Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[AtomicWombat]

Four units and four different failure modes leads to one conclusion:
BWR are not as safe as they are said to be. It is time to switch them off.


Conclusions already made by industry experts (see attached pdf file)
1. All existing power plants' passive emergency cooling systems (BWR's
RCIC and PWR's turbine-driven auxiliary feedwater system) should be inspected
and reinforced to assure their reliability during adverse condition. Onsite
emergency generators should be further protected.
2. PWR is more resilient than BWR because of its steam generator secondary
water inventory and size of containment. This gives larger margin to core damage
and containment failure. Further review is still necessary to improve the safety
level.
3. Spent fuel pool safety has been grossly overlooked. A hardened and
independent top spray system is necessary for all nuclear power plants.

Please read attached pdf file - the most authoritative analysis yet found.

From the attched pdf, "An immediate question is whether a PWR is more resilient to an
earthquake/blackout than a BWR. By using our PCTRAN PWR models it is
quantitatively analyzed in great details. We may conclude an affirmative “yes” -
but not by much - just buy you a few more hours to resume onsite power supply.
After that the consequence is the same."
This qualifies conclusion 2 considerably.

I'm quite sure conclusion 3 will be the most obvious outcome of this event - spent fuel will no longer be stored for decades in pools in the secondary containment.

I think your conclusions are far stronger than warranted by the report.

 

[PietKuip]

sorry I may have missed some posts but has the "Cl-38" mystery been solved or any hint for that ? Astronuc said that they could have been a typo and a confusion with "Cs -138" - there are also some reports of "Co-58" , is it a possibility? if Cl-38 has been indeed produced (despite the absence of Na-24 or Cl-36, but are all nuclides really listed in these reports), is it possible to explain the needed neutron flux without some parts of the reactor being near-critical , at least during some time?

A new mystery is the 10^9 Bq/ml of I-134 in reactor building 2 with a half-life of 53 minutes.

Now, 340 half-lives after the earthquake that is supposed to have switched off the production of fission products.

 

[Fresno Phil]

Also, I think Reactor 2 is now confirmed RPV breach due to levels of Cs-134 measured outside of core.

We had a de-facto breach of the RPV when they lost the primary cooling loop and instead started using the fire-suppression loop for cooling.

With no loop to work with, what goes in has to come out. Before, I though they were just letting it drain back into the ocean, but who knows what sort of piping survives in these plants now.

Reactor 2 was the one with the "bad noise" heard after venting. A hydrogen explosion compromising the suppression chamber would not be unthinkable. The reported pressure for the suppression pool has been "downscale" for almost 2 weeks now.

According to NISA's latest, they are injecting 280 litres/min into #2's core via the fire suppression line, yet water level is 1.2m below the top of the rods, and was worse for a long time. Drywell is currently being reported as unpressurized (1ATM abs), yet has the highest radiation level (42 Sv/h).

Who knows what's going on with this unit.

 

[wasteinc]

as PietKuip indicates (about I-134), and KateB has suggested (regarding radioactive Cl), do we have indications that some criticality still happens inside some of the reactors?

Is this why http://english.kyodonews.jp/news/2011/03/81325.html" news emphasizes the I-134 ?

"According to the latest data released Sunday, radioactive iodine-134, a substance which sees its radiation release reduced to about half in some 53 minutes, existed in water at the No. 2 reactor's turbine building at an extremely high concentration of 2.9 billion becquerels per 1 cubic centimeter."

As AntonL in post #1451 has posted a picture suggesting that i-134 is produced only during fission, and not as a result of a damaged core

If some part of U is critical, that means that new heat is produced and the numbers about the residual heat you already calculated here are off.

 

[jensjakob]

Well, gents, the focus on short halflife leads to some journalists writing stuff like "so it will disperse fast and not be a danger".

I do think that the perspective shown in here "If it has such a short halflife, why is it still there 14 days after shutdown" is much more important than the spin sold to journalists.

(Though it IS positive that it disperses so fast...)

Source:
http://www.bbc.co.uk/news/world-asia-pacific-12872707

Quote:
"The radiation found in the sea will no longer be a risk after eight days because of iodine's half-life, officials say."

 

[Gilles]

sorry if I speculate too much but
* we know that hydrogen has been produced , so temperature has been over 1200°C and some zirconium coats have been oxidized and probably molten
* we know that fission products are abundantly detected in water, which confirms the destruction of many rods;
* we know that periodically smokes of various colors are emitted, which seems to indicate intermittent steam overpressures
* presence of short-lived isotopes is reported (no typos possible for I-134 i presume..), either fission products or neutron activated nuclides (more dubious?) which can be explained only if active fission is present.
Is a "oklo -like " scenario possible, that enough fuel could have melt and gather in the reactor, and near critical conditions could be met somewhere , with cycles of successive presence of liquid water (moderating) -vaporized steam (less moderating), giving some kind of feedback stabilizing the system to near critical conditions - for how long then?

 

[HansHooligan]

A bit more about the basement-water:
http://mdn.mainichi.jp/mdnnews/news/20110327p2g00m0dm063000c.html

My questions:
1. What will they do with it?
2. What are the quantities?
3. Does it keep on coming?
4. Notice the part about needing "more pumps"

5. what happens if water evaporates, will remaining matter become critical?
6. If it's a thick enough slurry, can fission happen in those water pools and if yes then what?

 

[John5656]

Daft question alert.

I see that they are detecting these isotopes with short half lives, and that indicates fission is still taking place. But isn't this is what is keeping the fuel rods hot?

Are they not always decaying, and thus fission is occurring?

Their arrangement, boron, control rods is preventing them from going critical, but surely we would expect to find these isotopes if containment has been lost? Either in the reactor or the SFP?

 

[Gilles]

Daft question alert.

I see that they are detecting these isotopes with short half lives, and that indicates fission is still taking place. But isn't this is what is keeping the fuel rods hot?

Are they not always decaying, and thus fission is occurring?

normally not, what heats the residual fuel is radioactive decay of fission products, but a chain reaction is not supposed to occur anymore if the control bars have been plunged into the reactor - it should be subcritical. Neutron induced fission is quite different from radioactive decay.

 

[jensjakob]

5. what happens if water evaporates, will remaining matter become critical?
6. If it's a thick enough slurry, can fission happen in those water pools and if yes then what?

Welcome to the Forum, Hans.

To my best knowledge, the answer to these 2 questions are a big no. Fortunately ;-)

 

[|Fred]

normally not, what heats the residual fuel is radioactive decay of fission products, but a chain reaction is not supposed to occur anymore if the control bars have been plunged into the reactor - it should be subcritical. Neutron induced fission is quite different from radioactive decay.

I think I can reformulate John5656's questions: is the radioactivity of those isotope incoherent with the amount of radioactivity suppose to be in the rod when the reactor scramble.

Nt x 2^(number of half-lives)= No

Where:
Nt = amount of isotope remaining (mesured)
No = original amount of isotope
number of half-lives = time / half-life

 

[jensjakob]

To those wondering how much the NRC might know, google gave me this from Hanford Hills (DOE)
http://msa.hanford.gov/hills/lesson.cfm?id=2458

Guess that NRC has quite some information - and I view it VERY positive.

TEPCO and Japan needs to understand that truth is out there - and they can't play the "silent game"

 

[John5656]

normally not, what heats the residual fuel is radioactive decay of fission products, but a chain reaction is not supposed to occur anymore if the control bars have been plunged into the reactor - it should be subcritical. Neutron induced fission is quite different from radioactive decay.

To quote, from wikipedia (I know what your thinking. I'm not a physicist, just trying to understand what is going on)

Uranium-235 undergoes a small rate of natural spontaneous fission, so there are always some neutrons being produced even in a fully shutdown reactor. When the control rods are withdrawn and criticality is approached the number increases because the absorption of neutrons is being progressively reduced, until at criticality the chain reaction becomes self-sustaining.

Even in a subcritical assembly such as a shut-down reactor core, any stray neutron that happens to be present in the core (for example from spontaneous fission of the fuel, from radioactive decay of fission products, or from a neutron source) will trigger an exponentially decaying chain reaction. Although the chain reaction is not self-sustaining, it acts as a multiplier that increases the equilibrium number of neutrons in the core.

http://en.wikipedia.org/wiki/Nuclear_reactor_physics

So even though we have a scram, surely some decay will be occurring, producing the short half lives found...? We don't have to have a chain reaction to find them, or do we?

 

[AtomicWombat]

A bit more about the basement-water:
http://mdn.mainichi.jp/mdnnews/news/20110327p2g00m0dm063000c.html

My questions:

My (best-guess) answers:

1. What will they do with it?

Ideally filter the radiaoactive particles before pumping the water out to sea. In reality probably just pump it out to sea.

2. What are the quantities?

Quantities of what? Radiaoactive contaminants OR water? An ealier estimate was about 6000 tonnes. I estimate about 2500-3000 tonnes - the approximate mass of water pumped into reactor 3.

3. Does it keep on coming?

As long as they keep pumping water into reactors that leak directly into the turbine buildings, yes it will keep coming.

4. Notice the part about needing "more pumps"

Yes and it strikes me they are making a bad situation worse by dispersing the radioactivity from the reactor cores (esp. no. 3) to the turbine buildings. But I guess that comes from not clearly understanding the situation before acting.

 

[PietKuip]

So even though we have a scram, surely some decay will be occurring, producing the short half lives found...? We don't have to have a chain reaction to find them, or do we?

Chlorine-38 is not a fission product. It can only occur at these levels when seawater is exposed to an ongoing (or very recent) neutron flux.

Neither can I-134 be present at such levels in a reactor that has been off for two weeks. Beta-rays or gammas do not produce iodine-134.

There are (intermittent? Oklo-type?) chain reactions going on at least two reactor buildings.

 

[daumphys]

From the attched pdf, "An immediate question is whether a PWR is more resilient to an
earthquake/blackout than a BWR. By using our PCTRAN PWR models it is
quantitatively analyzed in great details. We may conclude an affirmative “yes” -
but not by much - just buy you a few more hours to resume onsite power supply.
After that the consequence is the same."
This qualifies conclusion 2 considerably.

I'm quite sure conclusion 3 will be the most obvious outcome of this event - spent fuel will no longer be stored for decades in pools in the secondary containment.

I think your conclusions are far stronger than warranted by the report.

But at the point of nuclear reactor control, Is this conclusion always right?
Is the time lag of PWR model more short than BWR model? Is the response time of the BWR model short?

 

[AtomicWombat]

5. what happens if water evaporates, will remaining matter become critical?

No. These are not fissionable isotopes. Only the U238 and Pu239 (IIRC in these reactors) are fissionable. These are in their oxide form and are highly insoluble.

6. If it's a thick enough slurry, can fission happen in those water pools and if yes then what?

No again. See Q5 answer.

 

[AntonL]

Reactor 2 was the one with the "bad noise" heard after venting. A hydrogen explosion compromising the suppression chamber would not be unthinkable. The reported pressure for the suppression pool has been "downscale" for almost 2 weeks now.

According to NISA's latest, they are injecting 280 litres/min into #2's core via the fire suppression line, yet water level is 1.2m below the top of the rods, and was worse for a long time. Drywell is currently being reported as unpressurized (1ATM abs), yet has the highest radiation level (42 Sv/h).

Who knows what's going on with this unit.

We also know that all three reactors cores were severely damaged due to lack of cooling after the Tsunami struck. check the early reports.

Read my https://www.physicsforums.com/showpost.php?p=3209639&postcount=1218"
in reactor 2 residue heat should be 2.2MW which would boil away 6.3m3/h
any water above this quantity either fills the reactor or is boiled away or combination of both

280 l/m is 16.8m3/h and the temperature is fairly constant around 100 degrees C
should all this be boiled away to keep the temperature then there is maximum 3MW
too much heat or 0.1% of the reactor designed 2380MW thermal heat capacity.
With the huge amounts of water now in the basement the 3MW of too much heat
is a too high estimate, is is probably a fraction of that.

 

[|Fred]

Ideally filter the radiaoactive particles before pumping the water out to sea. In reality probably just pump it out to sea.

Tepco is planing to pump the water in the condenser (at the moment)

 

[AtomicWombat]

Daft question alert.

I see that they are detecting these isotopes with short half lives, and that indicates fission is still taking place. But isn't this is what is keeping the fuel rods hot?

Are they not always decaying, and thus fission is occurring?

Their arrangement, boron, control rods is preventing them from going critical, but surely we would expect to find these isotopes if containment has been lost? Either in the reactor or the SFP?

If a full meltdown has occurred it may be possible for critical mass arrangements of molten fuel, cladding and control rods to form by chance. In any case there would be a tendency for the components of the melt to separate based on different melting temperatures, chemical reactivity, solubility and density. So it would not be surprising for fuel to clump into a porous structure that allows water circulation.

However, this is speculation based on the evidence that fission continues. I suspect there have been no detailed studies of such a process.

 

[Gilles]

So even though we have a scram, surely some decay will be occurring, producing the short half lives found...? We don't have to have a chain reaction to find them, or do we?

John, the figures are totally inconsistent with http://en.wikipedia.org/wiki/Spontaneous_fission" . The decay half-life of U235 is 7E8 years, i.e 2.E16 s - so we have a decay rate of 5E-17 per second and per nucleus. The fission probability is 7E-11 - meaning 4E-27 fission per nucleus per second. In 1 t of U235, you have 1E6/235 *6E23 = 2.5E27 nuclei, so around 10 fissions per t per second. If I-134 concentration is the result of a steady state between production and decay, the production rate must exactly balance the decay rate : the reported activity is 2.9 billion Bq/cm^3 = meaning a production rate of 2.9 billions of nuclei per s and per cm^3 - just multiply by the volume of water and you'll have an idea of the numbers of fission events you need (actually it's more because you still have to correct from the I-134 yield ). We are orders and orders of magnitude over spontaneous fission.

 

[Borek]

it strikes me they are making a bad situation worse by dispersing the radioactivity from the reactor cores (esp. no. 3) to the turbine buildings. But I guess that comes from not clearly understanding the situation before acting.

To all: please refrain from this kind of comments. We are all judging situation based on partial information, I suppose they have reasons to do what they do.

I am not assuming they are not making mistakes, but knowing better in this situation is completely unjustified.

 

[John5656]

John, the figures are totally inconsistent with http://en.wikipedia.org/wiki/Spontaneous_fission" . The decay half-life of U235 is 7E8 years, i.e 2.E16 s - so we have a decay rate of 5E-17 per second and per nucleus. The fission probability is 7E-11 - meaning 4E-27 fission per nucleus per second. In 1 t of U235, you have 1E6/235 *6E23 = 2.5E27 nuclei, so around 10 fissions per t per second. If I-134 concentration is the result of a steady state between production and decay, the production rate must exactly balance the decay rate : the reported activity is 2.9 billion Bq/cm^3 = meaning a production rate of 2.9 billions of nuclei per s and per cm^3 - just multiply by the volume of water and you'll have an idea of the numbers of fission events you need (actually it's more because you still have to correct from the I-134 yield ). We are orders and orders of magnitude over spontaneous fission.

I'm with you. Many many thanks for the explanation.

 

[curious11]

We are orders and orders of magnitude over spontaneous fission.

By that, do you mean it must be continuous fission?

 

[HansHooligan]

Tepco is planing to pump the water in the condenser (at the moment)

Storing it to a leak free place to prevent it leaking to sea or to underground water deposits?

Or maybe the think that since condenser has not blow up yet, they want to create some purpose for it to explode... ;)

 

[PietKuip]

By that, do you mean it must be continuous fission?

There is a chain reaction. Might be intermittent.

Which can also be seen in the "innocent" data http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110327e2.pdf".

Low levels, but the levels of I-132 (half-life 2 hours) are comperable to other fission products.

 

[Gilles]

By that, do you mean it must be continuous fission?

yes , more or less. Actually the presence of short half-life isotopes means for me that there must have been at least a burst of fissions just a few hours before the measurement - we have no idea of how concentrations are varying with time. I can't imagine any other explanation - if somebody could offer one here, I would be glad - and relieved - to hear it.

 

[Dancewithbear]

yes , more or less. Actually the presence of short half-life isotopes means for me that there must have been at least a burst of fissions just a few hours before the measurement - we have no idea of how concentrations are varying with time. I can't imagine any other explanation - if somebody could offer one here, I would be glad - and relieved - to hear it.

Assuming (given) there is fission... what do they do to stop it?

Watering just appears to be making a mess.

 

[rmattila]

There is a chain reaction. Might be intermittent.

Which can also be seen in the "innocent" data http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110327e2.pdf".

Low levels, but the levels of I-132 (half-life 2 hours) are comperable to other fission products.

I-132 is produced by decay of Te-132 (half-life > 3 days), so it is not necessarily a sign of recent fissions taking place.

However, the concentrations given for I-134 in the unit 2 turbine building are very difficult to explain. It would take a very large number of fissions to produce this concentration of the isotope in the cooling water - of the order of several hundred megawatt-hours, if my (rapid and as yet unchecked) calculations are correct. Surely there should be other signs of significant number of fissions having occurred (i.e. activation products such as Na-24), if this result would be true.

 

[PietKuip]

I-132 is produced by decay of Te-132 (half-life > 3 days), so it is not necessarily a sign of recent fissions taking place.

Yes, you are right.

 

[Astronuc]

Perhaps someone knowledgeable could explain to me why they haven't started closing these plants up with concrete? How much longer do we need to wait?
Does anyone perhaps expect something could be salvaged in those plants?

There are several complications with that.

1. The containment is closed except for the cooling pipes of the feedwater system and other systems. Therefore the concrete slurry would have to be pumped though those pipes without setting up. It would have to get passed pumps and valves. One would have to get the concrete source as close to the containment as possible.

2. The volume of concrete would displace an equal volume of radioactive water. Where would that radioactive water go?

3. The structure is not designed for the additional mass of concrete.

4. The concrete would not allow cooling of what remains in the core.

As for salvaging the plant, the primary cooling system has been been exposed to seawater for about 2 weeks. There may be enough corrosion, particularly of the core components, such that they cannot be used again. The fuel is damaged (so the core would have to be replaced), but more importantly, the control rods and the drive mechanisms would have to be replaced. And likely the recirculation systems have been compromised, so essentially, much or all of that needs to be replaced. All those components would have to be decontaminated and scrapped. Given the contamination at the plant, that will take years.

 

[Astronuc]

Why would 'special equipment' be needed to detect Plutonium isotopes??

unconfirmed translation from twitter: Tepco may have just stated that the device they need is at Daiini

I think TEPCO wanted to use a detector in an area of relatively low background. The activity around Daiichi is now relatively high.

 

[Joe Neubarth]

From the attched pdf, "An immediate question is whether a PWR is more resilient to an
earthquake/blackout than a BWR. By using our PCTRAN PWR models it is
quantitatively analyzed in great details. We may conclude an affirmative “yes” -
but not by much - just buy you a few more hours to resume onsite power supply.
After that the consequence is the same."
This qualifies conclusion 2 considerably.

I'm quite sure conclusion 3 will be the most obvious outcome of this event - spent fuel will no longer be stored for decades in pools in the secondary containment.

I think your conclusions are far stronger than warranted by the report.

Quite frankly this entire crisis would not have happened if the Emergency Diesel Generators were not placed in an area where their operation could be interrupted by a Tsunami. They needed to be placed far above any area where a Tsunami could reach them. An Emergency Power generating station on the hills behind the Fukushima power plant would have been ideal as long as the power lines could not have been broken by a Tsunami action.

 

[timeasterday]

Now they say the high radiation measurement was not accurate.

 

[jensjakob]

Now they say the high radiation measurement was not accurate.

Source? Link?

To all, please allways include a source and link - we need to be very factual in here.

 

[timeasterday]

Source? Link?

To all, please allways include a source and link - we need to be very factual in here.

http://hosted.ap.org/dynamic/stories/A/AS_JAPAN_EARTHQUAKE?SITE=NCAGW&SECTION=HOME&TEMPLATE=DEFAULT

 

[jensjakob]

TEPCO is quoted for saying that the numbers are not credible, and they are taking additional samples - but they don't have the new numbers yet:
http://www.japantoday.com/category/national/view/huge-jump-in-radiation-reported-inside-stricken-no-2-nuclear-reactor

Fair to say that they want a second sample, but not fair to state "current numbers are not credible"... (IMHO)

 

[dtaipei]

Japanese press says that the error was not the reading, but the isotope (stated to be I-134) and therefore the "10 million" multiplier.

 

[Gilles]

TEPCO is quoted for saying that the numbers are not credible, and they are taking additional samples - but they don't have the new numbers yet:
http://www.japantoday.com/category/national/view/huge-jump-in-radiation-reported-inside-stricken-no-2-nuclear-reactor

Fair to say that they want a second sample, but not fair to state "current numbers are not credible"... (IMHO)

i would say that 2 millions Bq/cm^3 of I-134 may be more realistic than 2 billions, but as ominous.

 

[Astronuc]

>slide explaining the isotopes found in a reactor
If the reactor is working properly I thought that the isotopes were contained in the Zircaloy casing

If the cladding remains intact, those fission products remain contained within the fuel rod (cladding and endplugs). There is some tramp uranium on fuel, but it is very low level. However, in the normal course of operation, some fuel rods do fail due to PCI, debris, perhaps unusual corrosion. In that case, Xe and Kr isotopes escape from the breach, and so do I-isotopes, Cs-isotopes, and a few others. If the fuel operates long enough with the breach or at power, and if the breach opens (guillotine break or axial split), then more of the solid fission products escape to the coolant, as the fuel matrix is oxidized.

In the current context, the fuel does not have to melt. Rather is only needs to split open to release a large inventory of fission products and allow the coolant (seawater) to interact with the fuel material. Normally the coolant is purified water, but seawater has NaCl and other salts. I don't know of any research that has looked at the solubility of irradiated fuel in seawater.

There are normally activitation products of Fe, Ni, Cr, and the activition of Ni is a source of Co (n,p reaction). The oxides of Fe, Ni and Cr come from the normal corrosion of stainless steel or Ni-alloys (structural materials), which are deposited on the fuel where they absorb neutrons and become activated. In addition, the control rod structures are mostly stainless steel, and some are used during operation to control reactivity. The introduction of seawater 'shocked' the system, and those activated products are released from the core to the coolant. One typically refers to a crud burst.

The presence of short-lived isotopes is somewhat of a concern. If the reactor, shutdown two weeks ago, and one is detecting short-lived isotopes, then one must ask if that is consistent with the reactor shutdown. If the detected levels are more consistent with a near term fission process, then when and where did that fissioning occur.

There are spontaneous fission in Pu-240 and Pu-242, and isotopes of Cm, Am. But are those fission rates sufficient to activate Na-23, Cl-35 and Cl-37, as well as producing I-132, I-134.

Meanwhile:

Unit 1 Dry Well 35.4 Sv/h or 3540 R/hr
Unit 2 Dry Well 43.2 Sv/h or 4320 R/hr
Unit 3 Dry Well 36.1 Sv/h or 3610 R/hr

This would be consistent with the release of fuel and corrosion products from the core into the coolant (seawater), which then found its way to the drywell (torus?).

 

[AtomicWombat]

0:27 and 1:31 - gives you an idea of the size of the RV cap. I don't think it has blasted anywhere.

But good illustratitions and good narrative.

"Wow it looks too big" is a weak argument about whether an explosion can blast a pressure vessel or other object away.

The reactor lid weighs about 80 tonnes (assuming 6 metre diameter 180mm thick steel). In Chernobyl the upper biological shield (the plug) weighed 1000 tonnes. It was dislodged by the explosion there. The water circulation operated at 70 kg/cm^2 (about 70 atm) - close to the 1000 psi operating pressure of BWRs.

[PLAIN]http://www.world-nuclear.org/images/info/chernowreck2.gif

See:
https://netfiles.uiuc.edu/mragheb/www/NPRE%20402%20ME%20405%20Nuclear%20Power%20Engineering/Chernobyl%20Accident.pdf"

Size is not good guide to surviving explosions:

[URL]http://4.bp.blogspot.com/_MfX4tKGzQ5I/S4UfOTPv07I/AAAAAAAAATA/wFqGhGE02Nw/s1600/Lees-Bleve_Mexico1.JPG[/URL]

[URL]http://1.bp.blogspot.com/_MfX4tKGzQ5I/S4UfO87SaDI/AAAAAAAAATI/vO1eUgbypX8/s1600/Lees-Bleve_Mexico2.JPG[/URL]

 

[Astronuc]

Quite frankly this entire crisis would not have happened if the Emergency Diesel Generators were not placed in an area where their operation could be interrupted by a Tsunami. They needed to be placed far above any area where a Tsunami could reach them. An Emergency Power generating station on the hills behind the Fukushima power plant would have been ideal as long as the power lines could not have been broken by a Tsunami action.

Yes - that was made painfully obvious the moment the EDGs (and/or their fuel system) were taken out by the tsunami, while at the same time, the site had lost connection to the grid. And the fact that they only had battery backup, and I'm sure that the batteries were not designed to run pumps, but rather are intended to provide power to the monitoring systems.

 

[wasteinc]

We have an on the record acknowledgment from TEPCO that there is a possibility of re-criticality . Read http://uk.news.yahoo.com/5/20110317/twl-japan-admits-nuclear-problem-is-seve-3fd0ae9.html" :


"We have to keep cooling the fuel so it doesn't reach criticality," the Tepco spokesman said, adding that radiation levels have barely fallen at the site. "

and this acknowledgment was from 10 days ago. (17March).

While I cannot comment on physics and radiochemistry, I can understand one or two things about news. So let me put that in perspective.

On the 17th TEPCO spokesman admits that there is a possibility of re-criticality.

Then people here see that the I-134 and Cl-38 found in the water cannot be explained by the normal decay process in sub-critical conditions.

http://english.kyodonews.jp/news/2011/03/81325.html" talks about the isotopes found in the water and seems to weight particularly the presence of I-134 which is the only other isotope it pays attention to apart from the famous couple (I-131 , Cs-137)

I don't know if recriticality is a possibility , but TEPCO seems to thinks so

 

[rmattila]

And the fact that they only had battery backup, and I'm sure that the batteries were not designed to run pumps, but rather are intended to provide power to the monitoring systems.

Not just for the monitoring systems, but also for managing power-operated valves - such as those needed for reducing the reactor pressure (blowdown system), providing steam for the RCIC turbines and enabling the feedwater to be pumped into the core. I'm not sure how the Japanese plant is equipped in this respect, but it appears that loss of DC could have been one factor contributing to the core uncovery.

 

[|Fred]

If some of you do speak good Japanese here are links to video streams , who fully broadcast all the NISA and TEPCO Press Conference and Press Q&A
Please note that they are in japanese and NOT translated, and that most of the time the camera is filming although the Conference ended ot did not start

It is the most up to date information but without translation it is useless

http://iwakamiyasumi.com/ustream-schedule/ustream1

some are archived there
http://www.ustream.tv/channel/iwakamiyasumi

 

[AntonL]

what to do with all the water was asked earlier and we puzzled about the fact of it being moved to the condensers. This is the current plan, the condensers have a environmental shield around them, (red encasing) and the plan seems to be to fill these according to below info-graphic.

 

[Joe Neubarth]

If a full meltdown has occurred it may be possible for critical mass arrangements of molten fuel, cladding and control rods to form by chance. In any case there would be a tendency for the components of the melt to separate based on different melting temperatures, chemical reactivity, solubility and density. So it would not be surprising for fuel to clump into a porous structure that allows water circulation.

However, this is speculation based on the evidence that fission continues. I suspect there have been no detailed studies of such a process.

Actually they garnered a heck of a lot of information from Chernobyl and Three Mile Island. AT Chernobyl, the Lava that was generated from the melt down actually flowed through pipes under the reactor and out onto a basement corridor floor. Photos are available all over the Internet, but the easiest one to locate is a Wiki. Three Mile Island had accumulation at the base of the reactor vessel. That mass was analyzed for content and it consisted primarily of Zirconium and Uranium with far smaller amounts of Steel, Nickle (Inconel), and Chromium. When I read that report I was wondering what happened to the control rods. It turns out the Boron (If the control rods have melted) eventually becomes Boric Acid in solution. As the Japanese were pumping sea water into the reactor, they were diluting the Boric Acid and it was flowing out into the building. Do that long enough, and you can make your corium glow with numerous fissions, especialy if it started out as an old core operating at a high rate of power when the troubles began.

 

[Astronuc]

I-132 is produced by decay of Te-132 (half-life > 3 days), so it is not necessarily a sign of recent fissions taking place.

However, the concentrations given for I-134 in the unit 2 turbine building are very difficult to explain. It would take a very large number of fissions to produce this concentration of the isotope in the cooling water - of the order of several hundred megawatt-hours, if my (rapid and as yet unchecked) calculations are correct. Surely there should be other signs of significant number of fissions having occurred (i.e. activation products such as Na-24), if this result would be true.

The presence of short-lived fission products and activation products is somewhat puzzling, although there appears to be a significant release of fuel material into the coolant (seawater). I would like to know the relative activities of the I-isotopes, the Cs-isotopes, and isotopes such as Ce-144 and Nd-146. The matter will also be complicated by different solubilites.

With repsect to Cl-38, I would also expect Cl-36 (but low activity due to long half-life) and Na-24.

See the (n,γ) cross-section plots attached.
blue = Na-23
green = Cl-35
red = Cl-37

 

[Joe Neubarth]

We have an on the record acknowledgment from TEPCO that there is a possibility of re-criticality . Read http://uk.news.yahoo.com/5/20110317/twl-japan-admits-nuclear-problem-is-seve-3fd0ae9.html" :"We have to keep cooling the fuel so it doesn't reach criticality," the Tepco spokesman said, adding that radiation levels have barely fallen at the site. "

and this acknowledgment was from 10 days ago. (17March).

While I cannot comment on physics and radiochemistry, I can understand one or two things about news. So let me put that in perspective.

I am willing to bet that the damn thing can pulse.

On the 17th TEPCO spokesman admits that there is a possibility of re-criticality.

Then people here see that the I-134 and Cl-38 found in the water cannot be explained by the normal decay process in sub-critical conditions.

http://english.kyodonews.jp/news/2011/03/81325.html" talks about the isotopes found in the water and seems to weight particularly the presence of I-134 which is the only other isotope it pays attention to apart from the famous couple (I-131 , Cs-137)

I don't know if recriticality is a possibility , but TEPCO seems to thinks so

The real consideration is self sustaining criticality. Any time you have a Uranium atom split from a neutron strike and it releases its 2+ Neutrons and at least one of them causes another Uranium atom to split and that goes on for a few seconds, you have a continuing chain reaction..

In the present state it can not be sustained even if they are flushing all of the BoricAcid out of the reactor and creating an ideal situation for a hot box for a hundred years.

 

[jensjakob]

I read somewhere (sorry for not being able to provide link right now) that the EDG's was swamped by the wave - e.g. the air intake was flooded - which leads to immediate flooding of EDG's - e.g. hydrolock of the cylinders.

http://en.wikipedia.org/wiki/Hydrolock