the logs from reactor 1 SCRAM seem to show that the rods insertion was successful.
I am absolutely no expert, but that is what I understand from the line "ALL CR FULL IN ... ON" :

That image is an excerpt from this document : http://www.tepco.co.jp/nu/fukushima-np/plant-data/f1_3_Keihou1.pdf.
It was already discussed in this thread, at least through David Lochbaum's analysis "Fukushima Dai-Ichi Unit 1: The First 30 Minutes".

 

[zapperzero]

So my question is, what could cause a steam explosion in a pool that was already boiling? If I am wrong to think that is low credibility, my apologies for ommiting that as a possibility.

A sudden drop in pressure maybe. Such as when there's a fuel-air explosion above the pool. The high-pressure wave is "followed" by a very low pressure front which is relatively long in duration.

This has been mentioned before, but not by me. Apologies to whoever it was, I can't find that post :(.

We can verify this, by the way. Was there a drop in #3 SFP level post-blast? I still think it's low-probability, btw.

 

[zapperzero]

I don't know how to improve on this, its still a pretty broad range of possibilities and I don't know what sort of data it may be possible to use to estimate what percentage of cores have left the RPV's. Am I right to think we may be waiting a very long time indeed to learn much more about this?

Not realy. If the core is flowing, it will keep flowing, slowly or fast, doesn't matter... We're talking at least a year, if not more, until it is no longer hot enough to eat through its own crust. I believe the percentage can be safely assumed to be close to 100%, on a long enough timeline.

As for how to get data, I've said it before. Find suitable pipes (of which sadly there should be many, in this design), put borescopes in.

 

[~kujala~]

What happens on the unit 3 chart between about 5/27 and 6/2 is iodine coming back up again to the level of cesium. That means some inflow of water in which iodine was at least as prevalent as cesium. About 10 half-lives after the SCRAM (i.e. a 3 order of magnitude drop in iodine) there shouldn't be any such water in Fukushima 1, unless limited re-criticality occurred at some point.

I have heard that soil chemistry is complicated.

Instead of comparing cesium/iodine I think we should first check if the starting level of iodine is still in reasonable range.

The change for the unit #3 occurred on 1st of June, the absolute value of iodine being 1,9 Bq/cm3:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110602e13.pdf

I calculated there is 82 days between 11th of March and 1st of June. From there I calculated that the starting amount of iodine should be 1 945,6 Bq/cm3.
(Somebody might want to check these calculations... )

I think this is still in reasonable range. Just to assess the level of scale there was 300 000 Bq/cm3 of iodine in seawater at the screen of the unit #2 on April 2nd:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110405e31.pdf

There could be hot spots of iodine on the debris/in the ground and then depending on how water is flowing/diluting we could see some sudden changes in the relative amount of cesium/iodine although this would not necessarily prove re-criticality.

 

[htf]

If the quake damaged both the control rods, preventing them from being inserted, and broke a main pipe, leading to loss of water, how long would it take for a reactor of that design to fail in a catastrophic way?

Some time ago a link to a report on a simulation of a station blackout at Brows Ferry has been posted - not that 250 page monster, just a 30 page report. In this report it is shown that the core will be uncovered after about 5 hours. They assume a reactor that had a successful SCRAM. During this 5 hours it has to be vented several times to reduce the pressure. If it were still running at full power it would produce ~20 times as much heat. For a rough estimation I would divide the time scale by 20. So after 15 minutes the core should be uncovered and during this 15 minutes a huge amount of steam would be produced. I don't think that we have seen this at Fukushima.

 

[zapperzero]

But that doesn't include a meltdown scenario with the core being still at full power, does it? He asked how long a meltdown would need if the control rods weren't inserted.
I'd say it would be a matter of minutes.
If coolant flow is cut off and control rods are not inserted, there's an accumulation of 1,4 Gigajoule thermal energy every second. I don't think the RPV will withstand such stress for more than a few minutes... but the thermal energy production will probably decrease as soon as the fuel melts.
Still I don't think that something like this happened. It was told that all reactors scrammed successfully.

I think you'd get a blast of some kind pretty quickly (as in, seconds). Fuel would fuse and be vaporized (boiled off)to some extent in place, huge increase in pressure from superheated steam and noble gasses, hydrogen production on a massive scale, oxygen from the PuO2 and UO2 being released in elemental form etc etc. But yea, the reactors all scrammed just fine. Seems a scram is not enough to make them safe, though.

 

[artax]

Apparently they reduced the flow of water from 18 to 11.5 tons per hour in the hope of delaying the trenches from overflowing, as they are running out of options until the water treatment plant is up and running, but the temperature in the reactor appeared to rise as a result.

It also says that they are facing a difficult judgement as to how much cooling water to pump as they try to balance the risk of overheating the reactor vs overflowing the basements - "燃料を冷やすための注水量について難しい判断を迫られることになります".

The article does not say which way TEPCO are leaning, except to point out that to let the reactor get too hot would be a 'dangerous state of affairs'.

If you were TEPCO, what would you do?

Yes... a very telling pointer as to how they're still battling, and haven't had the time to really think ahead. It's been out of the main news for a good while but something will give.
So three reactors have melted through the 6inch thick steel pressure vessels. and corium is all over the place... if they've not had good scientists they've certainly had good PR people to get that news out so late and so inconspicuously!

 

[Borek]

A sudden drop in pressure maybe. Such as when there's a fuel-air explosion above the pool. The high-pressure wave is "followed" by a very low pressure front which is relatively long in duration.

This has been mentioned before, but not by me. Apologies to whoever it was, I can't find that post :(

The idea was posted at least twice, first here:

https://www.physicsforums.com/showpost.php?p=3199497&postcount=641

then here:

https://www.physicsforums.com/showpost.php?p=3293073&postcount=6381

 

[artax]

RPV bottom head failure in a severe accident, according to US BWR beliefs, will occur in an ablating fashion. Uncooled core debris in contact with the inside of the RPV bottom head is likely to penetrate the head at an incore instrument penetration or CRDM housing penetration. When this occurs, it is believed that the hole will rapidly increase in size and a large portion of the molten debris will rapidly flow into the under vessel area. Some IPE-PRA studies claim this could occur as soon as an hour after core uncovery (in worst case scenarios). To avoid this situation, sufficient RPV injection is required to at least remove decay heat and thus keep the debris cooled enough to keep the RPV bottom head from failing. Of course, this assumes that all the RPV injection actually comes in contact with the debris. If this can't be done, the BWR strategy is to flood the primary containment to at least the elevation of the RPV bottom head and thereby contact the outer RPV with water and hopefully prevent or delay bottom head failure. If the RPV is breached by core debris, a combination of parameters should be observed such as RPV pressure decreasing while drywell pressure increases, drywell temp increasing, hydrogen detected in drywell, RPV water level below the bottom of active fuel, etc.

The frustrating thing about trying to figure out what happened at Fukushima is the lack of values for all these parameters. By our SAGs, we cannot positively say that RPV breach occurred. On the other hand we cannot say it hasn't. Even without this information, however it is very, very hard not to believe that much of the core debris has migrated onto the drywell floor simply for the extremely long time the cores have remained uncovered. The reliance on data from the couple RPV metal TCs is questionable. Sure, they track with changes in RPV injection flowrate but they only sense the outside surface of the RPV. For all we know these TCs are simply swinging in the breeze, especially the TC on the bottom head.

All the media talk about % fuel melt is meaningless. The questions that should be asked are: where did the fuel go? and, what can be done about it?

Good post.

I wonder what Tcups is busy on?

 

[MiceAndMen]

Apparently they reduced the flow of water from 18 to 11.5 tons per hour in the hope of delaying the trenches from overflowing, as they are running out of options until the water treatment plant is up and running, but the temperature in the reactor appeared to rise as a result.

The treatment plant can only process 1200 tons a day, and I'm very surprised they haven't already started filling some of the tanks they've been bringing in with contaminated water.

They've admitted they don't really know where the melted fuel is inside the reactors. Some could still be at the bottoms of the RPVs, some could be on the PCV floor in the pedestal area. The ostensible purpose of the water treatment plant is to eventually recycle the water in a closed-loop cooling system for the reactors. I don't even know how one would plan for a closed-loop cooling system without knowing exactly where the stuff is that needs to be kept cool. Makes absolutely no sense to me. So maybe they will send in those borescope cameras for a look around sooner rather than later.

Remember, when this plan was conceived they thought they were going to fill the PCVs with water. Then Murphy intervened. I can easily think of a few ways to implement closed-loop cooling in large closed watertight volumes (such as intact PCVs), but I'm baffled as to how they plan on doing it now.

 

[zapperzero]

The idea was posted at least twice, first here:

https://www.physicsforums.com/showpost.php?p=3199497&postcount=641

then here:

https://www.physicsforums.com/showpost.php?p=3293073&postcount=6381

Thanks.