Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[zapperzero]

The context requires interpreting what the detail tells us. Was the high radiation due to loss of shielding water level from the spent fuel pool? Was the level from a release plume from damaged fuel in the SFP? Was the drywell Cap displaced? Was the level from shine from the drywell? Was the level from an ongoing release plume due to containment leakage? If the radiation was from I-131 it would indicate recently irradiated fuel. If it was all gamma radiation it would indicate shine instead of a plume. What is the radiation level today?

There is at least some context - it was measured from a JSDF helo and so it is, must be, all gamma, because that's all the military cares about - how long can their soldiers operate the equipment. It's not likely at all that someone bothered to pop a probe out the window just for the thrill of counting beta decays. In fact, I'd wager good money that they were buttoned up.

Look at that anemic plume of steam, hard to believe that the helo is getting 3 Sv/h from that (and if it was, people on the ground would have been getting it too), it's not like they are flying directly through:



The reactor well cap was not displaced, that we know of.

As for the radiation level today, that is also unknown. There are reports of dose rates on-site decreasing very significantly after the pools were watered.

 

[SpunkyMonkey]

This may be the missing Unit 3 refueling crane fallen into the spent-fuel pool as seen in an April, 14 2011 image here:

The graphic shows similar objects between this piece of wreckage in the Unit 3 pool and the intact Unit 4 refueling crane. It also shows a similar spatial conjunction of similar objects, and this meta-similarity makes me confident we're looking at Unit 3's refueling crane.

There are many pre-tsunami photos of the refueling crane here.

Why isn't the proposed refueling crane also bright green? My guess is that the fire that blasted out the south side over the pool and thus onto the crane scorched off the paint.

 

[SteveElbows]

Thanks for the additional info. I'm sort of with NUCENG with this one, in so much as I am hesitant to attribute the reading to a particular source with any great certainty. Especially as they were high enough in the air that I cannot claim that they were only measuring stuff that must be related directly to reactor 3.

I'm basically still stuck at the point of being able to say that the fuel pools are still of interest, and that reactor 3's pool may be more interesting than reactor 4's. I expect that at some point we will learn more about this, but I doubt I am going to figure much more out in the meantime.

 

[tsutsuji]

It says "strong possibility of uncovered fuel" to me.

Sorry for asking again what was probably mentioned a dozen times in this thread, but:

Was there no instrumentation telling the SFP water level in real time, or was that instrumentation broken ?

I have the same question about temperature instrumentation.

If the fuel uncovered, how ? Was the water splashed out during the earthquake ? Or during the explosion ?

 

[SteveElbows]

This may be the missing Unit 3 refueling crane fallen into the spent-fuel pool as seen in an April, 14 2011 image

Sorry but that photo is a pretty poor analysis, the objects in the photo are a poor correlation for the circular items of the fuel handling bridge.

People did spend a lot of time looking at a variety of photos around reactor 3 for signs of the refuelling bridge. No useful conclusions were formed, other than being able to say that its not intact above the pool like reactor 4's is.

Some bits of it could be in the pool, but its also quite possible that it was ejected from the reactor building. And not necessarily dramatically either, it may have blown out in such a way that it did not travel high into the sky, but rather toppled south and fell to the ground between reactors 3 & 4, and area where quite radioactive debris was detected and dealt with later. And we know from the level of information given out over the course of the disaster that they were unlikely to bother telling the public the detail of what the debris consisted of. People were also interested in the hole in the roof of reactor 3 turbine building.

Given the size of the explosion at reactor 3 building, I am really not sure that we could expect to learn anything useful from the final resting spot of the refuelling bridge anyway.

 

[SteveElbows]

Sorry for asking again what was probably mentioned a dozen times in this thread, but:

Was there no instrumentation telling the SFP water level in real time, or was that instrumentation broken ?

I have the same question about temperature instrumentation.

If the fuel uncovered, how ? Was the water splashed out during the earthquake ? Or during the explosion ?

The way that the SPF water level is measured is one of the weaknesses that the disaster revealed. Even at the best of times it seems that such information was not easily obtained without actually being on the refuelling floor. And its more often obtained by looking for signs that the pool has overflowed into the skimmer surge tank, rather than measuring the water level directly.

As for how it came to run out of water, the decay heat of the fuel causing it to boil away is the main area of focus. Obviously if the pool lost integrity and leaked then this would be another way that water level could be lost, but even if the pool remains intact the water is still lost at quite a high rate once the pool reaches a certain temperature.

 

[SteveElbows]

I need some help with some relatively short Japanese documents that were released in October but were written in the days following the disaster.

Specifically these two documents that are to do with neutron detection, can you give me an overview of what they say?

http://www.jnes.go.jp/content/000119688.pdf

http://www.jnes.go.jp/content/000119689.pdf

Also this one which mentions drywall vent pipe & pits:

http://www.jnes.go.jp/content/000119681.pdf

 

[jim hardy]

I remember those days well.

I felt at the time the pool level was getting low and there was significant "shine" up through the little water left, and backscatter down was reason for high readings near building. They got the "elephant" there just in time and readings came down as they watered the pool.

Also if i recall correctly there was what looked to me like the missing crane near top of the debris pile on N side of Unit-3, itself pretty well covered by rubble.

Not to turn this thread back into the Unit 3 explosion thread.
Just my 2 cents worth of memories from last year.

Was the water splashed out during the earthquake ? Or during the explosion ?

I think it's safe to presume the explosion caused some leaks that lowered level. Sloshing during quake probably put contaminated water in basement early on.
I am not ready to make a strong claim whether fuel got uncovered, though I think it didnt.
Someplace there's radionuclide analysis of SFP water and that was my basis for that.

Still waiting on that Nova show.

 

[SteveElbows]

Also if i recall correctly there was what looked to me like the missing crane near top of the debris pile on N side of Unit-3, itself pretty well covered by rubble.

No, that device got plenty of attention here, its the carousel that's used for retensioning the bolts of the reactor or containment cap (I forget which at this precise moment in time).

 

[SteveElbows]

Looks like the temperature sensor for reactor 2 RPV Supporting skirt upper part has started to fluctuate more in the last few days:

http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/12031212_temp_data_2u-e.pdf

Seems they are going to send a remote camera vehicle into spent fuel pool of reactor 4 to look at the debris, and they are also considering moving the control rods from the fuel pool to the reactor at some future point when they start to tackle the fuel in that pool.:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120312_01-e.pdf

 

[r-j]

This may qualify as a dumb question, but I must ask. It's been almost a year since the explosion of building three. From what I read, it seems there is no information about the state of the spent fuel storage pool that used to be inside the containment building.

Is that true?

A related question. If there is no evidence of the condition, is there any scientific reason not to snake a camera in there and look at it?

Which brings up another question. Could the condition of fuel pond be verified in any other way?

 

[NUCENG]

There is at least some context - it was measured from a JSDF helo and so it is, must be, all gamma, because that's all the military cares about - how long can their soldiers operate the equipment. It's not likely at all that someone bothered to pop a probe out the window just for the thrill of counting beta decays. In fact, I'd wager good money that they were buttoned up.

Look at that anemic plume of steam, hard to believe that the helo is getting 3 Sv/h from that (and if it was, people on the ground would have been getting it too), it's not like they are flying directly through:



The reactor well cap was not displaced, that we know of.

As for the radiation level today, that is also unknown. There are reports of dose rates on-site decreasing very significantly after the pools were watered.

You may be right, but look at what you said.

"it is, must be, all gamma, because that's all the military cares about." I'm not sure that assumption is true based on my military service. Do we know what type of dosimetry they had on the helicopter?

"Look at that anemic plume of steam," Water vapor (steam) is not radiation. A radiation plume does not have to be visible to be deadly. In fact gas releases are likely to be invisible,

"if it was, people on the ground would have been getting it too" Depending on wind speed, direction, and atmosppheric stability and the temperature of the released plume, people on site at ground level may not have been as exposed. If it was shine from the SFP or the drymell the surrounding concrete and debris could have provided shielding to personnel at ground level.

"The reactor well cap was not displaced, that we know of." Exactly!

Are these alternative explanations true or false? I don't know, but they illustrate that your conclusions include inherent assumptions that we cannot yet verify. That is the best service this forum has provided - allowing ideas to be introduced and hypotheses to be tested.

 

[tsutsuji]

The way that the SPF water level is measured is one of the weaknesses that the disaster revealed.

Thanks for your reply. Were there SFP temperature readings available at that time ?

 

[duccio]

A radiation reading was taken above the Unit 3 and, and if correct, was recorded at 3.75 Sv/hr.

4 Sv/hr 100 meters above reactor 3, should we take this reading seriously? Maybe right on top of exhaust stack during dry venting, but it's two orders of magnitude higher than the other readings taken 100 meters from the building

 

[SteveElbows]

Thanks for your reply. Were there SFP temperature readings available at that time ?

Not during the time that they most needed such readings. They had to resort to using infrared camera from a helicopter to estimate the pool temperatures during the week that they were most concerned about the pools.

For example with unit 4 pool they had a temperature reading of 84 degrees C around March 14th, but after that they did not get another proper temperature reading from that pool for a very long time.

 

[SteveElbows]

This may qualify as a dumb question, but I must ask. It's been almost a year since the explosion of building three. From what I read, it seems there is no information about the state of the spent fuel storage pool that used to be inside the containment building.

Is that true?

A related question. If there is no evidence of the condition, is there any scientific reason not to snake a camera in there and look at it?

Which brings up another question. Could the condition of fuel pond be verified in any other way?

Thats not the case. There has not been any fascinating new information about reactor 3 pool for ages, but there was information supplied ages ago.

They did some analysis of the water to see what levels of various radioactive substances were in it.

They also stuck a camera into it and published the video, probably about 10 months ago now. Unlike the video of the pool at reactor 4, its very hard to see anything useful in this video, because the pool has lots of debris in it.

 

[zapperzero]

You may be right, but look at what you said.

"it is, must be, all gamma, because that's all the military cares about." I'm not sure that assumption is true based on my military service. Do we know what type of dosimetry they had on the helicopter?

Nope. We don't know. We probably won't ever find out. What do you think is more likely to have been used, internally mounted AN-VDR 2 that is standard JSDF gear or some sort of scout setup with an external probe?

"Look at that anemic plume of steam," Water vapor (steam) is not radiation. A radiation plume does not have to be visible to be deadly. In fact gas releases are likely to be invisible

So you're thinking clouds of Iodine? Why would it take a different path than the water vapor?

"if it was, people on the ground would have been getting it too" Depending on wind speed, direction, and atmospheric stability and the temperature of the released plume, people on site at ground level may not have been as exposed.

Yeah you're right.

If it was shine from the SFP or the drywell the surrounding concrete and debris could have provided shielding to personnel at ground level.

Yep. The decrease in dose rates after water was poured provides circumstantial evidence of this.

"The reactor well cap was not displaced, that we know of." Exactly!
Are these alternative explanations true or false? I don't know, but they illustrate that your conclusions include inherent assumptions that we cannot yet verify. That is the best service this forum has provided - allowing ideas to be introduced and hypotheses to be tested.

I'd hate to call them conclusions. More like hypotheses. But yes, I like to believe that what we're doing here is useful

 

[Rive]

"The reactor well cap was not displaced, that we know of." Exactly!

Even some parts of the top concrete plug were spotted under the rubble. So physical displacement can be excluded.

However: as we learned from case of U2 both the equipment hatch plug and the top concrete plug/containment cap likely released pressure: and in case of U3 steady steam plumes were spotted on the early videos around the reactor well. It's not known if they were from the RPV or the drywell, but possibly they can explain some wild radiation readings.

Ps.: U3 RPV is which is on atmospheric pressure, am I right?

4 Sv/hr 100 meters above reactor 3, should we take this reading seriously? Maybe right on top of exhaust stack during dry venting, but it's two orders of magnitude higher than the other readings taken 100 meters from the building

IMHO yes. There was those steam plumes... And in those early days there was also the more mobile Iodine with the Cesium... I wonder if the birds were checked for contamination afterwards.

 

[clancy688]

4 Sv/hr 100 meters above reactor 3, should we take this reading seriously? Maybe right on top of exhaust stack during dry venting, but it's two orders of magnitude higher than the other readings taken 100 meters from the building

We can certainly say that at least the JSDF did take those readings seriously. You only try your luck in filling the SFPs with dropped water from high altitude fly-overs if there's something so absolutely nasty in the air above the reactors that even hovering (and thus enormously improving your aim) for a couple of seconds is out of the question.

 

[clancy688]

Unit 4 Spent Fuel Pool:

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201203080066 "Fukushima No. 4 reactor saved by upgrade mishap"

According to the article, there was no separator gate in place between the Spent Fuel Pool and the Reactor Well, allowing for 1000 additional tons of water to flow to the SFP. Was that fact already known?

 

[zapperzero]

Unit 4 Spent Fuel Pool:

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201203080066 "Fukushima No. 4 reactor saved by upgrade mishap"

According to the article, there was no separator gate in place between the Spent Fuel Pool and the Reactor Well, allowing for 1000 additional tons of water to flow to the SFP. Was that fact already known?

News to me. Although the possibility of water flowing INTO reactor well has been discussed iirc.

 

[SteveElbows]

Unit 4 Spent Fuel Pool:

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201203080066 "Fukushima No. 4 reactor saved by upgrade mishap"

According to the article, there was no separator gate in place between the Spent Fuel Pool and the Reactor Well, allowing for 1000 additional tons of water to flow to the SFP. Was that fact already known?

No, I think this is new. The previous official explanation was that as the water level in the fuel pool fell, the gate lost its seal and water gradually came in from the reactor well to the pool. If the gate wasn't in place at all then the details of how the 2 bodies of water came to be connected is quite different.

 

[r-j]

Thank you Steve.

They did some analysis of the water to see what levels of various radioactive substances were in it.

What did the analysis show? Would it be material from the used fuel? Or from the reactors?

They also stuck a camera into it and published the video, probably about 10 months ago now. Unlike the video of the pool at reactor 4, its very hard to see anything useful in this video, because the pool has lots of debris in it.

Well at least it didn't leak.

 

[SteveElbows]

Unit 4 Spent Fuel Pool:

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201203080066 "Fukushima No. 4 reactor saved by upgrade mishap"

According to the article, there was no separator gate in place between the Spent Fuel Pool and the Reactor Well, allowing for 1000 additional tons of water to flow to the SFP. Was that fact already known?

OK I just read the article and it does not say that the gate was missing.

The mishap they are referring to is that the shroud replacement work was slightly behind schedule, and the d/s pit and reactor well were still full of water as a result.

So the article does not actually contradict the previous explanation for how water got from the reactor well & d/s pit to the fuel pool.

 

[Rive]

News to me. Although the possibility of water flowing INTO reactor well has been discussed iirc.

Yes. That theory was backed up by the first thermographic photos which showed high temperature in the reactor well (of U4).

Also, a week or two ago some water leakage from pool to reactor well were found. As countermeasure they started to watch and maintain the water level in the well.

 

[SteveElbows]

Thank you Steve.

What did the analysis show? Would it be material from the used fuel? Or from the reactors?

I am not knowledgeable enough to analyse the results myself. They did not attract a vast amount of attention here at the time, so I assume they didn't show anything too extreme, but I would be more than happy if someone is willing to explain them again now.

 

[clancy688]

Thank you Steve.
What did the analysis show?

Very high contamination. Up to several hundreds of thousands Becquerel per cubic centimetre of water (I131, C134 and C137), if I remember correctly. But very low contamination for the Unit 4 pool (only a couple of hundreds Becquerel). I'll look if I can find the reports.

OK I just read the article and it does not say that the gate was missing.

In reality, however, a displaced separator gate between the spent fuel storage pool and the adjoining reactor well apparently created an opening, allowing about 1,000 tons of water to flow from the reactor well into the storage pool, it was learned later.

Um, sure? For me that's pretty much obvious. Am I missing something?

 

[SteveElbows]

Displaced is not the same thing as missing.

 

[r-j]

Very high contamination. Up to several hundreds of thousands Becquerel per cubic centimetre of water (I131, C134 and C137), if I remember correctly. But very low contamination for the Unit 4 pool (only a couple of hundreds Becquerel). I'll look if I can find the reports.

Does that mean the radiation came from the reactor? Not damaged fuel rods?

 

[clancy688]

Does that mean the radiation came from the reactor? Not damaged fuel rods?

I'm no expert on that matter. I have no idea how big the concentrations would be in case of damaged fuel rods. You should ask NUCENG, jim or rmattila.

Regarding the actual values - found at least something:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110825_02-e.pdf

The concentrations in SFPs 1 to 3 are 1000-10.000 times bigger than in SFP 4. Again, I'm no expert, but I'd say that practically eliminates the probability of fuel rod damage in pool 4.
Btw, what are "chloride ions", and why are they so many of these things in Unit 2-4, but little in Unit 1?

Displaced is not the same thing as missing.

Sorry for my inaccurate wording, but with "no gate" I meant "open" and not "doesn't exist". ;)

 

[jim hardy]

Btw, what er "chloride ions",

Around a boiler, usually from salt water.

 

[clancy688]

Thanks. So... there was salt water injected in SFP 2-4, but not in SFP 1?

 

[jim hardy]

Thanks. So... there was salt water injected in SFP 2-4, but not in SFP 1?

A first glance at that table would sure make one think so.

Even that 3.9 ppm seems high to me, so i'd feel more comfortable with saying its pool got far less than the others.

3.9ppm is what, about 7600 to 1 dilution of seawater? Almost plausible it was from fire trucks overspray. I just don't remember anymore.

 

[NUCENG]

Nope. We don't know. We probably won't ever find out. What do you think is more likely to have been used, internally mounted AN-VDR 2 that is standard JSDF gear or some sort of scout setup with an external probe?


So you're thinking clouds of Iodine? Why would it take a different path than the water vapor?


Yeah you're right.


Yep. The decrease in dose rates after water was poured provides circumstantial evidence of this.



I'd hate to call them conclusions. More like hypotheses. But yes, I like to believe that what we're doing here is useful

I have no idea what that helo had on board for dosimetry. There was a SDF NBC team, on site when Unit 3 exploded. If these teams are similar to US NEST teams they have a broad range of radiation detection equipment available. Or they could have added equipment from civilian or academic sources or even foreign assistance. I know that when US nuclear ships and submarines made port visits to Japan there was a lot of concern over potential leaks so they had teams sampling and monitoring. There was time available to get that instrumentation to Fukushima, but I don't know.

In the first few days, releases would have included noble gasses and part of the iodine. Most iodine would have been in particulate form not gas according to source term studies. Those particulates could be included in droplets in the steam plumes. But even steam plumes become invisible as the water vapor diffuses into the air and drops below saturation conditions.

The reduction of dose rates after water was added to the spent fuel pool is strong circumstantial evidence and could mean the shielding was restored as water levels increased. Or it could be that the radioactive gas releases slowed as pressure dropped in the vessels and containments, or that what was there to be released had been released. Even more speculative, if corium was melting into the concrete below the vessel (below ground level) shielding would also tend to increase.

I wxpect we will learn more as the debris is eventually removed from Unit 3 and they find where the leaks were and how much damage to the fuel in the SFP resulted. When they actually can see the fuel in the SFP they should be able to figure out if it was ever exposed. Quite a while ago, while we were trying to figure out the source of the Unit 4 explosion, a couple of posters did some rough calculations of how much boiloff could have occurred in Unit 4 which had a full core offload into the SFP and therefore the highest decay heat. At that time we theorized that the pool could have boiled, but would not have exposed the fuel. The calcs didn't include water loss due to sloshing from the earthquake or leakage from the SFP.

In the meantime brainstorming all the possibilities can help develop a list of tests or measurements that could lead to finding out what actually happened. It also could help make eventual defueling tasks less likely to come up with unpleasant surprises. I urge everyone to keep thinking and sharing and be willing to discuss without defensiveness. After a full year, I still think the discussions are interesting and worthwhile.

 

[NUCENG]

Does that mean the radiation came from the reactor? Not damaged fuel rods?

I thought Unit 4 reactor was defueled for the shroud replacement project. All fuel was in the SFP. Has that changed?