Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[~kujala~]

I have been thinking about possible routes from unit 4 SFP to the basement of unit 4.

If no "direct route" is possible, there is of course always the possibility of a "back door" route.

In this case it would be this: The contaminated water would go down, down, down until it reaches the bottom concrete in the reactor building. Then it would infiltrate through the concrete (inside out). Even if they have a waterproof floor in the reactor building the waterproof systems might have become fragile over years and quake might also have caused some holes in them.

Once infiltrated through the concrete the contaminated water would reach the groundwater which would also be contaminated. The groundwater is moving towards the sea. The level of groundwater might be elevated because of the tsunami waters. Because of these higher than normal levels the sub-drain system might not catch all the moving groundwater.

The moving groundwater could once again infiltrate through the concrete into the basement of reactor 4 building (outside in). And so we would see some radiation in the basement of the turbine building. BUT here is the bottom case: if this would be the case we would see no radiation in the upper parts of the turbine building. (Unless there is contaminated water coming from somewhere else, like the unit 3 turbine building.)

Once we get better data for the radiation in the different levels of turbine buildings we can make better estimations for the routes of water.

 

[rowmag]

Here is TEPCO's latest thinking on what happened to Unit 4:

http://www.yomiuri.co.jp/feature/20110316-866921/news/20110428-OYT1T00663.htm

They now think the fuel rods in SFP4 came very close to melting, and were saved from doing so by the the explosion in the building, which damaged the gate between the SFP and the reactor well, allowing water from the reactor well to flow into the SFP.

This brings up a point that I don't think had been clear previously, which is that apparently the reactor well was still filled with water. The illustration accompanying the above article shows the reactor well and the equipment storage pool both full of water:
http://www.yomiuri.co.jp/zoom/20110428-OYT9I00660.htm

From the force of the explosion, they assume it was hydrogen, produced after the water level in the SFP dropped enough to expose the fuel. Had the explosion not occurred and damaged the gate, the fuel might have melted and created a much greater radioactive release than has occurred so far.

What is not discussed is how this squares with their earlier measurements of the water contamination, which indicated insufficient fuel rod damage to explain hydrogen generation. Could those measurements now be explained by dilution, since the water volume is now effectively much bigger (including the reactor vessel, and possibly the equipment storage pool on the other side if that gate was also damaged) than was being considered before (just the SFP)? Or can you get hydrogen generated before the zircaloy heats up enough to crack?

 

[Jorge Stolfi]

If there was an explosion in the drywell on the 14th, why did Unit 3 not lose drywell pressure until a week later?

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/plot-un3-full.png

Perhaps the pressure meter inlet in the drywell was under water. That adds 10 kPa of pressure for each meter of depth.

 

[Borek]

With 500 people on site, versus the usual 5000, they are clearly biding their time.

Please note that out of these 5000 people many were doing things unrelated to reactors maintenance - so their presence on the site now doesn't make sense.

TEPCOs approach, going slow, building water treatment plants and cleaning up the site may be right or entirely wrong.

However, unless someone has a plausible plan that shows real benefits, it is unreasonable to push for an acceleration, because the human cost would rise dramatically.

Amen to that. Sadly, "why they don't do what I know will be better than what they do now" approach is quite popular.

 

[Borek]

Yesterday they said SFP was leaking. Today they say it is not. QED

And that's the problem. They have to act using the information available, and this information is incomplete and can be false, because that's the characteristic of the situation, broken sensors, not access to important parts of the building and so on.

On the one hand we want them to publish every bit of information, on the other hand we bash them whenever the information is wrong. They are damned when the do, they are damned when they don't?

It was said earlier in this thread: do not condemn until you have walked in their shoes.

 

[Rive]

Here is TEPCO's latest thinking ...

Can somebody confirm that it's TEPCO's thinking? I could not find it anywhere else.

 

[SteveElbows]

Hmm. Such revisions are pretty scary. I do hope for everyone's sake its some sort of miscommunication and they don't actually have to pour 175 tons of water per day, that it was just some 'whoops water level below optimal, need to add a lot of water' day.

It was a weird day for them to make that 'mistake', given that they had just announced that they would be careful with unit 4 pool and only spray the minimum required so as not to cause problems to the structure due to the weight of the water. I believe this is where the 70 tons stuff came from, and unlike what the earlier poster said, this news came out a day or two before the 27th.

Anyway they pumped 100t on the 20th, 140t on the 21st, 200t on the 22nd, 140t on the 23rd, 165t on the 24th, 210t on the 25th and 130t on the 26th, so it was not a one-off decision to pump more. During this time period the water level was reported as being 4200mm and 4250mm. In an earlier period from 1st April->15th April the water level tended to average around 4900mm, starting as high as 5150mm and dropping as low as 4700mm during some points. Over this period of time they sometimes pumped 180t in one go, but between the 5th and the 12th they only pumped 3 times, amounts of 20t, 38t and 90t, yet the water level only fell from 4900mm to 4700mm.

 

[Jorge Stolfi]

Here is the current state of my POV-ray model of Fukushima Daiichi reactors #2--#5:

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/out/fig_un4_skinless_NW.png

There are still many missing details, such as the supports for the crane rails, the entrance gallery, etc. Apart from that, I tried to respect the dimensions shown on the blueprints mentioned before in this thread, namely

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/good/un3_cut_N_1.png
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/good/un3_cut_W_1.png
http://www.ic.unicamp.br/~stolfi/EX...a/povray/blueprint/good/un3_service_floor.png

These blueprint are clearly labeled 'unit 3' but they sem to match also all details of #4 that are visible through the holes blasted by the explosion. Of course, in #4 the shroud (yellow in my image) should be out of the refueling pool and onto the service floor, near the midle of the West wall.

In this image I have removed the walls of storeys 3, 4, and 5, and the top roof, leaving the main concrete pillars and beams (that are actually half-embedded in the outer walls). The view is from the southeast. The topmost visible floor here is the service flor (storey 5), with the spent-fuel pool on the left (south) and the steam-dryer storage pool on the right (north). The SFP spans storeys 3 and 4; its bottom is at the same level as the floor of storey 3, but the concrete around and below it is much thicker (about 1.5 meters by the blueprints).

Note that the explosion of #4 blasted away three whole pillars (including the extra-thick pillar near the east wall) and 2/3 of the mid-height beam on the south side of the service storey, thus creating the "panoramic window" that allows drones to peek into the SFP. If the blueprints are to be trusted, those pillars measure at least 4 by 5 feet in cross-section.

The tiny stud on the terrace is a 6 feet tall human model, for scale.

The two yellow circles show the location of the "Mickey Mouse Ears" of the mysterious "Hole" that a previous poster noticed on the East wall of #4, before the explosion, as per this image previously posted here:

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/misc/un4_position_hole_leak.jpg
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/misc/un4_position_hole_leak_w_floors.jpg (with floor levels marked)

I am now 80% convinced that the Ears are two holes on the wall from which some Dark Goo oozed out, ran down the wall, pooled on the terrace, then ran down its south face, over a window (not yet modeled). Note that the "ears"lie close to the floor of storey 4, slightly above the top of the first layer of spent fuel (strong blue in the model) but several meters below the normal water line in the pools. Not for a second did I think that it was corium from the spent fuel

By the way, before the earthquake there was an external staircase on the south face leading to the Mysterious Green Box on the terrace. Between the earthquake and the explosion, the Box and the staircase disappeared, and the Ears and the Goo appeared where the Box was. After the explosion the Ears disappeared due to destruction of the wall and the Goo runoff marks below them got buried in the rubble. However the runoff marks from the terrace down the south wall are still visible.

I hope these models will help the discussion. Suggestions and requests (special cutaways etc) are welcome, although I may not have time to work on them for a week or so.

 

[Jorge Stolfi]

...

Here is another cutaway view of my POV-Ray model:
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/out/fig_un4_building_cut_NW.png

 

[Dmytry]

The fuel in the SFP is 'spent', in addition to the fact that is started with low enrichment. The available reactivity is low because it is 'spent'. The rate a which positive reactivity could be inserted is relatively low, so a prompt critical event is unlikely. Coming out of a subcritical configuration with a very low neutron source, rather than starting at a critical configuration, I don't believe the configuration in the SFP supports prompt supercritical.

In the #4 they had the fresh fuel, and half-spent fuel. Also my understanding is that fuel is spent when you can't use it in reactor because of neutron poisons (xenon iirc) produced during reaction limiting the energy output, right? It can still go critical then, until enough of neutron poisons are produced to stop the reaction.

The explosions at Units 1 and 3 occurred well before the pools would have dried out, and it is more likely the hydrogen came from oxidation of the cladding in the cores.

I don't see the explosions being nuclear.

If the pools had dried out, there certainly wouldn't be any moderator to allow criticality. If there was water covering the fuel at the time of the explosion, the pressure in the pool would have been more of an increase in hydrstatic pressure, and that would crush the fuel into a more critical configuration.

Re-criticality would have been a concern AFTER the hydrogen explosions, when they TEPCO was reintroducing water into the SFPs. However, I would have expected them to borate that water.

All I see are chemical (H₂+O₂) explosions, not nuclear.

What I see is that #3 had explosive venting (and pressure drop), perhaps the lid of the drywell was lifted some and come back down. The mushroom cloud does not indicate nuclear explosion, but it does indicate a lot of heat, the gasses that are still very hot after they fully expand, something that doesn't easily happen with chemical explosions, despite what Hollywood would make you believe.

 

[Dmytry]

It was a weird day for them to make that 'mistake', given that they had just announced that they would be careful with unit 4 pool and only spray the minimum required so as not to cause problems to the structure due to the weight of the water. I believe this is where the 70 tons stuff came from, and unlike what the earlier poster said, this news came out a day or two before the 27th.

Anyway they pumped 100t on the 20th, 140t on the 21st, 200t on the 22nd, 140t on the 23rd, 165t on the 24th, 210t on the 25th and 130t on the 26th, so it was not a one-off decision to pump more. During this time period the water level was reported as being 4200mm and 4250mm. In an earlier period from 1st April->15th April the water level tended to average around 4900mm, starting as high as 5150mm and dropping as low as 4700mm during some points. Over this period of time they sometimes pumped 180t in one go, but between the 5th and the 12th they only pumped 3 times, amounts of 20t, 38t and 90t, yet the water level only fell from 4900mm to 4700mm.

Hmm. So a criticality or a hole or both.
If it is a hole, and they borate water, they may run out of borated water, which means higher risk of criticality, or a certain criticality if borating the water is necessary and not a precaution.

Furthermore observing a hole implies higher probability of there being cracks or other structural instability. (But we shouldn't worry, the NRC has "calculated" the probability of this happening as one in 700 000 reactor years...)

 

[clancy688]

Here is TEPCO's latest thinking on what happened to Unit 4:

http://www.yomiuri.co.jp/feature/20110316-866921/news/20110428-OYT1T00663.htm

Some people asked why the Unit 4 thermal images showed heat where the RPC was located. If the RPV is now connected to the SFP, hot water would flow into it.

 

[artax]

That's nice work George. And I think it's probably the correct way forwards.. as I'm beginning to see ourselves sitting here during the 2012 Olympics still trying to figure out what's going on at Fukushima because it has been completely covered up.
I agree with another poster that they need more still, hi res images rather than video and will probably have collected from T-hawk but not released.

I am beginning to fear that a full core meltdown might have been more favourable than a partial meltdown whatever percentage it was. There's a department where I work that researches the isolation of radioisotopes in weather resistant/environmentally friendly materials (glasses) so as to seal them away before burying in mines for the next 10,000years or however long is necessary.

This is what happened at Chernobyl with that big elephants foot the meltdown meant that much of the fuel is sealed in it like a glass as it melted the sand they poured on it.
brief overview here:- http://news.bbc.co.uk/1/hi/special_report/1997/chernobyl/33005.stm
With half damaged assemblies/rods, and having to continually pour water on them aren't they simply going to wash everything out that's water soluble.
OK hopefully they can contain this water and scrub it with Ion Exchangers, but I can't believe they'll ever get a closed water system, It'll be leaking out somewhere into the soil.

 

[SteveElbows]

Hmm. So a criticality or a hole or both.
If it is a hole, and they borate water, they may run out of borated water, which means higher risk of criticality, or a certain criticality if borating the water is necessary and not a precaution.

I've not made any conclusions myself. I should probably graph the pool water level data and the spraying data and see if it sheds any light on the numbers I mentioned previously. I have entertained the possibility that the April 11th earthquake made a difference to the unit 4 pool, but I am not really sure, especially as I don't know if I can trust the water level numbers they release at all.

 

[maddog1964]

Here is the current state of my POV-ray model of Fukushima Daiichi reactors #2--#5:

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/out/fig_un4_skinless_NW.png

There are still many missing details, such as the supports for the crane rails, the entrance gallery, etc. Apart from that, I tried to respect the dimensions shown on the blueprints mentioned before in this thread, namely

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/good/un3_cut_N_1.png
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/good/un3_cut_W_1.png
http://www.ic.unicamp.br/~stolfi/EX...a/povray/blueprint/good/un3_service_floor.png

These blueprint are clearly labeled 'unit 3' but they sem to match also all details of #4 that are visible through the holes blasted by the explosion. Of course, in #4 the shroud (yellow in my image) should be out of the refueling pool and onto the service floor, near the midle of the West wall.

In this image I have removed the walls of storeys 3, 4, and 5, and the top roof, leaving the main concrete pillars and beams (that are actually half-embedded in the outer walls). The view is from the southeast. The topmost visible floor here is the service flor (storey 5), with the spent-fuel pool on the left (south) and the steam-dryer storage pool on the right (north). The SFP spans storeys 3 and 4; its bottom is at the same level as the floor of storey 3, but the concrete around and below it is much thicker (about 1.5 meters by the blueprints).

Note that the explosion of #4 blasted away three whole pillars (including the extra-thick pillar near the east wall) and 2/3 of the mid-height beam on the south side of the service storey, thus creating the "panoramic window" that allows drones to peek into the SFP. If the blueprints are to be trusted, those pillars measure at least 4 by 5 feet in cross-section.

The tiny stud on the terrace is a 6 feet tall human model, for scale.

The two yellow circles show the location of the "Mickey Mouse Ears" of the mysterious "Hole" that a previous poster noticed on the East wall of #4, before the explosion, as per this image previously posted here:

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/misc/un4_position_hole_leak.jpg
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/misc/un4_position_hole_leak_w_floors.jpg (with floor levels marked)

I am now 80% convinced that the Ears are two holes on the wall from which some Dark Goo oozed out, ran down the wall, pooled on the terrace, then ran down its south face, over a window (not yet modeled). Note that the "ears"lie close to the floor of storey 4, slightly above the top of the first layer of spent fuel (strong blue in the model) but several meters below the normal water line in the pools. Not for a second did I think that it was corium from the spent fuel

By the way, before the earthquake there was an external staircase on the south face leading to the Mysterious Green Box on the terrace. Between the earthquake and the explosion, the Box and the staircase disappeared, and the Ears and the Goo appeared where the Box was. After the explosion the Ears disappeared due to destruction of the wall and the Goo runoff marks below them got buried in the rubble. However the runoff marks from the terrace down the south wall are still visible.

I hope these models will help the discussion. Suggestions and requests (special cutaways etc) are welcome, although I may not have time to work on them for a week or so.

first time here so apologize if i don't do this correctly... while you are working on Bld# 4 assumtions it is importantant to remember that the reactor was in "maintaince and being prepared to be refuled... we have knowway of knowing what systems were " open/closed" due to personal working on them.. when you open a piping/tank system it will be "normaly" locked out (with locks, that may number in the hundreds, depending on how large the systems are...) This is to prevent any accidental energizing of the system to the employes working on the piping/mechanical systems... also any "physical energy" will be locked out to prevent it from being energized... this would also include electrical systems... (I DO NOT WORK AT NUKE HOUSES AND DO NOT KNOW WHAT THE PROCEDURE IS THERE, NOR JAPANESE REG'S) It would make sense that they were working on many items, not just the core... repairs to hydraluic lines... cooling systems.. ventalation/electrical, equipment replacement... On bld #4 you have to think outside the box... have not seen the -- the green box/stairs.. but could it have been something that the construction contractors were using? the outage i believe is months, not days or weeks... thanks

 

[TCups]

If there was an explosion in the drywell on the 14th, why did Unit 3 not lose drywell pressure until a week later?

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/plot-un3-full.png

Where is the drywell pressure measured, above or below the drywell cap? Overpressure in the drywell let's hydrogen and steam escape the drywell cap seal, and could permit an explosion in the upper containment venting though the chute, as well as hydrogen and steam venting from below, through the tours pool or through some alternate route opened by the quake (lateral acceleration exceeded design parameters of the building), explaining accumulation of gas and additional explosion damage in the lower building. So, perhaps an explosion initially coming out of the upper containment above the drywell cap, but inside the transfer chute gate would be more precise than explosion coming out of the drywell and still fit the basic theory.

Photographic evidence seems to show steam escaping not only from the region of the transfer chute, but also from the gate region of the equipment pool after the explosion. How does that happen without loss of integrity of the drywell cap and continued generation of steam (and pressure) within the drywell?

The drywell pressure has been decreasing since the explosion, eventually coming to ambient atmospheric pressure if I read the graph correctly.

BTW, how does the drywell pressure come to ambient atmospheric pressure if the drywell is flooded?

Perhaps it is a chicken or the egg how the drywell containment was damaged.

Or perhaps there are a lot of hard data I don't keep track of very well and I am just completely wrong. Lay person that I am, I have selectively weighted what my eyes tell me over what the pressure and temp data tell me, which is fraught with error, I suppose.

But why would an unconfined explosion in the service floor portion of the building selectively vent to the southeast, over the SFP, and more laterally than vertically, forming a fireball, before the whole top floor exploded outward and upward (as did Bldg 1, and even considering differences in construction), and before the large vertical plume of steam/smoke apparently arising from the SFP?

Perhaps one day we may know for sure. Perhaps not.

 

[Dmytry]

first time here so apologize if i don't do this correctly... while you are working on Bld# 4 assumtions it is importantant to remember that the reactor was in "maintaince and being prepared to be refuled... we have knowway of knowing what systems were " open/closed" due to personal working on them.. when you open a piping/tank system it will be "normaly" locked out (with locks, that may number in the hundreds, depending on how large the systems are...) This is to prevent any accidental energizing of the system to the employes working on the piping/mechanical systems... also any "physical energy" will be locked out to prevent it from being energized... this would also include electrical systems... (I DO NOT WORK AT NUKE HOUSES AND DO NOT KNOW WHAT THE PROCEDURE IS THERE, NOR JAPANESE REG'S) It would make sense that they were working on many items, not just the core... repairs to hydraluic lines... cooling systems.. ventalation/electrical, equipment replacement... On bld #4 you have to think outside the box... have not seen the -- the green box/stairs.. but could it have been something that the construction contractors were using? the outage i believe is months, not days or weeks... thanks

That's actually a very good point, thanks.

 

[|Fred]

They were posted in this thread several times over the last few weeks. The first one I remember was on 7 April by Sirius (b), and it's possible his wasn't the first.

Yes I was the first to post them, before Sirius, my source was a anonymous on a Russian board, but before that I posted Hitachi's BWR MK1 BP. Sourced from free patent online.
Point is if anything it's GE or Hitachi or Toshiba's IP not Tepco.

Now a few point to consider.
1) About the INES, I understand the argument, one should have figured that the situation would not be containable and would go worse as it did.. None the less one should not have Hope so. IAEA stated on numerous occasion in the early days that at the given time INES rating was appropriate. So really rating Fukushima at the INES level 7 from day one might not have been really appropriate.

2) I'm not convinced that the Japanese government has the power nor the will to mussel the press of smear the situation. I may be wrong.. From what I see among general public oversea, most European are convinced that Japan have become hell on earth, and irrational fear is rampaging. This is damaging to the Japanese public image and economy, and I do understand them trying to mitigate that damage.

In the case of Unit 1, the maker was General Electric, so maybe they're trying to cover their butts with GE. I don't see that the technical details have any value whatsoever today. Nobody looking to compete with them in the reactor-building business is going to glean any useful information from those old Mark I designs.

Yep my point soory I reply before reading your answer

 

[jlduh]

I don't know if Dmytry already posted this doc on this thread or only on an other thread of this forum where i found it, but to me this NRC doc is very informative about the risk assessment of SFPs , especially after re-racking. I've been very surprised by this study and by it's hypothesis and conclusions, so i repost it here with my comments, expecting comments of other members espcially as we talk again a lot about SFP 4 and the variable explanations from tepco to try to explain why the water injected volume to water level measurement correlation seems so imprevisible: leak, criticality or?

This complete doc is here as posted by Dmytry:

http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr0933/sec3/082r3.html

This extract is very informative of the scenario that we can see appearing at any of the Fukushima pool if the situation deteriorates on any of the reactor and the level of water goes to zero in the spent pool. And this risk is going to last for a very long time as i don't see know how to secure this scenario to happen, based on the more than fragile (but in fact we may say lucky after all!) situation in which the Fukushima plant is now:

If the pool were to be drained of water, the discharged fuel from the previous two refuelings would still be "fresh" enough to melt under decay heat. However, the zircaloy cladding of this fuel could be ignited during the heatup.543 The resulting fire, in a pool equipped with high density storage racks, would probably spread to most or all of the fuel in the pool. The heat of combustion, in combination with decay heat, would certainly release considerable gap activity from the fuel and would probably drive "borderline aged" fuel into a molten condition. Moreover, if the fire becomes oxygen-starved (quite probable for a fire located in the bottom of a pit such as this), the hot zirconium would rob oxygen from the uranium dioxide fuel, forming a liquid mixture of metallic uranium, zirconium, oxidized zirconium, and dissolved uranium dioxide. This would cause a release of fission products from the fuel matrix quite comparable to that of molten fuel.545 In addition, although confined, spent fuel pools are almost always located outside of the primary containment. Thus, release to the atmosphere is more likely than for comparable accidents involving the reactor core.

Clearly it is recognized that the fact that there is no real strategy in place other than storing spent fuel has created the conditions for reevaluating the risks with SFP, because of increased volume of spent fuel and BECAUSE OF RERACKING... They reevaluated it but to do nothing because the probability was considered insignificant, after a very brilliant calculation. Obviously, big explosions as consequences of reactor damages that could deteriorate integrity of the pool, of even explode it completely and send in the air all its content were not part of the probabilities which end up terribly low -who would fear this so small risk? (really, didn't we go very close to this on reactor 3 when you see the force of the explosions and the amount of destructions, same thing at reactor 4, with these pools at the attics...).

I also like this sentence:

Ultimately, makeup to the pool could be supplied by bringing in a fire hose (60 gpm would suffice). Although one would expect that the failure probability associated with bringing in a hose (over a period of four or more days) would be very low, it must also be remembered that working next to 385,000 gallons of potentially contaminated boiling water on top of a 10-story building is not a trivial problem. We will assume, based purely on judgment, that the conditional failure probability for this method of makeup is on the order of 5%. When these probabilities are combined, the result is a frequency of 1.4 x 10-6/RY for an accident initiated by loss of spent fuel pool cooling.

Well at least they envisionned the difficulty if it could happen. But finally considered the probability to happen insignificant. Period.

I'm very surprised to see how risks assessment can be done without really taking into account domino effects. The only serious explosion that could destroy the pool is the one of a tornado missile... Well, well.

 

[rowmag]

http://japanfocus.org/-Makiko-Segawa/3516"

Thanks. Replied to here: https://www.physicsforums.com/showpost.php?p=3272263&postcount=35

 

[MadderDoc]

why would an unconfined explosion in the service floor portion of the building selectively vent to the southeast, over the SFP, and more laterally than vertically, forming a fireball, before the whole top floor exploded outward and upward (as did Bldg 1, and even considering differences in construction), and before the large vertical plume of steam/smoke apparently arising from the SFP?

But, the explosion in the service floor didn't vent selectively to the southeast, it appears from photos it blew away wall panels, pilllars and grey dust more or less to all sides. Naturally this explosion preceded (ever so slightly) those structure elements' being blown away by it. In this world like any other, cause must precede effect.

Here's what I can make out of the videos, with timing in seconds for the phenomena seen in the frames:

For comparison, the features of the unit 1 explosion:

Time (s)
0.0 - 0.1 | a detonation with a flash of fire (Note *1)
0.1 - 7 | an irregular cloud of dust is formed around the building
0.2 - 0.7 | a diffuse white steam cloud rises 150 m vertically above center building and dissipates/evaporates to invisibility.
0.5 -10 | the upper floor wall panels are seen flying in all directions 100 m or more, ballistically away from the building
7 | the cloud of dust can be seen spreading, dissipating with the wind

Features of the unit 3 explosion

0.0 - 0.4 | a detonation with a flash of fire from SE corner (Note *2)
0.4 - 3.5 | an expulsion of water/water vapor from center/SE of building
0.4 - 6.4 | a high buoyancy airmass rises vertically, dark and debris-filled eventually reaching a height of 500+ m
1.2 - 8 | an irregular cloud of dust/steam is being produced around the building
3.5 | base of the rising airmass from water expulsion starts drifting seawards
5.0 - 13+ | clouds of steam from expelled water is seen growing from along the surface out to 100s of meters away, incl. in directions counter to the wind.
6.4 | from 300+ m above, large and small objects start returning to Earth ( *3)
8 | the produced clouds of steam and dust start spreading, going with the wind kilometers oceanwards to eventually dissipate (Note *4)
14 | large objects from above start hitting surface or buildings, in zero to several hundred meters distance from unit 3

Note *1) The shock wave produced by the fire event in unit 1 caused damage to buildings several hundred meters away, indicating it was a detonation, not a deflagration.

Note *2) Massive damage to the building structure above service floor of unit 3 indicates there was a detonation. Some frames of the video suggest there may have been fire phenomena beyond 0.4 seconds, a) at the site of the initial detonation, b) spotwise in the rising airmass.

Note *3) Some of these objects can be seen still smoking on their way down, leaving each their own distinct downward smoke trails in the air.

Note *4) While the bulk of generated steam/smoke clouds around unit 3 are dissipating over the ocean, and after this has happened, two distinct smaller scale steam fans keep emanating for hours, from the area at the reactor lid, at north and south of the outer edges of the two fallen overhead crane booms.

 

[|Fred]

Clearly it is recognized that the fact that there is no real strategy in place other than storing spent fuel has created the conditions for reevaluating the risks with SFP, because of increased volume of spent fuel and BECAUSE OF RERACKING...

It does not make any difference strictly speaking in the theory but "high density storage racks" means re racking is your assumption ? or is it a fact?

About the theory I have a question: If fuel damaged fuel take fire, shouldn't there evidence of transuranian isotopes?

 

[etudiant]

It does not make any difference strictly speaking in the theory but "high density storage racks" means re racking is your assumption ? or is it a fact?

About the theory I have a question: If fuel damaged fuel take fire, shouldn't there evidence of transuranian isotopes?

http://www.tepco.co.jp/en/press/corp-com/release/11042711-e.html

This is from TEPCOs Mar 21st soil analysis. It notes:

Besides, as the result of the americium and curium analysis in the soil
from 2 samples among the 3 periodic sampling spots in which plutonium was
detected on March 28th amerium 241, curium 242, 243, and 244 were detected.

Is this the kind of evidence you have in mind?

 

[jlduh]

Fred: if your question is: was there re-racking at Fukushima plant? it seems it has been said by american experts

http://www.scientificamerican.com/article.cfm?id=nuclear-fate-fukushima

and this document from Tepco also mentions it for Daichi (page 5):

http://www-ns.iaea.org/downloads/rw...essions/session-ten-b/session-10b-japan-1.ppt

Now if your question is Does re-racking end up with the exact equivalent of "high density racks", i have no idea of the possible differences, but again, what is even more surprising than re-racking (which just increases the effects in case of problem) is the way the probability for this risk to happen is assessed in this study. Obviously, as for the calculation for the height of the runup of water at Daichi being totally "outside of the actual target", this risk calculation from NRC seems a little bit "weak" to say the least. My main question relying to the fact that dominos effects (like explosion like at N°3 or N°4 reactors) seem not to be even incuded in the study which doesn't take into account this domino effect on SFPs which are sitting on top.

Note that the title of this document is (i added bold letters so emphasize): Resolution of Generic Safety Issues: Issue 82: Beyond Design Basis Accidents in Spent Fuel Pools

Major explosions from reactors below or around the pools seem to be beyond "Beyond Design Basis Accidents" .

It's a (Beyond) squared in fact... Fukushima accidents are Accidents beyond beyond design basis accidents.

So i guess there will be now "Beyond beyond design accidents resolution of safety issues". That's good, it's "continuous improvement"... I'm just figuring out how many "beyonds" we'll need to get safe design, if possible...

Just for the fun: If the info posted a few posts above is confirmed that Tepco explained that in fact the fuel rods went dry at n°4 and have been "saved" by the explosion of the building which damaged the pool gate and created a leak from the well to refill the pool (uhhh...) , they could even put this into the NRC study and reduce the probability factor for going dry over a long period of time, as this is an alternate (even lucky, cause you have to be in core maintenance mode !) way to fill it!

A kind of "self safe design"? (ok that was just for kidding a little ;o))

 

[|Fred]

Is this the kind of evidence you have in mind?

It could be, are the quantity found consistent with a fuel fragment being dusted away by an explosion or consistent with fire ionization of part of the damage fuel ? I can't tell

Jdluh my question was you suggest that the quoted paper implied re racking, I could not sees where, so I asked if high density rack was a code name for re rack. Anyhow as I said It does not change anything as far as the idea behind the paper is concerned.

 

[jlduh]

Ok Fred. I don't know if re-racking is equivalent to "high density racks". But i would imagine that re-racking started to find more room in existing pools, and high density racks might be the later inclusion of this layout from scratch in the design of new pools, but I'm not sure...

Just as a follow up of a discussion we had previously here with Pietkuip about radiation measurements with Radex 1503 type devices (measuring essentially betas and some gammas), i wanted to mention that i just posted this message ont the other thread, which i think is also important to complement the subject about the various health risks depending on the paths of contamination of the various emitters:

https://www.physicsforums.com/showpost.php?p=3272402&postcount=43

 

[triumph61]

Perhaps:
E-Pool and Spentpool are flooded. Goes almost no different. Reactor is not flooded (due to service work within etc). The earthquake damaged the gate ever between S-pool and Reactor. The explosion of B3 is the gate of the rest (or maybe even a defect in the earthquake), the water flows from S-pool gate to the lower limit (It be 5m amount of water (height from the gate)) in the reactor.
How quickly it happened, we can even open (depending on the damage).
The fuel rods are more and more free ... Whether the reactor vessel is completely sealed, possibly for service purposes are any pipes open is mE not be excluded. Thus an amount of water flowing out through the S-pool gate reactor in R Building.
Sorry for English, Translation by Google

 

[Astronuc]

Perhaps:
E-Pool and Spentpool are flooded. Goes almost no different. Reactor is not flooded (due to service work within etc). The earthquake damaged the gate ever between S-pool and Reactor. The explosion of B3 is the gate of the rest (or maybe even a defect in the earthquake), the water flows from S-pool gate to the lower limit (It be 5m amount of water (height from the gate)) in the reactor.
How quickly it happened, we can even open (depending on the damage).
The fuel rods are more and more free ... Whether the reactor vessel is completely sealed, possibly for service purposes are any pipes open is mE not be excluded. Thus an amount of water flowing out through the S-pool gate reactor in R Building.
Sorry for English, Translation by Google

What is the source and context of the text? Unit 4 was undergoing service in the Reactor Pressure Vessel, so the whole core had been off-loaded to the SFP. It appears from the text that the RPV was empty in order to perform whatever servicing was going on. It is possible that the gates were damaged in the earthquake, and that they were leaking water from the SFP and Equipment Pool. That's been an unknown. Ideally, the should have been flooding the RPV and cavity, in addition to the SFP.

 

[bytepirate]

Here is TEPCO's latest thinking on what happened to Unit 4:

http://www.yomiuri.co.jp/feature/20110316-866921/news/20110428-OYT1T00663.htm

They now think the fuel rods in SFP4 came very close to melting, and were saved from doing so by the the explosion in the building, which damaged the gate between the SFP and the reactor well, allowing water from the reactor well to flow into the SFP.

This brings up a point that I don't think had been clear previously, which is that apparently the reactor well was still filled with water. The illustration accompanying the above article shows the reactor well and the equipment storage pool both full of water:
http://www.yomiuri.co.jp/zoom/20110428-OYT9I00660.htm

From the force of the explosion, they assume it was hydrogen, produced after the water level in the SFP dropped enough to expose the fuel. Had the explosion not occurred and damaged the gate, the fuel might have melted and created a much greater radioactive release than has occurred so far.

What is not discussed is how this squares with their earlier measurements of the water contamination, which indicated insufficient fuel rod damage to explain hydrogen generation. Could those measurements now be explained by dilution, since the water volume is now effectively much bigger (including the reactor vessel, and possibly the equipment storage pool on the other side if that gate was also damaged) than was being considered before (just the SFP)? Or can you get hydrogen generated before the zircaloy heats up enough to crack?

this is a good explanation for the occurence in #4.

two things i hadn't considered before:
the reactor well is flooded in some phases of the core shroud replacement and it hold enough water to cover the fuel, when it flows through the demolished gate.

anyway, this raises a new question: how has the water vanished so fast from the SFP? if there is no leak, as TEPCO suggests, then the heat must be (a lot) greater than considered before.

 

[bytepirate]

What is the source and context of the text? Unit 4 was undergoing service in the Reactor Pressure Vessel, so the whole core had been off-loaded to the SFP. It appears from the text that the RPV was empty in order to perform whatever servicing was going on. It is possible that the gates were damaged in the earthquake, and that they were leaking water from the SFP and Equipment Pool. That's been an unknown. Ideally, the should have been flooding the RPV and cavity, in addition to the SFP.

reactor is flooded during (some phases of) shroud replacement:
'...core shroud is cutted under water...'
http://www.toshiba.co.jp/nuclearenergy/english/maintenance/replace/shroud03.htm

 

[triumph61]

Sorry it is not easy to write in English.
Is only an thaught of me.
The Fuel is unloaded from RPV in SFP. The Gates are closed. THe RPV is empty of Water because some Service is doing in the RPV. The Earthqake (or Explosion of Unit3) dameged the Gate between RPV - SFP. The Gate has a high of~5m. The Water goes from SFP to RPV till the lowest Point of the Gate. The Fuel is overheating. etc...
If the RPV is in Service, perhaps there are Pipes open. So the Water can be floded in the Reaktor Building.
On the Thermo Pictures you can see that the temperatur is the same in RPV and SFP but not in the Equipment Pool! So the Gate RPV - E-Pool is in order.

 

[Dmytry]

Well at least they envisionned the difficulty if it could happen. But finally considered the probability to happen insignificant. Period.

I'm very surprised to see how risks assessment can be done without really taking into account domino effects. The only serious explosion that could destroy the pool is the one of a tornado missile... Well, well.

Well IMO two issues with that doc are:
1: minor problem: degradation of boron absorber material (such as boral) is not addressed. (actually major problem, but it totally pales in comparison with #2)
2: the risk estimate (used in cost benefit analysis) is entirely meaningless. First of all, it addresses only a few low probability scenarios, and secondarily -
Even a small uncertainty in the completeness of understanding of geophysics results in much, much higher risk than one in 700 000 reactor years. Same for even a small distrust (1% risk of corruption) for the data acquisition and simulation in the presence of strong commercial incentive. Historical evidence points at a non-negligible rate of failure for data acquisition or scenario simulation in presence of commercial incentive in favour of the failure.

Furthermore even a single failed "resolution" by NRC is a strong evidence in favour of assigning relatively high probability to "incorrect resolution" scenario (relatively to the risks as estimated), thus rendering the low probabilities stated in resolutions entirely moot and unusable for the cost/benefit analysis. NRC resolutions have to be sampled randomly and carefully reviewed, to estimate the failure rate of NRC's risk analysis. Then the obtained failure rate should be added to any failure frequency indicated in NRC report. That may still be too conservative as it does not address the possibility that more severe issues with larger potential source terms can have higher probability of failure of risk estimate by NRC.
Every real world number is ±something, and every number has probability of being grossly incorrect. I do not see this addressed in the risk analysis.

 

[UNECCS]

Nobody came TEPCO & government english press conference.

 

[MadderDoc]

What is the source and context of the text? Unit 4 was undergoing service in the Reactor Pressure Vessel, so the whole core had been off-loaded to the SFP. It appears from the text that the RPV was empty in order to perform whatever servicing was going on. It is possible that the gates were damaged in the earthquake, and that they were leaking water from the SFP and Equipment Pool. That's been an unknown. Ideally, the should have been flooding the RPV and cavity, in addition to the SFP.

With respect, I believe the text is the words of triumph61, subjected to Google translation from triumph61's native language.

triumph61 appears to me to be saying that since core shroud replacement was in progress, the reactor was likely not flooded at the time of the earthquake -- while the SFP and the equipment pool had to be. Further, that due to service work being done on the PV one cannot exclude that the PV has had openings made through it, meaning it would not be able to hold a water level above the height of such openings.

In the event something has happened to the gate between the SFP and reactor, water level in the pool would tend to become critically low, any excess water put in the SFP would overflow into the PV, and the PV might overflow further down into the building, the spillage eventually finding its way to the basement.

 

[Danuta]

Nobody came TEPCO & government english press conference.

Yeah, there were only two guys who came last time. I guess the info given out at these press conferences is leaving more than seats empty.