Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[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?

 

[NUCENG]

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.

Alternatively they may be doing some cleanup in Unit 1 or the cover they installed is keeping that pool cleaner.

 

[westfield]

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

I don't know if they managed to get any salt water into it or even if they needed to but -

Unit 1's SFP was quite sheltered by the U1 RB's surprisingly together roof cladding.
Early on there was little opportunity to get any sort of water into it's SFP with the choppers or snorkel for that reason.

Additionally I seem to recall it wasn't nearly as urgent to top up Unit 1's SFP because the decay heat from Unit 1's spent fuel is considerably lower than any of the other pools and there is less spent fuel in there being a smaller design.

Shoot me down if required, it's been a year since then.

 

[zapperzero]

Shoot me down if required, it's been a year since then.

No, you are quite correct.

 

[zapperzero]

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

Nope, although there is much confusion over this subject, in other places which shall remain unnamed.

This is somewhat unrelated but... how hot is the RPV's interior? If some water leaked out of it, could it be the cause of the high doses found above the building, all by itself?

 

[SteveElbows]

I don't know if they managed to get any salt water into it or even if they needed to but -

Unit 1's SFP was quite sheltered by the U1 RB's surprisingly together roof cladding.
Early on there was little opportunity to get any sort of water into it's SFP with the choppers or snorkel for that reason.

Additionally I seem to recall it wasn't nearly as urgent to top up Unit 1's SFP because the decay heat from Unit 1's spent fuel is considerably lower than any of the other pools and there is less spent fuel in there being a smaller design.

Shoot me down if required, it's been a year since then.

Yeah they didn't need to touch that pool for quite a while. Eventually though they did spray it, through the damaged roof no less. I was quite surprised when I saw a video of it. But by then its quite likely they had a fresh-water supply, I will double-check these records when I get spare time.