Fukushima Japan Earthquake: nuclear plants Fukushima part 2

[MadderDoc]

<..>
Now we know unit 1/2 aren't leaktight anymore due to the damage they had. Neither one is capable of submerging the undervessel grating. However unit 3 looks like it's still nearly leaktight so this may be an option.

Now, they are pumping in 70m3/day, so that would presumably be the volume that is leaking daily, at the present level of flooding. As I recall it, they were pumping in close to double that rate in early 2014, then cut it down to about 100m3/day later during that year. At about that time a significant leak from the PCV was detected at the level of the MSIV penetration (X-7) (~ at O.P. 12.000, which would be on the first floor of the reactor building). Apparently that is also the level to which the vessel is currently flooded. Due to the leak at MSIV penetration, they may not be able to flood the containment to a higher level, lest it spills over there.

 

[Hiddencamper]

Thanks Sotan

my Windows is dyng of update poisoning, Microsoft's preferred means of demise. It downloaded the file but refuses to play it. Perhaps i'll try the other machine tonight.

Splattered ? As in perhaps thrown against the walls by expanding steam ? That might explain a lot.

I would be very interested to see upper head area of the drywell (or is PCV correct term? The big light bulb..) Do you recall any photos ? . .

The outside of the upper head of the drywell requires you to drain out the spent fuel pool and upper cavity and remove the shield plugs.

To see the inside of the drywell head you need to go to the upper elevation of the drywell and open some bellows hatches. Not something a robot can accomplish.

 

[Hiddencamper]

My apologies for not posting links to the suspected molten fuel deposit videos, I assumed they were commonly known as mainstream media have been covering it quite a lot over the last few days. As I said in my earlier post, the notion that this is ejected fuel isn't based on seeing the video images, TEPCO spokesman Takahiro Kimoto is on record since last week indicating they suspect the images are of melt out fuel. "You can see something melted and solidified fallen from the inside of the reactor" he said. (Images and the quote source are here: www.cnn.com/2017/07/24/asia/fukushima-robot-nuclear-fuel-detected/index.html)

Unit 2 inspection already showed very strong indications of gross melt out there so I don't think it should be any surprise for unit 3.

As you say, as far as the ratio of fuel that exited the RV, I don't think the size of the hole in the CRD roof is relevant. Molten fuel being a liquid, once container penetration is achieved, the entire contents are able to exit the RV just as well through a small bore hole as a large one. Bottom loading control rods are a known inherent weak-point in this particular reactor design after all. News sources are calling the deposit sizes 'large' but whether that is from casual arm chair eyeballing or from actual TEPCO officials looking at known equipment and CRD remains captured in inspection videos and using them for scaling is unknown. If we get enough images to tile together as was done for Unit 2, we should have a clearer picture.

@Hiddencamper , Thank you very much for such an informative reply. I had no idea that the PVC was inherently designed to be water tight that way. This explains so much about events during the accident with the helicopters dumping water on the reactor buildings and what they were trying to achieve. Very interesting.

As far as this part:I understand that it is better to have RV depressurisation than pressurised RV rupture, but if the depressurised reactor then goes on to suffer a melt through anyway, what difference does it ultimately make? I am correct is assuming that it only matters as far as trying to calculate how much the concrete under the reactor will be damaged/attacked and how long you have to re-establish cooling before radioactive materials leak directly outside?

Dumping water from helicopters was only for the spent fuel pool. Not the containment. No real reason to do that.

If you have a pressurized melt while the containment is already beyond its limits the steam explosion can catastrophically damage the containment. We are talking about a small breach in the bottom head region, where the sudden and rapid expansion of steam out of the breach causes a catastrophic failure. The drywell is designed to handle this only when it is within certain initial conditions, and if you already exceed the primary containment pressure limit (PCPL) and the suppression pool exceeds the heat capacity temperature limit and suppression pressure, then drywell failure is very likely during a pressurized vessel breach.

When you initiate ADS, the steam from the reactor is discharged into the suppression pool. Even if the pool is already at saturation temperature, this is a controlled discharge of 25-40% rated steam flow, and as the containment system pressurizes slowly the suppression pool helps to act as a buffer to prevent an instantaneous failure of the drywell.

During a LOCA in a BWR, even if initial conditions are all met, drywell pressure momentarily exceeds the design pressure before the suppression pool can do its job. If you already exceed the pool and drywell limits and a hot debris ejection occurs, the pressure spike will likely fail the containment.

Remember that SRVs discharge to the suppression pool, while a vessel rupture discharges to the drywell and only eventually makes its way to the suppression pool after vent clearing.

Additionally in the case of unit 3, the ADS blowdown caused the containment vent rupture disc to finally rupture, allowing a controlled vent of decay heat to protect the containment system.

 

[Hiddencamper]

Now, they are pumping in 70m3/day, so that would presumably be the volume that is leaking daily, at the present level of flooding. As I recall it, they were pumping in close to double that rate in early 2014, then cut it down to about 100m3/day later during that year. At about that time a significant leak from the PCV was detected at the level of the MSIV penetration (X-7) (~ at O.P. 12.000, which would be on the first floor of the reactor building). Apparently that is also the level to which the vessel is currently flooded. Due to the leak at MSIV penetration, they may not be able to flood the containment to a higher level, lest it spills over there.

The Main steam lines are typically 260 inches above the top of active fuel. Give or take a foot or two based on vessel size.

 

[turi]

Results for Unit 3 muon measurements are in: No massive material has been found in RPV, meaning that the fuel has mostly be gone from the RPV. Page 8 shows a nice overview of the expected fuel locations and water levels in all 3 units:
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170727_01-e.pdf

 

[turi]

New analysis of the unit 1 investigations: For one location they eliminated the possibility that there is fuel debris, for two other they are not sure because deposits above possible melted fuel might provide shielding. http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170727_02-e.pdf

 

[turi]

Dose rates at unit 2 were reestimated. The first estimates from the image noise level were too high:
"[...] when making preparations to conduct the internal exploration of the PCV in a low radiation level environment, the threshold values were lowered to 50 in order to check operation of the equipment, but were never returned to 70 before conducting the PCV internal exploration".
So estimates at the CRD went from 530 Gy/h to 70 Gy/h. The latter value is also under the assumption "that Cesium 137 is the single major radiation source in the Primary Containment Vessel".
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170727_03-e.pdf
Edit: Corrected whitespaces.

 

[Charles Smalls]

All three unit results pretty much as expected:

The latest Unit 1 update report is one of the more interesting. The Unit 1 muon scans already indicated the RV was mostly empty and the most likely direction for the liquid fuel to travel was out through the pedestal opening into the PVC proper. The fact that a mass of deposited material was picked up by the probe cameras in this area suggested fuel remains. Now the new readings from this material suggests that the radioactivity levels are actually too low for it to be actual fuel.

To quote the July 27, 2017 report:
"Existence of fuel debris cannot be examined in the case of thick deposits due to their shield. [They consider that] there is no fuel debris, or that thick deposits and structures have profound shield effect."

I suggested before that hot fuel-concrete interactions can result in a process known as spalling where the high heat breaks up and redeposits the spalled concrete material in a1 process. (I think there's a video attached in one of my May or June posts.) But due to the results of this new relatively weak reading, I think the likelihood has been increased that this sediment material coating the surfaces in Unit 1 is actually spalled or deposited concrete of the basemat with the actual fuel melt further down in the building footings.

The Unit 2 results also make sense given the assumed picture of the three reactors. The incredibly high contamination readings didn't fit with the expectation that the gross amount of fuel had melted down through the CRD room and into the basemat. To pick up 530 Sv/hr readings near the x-6 penetration at the top of the PVC didn't fit the likely situation of large scale downward relocation of fuel.

Unit 3 scans show the reactor vessel was empty as the fuel appears to have melted out through the bottom head i.e. hot ejection. This means that the muon scan and it's target area was misdirected as I suspected. If they had been more pessimistic/realistic and used the results of the first two scans, they could have adapted the plan here to observe the lower portion of the pedestal area to gain valuable information to match up with the new probe results and provide more insight to the situation.

Just to go back to @Hiddencamper , this is what I meant by hot debris ejection being a relative term. Data may show that preemptive steps like ADS steam purging took place, but either way, a gross fuel exit and spread seems to have occurred and as we know large explosions took place inside the unit building so the end result is largely the same.

Very interesting to see the growing picture of the situation across the units and glad Tepco is sharing as much as they are. Many thanks to Sotan, Turi and others for providing the information and translations.

 

[HowlerMonkey]

Post worst case opinion, get refuted...repeat.

 

[jim hardy]

The Unit 1 muon scans already indicated the RV was mostly empty

More correctly they failed to show where is the fuel.

a gross fuel exit and spread seems to have occurred and as we know large explosions took place inside the unit building so the end result is largely the same.

You're looking for reasons to believe there was a "hot ejection". Maybe there was. Please don't stretch the evidence.

I have my own ideas too.

TEPCO seems to be proceeding with meticulous caution and attention to detail. Patience is the best policy for us "Sidewalk Superintendents" ..

 

[Charles Smalls]

More correctly they failed to show where the fuel is

Direct quote of the TEPCO July 27, 2017 Press release, page 8:
Unit 1- No massive fuel in the core area.[...] Most of melted fuel fell into the PVC and there is little fuel in the reactor core. (Source:
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170727_01-e.pdf)

That is word for word what I said. I made no comment on where the fuel currently is, only that results showed the RV, the reactor vessel was almost completely empty. I don't think you have grounds to criticize my statement.

On the follow up matter of fuel-concrete interactions and it's potential indications, I can't pretend to know. HOWEVER given the data and surveys TEPCO have taken and shared, I believe the hypothesis I put forward a couple of months ago has been reinforced by the latest results. If you see anything in the offical data to counter that viewpoint, be sure to comment.

You're looking for reasons to believe there was a "hot ejection". Maybe there was. Please don't stretch the evidence.

Belief is no part of my argument. All points I raise are cited and backed by current and relevant sources. 9 times out of 10 from TEPCO themselves. What I said on April 28th was that the Muon scan was very likely a pointless exercise. The data and the conditions in the sister units strongly suggested that the major amount of fuel had already melted out of the unit 3 reactor vessel and would not be seen on the muon scan. That has now proven true. As far as calling this fuel melt out a "hot ejection", that is not a term I coined. I am not familiar enough with industry terminology to make that statement. The point I raised with yourself and @Hiddencamper is that it doesn't matter whether it occurred under that definition. The outcome is largely the same. The gross amount of fuel has melted out of the bottom head and onto/into the basemat. The camera data and muon results prove that. As I stated, to my understanding unless you want to calculate potential concrete damage/penetration, the pressure of the vessel at the time of melt out is largely irrelevant.

Again if there is any data or relevant experience to counter this view be sure to raise it.

 

[turi]

To pick up 530 Sv/hr readings near the x-6 penetration at the top of the PVC didn't fit the likely situation of large scale downward relocation of fuel.

The 530 Sv/h estimation is the one they have reestimated to be 70 Gy/h.

 

[Charles Smalls]

The 530 Sv/h estimation is the one they have reestimated to be 70 Gy/h.

That is what I meant. The original 530Sv/h number was difficult to account for given the likely model of gross fuel meltout into the pedestal area with marginal splatter along the way. This revised 70 Sv/h fits much more into the expected scenario and brings the situation across the 3 units into greater alignment. There are probably many circumstances or chain of events that could have caused a 530 Sv/hr reading around that area but having it recalibrated to ~70Sv/hr means there is one less "mystery" to be solved and the situation inside the unit becomes more textbook and as expected.

 

[Astronuc]

The Unit 2 results also make sense given the assumed picture of the three reactors. The incredibly high contamination readings didn't fit with the expectation that the gross amount of fuel had melted down through the CRD room and into the basemat. To pick up 530 Sv/hr readings near the x-6 penetration at the top of the PVC didn't fit the likely situation of large scale downward relocation of fuel.

However, the X-6 penetration is not at the top of the Primary Containment Vessel (PCV), but rather it is at the elevation of the bottom of the CRD housing.
See page 6 of handouts_170727_03-e.pdf.

That is what I meant. The original 530Sv/h number was difficult to account for given the likely model of gross fuel meltout into the pedestal area with marginal splatter along the way. This revised 70 Sv/h fits much more into the expected scenario and brings the situation across the 3 units into greater alignment. There are probably many circumstances or chain of events that could have caused a 530 Sv/hr reading around that area but having it recalibrated to ~70Sv/hr means there is one less "mystery" to be solved and the situation inside the unit becomes more textbook and as expected.

There is nothing 'text book' or 'expected' about what is being discovered. The change from 530 Gy/h to 70 Gy/h is apparently due to a recalibration. On page 6 of handouts_170727_03-e.pdf, there is one reading of 650 Gy/h that was revised to 80 Gy/h, and another reading of 210 Gy/ revised to 70 Gy/h. These readings (outside the pedestal (about 5 to 7 m from the inner surface of the pedestal), not immediately under the RPV) are still higher than approx. 20 Gy/h (now revised to less than approx. 10 Gy/h) in the region above the platform and immediately beneath the RPV at the inner surface of the pedestal. I would like to see more readings, particularly underwater, and if they can do gamma spectrometry, I'd want some idea of what radionuclides are being detected.

Readings on the dose level made on 1/26, 1/30 and 2/9 were apparently deduced from the camera noise, i.e., the effects of radiation on the camera electronics (CCD). According to the text on page 6 of handouts_170727_03-e.pdf, the radiation measurements on 2/16 were made with integral dosimeters, which are ostensibly on the self-propelled survey robot.

 

[Charles Smalls]

However, the X-6 penetration is not at the top of the Primary Containment Vessel (PCV), but rather it is at the elevation of the bottom of the CRD housing.

I know, you can see it clearly in this TEPCO handout:

Location of the measurement readings here:

What I am saying is that the x-6 penetration and the area of the assumed 500-600Gy/h readings are relatively high up in the containment, around the middle of the 'lightbulb' curve area compared to the PVC floor proper below. This was difficult to account for given the other data. The picture across all three units now seems to be gross fuel exit from all three reactor vessels, with the fuel melting through the perforated bottom-heads and falling from the RVs down onto the basemat/ pedestal floor (red star). They all present visual and analytical signs of that being the case. Having ultra high ~500Gy/h readings in unit 2 so far above the PVC floor where the fuel is likely to have landed and spread didn't fit in with this hypothesis. If accurate it would require an alternate scenario where a large mass of fuel or other huge contamination source would have to be localised somewhere in that immediate area to account for it. With the new more accurate readings, that alternate theory is no as longer necessary. General fuel splatter and nearby pipework with contaminated contents can explain these readings quite well. There is now less mystery surrounding possible locations for the bulk of the heavily radioactive material in Unit 2. Due to the negative Muon results, probe dosimeter readings and camera footage, we can now presume the bulk of Unit 2s 150 tons of nuclear fuel to be somewhere in or under the building basemat rather than floating around somewhere above the PVC floor. Again, this is a much more likely scenario given not just the data inside the building but also the persistent high level groundwater contamination around the reactor buildings themselves. I believe we are getting good data and information from TEPCO and that the more likely condition of the reactors and buildings will be the one that ties all the data together into on coherent picture rather than a jumble of poorly understood information.

If there is any relevant data or information I have missed, be sure to present it.

 

[Astronuc]

What I am saying is that the x-6 penetration and the area of the assumed 500-600Gy/h readings are relatively high up in the containment,

Actually, one made the statement ". . . the x-6 penetration at the top of the PVC . . .". The top of the PCV is about 35 m or so above the location of the X-6 penetration, which is about 7 m or so above the basemat.

General fuel splatter and nearby pipework with contaminated contents can explain these readings quite well.

Actually, it doesn't. If fuel splatter caused that higher activity outside the pedestal, then we should see high activity at the inner surface of the pedestal rather than lower activity (the green dot in the image one posted). And we don't. And there is no nearby pipe work to explain those activities.

Having ultra high ~500Gy/h readings in unit 2 so far above the PVC floor where the fuel is likely to have landed and spread didn't fit in with this hypothesis. If accurate it would require an alternate scenario where a large mass of fuel or other huge contamination source would have to be localised somewhere in that immediate area to account for it.

Actually, it depends on what radionuclides are causing the radiation, and the most radioactive nuclides are fission products, and the fission products that could find their way outside of the pedestal area are gases (Kr, Xe) and volatiles (Cs, I, Br, and possibly Te). Now, Te is in a decay chain that goes like Sb->Te->I->Xe->Cs->Ba->La. There is a decay chain involving Kr: As->Se->Br->Kr->Rb->Sr->Y->Zr. One of the high yield fission product pairs involved Zr¹⁰⁰ and Te¹³⁴, and there are combinations of Sr, Xe isotopes, including Sr⁹⁷ and Xe¹³⁷. Xe¹³⁷ decays by beta decay to Cs¹³⁷.

Fission from Pu-239 shifts the nuclides pair up in mass and Z, and Pu fission produces a higher ratio of Xe to Kr, and so one can see that fission favors the presence of volatiles in the Xe-decay chain. Chemically, there are a number of compounds involving Cs, I and Te, which contribute to the mobility of these species, and which favors the mobility of Cs. Volatiles and Xe transport with steam, so if the RPV was breached, it's possible that any vapor escaping the RPV would transport Cs and its precursors into the area below the core and out through the opening in the pedestal wall. Cs and I are also soluble in the water, so they could be carried to wherever the water flows, or seep into unprotected concrete.

Regarding the activity levels measured, from the Unit 1, the debris on the basemat floor has activity of about 5-15 Gy/hr, or an average about 10 Gy/hr under water. (handouts_170727_02-e.pdf, pages 8,9,12,13). TEPCO posits that fuel debris and some deposit (corrosion) is sitting on the floor below the RPV.

If one refers to handouts_170727_01-e.pdf, page 9, TEPCO compares the expected fuel location with what the muon scans reveal.

U1: ·No massive fuel in the core area. (Lower area of the RPV is not measured.)
My comment: So TEPCO doesn't know how much might be left in the RPV.

U2: ·High density materials that is considered fuel debris were found at the lower area of the RPV.
·Part of fuel possibly exists in the reactor core area.
My comment: TEPCO's analysis so far does not indicate that the bulk of the fuel in U2 left the RPV, and it certainly does not support the fact that fuel ended up below the basemat. It could be the bulk of the fuel is still in the RPV, but I have no way to assess the muon scans. It would be good if they could scan a non-damaged, or intact, BWR/4 of similar size and composition.

U3: ·The evaluation at present shows possibility that some fuel debris remain inside the RPV, but massive and high density material has not been found. (Measurement and detail evaluation are continuing.)
My comment: It was not pointless to do the muon scan, as one asserted on April 28 and reiterated on this page. Based on the scan of U2, which is of similar design, there was some expectation that they might find fuel in the core and RPV. It appears there is less fuel than is believed to be in U2. They are still measuring and evaluating.

In order to use muon imaging, one has to shoot through the intended mass toward the sky, since muons originate in the upper atmosphere by virtue of interactions of cosmic rays with protons or nuclei in the atoms in the air molecules. Muons come from the decay of charged pions or Kaons, which come from the annihilation of anti-protons or resonance particles. The count rate is so low, they probably do the scans over several months (based on the dates of the scans on page 10 of handouts_170727_01-e.pdf).
Ref: http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/cosmic.html#c2

Aiming west toward the hill, or downward do the ground, there would be no muons traveling toward the detector. To scan at the basemat floor from the turbine building (east of containment), they'd have to be below the elevation of the torus. From the westside, they'd have to be in the containment building where the torus is located. That's probably flooded and/or exposed to high levels of radiation. I don't think anyone is going into containment any time soon.

 

[jim hardy]

I don't think you have grounds to criticize my statement.

The camera data and muon results prove that.

No, they only suggest it's possible.

Muon imaging also suggests it might be up in the steam separator region.
We know there's fuel in the SFP
compare density of regions circled in yellow.

I certainly don't assert that's where the fuel is
I do assert that muon imaging failed to show us where it is and only suggests where it is not.

 

[MadderDoc]

The Main steam lines are typically 260 inches above the top of active fuel. Give or take a foot or two based on vessel size.

Yeah, yeah. But the MSIV (main steam isolation valve), which I was talking about, close to which the leak was detected back in 2014, is not at that level. It is situated much lower, in the MSIV room on the 1st floor of the unit 3 reactor building, neighbouring the TIP room. That's where the four main steam lines exit through the PCV wall, to go to the turbine. The leak was found at the steam line that comes out through the X7-D penetration, apparently at the expansion joint between the (outer) MSIV valve on that line and the outer PCV wall.

 

[MadderDoc]

Schematically, indicating where a leak was found in the MSIV room of unit 3 in 2014. Red dot marks the spot. From what I have seen about the current investigation of the PCV of unit 3, it appears to be flooded currently to closely the level of that leak.

 

[MadderDoc]

Compared to the east wall of unit 4, very little debris was found remaining at or close to the foot of the east wall of unit 3, after the explosions on March 14-15 in 2011. I wonder by which mechanism or force it happened to be like that, and where did the debris go.

 

[jim hardy]

I wonder by which mechanism or force it happened to be like that, and where did the debris go.

You'd think somebody would have written his memoir by now.
There's this old report http://www-pub.iaea.org/MTCD/Publications/PDF/Pub1710-ReportByTheDG-Web.pdf

If you recall the videos

unit 3 ejected a black cloud straight up

my guess is debris got scattered far and wide
you can see some of it on top of turbine building and a sizeable hole in the roof

The Japan Self-Defense Force guys described chunks of concrete falling on their vehicles.

Schematically, indicating where a leak was found in the MSIV room of unit 3 in 2014.

Hmmm if upstream valve wasn't shut off tight and that expansion joint failed in the 'quake or one of the aftershocks, it'd be a hydrogen leak down low in the building...

I wonder by which mechanism or force it happened to be like that,

Prevailing thought is still AFAIK hydrogen explosion. Have you heard any different ?

 

[etudiant]

Hmmm if upstream valve wasn't shut off tight and that expansion joint failed in the 'quake or one of the aftershocks, it'd be a hydrogen leak down low in the building...Prevailing thought is still AFAIK hydrogen explosion. Have you heard any different ?

A hydrogen leak lower in the unit 3 structure might help explain the explosion of unit 4.
It is difficult to envision a leak from near the top of building 3 somehow infiltrating unit 4 selectively.
Hydrogen leaks ferociously well, but if there is a path it will escape upward and there is no connection afaik except through the vent stack, which is connected pretty low. Or am I missing something obvious?

 

[MadderDoc]

Obviously, there was a hydrogen explosion in the building, and it is in the nature of such an event to scatter debris far and wide. However, after the explosion, you'd expect to find increasingly more debris lying around, the closer you get to the wreck of the building. But not so, closing in on the foot of the east wall of unit 3. You think black cloud cleaned that up?

As regards the leak in the MSIV room Tepco says it is at the bellows (or expansion joint) on the southmost steam line, I do not know how they know. In the video one could only discern the stream of water (estimated by Tepco to about 1.5-4.5 m3/h) coming down from that general area, while the southmost steamline itself and its expansion joint is hidden from sight by the next steamline in line. Presuming the inner main steam valve on the leaking steamline was shut, as it should be (they fail shut) the steamline would still be blocked for exiting steam and hydrogen from the RPV, irrespective of a failing expansion joint on the line outside the wall of the PCV:

 

[Astronuc]

It is difficult to envision a leak from near the top of building 3 somehow infiltrating unit 4 selectively.
Hydrogen leaks ferociously well, but if there is a path it will escape upward and there is no connection afaik except through the vent stack,

As far as I know, TEPCO believe that the hydrogen traveled between Units 3 and 4 through the ducts that were connected to a shared vent stack. See lower left in photo Jim posted. The round (circular) ducts are about the elevation near top of primary containment or near base of the secondary containment. Unit 4 had a fire (deflagration) in the upper containment, while Unit 3 had an explosion.

Obviously the hydrogen had to escape the RPV, where the Zircaloy was reacting with the water coolant. Hydrogen then had to flow out of the RPV in the PCV, then into secondary containment.

After the earthquake, we don't know how much damage was done to joints and seals in the various systems, or cracks in the structures.

 

[MadderDoc]

At 14:31 on March 13, Tepco employees observed over 300mSv/h at the north side airlock on the first floor of unit 3, R/B while noting that "there was white gaseous substance inside", in other words, steam. that had come from within the primary containment was gushing into the first floor of the building. The measured pressures in the RPV and PCV of unit 3 had at that stage started tracking each other closely, consistent with a failed barrier between them.

The pressure of the presumably combined system came at times close to, but not much above the max design pressure for the PCV, until the next day March 14 when the explosion in the building occurred shortly before noon during a 'high' excursion of the pressure to slightly above the max design pressure for the PCV:. Throughout that period one can reasonably assume, that steam from within the RPV/PCV, as was observed in the afternoon on March 13, had been continually leaking out into the first floor of unit 3. The leak at the MSIV could've been a source, inasmuch , judging from the video, everything in the MSIV room shows sign of having been exposed to steam for an extended time.

 

[jim hardy]

However, after the explosion, you'd expect to find increasingly more debris lying around, the closer you get to the wreck of the building.

I'd expect heavy debris to get hurled by an explosion not so far as light stuff like wall and roof panels.
Indeed those plank looking pieces on top of turbine building are, if i recall correctly, pieces of trim-like panel .
The massive concrete columns on ocean side remained standing , those on West side toppled over but didn't go anyplace.

But not so, closing in on the foot of the east wall of unit 3. You think black cloud cleaned that up?

No, i think it threw the debris further Eastward probably a lot of it clear into the water. It moved some heavy stuff, recall what looked like an airconditioner hanging off East side and head bolt tensioner pushed out on North side.

What's your thoughts ? Do you think there was steam in it ? I don't remember any reports of water raining out of it.

I'll look for that Cryptome satellite picture taken just minutes after the explosion... Probably not quite enough resolution in it though.

 

[MadderDoc]

What's your thoughts ? Do you think there was steam in it ? I don't remember any reports of water raining out of it.

There was obviously steam in it, and quite a lot, or its buoyancy becomes inexplicable.
http://gyldengrisgaard.dk/fuku_docs/unit3cloud45/

 

[MadderDoc]

I don't remember any reports of water raining out of it.

I'll look for that Cryptome satellite picture taken just minutes after the explosion... Probably not quite enough resolution in it though.

No, it may have rained from it and you wouldn't be able to see it from that satellite photo:
http://gyldengrisgaard.dk/fuk/20110314_1104 satellite/index.html

The only indication that it might have rained out of it would be the vertical dark streak that develops under it and follows it, during the first dozen seconds of its lifetime, while it travels towards the ocean, then disperses. That could perhaps be interpreted as black rain.

 

[MadderDoc]

As far as I know, TEPCO believe that the hydrogen traveled between Units 3 and 4 through the ducts that were connected to a shared vent stack. See lower left in photo Jim posted.

The ducts Tepco believe carried the hydrogen from unit 3 to unit 4 are of too small a diameter, much smaller than the quite visible 'fat' ducts, in order to be visible in the photo Jim posted. These smaller diameter ducts are meant to carry the exhaust from the SGTS in units 3 and 4 respectively, and they merge close to the stack to a single duct that goes to the stack. The same ducts are used to carry the exhaust from vent operations, whether it be from the PCV, or from the suppression pool, to the stack. Tepco believe vents going out from unit 3 through the duct unintendedly didn't all go up the stack, but rather backflowed through the duct coming from unit 4 to end up there, entering the building through its SGTS system (the isolation valves in this system fail open) -- thus providing the fuel for the explosion.

 

[jim hardy]

Thanks Doc for that Glyndengaard link. I'd forgotten where that was.
Big black chunks falling out of the initial black cloud that got projected up then moves right with wind

Followed by white smoke or steam ?

Not to throw the conversation back six years, just refreshing my memory.

old jim