Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[joewein]

Anyone want to guess how many Bq was in that ton of water?

The http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110622_04-j.pdf" on June 22 stated these values for the water after purification:

I-131: 890 Bq/cm3
Cs-134: ND (<100 Bq/cm3)
Cs-137: ND (<100 Bq/cm3)

If the water was from the same set and if the salt removal didn't change the above concentrations (a big if) then it was 890 MBq of iodine per ton and less than 100 MBq per ton for each of the cesium isotopes.

 

[robinson]

How can there be so much radioactive Iodine still? It's been three months since it was being produced.

 

[Joe Neubarth]

How can there be so much radioactive Iodine still? It's been three months since it was being produced.

Sushhhhhhhh! You are not supposed to point out things like that. It sets the nuclear industry on edge.

 

[clancy688]

How can there be so much radioactive Iodine still? It's been three months since it was being produced.

One of my favourite quotes of this forum is NUCENGs "Half of a big number is still a big number". The water in Units 2's basement had over 10 MBq/cm³ I131 back in end of March. That's eleven half times. There'd still be enough of that stuff left to get 1kBq/cm³.

How's the plant processing iodine? Is it processing iodine at all?

 

[robinson]

No seriously, I am no expert, but why is there so much?

 

[clancy688]

No seriously, I am no expert, but why is there so much?

I did answer seriously...

On March 27th, water in the Unit 2 basement had 13 MBq/cm³ I131. It's been 87 days since March 27th, so roughly 11 half times. That leaves 12 kBq/cm³ I131 TODAY. According to the TEPCO pdf posted a couple of pages above, unprocessed water had ~ 7 kBq/cm³ (at June 17th, over one week or one half time ago, so double my 12 kBq/cm³ for today).
So where's the problem?

 

[robinson]

The water in Units 2's basement had over 10 MBq/cm³ I131 back in end of March.

Where is that data from? I never saw any report on the amount of radioactivity in the basement water back in March.

 

[clancy688]

Where is that data from? I never saw any report on the amount of radioactivity in the basement water back in March.

http://www.tepco.co.jp/cc/press/betu11_j/images/110603a.pdf Page 8.

 

[SteveElbows]

There has been precious little analysis or narrative about anything that happened past the first 5 days or so.

The entire period March 16th->March 24th interests me, rather than just one of the interesting smoke days, but I've reduced my expectations in regards to finding out more about this in the near future.

Also missing from most official analysis is much detail about any of the explosions, or the exact detail as to why reactor 2 is blamed for the vast bulk of the estimated releases, although we can make some assumptions in that regard.

Thought of one more aspect where the lack of detailed and ongoing narrative, by the press as much as government & corporation, drives me totally batty.

Namely stuff that has happened with reactor 3 temperatures a month and more after the initial disaster. And the fact that they continue to inject water intot he reactor at 3 at far higher rates than for 1 & 2.

Granted in the absence of firm facts and more data, it is hard to draw conclusions about any of these things, so maybe there simply isn't much they could say about these matters, but it still hurts my brain that so many things have received little attention past the initial reporting of them.

For example I believe that some days back someone here commented on possible realities of core at reactor 2, given that the temperature data did not seem to change much even though they reduced water injection rate. At the time it was a bit too soon for me to comment, and even now the rather mixed temperature picture at the other two reactors makes me hesitant to make any assumptions based on the reactor 2 temperature data after water rate injection decrease.

Frustrating as it is, I think I am just going to have to live with the fact that the answers we seek on a whole range of fronts are simply not available with the data we have, and apart from getting the chance to maybe find out the state of containment and cores one day, there is no indication that better quality data will ever become available to us.

 

[robinson]

http://www.tepco.co.jp/cc/press/betu11_j/images/110603a.pdf Page 8.

None of those measurements of Iodine match your figure.

 

[clancy688]

None of those measurements of Iodine match your figure.

[PLAIN]http://imgf.tw/533294398.jpg

 

[robinson]

None of those measurements say what you said. Are you adding up the different areas? How does that match the source of the figure for the spilled ton of water?

 

[clancy688]

None of those measurements say what you said. Are you adding up the different areas? How does that match the source of the figure for the spilled ton of water?

Okay, a different approach:

What did I say that doesn't fit to those measurements? (This isn't sarcasm, I'm really puzzled... I don't know what your problem is)

 

[SteveElbows]

One of my favourite quotes of this forum is NUCENGs "Half of a big number is still a big number". The water in Units 2's basement had over 10 MBq/cm³ I131 back in end of March. That's eleven half times. There'd still be enough of that stuff left to get 1kBq/cm³.

How's the plant processing iodine? Is it processing iodine at all?

Yeah, both half-life and decay heat curves seem to be factors in this crisis that can easily be misunderstood by some people, creating the wrong impression.

As for iodine processing, although I haven't heard it talked about so much, at least not compared to the cesium decontamination, it is featured in the diagram on the last page of this recent handout:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110627_01-e.pdf

It leaves me with the impression that the iodine, cesium & technetium towers are usually all referred to with the the oversimplified label 'Cesium Absorption Device' .

 

[robinson]

On March 27th, water in the Unit 2 basement had 13 MBq/cm³ I131.

How does that relate to the current iodine levels in the water they are working on?

 

[SteveElbows]

How does that relate to the current iodine levels in the water they are working on?

How does that relate to the current iodine levels in the water they are working on?

Seriously, we need to find out which bit of the communication you are having trouble with, as this recent discussion is doing my head in.

Look, the question you ask again is already answered perfectly with the following that was said to you not very long ago:

On March 27th, water in the Unit 2 basement had 13 MBq/cm³ I131. It's been 87 days since March 27th, so roughly 11 half times. That leaves 12 kBq/cm³ I131 TODAY. According to the TEPCO pdf posted a couple of pages above, unprocessed water had ~ 7 kBq/cm³ (at June 17th, over one week or one half time ago, so double my 12 kBq/cm³ for today).
So where's the problem?

So what is the problem? Are you having trouble with how the numbers are expressed as MBq, kBq or in E+07 formats?

The calculation above demonstrates that taking half-life and the original water figure we have from end of March into account, there is nothing weird with iodine figures around 12 kBq/cm³ now, or 24 kBq/cm³ a week ago. 7 kBq/cm³ is the reported figure from over a week ago, and that's less than 24 kBq/cm³, so its within expectations and so is not evidence of anything interesting.

 

[clancy688]

How does that relate to the current iodine levels in the water they are working on?

Well, because that's where they get water they're processing from.

This recent TEPCO-PDF was posted:

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110622_04-j.pdf

After purification, there's 890 Bq/cm³ I131 left and you asked why there's still so much I there. The water was taken from a place called "RW3", and before it was processed, it had 6900 Bq/cm³ I131 (at June 17th).

Now we look at the TEPCO file listing all previous basement water contaminations:

http://www.tepco.co.jp/cc/press/betu11_j/images/110603a.pdf

If we look for the RW3 place, we can see that there are two different measurements: 13 MBq/cm³ (taken on March 27th) and 0.66 MBq/cm³ (taken on April 22th).
Now we calculate the time between the basement measurements and the June 17th measurement.

It's 82 days from March 27th to June 17th and 56 days from April 22th to June 17th, hence 10 and 7 half times.

Next step: We calculate how much of the basement water iodine would be there at June 17th:

(13 MBq/cm³) / 2^10 ~ 12.000 Bq/cm³ (it seems I had a little error in my previous calculation)

(0.66 MBq/cm³) / 2^7 ~ 5000 Bq/cm³

So based on our previous measurements, we'd expect to measure 12.000 and 5000 Bq/cm³ in the water around June 17th. We did measure 6900.
So, this number is totally to be expected.

 

[jim hardy]

PLG ""I am not sure a corium turns off by itself once it becomes active after a criticality,"

there are a couple turnoff mechanisms.
One is "Doppler Broadening", when the corium gets very hot it is more likely to absorb neutrons in a non-fission neutron capture. That's called "Doppler" and tends to limit a runaway. Google "Triga reactor" and watch the youtubes.

Another is 'boil out' , water's ability to moderate is a function of its temperature because the molecules are closer together when it's cold. When they spread apart into steam the neutrons don't get slowed down so well and are more likely to get absorbed in a non-fission capture in fuel or in reactor structural steel.. Anything increases nonfission capture fraction is a shutdown mechanism.

Another is 'displacement' , a euphemism... a steam explosion will disassemble things spreading the fissile material out, increasing "neutron leakage". 'Leakage' is the probability a neutron leaves the neighborhood without hitting a fissile nucleus. Anything that increases leakage is a shutdown mechanism.

Here is a dirt simple primer on reactor physics (that's been posted before, old hands kindly forgive repeat for interested newcomer.) Really it is a not complex subject.
http://www.if.uidaho.edu/~gunner/ME443-543/LectureNotes/ReactorPhysics.pdf
I took a course forty something years ago and this was a great re-introduction. Since you have access to nuke engineers i'd suggest you print it out - you can absorb it easily in one evening if your friends will help you out with vocabulary.

and here's a paper on corium reactivity that's got way too much math for me. it's some fellow's PHD thesis. I found it direct via Google so its not like i snooped the guys' emails. It is several places around 'net now. You'll find his calculations used in the Nureg 5653.

http://list.ans.org/pipermail/ncsd-fukushima/attachments/20110318/f20efbc8/thesis-0001.pdf
Your engineer friends may understand it, mostly i don't. It supports the self regulating nature of water moderated fission though.

Now i think it was zapperzero used a phrase some posts back re corium ::: ".. still stuck to the walls..."
uhhh, zz , was that just toying with words? do you know something i dont? Seen any analysis of what was on that 1Sv piece of concrete rubble?

SteveE has it ::: ""Frustrating as it is, I think I am just going to have to live with the fact that the answers we seek on a whole range of fronts are simply not available with the data we have, and apart from getting the chance to maybe find out the state of containment and cores one day, there is no indication that better quality data will ever become available to us. ""
one knows there were aircraft samples of plumes and better photos around the buildings.

TPTB know.
As a mere civilian i have to wait for the NOVA show.

old jim

 

[SteveElbows]

(13 MBq/cm³) / 2^10 ~ 12.000 Bq/cm³ (it seems I had a little error in my previous calculation)

(0.66 MBq/cm³) / 2^7 ~ 5000 Bq/cm³

So based on our previous measurements, we'd expect to measure 12.000 and 5000 Bq/cm³ in the water around June 17th. We did measure 6900.
So, this number is totally to be expected.

Ah yes, I just noticed your error when I went to test this out for myself in an extremely basic way that eliminates confusion from magnitude and the use of anything but the most basic buttons on a calculator.

Anyway, here is how I would describe the same calculation in this fashion, just in case it helps anybody out there who is struggling, to understand what you've said.

We are starting with a big number, 13000000.

Divide this number in half for every 8 days of time that has passed.

So I do this the long and boring way by typing 13000000 into my calculator, then dividing by 2, then dividing by 2, etc etc until I've done that operation 10 or 11 times.

After 11 weeks, the number is just over 6347.

So if I was seeing unprocessed water recently with levels very much over 6347 Bq/cm³ then I would be looking for an explanation. But the figures we have seen are lower than this, so everything seems to fit ok.

Obviously this version of my explanation is simplified compared to what clancy688 has done, I'm just trying to see if I can explain the same thing in a simplified way with different words.

 

[SteveElbows]

Now i think it was zapperzero used a phrase some posts back re corium ::: ".. still stuck to the walls..."
uhhh, zz , was that just toying with words? do you know something i dont? Seen any analysis of what was on that 1Sv piece of concrete rubble?

Reactor vessel walls I presume, not concrete walls that may have been lying around the site in little pieces.

one knows there were aircraft samples of plumes and better photos around the buildings.

TPTB know.
As a mere civilian i have to wait for the NOVA show.

old jim

Actually that isn't quite what I meant. Although it is impossible to know exactly what they ma know about things that the public do not, it seems likely to me that a lot of the missing data that I am moaning about is unknown to humanity at large, not just the public.

I expect to eventually learn more about the buildings, containment, cores. I am not sure how much more I shall ever learn about the plumes, I don't know what other data may exist from crucial time periods early on that we haven't seen yet, although I expect much analysis can be done based on what settled on the ground. As I am interested in reactor 2 and the rather hefty estimates they came up with for release from that reactor, I looked at what sort of data it sounds like they used to make these estimates, and lots of data holes become apparent. For example on March 15th when much of the contamination is thought to have occurred, they seem to be missing data based on dust sampling for an important portion of that day, because the weather was wet and that spoils those tests.

 

[sheffters]

So based on our previous measurements, we'd expect to measure 12.000 and 5000 Bq/cm³ in the water around June 17th. We did measure 6900.
So, this number is totally to be expected.

What isn't so expected is that TEPCO didn't do the math on their own and seemed a bit surprised the filtration system was clogged up with activity and had to be turned off for a bit (maybe it's just the way it got reported in the media?).

Surely these things have quoted limits as to what they can absorb, so the math based on what you measure, what you chuck into the system and how long it can be expected to run for between cleanings can't be that difficult?

 

[clancy688]

What isn't so expected is that TEPCO didn't do the math on their own and seemed a bit surprised the filtration system was clogged up with activity and had to be turned off for a bit (maybe it's just the way it got reported in the media?).

Surely these things have quoted limits as to what they can absorb, so the math based on what you measure, what you chuck into the system and how long it can be expected to run for between cleanings can't be that difficult?

Yeah, but those were problems with the cesium absorption towers. You don't have to do any halftime math for C because C137 decays with a 30 year halftime. Or 2 years for C134. Anyway, the water they're processing now has a C:I activity ratio (for both C134 and C137) of ~ 1000:1, so whatever radiation problems they get, the iodine is only responsible for a tiny fraction of the resulting radiation.

As for what TEPCO did / calculated wrong, I have no idea. I'd like to know the answer for myself.

 

[clancy688]

How much of the water from the #2 basement would it require to be leaked into the environment before you would see it as a "significant amount"?

Many people probably won't agree with me, but I tend to say that I simply don't care for any (sea)water contamination. It's really of absolutely no concern if you compare it to the damage which airborne releases can do and obviously have done (100.000-150.000 displaced people).

Radioactive water leaking in the underground will either reach the open sea where it dilutes or it will contaminate the local groundwater - which makes no difference at all since there's already no resident left in the affected area. But it can't do the damage aerial releases do. All those NISA and NSC release estimates are ONLY airborne releases - the 370.000, 630.000 and 770.000 numbers ONLY cover releases to the air. Nothing else. Because that's what's giving us headaches magnitudes bigger than for any other release path.

 

[PLG]

Hi Jim (#10333)

(sorry to intrude on the other discussions taking place in between -maybe we should have a "corium" thread?)

Anyway, thanks a million for the paper. I did maths in my youth, am still able to read the course on neutronics, I can't say I understand every equations but the simpler ones are within my means...

A quick question to check if I got you right: it actually all boils down to the corium being on the whole subcritical, with k(eff)<1, right? Total neutron absorption is superior to neutron production in a corium, so no need to worry (well, not too much. It all depends on dN/dt, the higher the better).

Once neutrons stop being produced (fissions stop), we are left with RA decay, which is bad enough but shouldn't enable the corium to gnaw its way through concrete.

Got it right?

I also had a look at the conclusions of the thesis (differentials are about as far as I get, so I was limited there), and noticed that the guy assumes heavily borated water, so I am not sure it applies to our case.

Oh, and a quick and silly question: p. 25 of your course an element which has a very high moderating ration is noted D, and later D2O. Couldn't find a D on my Mendeleiev Table... It's not a "B", by any chance? I would understand better then...

Anyway, thanks a lot, again! Will be back if I get more info.

Pierre

 

[MiceAndMen]

Hi all,
...
Last but not least, I know this is hearsay, but from French nuclear engineers, so it's a little less than pure specualtion, anyway it seems that the concrete basemat was hollowed out for seismic resistance reasons at Fukushima. So the drywell and its embedded shell sit atop a cavity which could indeed act as core-catcher, provided the corium is cool enough.

That is something I would like to see finally verified or disproven one way or the other with certainty. Plant drawings or blueprints from TEPCO would make an awful lot of ambiguous things clearer (even if not totally clear). Their reasons for not releasing those are absurd at this point and in light of recent revelations.

 

[Borek]

Oh, and a quick and silly question: p. 25 of your course an element which has a very high moderating ration is noted D, and later D2O. Couldn't find a D on my Mendeleiev Table...

H for Hydrogen, D for Deuterium, T for Tritium.

 

[jim hardy]

PLG

it'll soak in over next few says as your brain chews on it while sleeping.

You have it - Keff < 1 means the chain reaction is progressing toward smaller numbers.

a chain reaction is exactly analogous to a "chain multiplication" on a calculator.
Enter any number, multiply it repeatedly by some Keff that's near 1.

EG 10 X 1.000 = 10 forever, you can multiply that all day long. That's exactly critical with neutron population 10.
Similarly 1000 X 1.000 = 1000 forever, and 1E14 X 1.000 = 1E14 forever.

Now 10 X 1.0001 = 10.001, next time 10.0020001, that is slightly supercritical because Keff 1.0001 which > 1 and neutron population grows.

Indeed when fission tapers off you have only radioactive decay.
Indeed the "D" is deuterium, heavy hydrogen. It is preferred moderator because it has little appetite for neutrons.
Light hydrogen atom is prone to absorb an occasional neutron and become heavy hydrogen; that neutron is unavailable to fission process. Deuterium is less likely to grab a neutron and become tritium...but it can
Here's a handy periodic table
http://environmentalchemistry.com/yogi/periodic/H.html
select any element and click 'nuclides'

if you're not familiar with "chart of the nuclides", pls advise i can pm you an intro no need to clutter board with it.

Do you see how simple they made reactor physics? Those four factors they arranged to all be close to 1, when you multiply them result tells immediately whether you are K< 1 > .
Fuel pools here are by regulation designed for K<0.95, and a BWR core with all rods in is <0.9.

Yes you got it right. Ask your nuke friends about chart of the nuclides
i use this one but there's plenty around 'net...
http://www.nndc.bnl.gov/chart/reColor.jsp?newColor=dm

glad you're enjoying.

 

[nikkkom]

Many people probably won't agree with me, but I tend to say that I simply don't care for any (sea)water contamination. It's really of absolutely no concern if you compare it to the damage which airborne releases can do and obviously have done (100.000-150.000 displaced people).

Radioactive water leaking in the underground will either reach the open sea where it dilutes or it will contaminate the local groundwater - which makes no difference at all since there's already no resident left in the affected area.

Exactly. The guys at Fukushima have their plate quite full already. Contaminated groundwater can be drilled and pumped up later, after flooded basements are dealt with.

 

[Borek]

My understanding is that due to the local geology groundwater is expected to go to the sea, not inland.

 

[PLG]

Um, yes. Groundwater eventually goes to sea generally speaking, and all the more so when you are fifty yards away from the sea, so pumping the stuff back up is not really an option in the medium to long run. If there were corium leaks at some point, the material is going toward the ocean at a relatively slow rate of several centimeters a day (it"s slow because the ground is made up of impermeable argilite). There was a long, detailed post in another thread:

https://www.physicsforums.com/showpost.php?p=3356008&postcount=9753
also
https://www.physicsforums.com/showpost.php?p=3345426&postcount=9285

Pierre

 

[sp2]

Many people probably won't agree with me, but I tend to say that I simply don't care for any (sea)water contamination. It's really of absolutely no concern if you compare it to the damage which airborne releases can do and obviously have done (100.000-150.000 displaced people).

Radioactive water leaking in the underground will either reach the open sea where it dilutes or it will contaminate the local groundwater - which makes no difference at all since there's already no resident left in the affected area.

I have to respectfully call this nonsense.

You have no idea how much damage the sea-water or ground-water contamination may or may not do (or how far its effects may spread), and neither does anyone else.
That's really the whole point.

To imply that it's trivial, simply because it's probably less bad than atmospheric release is a little ridiculous.

(It's like saying 9/11 was no big deal, because it would've been a lot worse if it had happened an hour later.)

 

[sp2]

P.S. Anybody betting that the total release from Fukushima will end up at only 10% of Chernobyl would be laughed out of Town by any bookie in Vegas. (Though only after he took all your money, of course.)

 

[Duffer]

I have to respectfully call this nonsense...

Thank you
You have restored some of my confidence in this thread.

I was waiting to see if anybody challenged that (insert word.)

I will also point out that were we (the people living now) were to allow TEPCO to dump their problem into the Pacific, we would be setting a precedent that a thoughtful people would not want to set.

 

[elektrownik]

Is unit 4 sfp skimmer surge tank leaking ? or they change something ? It is only 700mm now, it always was much higher (4500-6500mm)...

 

[clancy688]

P.S. Anybody betting that the total release from Fukushima will end up at only 10% of Chernobyl would be laughed out of Town by any bookie in Vegas. (Though only after he took all your money, of course.)

Again, you can't compare ALL those numbers.

The Chernobyl number was calculated only for airborne releases. With the (in)famous IAEO iodine conversion method (the conversion factors they used can only be applied for airborne releases btw).
If nothing serious happens (another hydrogen explosion for example), the airborne release number WON'T go up. Well, the actual one.
There always is the possibility that TEPCO, NISA and NSC didn't tell the whole truth and the release was significantly bigger than reported.

But what I'm trying to say is: The official, often quoted number, will, even in the future, most likely only contain airborne released. Since the airborne release is finished, the real value of this number won't go up.

It's important to understand this issue if working and quoting official numbers. It doesn't have to be right (well, I think it's the correct approach, but that's only a personal opinion and not everybody thinks the same way, which I expected).

Water contamination is an entirely different thing. For example there's 140.000 TBq each of C134 and C137 loose in the basements. That's each twice the the size of the Chernobyl airborne release and half of a Chernobyl core's worth of C.

As I said, it doesn't have to be the right way. But water contamination DOESN'T count in official release numbers. Remember this.

 

[tsutsuji]

http://www.yomiuri.co.jp/science/news/20110629-OYT1T00674.htm and http://news24.jp/articles/2011/06/29/07185418.html# : The injection into reactors of decontaminated, desalinated water was stopped at around 11:00 AM and started again at 1:33 PM. At 8:10 AM, the hose had been found to be punctured in two places. Incidentally, the tank for liquid waste at the desalinating facility was also found leaking, without much consequence. The cause was a cap removed from a pipe.

http://www.yomiuri.co.jp/science/news/20110628-OYT1T01036.htm 15 tons of 7 μSv/h low contaminated water leaked into unit 6's turbine building basement. The cause is the failure of the attachment of a tube that is part of a level gauge at a low contaminated water tank.

 

[Cire]

You have no idea how much damage the sea-water or ground-water contamination may or may not do (or how far its effects may spread), and neither does anyone else.
That's really the whole point.

I think the ocean around the bikini Atoll would disagree with your premise. If you had no choice but to leak radioactive materials somewhere then the ocean would be your first choice.

Don't under estimate the ability of 187 quintillion gallons of water to dilute the problem.

 

[nikkkom]

Um, yes. Groundwater eventually goes to sea generally speaking, and all the more so when you are fifty yards away from the sea, so pumping the stuff back up is not really an option in the medium to long run.

It is. If boreholes would be drilled significantly deeper than sea level, and then all water which drains into them is pumped up and decontaminated, then almost all underground water will flow into these boreholes, not into sea.

 

[nikkkom]

I have to respectfully call this nonsense.

You have no idea how much damage the sea-water or ground-water contamination may or may not do (or how far its effects may spread), and neither does anyone else.

My point is, underground water moves slow enough so that there is no need to deal with it _right now_, when we have much more pressing issues (like continuing releases of radioactive steam, overflowing basements with 1 Sv/h water and such).

 

[NUCENG]

Yeah, but those were problems with the cesium absorption towers. You don't have to do any halftime math for C because C137 decays with a 30 year halftime. Or 2 years for C134. Anyway, the water they're processing now has a C:I activity ratio (for both C134 and C137) of ~ 1000:1, so whatever radiation problems they get, the iodine is only responsible for a tiny fraction of the resulting radiation.

As for what TEPCO did / calculated wrong, I have no idea. I'd like to know the answer for myself.

Hopefully they realized that most of the Cs released is stable, but it will clog up their filters.
I once found a calculation at a NPP that only considered radioiodine and radiocesium for their filter loading estimates. The author was wondering why the filters were so much larger than they needed to be. He had used the ORIGEN2 output for Ci/MWt but didn't look at the output for gm/MWt which listed yhe stable fission product isotopes.

 

[NUCENG]

PLG ""I am not sure a corium turns off by itself once it becomes active after a criticality,"

there are a couple turnoff mechanisms.
One is "Doppler Broadening", when the corium gets very hot it is more likely to absorb neutrons in a non-fission neutron capture. That's called "Doppler" and tends to limit a runaway. Google "Triga reactor" and watch the youtubes.

Another is 'boil out' , water's ability to moderate is a function of its temperature because the molecules are closer together when it's cold. When they spread apart into steam the neutrons don't get slowed down so well and are more likely to get absorbed in a non-fission capture in fuel or in reactor structural steel.. Anything increases nonfission capture fraction is a shutdown mechanism.

Another is 'displacement' , a euphemism... a steam explosion will disassemble things spreading the fissile material out, increasing "neutron leakage". 'Leakage' is the probability a neutron leaves the neighborhood without hitting a fissile nucleus. Anything that increases leakage is a shutdown mechanism.

Here is a dirt simple primer on reactor physics (that's been posted before, old hands kindly forgive repeat for interested newcomer.) Really it is a not complex subject.
http://www.if.uidaho.edu/~gunner/ME443-543/LectureNotes/ReactorPhysics.pdf
I took a course forty something years ago and this was a great re-introduction. Since you have access to nuke engineers i'd suggest you print it out - you can absorb it easily in one evening if your friends will help you out with vocabulary.

and here's a paper on corium reactivity that's got way too much math for me. it's some fellow's PHD thesis. I found it direct via Google so its not like i snooped the guys' emails. It is several places around 'net now. You'll find his calculations used in the Nureg 5653.

http://list.ans.org/pipermail/ncsd-fukushima/attachments/20110318/f20efbc8/thesis-0001.pdf
Your engineer friends may understand it, mostly i don't. It supports the self regulating nature of water moderated fission though.

Now i think it was zapperzero used a phrase some posts back re corium ::: ".. still stuck to the walls..."
uhhh, zz , was that just toying with words? do you know something i dont? Seen any analysis of what was on that 1Sv piece of concrete rubble?

SteveE has it ::: ""Frustrating as it is, I think I am just going to have to live with the fact that the answers we seek on a whole range of fronts are simply not available with the data we have, and apart from getting the chance to maybe find out the state of containment and cores one day, there is no indication that better quality data will ever become available to us. ""
one knows there were aircraft samples of plumes and better photos around the buildings.

TPTB know.
As a mere civilian i have to wait for the NOVA show.

old jim

The NOVA show will probably be a disappointment for most of those participating in this forum. We are probably well beyond their target audience already. But we'll all probably watch, if only to catch any mistakes. BTW no criticism meant, I love NOVA.

 

[tsutsuji]

http://www.yomiuri.co.jp/science/news/20110629-OYT1T00850.htm and http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110629_02-j.pdf : The water treatment facility was stopped at 2:53 PM after an alarm signalling a leak at the site bunker building (1) rang. It had been also stopped for flushing and adsorption tower replacement between 10:45 AM and 2:13 PM. The reason why the alarm rang is under investigation.

(1) the orange box on http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110627_01-e.pdf

 

[elektrownik]

Is unit 4 sfp skimmer surge tank leaking ? or they change something ? It is only 700mm now, it always was much higher (4500-6500mm)...

now 450mm any comments ?

 

[joewein]

Is unit 4 sfp skimmer surge tank leaking ? or they change something ? It is only 700mm now, it always was much higher (4500-6500mm)...

The one thing that has changed is that they are no longer using the "giraffe" concrete pump truck. On the 16th they installed a pipe from an electric pump to the top of the pool, replacing a pipe destroyed in the unit 4 SFP blast. Their goal is to also install a heat exchanger, effectively restoring the pool cooling and cleaning system.

Most likely the concrete truck was simply injecting fresh water from a pipe carrying water from the dam (via some storage tank), but was not drawing any water from the skimmer surge tank. Now, with TEPCO working towards restoring pool cooling, they probably are cycling water from the skimmer surge tank back into the pool, combining it with fresh water to make up for evaporation.

In any case, less water in the skimmer surge tank is not a problem. Less water in the SFP would be a problem, but with the water topped up the other side of the gate (in the reactor pit and tool bay) for radiation protection there is also more of a safety margin: if the water in the SFP drops below the reactor pit level, the gate starts leaking, topping up the pool again.

Also, as long as the truck is still there they would still have its camera to watch the water level. Perhaps they installed one anyway, I certainly would, with 1500+ fuel assemblies in the pool!

 

[biffvernon]

Don't under estimate the ability of 187 quintillion gallons of water to dilute the problem.

But don't underestimate the ability of biology to act in the opposite direction.

 

[zapperzero]

Now i think it was zapperzero used a phrase some posts back re corium ::: ".. still stuck to the walls..."
uhhh, zz , was that just toying with words? do you know something i dont? Seen any analysis of what was on that 1Sv piece of concrete rubble?
old jim

Nope. Haven't seen anything you haven't, but I do seriously think that there is some corium, based on the high temps still being recorded by the various RPV sensors, much higher than for the other two reactors.

 

[zapperzero]

Not necessarily. It is all a matter of amount of energy stored. If you have hot corium splitting water into hydrogen and oxygen in a closed tank situation doesn't get worse - amount of energy present inside is still the same. It can get worse if the gases get outside and explode there, but that's a slightly different thing.

Given that all three containments are at atmospheric pressure, I think the point is moot.

 

[Astronuc]

Nuclear Engineering International: Closed-loop circulation starts at Fukushima Daiichi
28 June 2011
http://www.neimagazine.com/story.asp?sectioncode=72&storyCode=2059992

TEPCO has begun injecting decontaminated water into units 1, 2 and 3 of the Fukushima Daiichi nuclear power plant.

Some diagrams and numbers provided.

 

[Jorge Stolfi]

Since the airborne release is finished, the real value of this number won't go up.

Is that correct? All four reactors are still releasing steam to the atmosphere. That steam is water that boiled off in contact with the molten cores and/or SFPs, hence it must not be quite Perrier. Are there any estimates of the amount of radioactivity that is being released that way?

 

[zapperzero]

Is that correct? All four reactors are still releasing steam to the atmosphere. That steam is water that boiled off in contact with the molten cores and/or SFPs, hence it must not be quite Perrier. Are there any estimates of the amount of radioactivity that is being released that way?

Of course it is not correct. TEPCO sampled a steam plume a few days ago, but I don't recall them having released the results.