Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[swl]

Wait, what ? Unit 5 is at atmospheric pressure, there was info that RPV was open to refueling but look what I found in report:

Dont understand this, so there was no water in reactor after earthquake ?
How they reduced RPV pressure ?

According to the quote you posted, there was water and fuel in the reactor during the quake. Water and fuel were in there for pressure testing of the RPV. The water and fuel may have been necessary to simulate the loading and mechanical stresses on the system during normal operation.

The system was then pressurized by what I assume was a gas. After the blackout, the pressurization system for the test stopped, so the rpv pressure began to drop (which might indicate that the system was in fact leaking, but it may have been leaking backwards through check valves back into the test equipment, or from any other path that may have existed either before or after the quake). After a time at a lower pressure, the decay heat of the fuel (that was not critical at the time of the quake) increased the pressure in the RPV. Which makes me wonder about the leak that existed after the quake; was it secured by the ever competent staff, or did the system continue leaking. Anyway, they then vented gas from the reactor and eventually succeed in controlling the pressure and water level.

If true, this makes me wonder. Did this reactor also suffer fuel damage? Maybe not, since it didn't explode. ;-)

 

[SteveElbows]

If true, this makes me wonder. Did this reactor also suffer fuel damage? Maybe not, since it didn't explode. ;-)

Well they made holes in the roof of the building, suggesting that they were keen to avoid an explosion there, and that in theory the risk of explosion existed.

 

[SteveElbows]

I see that according to latest plant parameters, they measured unit 4 fuel pool temperature at 19:52 on the 8th June and it was 86-88 degrees C.

http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/11060906_table_summary-e.pdf

 

[NUCENG]

I'm sorry but your quote said it had a full load in the core and I take it the pressure test was done just before start up or re-starting. Whether they were pumping air to pressure check seals and for other leaks or using the heat generated by the fuel assemblies for the pressure check, the test was interrupted and they had a loss of cooling circulation for whatever reason and then the decay heat continued building up until cooling circulation was reestablished and lowered the pressure. And yes with no cooling water circulation with assemblies in the core, it is going to heat up no matter what just from decay heat. They got cooling circulation back and the heat that caused the pressure build up is gone now or it would heat up/pressurize and blow the seals or something else.

Prior to startup from a refueling outage, one of the normal tests is a hydrostatic pressure test. This is performed after the fuel has been reloaded, and the vessel has been reassembled and the head has been installed and torqued. The usual procedure is performed using recirculation pumps to heat up and pressurize the system to a proof pressure above the normal operating pressure, but below SRV setpoints. There is no air or nitrogen involved. The reactor remains shutdown with all control rods inserted. The containment is not inerted with nitrogen during this test.

 

[elektrownik]

Well they made holes in the roof of the building, suggesting that they were keen to avoid an explosion there, and that in theory the risk of explosion existed.

Unit 5 is at atmospheric pressure so the question is if they are venting it science earthquake ? I understand that is RPV is closed (it must be during pressure tests) the pressure shouldn't be at atmospheric level. Someone should look into raw data of unit 5&6, it could be find here: http://www.tepco.co.jp/nu/fukushima-np/index10-j.html
and here is translation of this page (but data arent in english): http://translate.google.pl/translat....co.jp/nu/fukushima-np/index10-j.html&act=url

 

[MiceAndMen]

Some things need to be included in considering offloading fuel with an external crane:

1. Debris or damage to fuel assemblies in the pools may make movement risky of further damage and radiation release.

2. Fuel assemblies are easily damaged by side loads so they need to be supported in whatever vessel or tank is used for the transfer.

3. If you provide sufficient support to prevent damage during transfer you need very fine control of location and speed of movement into the transfer support.

4. Movement in air will cause rapid heating and very intense radiation fields.

5. The transfer will be exposed to wind and elements.

6. A commercial grade crane could fail during transfer. If the assembly is out of the water when this happens it could get dicey. If the failure results in a dropped rod that would be bad.

7. What happens if there is another seismic event during transfer?

Supporting and protecting the pools and leaving the fuel there may not be best option but it also might not be the worst.

Very true, and I've thought about all that for the most part. To focus only on point 6, what are the statistics for industrial crane accidents? I'll bet the probability of an accident is less than the probability assigned by the designers of the plant to the possibility of a magnitude 9 earthquake and a 15m tsunami. And there are probably hard statistics to back that up, as opposed to just pulling it out of thin air and calling it my design basis.

Sorry for the snark :) Precautions would obviously be necessary. You don't paint without a dropcloth, cameras for observation underwater and above would be required, the vehicular transfer tanks would need the proper supports inside... all true. My opinion is it would still entail less risk than letting all that spent fuel stay 30 meters in the air for another year waiting for another earthquake. It all would depend on whose Probabilistic Risk Assessment numbers you believed. I sincerely do not believe such a plan would necessarily entail any more risk than they've already signed on for.

Thanks for the considered response, and again my apologies for the snark :)

 

[tsutsuji]

3. If the assumption is correct that they just fill the inner half of the room below the SFP with concrete this could make bad things even worse.
The walls are covered with thick epoxy painting, what makes up a very strong insulation. The concrete will not stick well to the wall, until this insulating paint cover is removed with demolition hammers, sanding etc.
There is no rebar connection to keep this heavy blob of concrete in place in case of a new heavy quake, as it does not adhere with the walls/floors.
So this loose giant thing will put heavy additional loads onto the already-weakened structure on the next big quake.

This kind of "support reinforcement" could finally pry open, crack and leak the still-intact SFP walls!

If Tepco is really so desperate doing such then I wonder what surprises this haunted plant still has for us what we have not been shown yet...

The pillars were included in the FEM analysis presented in a press release on 28 May : http://www.tepco.co.jp/en/press/corp-com/release/11052801-e.html , and the result is that they improve the safety margin against earthquakes. The 3D model including the pillars is shown on figure 1 page 115 (attachment 4-4-1) of http://www.tepco.co.jp/cc/press/betu11_j/images/110528b.pdf

 

[mscharisma]

The quote mentioning Japan Atomic Power Co. is obviously not about Fukushima II (or I) because they're operated by TEPCO, not JAPC. Instead the above description talks about the Tokai II NPP in Ibaraki prefecture.

It is in the report under this heading:
"(2) Seismic ground motion and tsunami height observed at Tokai Dai-ni NPS", so you are right. Sorry about that and thanks for pointing out my error. (Now I know why it instructs to not drive or operate heavy machinery on my latest prescription.) Deleted my post so as to not clutter up things here unnecessarily.

 

[NUCENG]

The articles in question are in Japanese, so quoting would be limited to Japanese text and asking someone to translate. We might ultimately end up with the whole article translated, which would completely be against the fair-use spirit of limited reproduction of copyrighted works. Then there is the matter of Japanese copyright law which I am totally unfamiliar with.

Being able to read the text would be nice, but my inability to read Japanese is my problem, not the author or publisher's. For the 2 articles in question, that's OK though because the diagrams and pictures convey substantial information by themselves.

I was using Google Translate to get some idea of the article text, but it's slow going. For example, first article, first section, title is which google translates as "For Example Oyster Or". I gave up soon thereafter.

Yes, my Japanese is also limited, and the technical terms are sometimes difficult to interpret. I have spent as much as four hours trying to read a single page. And Google translate has often been as bad as your example. It is a pretty intensive refresher, but won't really help the next time I visit a sushi restaurant.

 

[maddog1964]

Wait, what ? Unit 5 is at atmospheric pressure, there was info that RPV was open to refueling but look what I found in report:

Dont understand this, so there was no water in reactor after earthquake ?
How they reduced RPV pressure ?

could you please post your link for this information... as I believe that they may have been in the process of doing a "pressure test" and this is standard... required... and nothing scary!.. but without your source its very difficult to know what date and document your are looking at.

 

[SteveElbows]

Spraying of the creme-coloured agent onto one side of reactor 1 building shown on this timelapse video from the webcam:

http://www.youtube.com/watch?v=bPl1RKh548Y&feature=channel_video_title

Also the video of the hour prior to that shows multiple humans in the foreground near the camera at some points.

 

[NUCENG]

I see no data in support of that. No reduction of containment pressure was observed between the time PCV spraying is said to have been initiated (7:39 on March 13th ), and the time of the announcement that PCV spraying had been canceled (9:00 on March 13th).

That may be true. I was trying to explain that Containment Spray is a separate function from Core Spray. The question was what were they talking about when they said "spraying the PCV.

 

[NUCENG]

Thank you for the explanation.
Would these emissions be a plausible explanation for the cesium contamination in the sea water pooled in the basement?
I'm having a difficult time quantifying the scale of that problem, as contamination 30x the standard for release no longer sounds very threatening. Is this in line with some fuel rod breach or some steam leak from the turbines or what?

Probably not. Offgas extraction of steam would have ended at the time of the earthquake and scram and MSIV closure. The fans thyat exhaust steam to the offgas stack would have lost power as well. Fuel damage would not have begun until the station blackout occurred for units 2 and 3. Unit 1 may have lost decay heat removal before that if operators isolated the Isolation Condenser,

I would expect that the initial releases of cesium probably coincided with containment leakage from unit one due to rising containment pressure or containment venting. Unit 2 and 3 wouldn't have experienced significant fission product releases until HPCI and RCIC systems failed or batteries were depleted.

 

[NUCENG]

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

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

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

If you postulate a fuel air explosion, why do you need a steam explosion too?

 

[tsutsuji]

I had left the Onagawa nuclear power plant's happy-ending story with Pr. Omoto's 3 May 2011 presentation :

Site ground level → saved Onagawa units

page 9 https://www.sfen.fr/content/download/30655/1616957/file/1-ICAPP_Omoto2.pdf

This is not wrong, but we now know that it was a bit more complicated than that :

The observed tsunami height was 13 m, and despite the land sinking, the tsunami did not
cause the seawater pump room (on the site as high as 13.8 m, adjusted to sinking by
about 1 m) to be directly submerged. However, as the water level rose due to the tsunami,
the water level in the underground intake pit also rose as shown in Figure III-3-5, caused
by the siphon phenomenon. This resulted in seawater overflowing through the opening of
the tide gauge into the seawater pump room. Then the seawater flowed from the pump
room, via the trench, into the basement floors of the reactor buildings, causing the heat
exchanger room of the component cooling water system in the second basement to be
submerged. In addition, the component cooling water pump of Unit 2 was also
submerged, which thereby caused the cooling function of emergency diesel generators to
be lost, with two units stopped out of those three generators.

page III-50 (page 4 of http://www.kantei.go.jp/foreign/kan/topics/201106/pdf/chapter_iii-3.pdf)

 

[zapperzero]

If you postulate a fuel air explosion, why do you need a steam explosion too?

I don't need it, really. Others do, because it's really hard to for most people to believe that a "mere" hydrogen blast would lift so much stuff so high into the air and twist steel beams and scour paint off them and break steel-reinforced concrete pillars.

To most, I think, a fuel-air detonation is what happens when you get your fuel mix wrong and your engine starts "pinging". Annoying and possibly expensive, but not so dangerous, overall.

It's hard to make the jump from that to "flour mill wiped clean off the face of the earth" or "elevator cab blown literally a mile away in coal-dust mine blast" or "apartment building in Grozny demolished with one Shmel rocket".

 

[MadderDoc]

I am left wondering how it could possibly have been determined, that a fire was ongoing -- concurrent with the explosion -- in the oil of the recirculation flow control system M/G sets.

If they eyeballed a fire at that location once the initial dust from the explosion died down, they may reach that conclusion.

However, that would be a non sequitur, would it not :-)

Anyhow -- on a photo of the location once the initial dust from the explosion had died down there appears to be not one iota more of a lubricant fire to eyeball in the NW corner if unit 3, than there is on a photo taken 3 days later.

Here's the location 3 minutes after the explosion:

and here, the location 3 days after the explosion:

 

[Quim]

it's really hard to for most people to believe that a "mere" hydrogen blast would lift so much stuff so high into the air and twist steel beams and scour paint off them and break steel-reinforced concrete pillars.

I am one of the people who don't believe that a hydrogen explosion could have caused the vertical blast we see in the unit 3 explosion, but it is not because I don't believe a hydrogen explosion would be limited in power. To my eyes, the explosion, or the second part of the explosion of unit three, was a vectored blast.

I don't see the "mushroom cloud" as being merely a case of heat rising and carrying with it contaminates from a blast (as is the case in a surface burst nuclear explosion.) I see the vertical cloud as being the actual product of the blast itself. Imagine if you took all the shot out of a shotgun shell, replaced it with a dark powder of some sort and fired it into the air - that effect is what I see in the unit three blast,

I apologize if this explanation sounds too elementary or condescending but there are obviously some here who don't understand the significance of a vectored vertical blast - some force or some structure was responsible for containing the explosive force to a single direction.

The reactor containment structure can be ruled out as the vectoring agent simply because the equipment crane is lying on top of the containment structure with the remnants of the roof laying on top of that. These would not be so if the vertical blast had originated from the RPV or its containment,

The unit three explosion has to be seen as a two part event, a hydrogen blast (which did in fact break steel-reinforced concrete pillars) and a vectored vertical blast.

To jumble these two events and see them both as a single "explosion" would be to ignore the visual evidence.

 

[tsutsuji]

The approved storing capacity and water level at the process main building has been further extended :

maximum capacity : 14,200 m³ (up from previous 11,500 m³)
maximum level : OP + 5100 mm (this is 1.4 m above the 1st basement floor) (up from previous OP + 4200 mm)

However lowering that level back to the 1st basement floor level will be the top priority once the water purifying unit starts running.

http://www.meti.go.jp/press/2011/06/20110608003/20110608003.html

measured level : OP + 4507 mm as of 7AM 8 June 2011 : http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110608_01-j.pdf

 

[zapperzero]

some force or some structure was responsible for containing the explosive force to a single direction.

Ok. Something guided that plume upwards. It's going up faster than just heat would push it. There are big chunks in there that couldn't float up in a warm breeze regardless. So far, we are in agreement.

But how does all that make it necessary for a second explosion to have happened? There's any number of structures in there that could have shaped the hydrogen blast.

 

[Quim]

Ok. Something guided that plume upwards. Looks like that to me as well. How does that make it necessary for a steam explosion to have happened?

Let's not jump too fast here.

Forget the steam explosion for a moment, let's try and figure what vectored energy upwards.

I see only two possibilities:

1. a shaped charge sort of effect which I see as very unlikely because it would have had to have formed such a perfect 360 degree containment (in 3 dimensions)

or

2. the blast was contained by the walls of the fuel pond.

There's any number of structures in there that could have shaped the blast.

I can think of nothing except the two I mentioned above.

 

[joewein]

Most recent JAIF report on Daini:
http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1307247746P.pdf

Of relevant interest within:

Appears there is still an 8km evac area around the plant.

The limit around Fukushima II was at 10 km when it became 20 km for Fukushima 1. Since the plants are about 11 km apart, very little of the 10 km radius around F-II was not also inside the 20 km radius around F-I. So when F-I achieved cold shutdown, instead of lifting its exclusion zone they simply shrank it to 8 km, which was a no-go area anyway by virtue of being inside F-I 20 km evacuation zone.

 

[tsutsuji]

Tepco provided more details to NISA about the water purification unit which is supposed to start running at Fukushima Daiichi in the coming days. The following attachment includes a number of diagrams, photographs and a map showing the locations of the facilities and the new tanks : http://www.meti.go.jp/press/2011/06/20110609002/20110609002-3.pdf

The desalinated water will be vaporized in the final step to reduce its volume.
http://www.asahi.com/english/TKY201106080177.html

If this can be done safely without releasing radiations into the atmosphere, would not a similar process be useful at Fukushima Daini and avoid angering the fishermen with a discharge into the sea ?

 

[zapperzero]

I can think of nothing except the two I mentioned above.

I can. For instance, some arrangement of gantry cranes, plus a wall or two might have thrown big "shadows", stopping much of the ejecta, while the rest went upwards. The outer walls of the reactor building may have reflected some of the blast, bunching up the debris cloud as it was forming. And so on and so forth.

Even if the SPF shaped the blast (which it may have), it does not follow that it was anything else but a hydrogen blast. The highest concentration of hydrogen would have been found directly above the pool, no? And the pool would have been only half-filled.

 

[zapperzero]

So when F-I achieved cold shutdown, instead of lifting its exclusion zone they simply shrank it to 8 km, which was a no-go area anyway by virtue of being inside F-I 20 km evacuation zone.

Does not compute. If all is well, why maintain a "fictional" exclusion zone?

 

[etudiant]

Tepco provided more details to NISA about the water purification unit which is supposed to start running at Fukushima Daiichi in the coming days. The following attachment includes a number of diagrams, photographs and a map showing the locations of the facilities and the new tanks : http://www.meti.go.jp/press/2011/06/20110609002/20110609002-3.pdf



If this can be done safely without releasing radiations into the atmosphere, would not a similar process be useful at Fukushima Daini and avoid angering the fishermen with a discharge into the sea ?

Is it even realistic to think of evaporating 100,000 - 200,000 tons of water, apart from the contaminated steam aspect?
Seems to me they might need to restart unit 5 or 6 to supply that kind of heating.

 

[robinson]

Does not compute. If all is well, why maintain a "fictional" exclusion zone?

Keeps out the reporters. And the crazies. Protesters early on rammed the gate and drove around Fukushima Diani for a good while (protesting loudly all the while) until they could catch them and arrest them.

Yes, in the middle of all the post quake/tsunami/meltdown at Daiichi, protesters breached the security at Diani and drove around inside the plant. In a truck.

The story wasn't played up of course.

 

[joewein]

Unit 5 is at atmospheric pressure so the question is if they are venting it science earthquake ? I understand that is RPV is closed (it must be during pressure tests) the pressure shouldn't be at atmospheric level.

Units 5 and 6 are in cold shutdown, i.e. coolant is below 100 deg C and therefore the RPV doesn't have to be beyond atmospheric pressure to prevent boiling. Decay heat is being removed using the RHR system.

 

[Borek]

I can. For instance, some arrangement of gantry cranes, plus a wall or two might have thrown big "shadows", stopping much of the ejecta, while the rest went upwards. The outer walls of the reactor building may have reflected some of the blast, bunching up the debris cloud as it was forming. And so on and so forth.

Even if the SPF shaped the blast (which it may have), it does not follow that it was anything else but a hydrogen blast. The highest concentration of hydrogen would have been found directly above the pool, no? And the pool would have been only half-filled.

Discussion on the explosion is already buried deep somewhere in this thread. From what I remember speed of the explosion propagation heavily depends on the shape of the area (walls, columns, any other objects). No idea if that's enough to shape the explosion so that it is mostly vertical (that is, up becomes the path of the least resistance), but who knows.

 

[robinson]

Building One: Hydrogen explosion.

Building Three. Hydrogen plus something else.

Building Four: Unknown.

 

[zapperzero]

Building One: Hydrogen explosion.

Building Three. Hydrogen plus something else.

Building Four: Unknown.

At least make an effort to argue or source... such pronouncements add nothing of value.

 

[rowmag]

The articles in question are in Japanese, so quoting would be limited to Japanese text and asking someone to translate. We might ultimately end up with the whole article translated, which would completely be against the fair-use spirit of limited reproduction of copyrighted works. Then there is the matter of Japanese copyright law which I am totally unfamiliar with.

Being able to read the text would be nice, but my inability to read Japanese is my problem, not the author or publisher's. For the 2 articles in question, that's OK though because the diagrams and pictures convey substantial information by themselves.

My personal opinion is that most of the text does not seem very interesting unless one is a hardcore civil engineering otaku. The juicy bits of relevance for this thread are mostly in the illustrations, as you note.

I was using Google Translate to get some idea of the article text, but it's slow going. For example, first article, first section, title is
"1. まえかき"
which google translates as "For Example Oyster Or". I gave up soon thereafter.

Try "まえがき."

 

[robinson]

At least make an effort to argue or source... such pronouncements add nothing of value.

Please give us a source for your claim.

:)

Thinking about Building Three, it is highly probable that the building was full of not just hydrogen, but a lot of moisture. (this probably came up before, but I don't recall it at the moment)

If the hydrogen level was high, there wouldn't be enough oxygen to allow it to all oxidize at once, which clearly Building One suffered from. So the initial blast which clearly blew out the side allowed oxygen rich air to suck in, and the rest of the hydrogen went, but at the same time heating the moisture inside to turn into superheated steam, which would explain the obvious steam explosion. Obvious in the sense it clearly was not the type of instant flash you would see with a big hydrogen/oxygen explosion alone.

Experiments with concrete models and hydrogen, and hydrogen and a lot of moisture might actually learn us something about what can happen when you combine superheated boiling water pools, hydrogen, burning nuclear fuel rods, cesium hitting water, and various oils, gases and such, when it all goes terribly wrong.

 

[robinson]

Back to Power plant two:

Although the utility known as TEPCO told the agency that it will release the water after removing radioactive substances to an undetectable level, the agency is not approving the plan, leaving the fate of the 3,000 tons of the water accumulated in the nuclear power station, located 15 kilometers south from the crippled Fukushima Daiichi power plant, undecided.

If the water remains in tanks for a prolonged time, the storage facility may be corroded by salt in the water.

After being flooded by tsunami following a magnitude 9.0 earthquake that struck northeastern Japan on March 11, the Fukushima Daini power station saw about 7,000 tons of water accumulate in its facilities.

Of the water, 3,000 tons in the reactor, turbine and other buildings has been found to contain a small amount of radioactive materials such as cobalt.

TEPCO initially planned to let the water stay in the tank, but changed its mind after seeing rust in the storage facility and decided to release the water into the sea.

http://mdn.mainichi.jp/mdnnews/news/20110608p2g00m0dm090000c.html

While I don't believe most of what TEPCO reports, much less after it is filtered through the Japanese Government, something clearly went seriously wrong at Daini as well.

What exactly happened there seems shrouded in mystery.

 

[zapperzero]

If the hydrogen level was high, there wouldn't be enough oxygen to allow it to all oxidize at once

There would, if the hydrogen were to have been created by radiolysis of water into H2 and O2.