Fukushima Japan Earthquake: nuclear plants Fukushima part 2

[Rive]

Sorry for the confusion, I was wrong about who posted the thing.
https://www.osti.gov/scitech/servlets/purl/5630475
from here: https://www.physicsforums.com/threads/japan-earthquake-nuclear-plants.480200/page-62#post-3209801

Also: http://www.sciencedirect.com/science/article/pii/002954939090019T
from here: https://www.physicsforums.com/threads/japan-earthquake-nuclear-plants.480200/page-33#post-3199567

One more: https://www.physicsforums.com/threads/japan-earthquake-nuclear-plants.480200/page-349#post-3299360There might be other sources too. Generally, 'drywell head seal' is a good combination for searching in both part of the topic.

 

[jim hardy]

Sorry for the confusion, I was wrong about who posted the thing.

No apology - , Thanks for the link ! That was a week before i joined PF. Glad to see it .
I do remember making the calculation for drywell bolt stretch back in 2011 but likely for another forum that was following the accident.
And i have no recollection of what was the answer

old jim

 

[MadderDoc]

Those exits [those encircled in red] are really the supposed main exits of steam-hydrogen mixture. However, they are not the source of the upward thrust.

The sequence of events, as I see it:
- serious leak on the RPV/PCV top: possibly with relation to some event inside
- the leak is strong enough to dislocate the gates around the RPV-PCV cap and quickly fills up the interior of U3 with steam and hydrogen
- the hydrogen reaches the lower levels of the unit through the vertical shafts
- the hydrogen is ignited somewhere on the top floor, the blast clears the top section of the building
- the blast progressing toward the lower levels and in the closed space a high pressure area is building up
- the high pressure wrecks the building and through the vertical shafts creates an upward thrust, bringing along the dust and rubble still moving due the initial blast

Interesting thoughts. By vertical shart (singular), I would understand what is encircled in blue in image of the cleared unit 3 top below. What other exits do you have in mind (vertical shafts plural) involved in the creating of an upward thrust? Also, you say those exits encircled in red are the supposed main exits of steam and hydrogen -- But that is not meant to include the steam contained in the high rising, mushrooming hot 'steamball', is it?

As I see it, the 'steamball' does immediately appear to have been tightly linked to whatever caused the powerful upward thrust, which visibly set relatively massive objects in a fast upwards motion -- iow one is led to believe that the material exiting the building, delivering the initial kinetic energy to those objects, would be the same material which went on to produce the high-rising steamball.

 

[jim hardy]

Blue circle is equipment hatch, elevator shaft to its right ?

This is a video of what looks like rebar bent into 3's sfp., snip below
i tried to post justthe link but the video shows up . Click 'copy video url' for link.

Something was affecting reactor water level indication shortly before the explosion

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

but pressure was well behaved..

been scratching my head for 6½ years.

 

[MadderDoc]

but pressure was well behaved..

Well, during that period, while the water level indicators went wildly up and downscale. the PCV pressure about doubled, until at the time of the explosion, it abruptly fell back.

From basic physics, the pressure p inside the system during that period would have been directly proportional with the product of N and T, where N is the number of molecules present in the PCV atmosphere, and T is the absolute temperature. p=kNT. The simplest explanation of the observed behaviour of p would then seem to be, that during this periode, the temperature T inside the system gradually increased up to a point, after which the number of molecules inside the system was suddenly reduced.

 

[MadderDoc]

This is a video of what looks like rebar bent into 3's sfp

Yes, you mentioned that earlier. What is the significance of this observation, as you see it, I mean what does it tell?

 

[jim hardy]

Well, during that period, while the water level indicators went wildly up and downscale. the PCV pressure about doubled, until at the time of the explosion, it abruptly fell back.

Hmmm RPV and containment were coupled by then.

Just estimating from the log scale graph, 500 KPA is about 5 atmospheres , around 70-ish psi ? Likely that's enough to lift drywell head and vent a lot of steam & H2

Yes, you mentioned that earlier. What is the significance of this observation, as you see it, I mean what does it tell?

I have wondered for years where in the pool that was.
If it is a breached wall it must be up high else the pool would have drained.
Seems the weak spot would be about here, and on other side at equipment pool passageway.

which is where the steam wafted out after explosion.

But it's speculation - i have not seen any pictures of either passageway
.........

digression --

looked back at unicamp tabulations
Yes, drywell pressure, rightmost two went up around 500 KPA in last hour before the explosion

 

[jim hardy]

Any BWR I&C types here ?

Are your reactor pressure sensors gage or absolute? Are they mounted inside or outside the containment ?

old jim

 

[MadderDoc]

Just estimating from the log scale graph, 500 KPA is about 5 atmospheres , around 70-ish psi ? Likely that's enough to lift drywell head and vent a lot of steam & H2

It is ~the max design pressure for the drywell. It is absolutely not built to operate at that pressure.

I have wondered for years where in the pool that was.
If it is a breached wall it must be up high else the pool would have drained.
Seems the weak spot would be about here, and on other side at equipment pool passageway.

I think it is rebar from a concrete layer in the original upper roof construction. Quite a lot of a section of that appears to have crashed and remained as debris on the top of unit 3, there, in the area of the pool and around it. The section appears to have been pulled down towards the floor in connection with the collapse of the upper part of the southern wall. In the main, the lined pool wall appears rather intact. There are some damages in parts of the floor bordering to it, but hardly enough to explain the presence of that rebar seen in the pool video.

which is where the steam wafted out after explosion.

But it's speculation - i have not seen any pictures of either passageway

There are some. It is not like the gates are all broken, however passageways have opened nearby them, bypassing the layer of the top shield plugs. due some displacements. At the position you indicate with red, the tight barrier to the pool water consists of two hung up on hooks doors, with rubber seals, with the sealing held tight by the pressure of the water column in the pool. The inner door (facing the refueling cavity), has become unhinged and pushed out towards the outer door (facing the pool water). The outer door appears to be in original position. By the unhinging of the inner door, a channel was produced such as to become a preferred release route for steam blowout close to the side of the pool.

On the opposite side of the top shield plugs, towards the equipment pool there are no tight doors, just slabs of high density concrete plugs stacked on top of each other. The preferred steam blowout route there became naturally along the ends of the slabs, due some displacement with a channel along the westward ends being the main one.

 

[MadderDoc]

Besides those two dominant blow out routes, there are several other lesser release points from the area of the top shield plugs, along their outer perifery, up between the broken slabs and along cracks in them. Pressure will out.

 

[Hiddencamper]

Pressure and level gauges are outside the containment.

Could it have been some type of notching or reference leg boiling?

 

[MadderDoc]

Something was affecting reactor water level indication shortly before the explosion

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

The water level measuring system at the plant was not very advanced, and could not cope well with elevated temperature, and evaporation from the reference leg under these accident conditions. There was no way of correction for loss of water from the reference leg, meaning the readout values for the water level would likely systematically indicate a significantly higher level of water in the RPV, than the level actually was. The gross unsteadiness of the readings in the hours before the explosion come on the background of a period with limited and intermittent injection of coolant into a water starved RPV. One could say, perhaps it was the reactors way of saying "duck and cover or run"..

They had been injecting sea water by fire engine from the vertical shaft at the backwash valve since 1:12 pm on the 13th. In the period around midnight between the 13th and the 14th, they were running out of sea water from that source, searches for other sources in the area failed. At 01:10 am injection from the emptied vertical shaft had to be suspended, and a firetruck was used to supply more sea water to it. At 03:20 am they repositioned another firetruck, such that it could take water in from a deeper spot in the vertical shaft at the backwash valve, and injection was restarted. At 09:20 am, they had managed to get 2 firetrucks in position on the shallow draft quay at the seaside and arranged a line with a hose for water supply from there and up to the vertical shaft. At 11.01 am the explosion occurred and injection stopped, due to damage to the firetruck and the hose. A new injection line into the reactor had to be constructed, after which the injection of sea water could be restarted, at 16:30 pm.

 

[Hiddencamper]

Just to add to the last comment. When you start boiling in the reference legs due to elevated drywell temperatures, you see notching and level perturbations. Levels can bounce high and low as bubbles work their way out and eventually boiling occurs. Also, if a rapid depressurization occurs to less than 400 PSIG, it's not uncommon to see degassing happen which also causes level notching. We have a step in our procedures if our reference line keep fill system isn't in operation to slow the rate of depressurization around 400 PSIG to monitor for notching or degassing occurring, and to trip our transient data system for engineering evaluation.

The reference legs are subject to boiling (as are the variable legs during severe accidents). Obviously this happens as drywell temperature is high and rpv pressure is low.

At elevated drywell temperatures that do not cause boiling, your minimum usable level degrades. For example, my wide range level indicators can only indicate a minimum of -159" at normal containment temperatures. Above 100 degreesF in the containment and the minimum usable level is -149" (it may not indicate less than that, or be erratic below that point). At 200 degF it's -139". Engineering was nice to us and worked the numbers so the numbers round out at 10" : )

Anyways, it's hard to tell exactly what's going on with level during severe accidents, which is why drywell temperature and pressure is important to know, as they help give you the full picture.

On a loss of all level indicators or indications that instrument lines are boiling, operators are to immediately exit the current emergency operating procedure they are in and enter contingency 4, RPV flooding, to attempt to recover level above the main steam lines and verify water level is above the top of the fuel by indications of water overflow through the relief valves or drain lines. If the site has already transitioned to severe accident guidelines then they will just say in those, as the SAGs place no dependence on RPV water level indications and have you take conservative actions regardless of what level is or whether it is known or not.

 

[Sotan]

Japanese sites report that the removal of spent fuel bundles from (2 of?) the spent fuel pools of Fukushima Daiichi is to be postponed.

The video is in Japanese but there is English translation under it:
"Regarding the spent nuclear fuel of TEPCO's Fukushima Daiichi nuclear power plant, the government abandoned the start of taking out in 2020 and found that the policy of delaying it for several years was strengthened.
Nuclear fuels that have been used up at nuclear power plants are kept cold in large pools in the same building as the reactor. In Fukushima Daiichi Nuclear Power Plant, it is one of the greatest risks that this nuclear fuel remains, and it is considered necessary to extract this for "decommissioning furnace". Under these circumstances, in Units 1 and 2 of Fukushima Daiichi Nuclear Power Plant, it was found that the amount of workers' exposure was higher than the initial expectation due to the damage situation at the site, the government abandoned the start of taking out in 2020, It is said that the policy of delaying is settled. It is planned to be officially decided by the middle of this month.
If the withdrawal of spent nuclear fuel is delayed, there is a possibility that the schedule of the entire decommissioning work that it is supposed to finish in 30 to 40 years may be affected."
On another TV station they mentioned that the 2018 term planned for Unit 3 SFP is likely not to be affected by this decision. Another site reports that the start of the nuclear debris removal might be postponed by (only) a year.

 

[etudiant]

This seems a very significant decision.
The site radioactivity is not going to fall significantly for many years, decades really, so if exposure is too high now, it will still be too high when the Tokyo Olympics roll around and long after that.
Is this a first step towards permanent abandonment/entombment of Daiichi instead of rehabilitation?

 

[Sotan]

One page PDF file in Japanese, showing two samples - one taken from the bottom of the PCV of Unit 1 in April 2017 and another one, a small amount of material from the tip of a cable that has been inserted to check the state of a PIP duct in Unit 2 in 2013. On Sep 20 these samples have been sent to some outside facility for detailed analysis of shape/appearance and composition (chemical elements) of the surface.
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images2/handouts_170921_08-j.pdf
I wonder why it took so long.

 

[Azby]

<I wonder why it took so long.>

Yes, it's a bit baffling. Also, there's no indication of where the samples are being sent for analysis.

 

[jim hardy]

...bated breath...

 

[Azby]

Here's the English version of the press release about the samples:

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170921_01-e.pdf

 

[jim hardy]

Here's the English version of the press release about the samples:

ahhh so something did run down the TIP tube. Should be telling.

Can they estimate neutron spectrum from little samples like that ?

 

[Astronuc]

ahhh so something did run down the TIP tube. Should be telling.

Can they estimate neutron spectrum from little samples like that ?

Their may not be much in the way of TU nuclides. They could do inductively coupled plasma (ICP) emission spectroscopy, gamma spectroscopy and neutron activation analysis.

 

[jim hardy]

They could do inductively coupled plasma (ICP) emission spectroscopy, gamma spectroscopy and neutron activation analysis.

I guess you need glass or mica to see fission fragment tracks?

 

[MadderDoc]

ahhh so something did run down the TIP tube. Should be telling.

It is one of 'bonus'- samples that came out of the tests they did way back in July 2013, probing the soundness of the TIP lines of Unit 2. They didn't manage to get any of the probes past the TIP indexers. (That is about 8-10 meters in from the PCV wall). When the probes were withdrawn, some substances were withdrawn with them, adhered to the tips of the probes. The sample depictured in the recent handout, and which appears now to have been sent for external analysis for some reason, is material from inside of the TIP (B) line, collected somewhere between the line entry and the indexer.
http://photo.tepco.co.jp/en/date/2013/201307-e/130708-02e.html

 

[Astronuc]

I guess you need glass or mica to see fission fragment tracks?

The range of fission products is on the order of a few microns, which is less than a typical average grain size of 10 to 15 microns for UO₂.

One could do a mass spectrometer in vacuum, but they would more likely do a gamma spectrometer.

 

[Gary7]

Tokyo newspaper Tokyo Shinbun reporting today that the plan to remove spent fuel rods from Units 1 and 2 of Fukushima Dai-ichi has been pushed back 3 years, and is now expected to start in 2023. The reason given is the high radiation readings around the area where the work is required to take place. They note that for Unit 1, the destruction of the concrete lid of the containment vessel is allowing strong radiation to escape the reactor core. (nb. Italics are mine) The spent fuel from the pool of Unit 3 is expected to be extracted in mid-2018.

This was the first I'd heard anything about the destruction of the concrete lid of Unit 1, but I haven't been following this as closely as I used to.

 

[MadderDoc]

This was the first I'd heard anything about the destruction of the concrete lid of Unit 1, but I haven't been following this as closely as I used to.

Yes the concrete shield plugs in unit 1 are in severe disarray. Here is a link that may be used as an entry to the subject, and to the original handouts about the observations:
http://www.fukuleaks.org/web/?p=16279

 

[Rive]

Just found this link somewhere:
https://www4.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170928_01-e.pdf

 

[jim hardy]

Thanks, Rive ...

I take that to mean "The muon measurements, while interesting, suggest the fuel has left the core area but don't tell us much about where it actually is ."

 

[Azby]

I'm not sure if this has been posted here yet, but it's very informative regarding TEPCO estimates of fuel melt and disposition, including muon scan results. Unit 3 muon scans weren't available yet, I think:

Estimation of current status inside RPV and PCV at Fukushima Daiichi NPS
July 3, 2017
http://ndf-forum.com/ref/d2_mizokami_en.pdf

 

[etudiant]

I'm not sure if this has been posted here yet, but it's very informative regarding TEPCO estimates of fuel melt and disposition, including muon scan results. Unit 3 muon scans weren't available yet, I think:

Estimation of current status inside RPV and PCV at Fukushima Daiichi NPS
July 3, 2017
http://ndf-forum.com/ref/d2_mizokami_en.pdf

No expert, but for me, this document is impressive, a carefully documented and sober summary of the current situation.
TEPCO and the Japanese investigators have worked hard and it shows.
Of course, it also gives some idea of how very long the road will be still to clean up this mess.