Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[AntonL]

Then how about a huge blast from inside Bldg 4, maybe from hot fuel rods from SFP4 melting and dropping through, eventually into the torus suppression pool?! See post above.

TCups I admire your imagination and investigating every angle but here I have to disagree stretched a bit too far in my humble opinion

 

[TCups]

TCups I admire your imagination and investigating every angle but here I have to disagree stretched a bit too far in my humble opinion

I certainly hope so. . .

BTW, how do you explain the extent of damage seen to the exterior of Bldg 4? Far fetched as it seems, this is all I can come up with.

 

[Joe Neubarth]

The video of the blasts at 2, 3 were from the ground. More likely, things were starting to get "hot" and the camera crews were evacuated.

How the hell does the blast blow out all the east side panels at ground level, and yet, leave the north side panels at the same corner intact? It makes no sense.

I would love to get my hands on a full set of structural drawings of those buildings.

The only explanation I can put forth is a scary one --

1) the overhead crane protected the top north wall from the brunt of the blast force.
2) the explosion was more than hydrogen gas. It occurred in the spent fuel pool, and breeched not only the outside wall of the SFP, but also its inside wall and floor, with a large portion of the blast venting to the lower levels of Bldg 4.

The scary implication of this hypothesis is that the fuel in the SFP of Unit 3 melted "down" into the building or was blown down into the lower building when the hydrogen blast occurred. Nasty.

I have seen you guys ask questions that you are answering by yourselves over and over again. The direction of the blasts are shaped by the physical weakness of the structures around them, just like water flows where the least resistance is.

I have not followed your discussion much as I know from experience in reading numerous summary reports that we will only know the truth after the Japanese have decided what it is. That is going to be one hell of a report running thousands of pages, and it may not be written as it should if the decision is made to cap the whole reactor building, if, indeed, the reactor containment vessel exploded on three. Right now, all of the guess are just guesses. Since I am days behind most of your observations and have trouble telling one wall from another I am in awe of your summaries so far.

Let me go back and ask a simple question, "What was the large structure that was lifted hundreds of feet into the air that we can clearly see in the dark cloud explosion of Reactor Three? You can see it coming back down out of the top of the cloud and impacting the ground. Exactly where, I do not know, but I am certain you guys have already figured that out."

 

[jlduh]

If i try to summarize (and i try to keep it simple and understandable for non specialists):

1) dose and dose rate in mSv and mSv/h define the radioactivity at the point of measurement coming from various elements around emitting in alpha and beta rays. A dosimeter detects the various emissions and corrects (by calculation) them with factor taking into account the fact that alpha is more energetic than beta and so can cause more damages to cells. The corresponding results is expressed in mSv/h for example. RIGHT?

2) a specific element can be dangerous and toxic by:
2-A its chemical effects
2-B its radioactive effects
RIGHT?

3) If ingested of inhaled, then these to possible effects can add together.
RIGHT?

4) if ingested or inhaled, these effects are increased by the fact that they go closer to or even in direct contact with target organs that they can damage.
RIGHT?

Note that chemical effects have to take into effect the fact that byproducts of several chemical transformation in the body can appear and be also harmful. Don't know if it's the same with radioactive isotopes inside the body?

The particularity of radioactivity is that it can harm even at distance through rays, which is not the case of chemical effects (the chemical product can be inhaled or ingested or go through skin, but in this case, the distance is no more there of course). Again one element can have chemical AND radioactive effects, the difference has to be understood.

 

[TCups]

I have seen you guys ask questions that you are answering by yourselves over and over again. The direction of the blasts are shaped by the physical weakness of the structures around them, just like water flows where the least resistance is.

I have not followed your discussion much as I know from experience in reading numerous summary reports that we will only know the truth after the Japanese have decided what it is. That is going to be one hell of a report running thousands of pages, and it may not be written as it should if the decision is made to cap the whole reactor building, if, indeed, the reactor containment vessel exploded on three. Right now, all of the guess are just guesses. Since I am days behind most of your observations and have trouble telling one wall from another I am in awe of your summaries so far.

Let me go back and ask a simple question, "What was the large structure that was lifted hundreds of feet into the air that we can clearly see in the dark cloud explosion of Reactor Three? You can see it coming back down out of the top of the cloud and impacting the ground. Exactly where, I do not know, but I am certain you guys have already figured that out."

Uh, large pieces of the roof? "Clearly" may be a relative term here, though. I clearly see large holes blasted in the south, east and north sides of Bldg 4, for example. I don't know that I clearly see a single large piece of debris falling in the remnants of the explosion of Bldg 3, but it is certainly possible.

Here's a question, though: just how hot do dry fuel rod assemblies get? Hot enough to melt the steel lining of the SFP4 and damage concrete?

PS: Joe - I am neither a novelist nor an engineer. I am a radiologist. I spend all day, every work day looking at complicated pictures, asking myself questions about what is normal and what isn't, and then, hopefully, answering them for the patients and referring physicians who ordered the test and are counting on my best opinion of what I see and what I think it means. Sorry if I can't break out of that habit. Sometimes, though, such observations and speculation may lead others to lines of thought and conclusions they may not have otherwise considered. At least that is how it works in medicine.

 

[Astronuc]

If i try to summarize:

1) dose and dose rate in mSv and mSv/h define the radioactivity at the point of measurement coming from various elements around emitting in alpha and beta rays. A dosimeter detects the various emissions and corrects (by calculation) them with factor taking into account the fact that alpha is more energetic than beta and so can cause more damages to cells. RIGHT?

2) a specific element can be dangerous and toxic by:
2-A its chemical effects
2-B its radioactive effects
RIGHT?

3) If ingested of inhaled, then these to possible effects can add together.
RIGHT?

4) if ingested or inhaled, these effects are increased by the fact that they go closer to or even in direct contact with target organs that they can damage.
RIGHT?

Note that chemical effects have to take into effect the fact that byproducts of several chemical transformation in the body can appear and be also harmful. Don't know if it's the same with radioactive isotopes inside the body?

The particularity of radioactivity is that it can harm even at distance through rays, which is not the case of chemical effects (the chemical product can be inhaled or ingested or go through skin, but in this case, the distance is no more there of course). Again one element can have chemical AND radioactive effects, the difference has to be understood.

That's more or less correct.

Each radionuclide has a chemical effect and a radiological effect. Non-radioactive isotopes just have the chemical effect.

Heavy metal radionuclides (heavier than lead) have the chemical effect of being a heavy metal as well as the radiological effect of their radioemission - alpha, beta and gamma. Outside of the body, distance and shielding can limit the exposure. Alphas are stop by few cm of air or layer of skin, betas are bit more penetrating (which is energy dependent), and gammas are most penetrating (also depending on energy). Beta particles represent a continuous spectrum of energy from a given radionuclide (assuming its a beta emitter) while gammas generally have discrete energies due to characteristics of the particular nucleus and its characteristic energy levels.

When inhaled, radionuclides are on the surface of the lungs, and radiation can damage the cells lining the lung - which affects the transport of oxygen and CO₂ - as well as increasing the risk of lung cancer or pulmonary disease. Depending on the isotope, the radionuclide could pass into the blood stream where it would be transported anywhere in the body.

Similarly, if ingested, the radionuclides irradiate the cells lining the alimentary canal - mouth to anus. There is also the increased risk of the radionuclide entering the blood stream where it will be transported to and taken up by a particular organ, if not excreted.

Iodine favors the thyroid gland.

Cs, Rb, would like affect the systems using Na, K.

Sr, Ba, would be more likely to affect those systems using Ca.

Heavy metals damage nerves (brain), kidneys and other organs.


This is why fission products and transuranics (radionuclides) are supposed to kept out of the environment - and exposures are to be As Low As Reasonably Achieveable/Practicable (ALARA/ALARP)!

 

[rhody]

This thought has been percolating in my mind for a couple of weeks,
finally, the media choose to address it, something for all to consider... from the Washington Times

http://www.washingtontimes.com/news/2011/mar/24/fears-rise-that-japan-could-sell-off-us-debt/"

Some lawmakers and market analysts are expressing rising concerns that a demand for capital by earthquake-ravaged Japan could lead it to sell off some of its huge holdings of U.S.-issued debt, leaving the federal government in an even tighter financial pinch.

Others say a major debt sell-off by Tokyo is unlikely, but noted that the mere fact that questions are being raised speaks volumes about the risks involved in relying so heavily on foreign investors to fund U.S. debt.

“This natural disaster in Japan concerns me that it could speed up what’s coming, because they are the second leading buyer of our debt,” Sen. Rand Paul, Kentucky Republican, told The Washington Times. “Small degrees of differences in how much they buy of our debt, I think, can make a big difference in interest rates that we have to pay people to buy our debt.”

With the federal government having piled up $14.2 trillion in debt, budget experts are warning that the country is on an unsustainable fiscal path. Congress, they say, must find cuts in all areas of the budget, while reforming the entitlement programs — Social Security, Medicare and Medicaid — that are the biggest drivers of national spending.

Rhody...

P.S. Keep up the excellent postings, this is an amazing time capsule of events that warrant future academic study, captured here for all time (except for links that may be deleted before a study is done).

 

[AntonL]

Here's a question, though: just how hot do dry fuel rod assemblies get? Hot enough to melt the steel lining of the SFP4 and damage concrete?
.

The SFP in Unit 4 is generating about 2MW of heat by reports that I have seen, enough to support your idea

However, should the pool have been dry long enough for it to melt the steel lining and damage the concrete you would have had huge amounts of contamination etc. this did not happen in unit 4,

Forget that idea

 

[Dancewithbear]

If i try to summarize (and i try to keep it simple and understandable for non specialists):

I have looked at this over the past few days and it seems that examining a specific detail leaves out other factors to the extent that one misses the big picture.

A lot of links have been provided. This one has navigational links on the left to explore including detection and treatment.
http://orise.orau.gov/reacts/guide/define.htm

On the one hand mSV/h is mSV/h but to know what to do you need to know what the source is and what other risks are within scope.

i.e. Plutonium is most dangerous if you inhale or ingest it. Cesium will likely be more predominate (than PU) and with a 30yr half-live is likely the thing your most affected by in a practical sense while iodine may be the biggest short term/immediate concern. You need to know what is there and take appropriate measures based on what it is. In that sense mSV/h is a risk rating.

An analogy to this is like the effect of a football play. It may be negligible as an incomplete pass or it may be a game changing touchdown or may result in a career ending injury. Generally by itself its inconsequential when examined in terms of 32 teams with 16 games each for the season over 10 years. There are many random factors not immediately apparent. It’s the result of these random events that determine the final outcome.

In the end look at the probability of exposure to the contaminants present and take appropriate measures to mitigate risks.

 

[DrDu]

Fred
Ok thanks. My point is that until now, medias and autorities have based their conclusions given in their communicates on dose or doses/h, in millisievert or millisievert/h. Under a certain dose (dose rate X time of exposure) it is safe. Period.

My question around toxicity of Pu is: does this simple and UNIQUE equation

dose (mSv) < safe limit

is enough to caracterize the safety concerns even with for example Pu around?
Does it tell the all story?
Would be surprised about that but maybe I'm wrong...

Especially in case of Plutonium, all its detrimental health effects are due to it's radioactivity although there exists the persistent ( and wrong!) myth that Pu is so dangerous due to its chemical toxicity.

The problem with the simple statement of save dose in mSv is that in fact there are no instuments that would allow to measure directly the dose in mSv (although some counters for external gamma dose mainly are gauged in this way).
E.g. to receive a dose of 1 mSv in 50 years it requires about ingestion of about 80000 Bequerel of Caesium 137 but only about inhalation of 15 Bq of Plutonium. The activity in Bq in the environment is relatively simple to determine.

 

[Joe Neubarth]

Found this: http://yarchive.net/physics/plutonium_toxicity.html

As long as people are not snorting Plutonium dust or swallowing small quantities of Plutonium, they should be fine. I would be more worried about Cyanide in my diet.

 

[Astronuc]

I hear many sources, including some 'experts', mentioning the term partial meltdown or meltdown - based on hydrogen and the radionuclides. This is premature, and not necessarily the case. By melt, I assume the physical process of a solid becoming a liquid.

It is important to realize several things:

1. Hydrogen is produced by the normal Zr + 2H₂O => ZrO₂ + 2 H₂. It happens in normal operation, but at a very low level. The cladding normally oxidizes/corrodes with a range of 1-4 mils (25-100 microns) on fuel cladding. The hydrogen production is very low, and it normally interacts with other compounds. In some plants, hydrogen is injected in order to control corrosion and protect the stainless steel. In the past decade or so, some BWR operator inject noble metals such as Rh/Pd in order to reduce the hydrogen injection.

2. The presence of fission products means that the cladding is breached and the fuel is possibly exposed if the breach is sufficiently large, as opposed to a tight crack of few microns width. It could mean fuel melting - IF such conditions were achieved - but it doesn't necessarily imply melting.

3. If the spent fuel pools (SFP) went dry, then the Zr-2 cladding may oxidize in air, but there would be no hydrogen production. Hydrogen only comes from the Zr + H₂O reaction.

4. Where water is present, then that would preclude fuel melting. If steam is present, then fuel melting might be possible, if the steam is non-flowing, i.e., stagnant and dry (superheated). Steel (Tmelt = ~1400°C) melts before Zircaloy (Tmelt = ~1850°C). However, there would likely be chemical reactions (oxidation) of the metals before melting. For Zircaloy, this would mean oxidation with the water/steam.

 

[Reno Deano]

Both U and Pu are hazardous IF ingested - which is the key. As long as U and Pu stay outside the body, it's not a big deal. The problem arises when U and Pu get into the food or water cycle, or are inhaled, i.e., ingested. Both U and Pu are heavy metals, and they will do damage to certain organs, just as mercury (Hg), arsenic (As) and lead (Pb) would do damage IF ingested.

As far as I know, U is a problem for kidneys, and Pu may be taken up in the bones.

Both present a radiological hazard in addition to the chemical hazard. Pu isotopes have shorter half-lives, so the same number of atoms or mass presents a greater hazard IF ingested.


As for the source of the Pu (and U), there is a clear distinction on the isotopics that I amended (updated) to my previous post. However, it may not be so clear depending on how impure the Pu used in the Chinese detonations.

However, if there is Pu-238, then it more likely came from the spent fuel than another source.

For now, it appears that the Pu and U particles/fines are confined to the plant. However, like any dust, they could be transported - in minute quantities.

See this for various reports on Radiation Effects
http://www.hps.org/publicinformation/ate/cat25.html

Both Pu and U need to be in solublized form to be taken up by plants. It is not an over night thing. Surface contamination is another thing.

 

[Borek]

Cannot be confirmed, however I cannot imagine the quake to this kind of damage to the welds

I wonder if these are welds. It looks like something I see whenever I drive home from the city center - there is a pipe used to transfer heat from a CHP station to buildings in one of the city districts. It looks similar from the distance, but it is not welded, just a riveted metal sheets (relatively thin ones) that protect insulation below. You can rip the rivets with a good kick.

 

[|Fred]

E.g. to receive a dose of 1 mSv in 50 years it requires about ingestion of about 80000 Bequerel of Caesium 137 but only about inhalation of 15 Bq of Plutonium. The activity in Bq in the environment is relatively simple to determine.

Hi DrDu
Could you please breakdown the math ?

Thank you

 

[georgiworld]

Interesting video on TMI clean-up. Hope we can one day get there

 

[Joe Neubarth]

Have they survived quake intact?

What Anton is seeing are not ruptured welds. At least I do not think they are welds. Most of thpse external pipes have lagging on them to prevent people from getting burned or to prevent collection of ambient condensate which can rust the pipes. The lagging is usually covered by a thin metalic foil of some sort, most likely aluminum or thin stainless steel. It would be subject to shock wave wrinkling.

 

[jensjakob]

Those pipes are as far as I know vents from the Torus (and containment?) to the exhaust-stacks.

The bursting of the pipe could be due to the earthquake - but it could also be due to HIGH PRESSURE SHOCKWAVE inside the pipe.

Though my guess would be that such a shockwave would rupture the pipe in where it bends - so I lean towards the "buckled in earthquake" theory.

But keep on analysing TCups, I appreciate your thoughts.

We should begin to add <confirmed source=""> tags in front of the statements that can be confirmed by external sources - will helo us narrow down to the unknows.

The truth is out there

Jens Jakob

 

[Maclomer]

Here's a question, though: just how hot do dry fuel rod assemblies get? Hot enough to melt the steel lining of the SFP4 and damage concrete?

I assume the ultimate temperature of the melt would depend on the mass of the molten material and the equilibrium between internal heat generation and conduction/radiation of heat away from the melt. I presume it could get awfully hot - enough to easily melt steel and even concrete with which it is said to react chemically.

So many detailed practical questions and a lot of very smart people here putting out very ingenious conjecture here - all of which I find extremely valuable. This is one of the best sites for information at present.

My own question: imagine a suspended fuel rod undergoing partial melt - the cladding melts on one place - does the lower end of the rod then drop to the bottom of the containment? It seems the cladding alone gives the rod structural integrity?

Reactor cooling is presently being achieved by 'injection' using fire pumps and others -considering the required volume of water one must assume that this is a closed, albeit leaky, loop. How does this mode of cooling differ from the one which failed after the tsumami and which we are told they are trying desperately to restore?

 

[divmstr95]

I hear many sources, including some 'experts', mentioning the term partial meltdown or meltdown - based on hydrogen and the radionuclides. This is premature, and not necessarily the case. By melt, I assume the physical process of a solid becoming a liquid.

It is important to realize several things:

1. Hydrogen is produced by the normal Zr + 2H₂O => ZrO₂ + 2 H₂. It happens in normal operation, but at a very low level. The cladding normally oxidizes/corrodes with a range of 1-4 mils (25-100 microns) on fuel cladding. The hydrogen production is very low, and it normally interacts with other compounds. In some plants, hydrogen is injected in order to control corrosion and protect the stainless steel. In the past decade or so, some BWR operator inject noble metals such as Rh/Pd in order to reduce the hydrogen injection.

2. The presence of fission products means that the cladding is breached and the fuel is possibly exposed if the breach is sufficiently large, as opposed to a tight crack of few microns width. It could mean fuel melting - IF such conditions were achieved - but it doesn't necessarily imply melting.

3. If the spent fuel pools (SFP) went dry, then the Zr-2 cladding may oxidize in air, but there would be no hydrogen production. Hydrogen only comes from the Zr + H₂O reaction.

4. Where water is present, then that would preclude fuel melting. If steam is present, then fuel melting might be possible, if the steam is non-flowing, i.e., stagnant and dry (superheated). Steel (Tmelt = ~1400°C) melts before Zircaloy (Tmelt = ~1850°C). However, there would likely be chemical reactions (oxidation) of the metals before melting. For Zircaloy, this would mean oxidation with the water/steam.

My understanding of the mechanism in this case is that Zirconium Hydride (ZrH2 ZrH4), produced while the plant is operating by the presence of free hydrogen from the zirc-water reaction, radiolysis of water, and corrosion control, will release H2 above 300c and is also highly flammable. The H2 would have been responsible for the explosion.

Couldn't this be the cause of a zirconium fire if the SFP went dry with fuel that has a recent high power history? Isn't zirc-2 more prone to hyrdiding than zirc-4?

In either case the AMS data from DOE showing the highly contaminated area NW of Fukushima (out to 25 miles) seems to support the theory that there was a fuel fire. Based upon what everyone believes is the current status of plants 1-3 RPV and containment and the timeframe at which that occurred it seems unlikely that any other source caused that level of contamination.

 

[shogun338]

Good video showing MOX fuel production . http://www.liveleak.com/view?i=4e9_1300331821

 

[Astronuc]

I assume the ultimate temperature of the melt would depend on the mass of the molten material and the equilibrium between internal heat generation and conduction/radiation of heat away from the melt. I presume it could get awfully hot - enough to easily melt steel and even concrete with which it is said to react chemically.

The melting temperature is determined by the particular material. How hot the liquid gets is determined by the heat source (volumetric heat rate) and heat transfer mechanism (conduction, convection, thermal radiation)

My own question: imagine a suspended fuel rod undergoing partial melt - the cladding melts on one place - does the lower end of the rod then drop to the bottom of the containment? It seems the cladding alone gives the rod structural integrity?

Reactor cooling is presently being achieved by 'injection' using fire pumps and others -considering the required volume of water one must assume that this is a closed, albeit leaky, loop. How does this mode of cooling differ from the one which failed after the tsumami and which we are told they are trying desperately to restore?

The heat source currently is the decay of fission products in the ceramic fuel pellets minus that which has been lost to the coolant (water or steam). Some fission products are gases (Xe, Kr), and some are volatiles (i.e., low melting point, e.g., Cs, I), some of which are soluble in water.

The Zircaloy-2 cladding surrounds the ceramic pellets, but it has certainly breached (cracked or corroded) and MAY have melting IF the cladding temperature reached ~1800°C.
The fuel rods sit between stainless steel (SS304) tie plates. Stainless steel melts at ~1400-1450°C. Only if cooling is insufficient, i.e., stagnant superheated steam could the steel or Zircaloy reaches those temperatures. If water is present - it boils, so those temperatures would not be realized. If the steam is 'wet' or 'moist', then those temperatures are not realized.

Nevertheless, before those temperatures are reached, the Zircaloy-2 would chemically react with the steam/water as in oxidation/corrosion. In that case, the Zircaloy-2 cladding may open up through cracks or ruptured hydride blisters, in which case the water/steam can communicate with the ceramic pellets. That's how the fuel particles and fission products get out.

If the bottom tie plate is not uncovered, i.e., if the water level covers the bottom tie plate, it won't melt. Any broken away cladding or fuel pellet may fall between the gaps between the fuel pellets. About every 20 inches, spacer grids are located, and they would tend to capture fuel pellet fragments and pieces of cladding. Wherever water is present, the fuel does not melt.

BWR fuel assemblies are surrounded by Zircaloy-2 channels (which facilitate the axial/vertical flow of coolant in the core). These channels (assuming they don't melt) would confined the fuel fragments and cladding to the box formed by the channel and bottom tie plate.

The bottom tie plate sits on a block of stainless steel. If covered by water, it does not melt. Then there is the structure underneath the core that contains the control rod drives. If there is water there, that does not melt.

All of the above sits inside a stainless steel lined pressure vessel of carbon steel. If water is in the bottom of the pressure vessel, it does not melt. Underneath the pressure vessel is several thicknesses of steel reinforced concrete. I expect that the bottom of containment is flooded with water. As long as there is water present - there is no melting.

 

[2ndResponder]

Excuse the simplistic question, but, given the situation it seems to me that making a brand new and adequately large cooling pool for the spent fuel rods and moving them into it is going to be the only way to proceed -- even if it is just temporary. That would almost certainly require industrial radiation-hardened robots, which apparently do exist in other countries.

So my question is whether the unknown and or unknowable details of the situation change that conclusion. And then, if all paths anyone can think of will end up leading to that step, has anyone started it yet?

Or can that be avoided in some scenarios that everyone is still trying to determine?

 

[Dancewithbear]

Question about the building and containment construction regarding the diagram in post 1906.
https://www.physicsforums.com/showpost.php?p=3217183&postcount=1906

Is there another enclosing structure not shown in this diagram between 30, 38 and the outside building wall (that was destroyed)?
i.e. Is what is listed as 11 another structure inside the building outer wall?

30 (drywell containment vessel)
38 (Pressure Suppression Torus)

What is the structure the pipe labeled as 24 is going through? (It’s coming out of 22 the RPV)
For the moment I will call the structure in the above question “S1”
In the cutaway diagram I cannot tell if “S1” would incase the entire RPV or not… does it?

Assuming 11 is the building outside wall... if the RPV is cracked and either or both the drywell containment or the torus is breached and the building walls are blown out; there is nothing between the reactor core and the atmosphere (except a couple of twists and turns) correct?

 

[Astronuc]

My understanding of the mechanism in this case is that Zirconium Hydride (ZrH2 ZrH4), produced while the plant is operating by the presence of free hydrogen from the zirc-water reaction, radiolysis of water, and corrosion control, will release H2 above 300c and is also highly flammable. The H2 would have been responsible for the explosion.

Couldn't this be the cause of a zirconium fire if the SFP went dry with fuel that has a recent high power history? Isn't zirc-2 more prone to hyrdiding than zirc-4?

In either case the AMS data from DOE showing the highly contaminated area NW of Fukushima (out to 25 miles) seems to support the theory that there was a fuel fire. Based upon what everyone believes is the current status of plants 1-3 RPV and containment and the timeframe at which that occurred it seems unlikely that any other source caused that level of contamination.

Zr hydride is essentially ZrH₂. When Zr in Zr-2 or Zr-4 reacts with H₂O to form ZrO₂, some hydrogen is taken into the Zircaloy cladding. Zr-2 tends to take up a bit more the Zr-4, ostensibly due to the presence of Ni in Zr-2, which is not much in Zr-4. The amount taken up is less than 25%, and typically ~17% for Zr-4 and a bit higher for Zr-2. This is because the H₂O breaks down in the oxide, and the O has to diffuse to the Zr/ZrO interface to continue the oxidation process. The rest of the hydrogen is free to wander off in the water or steam.

A Zr fire is not necessary for noble gases (Xe, Kr) or volatiles (Cs, I, . . .) to escape. The fuel only needs to be breached (cracked or somehow perforated - localized corrosion/oxidation or ruptured hydride blister) to allow the gases and volatiles to escape.

The hydrogen explosions likely came from the hydrogen produced in corrosion of the Zircaloy cladding - unless there is another fuel source. A Zr fire in air would not produce hydrogen.

Now a Zr fire (in air) would increase the likelihood of fuel particles escaping from the spent fuel pool, but there would be significant contamination at the plant site if that was the case. I'm not sure the evidence indicates that is the case.

In units 1, 2 and 3, the source of hydrogen in considered to be the core. The SFP had older cooler fuel. In Unit 4, the core had been offloaded to spent fuel pool. It had about 3.5 months of cooling, in addition to what else was in the pool. The fuel in the SFP would have to be the source of hydrogen, unless there is some other source.

 

[Gilles]

The Zircaloy-2 cladding surrounds the ceramic pellets, but it has certainly breached (cracked or corroded) and MAY have melting IF the cladding temperature reached ~1800°C.
The fuel rods sit between stainless steel (SS304) tie plates. Stainless steel melts at ~1400-1450°C. Only if cooling is insufficient, i.e., stagnant superheated steam could the steel or Zircaloy reaches those temperatures. If water is present - it boils, so those temperatures would not be realized. If the steam is 'wet' or 'moist', then those temperatures are not realized.

Nevertheless, before those temperatures are reached, the Zircaloy-2 would chemically react with the steam/water as in oxidation/corrosion. In that case, the Zircaloy-2 cladding may open up through cracks or ruptured hydride blisters, in which case the water/steam can communicate with the ceramic pellets. That's how the fuel particles and fission products get out.

Astronuc, I was told that massive reaction of Zircaloy with water required 1200°C to produce hydrogen, do you confirm ? so at least this temperature has been reached, probably in all active reactors 1-3.
Also, high temperatures of 300-400°C have been measured when the pressure was only a few bars - clearly indicating overheating of the steam , much probably due to red-hot fuel rods out of water.
I assume that if the water level is high enough, thermal conductivity may prevent the emerged part of the rods to warm above 1000 °C - do you have an idea of how much must be out of water to reach such temperatures ?

 

[Astronuc]

Astronuc, I was told that massive reaction of Zircaloy with water required 1200°C to produce hydrogen, do you confirm ? so at least this temperature has been reached, probably in all active reactors 1-3.

The oxidation reaction is a function of temperature - it is described by an Arrhenius function. The reaction increases exponentially with temperature, i.e., the greater the temperature, the faster the reaction.

Also, high temperatures of 300-400°C have been measured when the pressure was only a few bars - clearly indicating overheating of the steam , much probably due to red-hot fuel rods out of water.
I assume that if the water level is high enough, thermal conductivity may prevent the emerged part of the rods to warm above 1000 °C - do you have an idea of how much must be out of water to reach such temperatures ?

The exact temperature of the fuel depends on the flow and moisture of the steam. As far as I know, that matter is being investigated, but I don't know the details.

I lack the details of the water levels in the cores (and SFPs) over the last two weeks. We do know that the water levels in the cores dropped pretty quickly, and the cores may have been ~2/3's uncovered. The explosions at U1 and U3 occurred pretty soon after the loss of power at the site. After the seawater was introduced, I'm not sure how much of the core was recovered and for how long. As long as some water is present in the core, that portion would not melt. It might corrode, but it wouldn't melt.

 

[divmstr95]

Zr hydride is essentially ZrH₂. When Zr in Zr-2 or Zr-4 reacts with H₂O to form ZrO₂, some hydrogen is taken into the Zircaloy cladding. Zr-2 tends to take up a bit more the Zr-4, ostensibly due to the presence of Ni in Zr-2, which is not much in Zr-4. The amount taken up is less than 25%, and typically ~17% for Zr-4 and a bit higher for Zr-2. This is because the H₂O breaks down in the oxide, and the O has to diffuse to the Zr/ZrO interface to continue the oxidation process. The rest of the hydrogen is free to wander off in the water or steam.

A Zr fire is not necessary for noble gases (Xe, Kr) or volatiles (Cs, I, . . .) to escape. The fuel only needs to be breached (cracked or somehow perforated - localized corrosion/oxidation or ruptured hydride blister) to allow the gases and volatiles to escape.

The hydrogen explosions likely came from the hydrogen produced in corrosion of the Zircaloy cladding - unless there is another fuel source. A Zr fire in air would not produce hydrogen.

Now a Zr fire (in air) would increase the likelihood of fuel particles escaping from the spent fuel pool, but there would be significant contamination at the plant site if that was the case. I'm not sure the evidence indicates that is the case.

In units 1, 2 and 3, the source of hydrogen in considered to be the core. The SFP had older cooler fuel. In Unit 4, the core had been offloaded to spent fuel pool. It had about 3.5 months of cooling, in addition to what else was in the pool. The fuel in the SFP would have to be the source of hydrogen, unless there is some other source.

I think we are on the same page regarding the possibility of a Zr fire in the SFP.

Regarding contamination levels the AMS data supports a fire. The difference between the dispersion model of an AGL release of fission products (in steam) and a fire is that a fire does not usually cause high contamination levels in the immediate vicinity but rather higher levels downwind. This is due to the difference in energies associated with the release (the dispersion model shows the contamination "hops").

 

[shogun338]

News sites are reporting now that unit#2 core has melted through the bottom of the pressure vessel down to the floor of the drywell .

 

[Astronuc]

I think we are on the same page regarding the possibility of a Zr fire in the SFP.

Regarding contamination levels the AMS data supports a fire. The difference between the dispersion model of an AGL release of fission products (in steam) and a fire is that a fire does not usually cause high contamination levels in the immediate vicinity but rather higher levels downwind. This is due to the difference in energies associated with the release (the dispersion model shows the contamination "hops").

Yes - it's about the nature of the fire and dispersion. However, a fire is not necessary for dipersion of gases or volatiles. Gases escape on their own, and volatiles can be carried by steam or air currents.

A Zr-fire would imply a significant exothermic reaction with temperatures of about 3000 K or greater - white hot - like a welder's arc. That would have lit up the containment and area. I don't think we saw that.

I believe the hydrogen explosion was over the containment - above the pool. The hydrogen was attributed to the core, not the SFP in Units 1, 2, and 3. In Unit 4, it has been assumed that the hydrogen did come from SFP - and probably the fuel that was offloaded last November from the core.

 

[Astronuc]

News sites are reporting now that unit#2 core has melted through the bottom of the pressure vessel down to the floor of the drywell .

Based on what evidence?

Please be careful about making such claims, and please avoid making unverified or unsubstantiated claims.

Please cite one's source.


See also - http://www.world-nuclear-news.org/RS_Trench_water_under_investigation_2903111.html

 

[timeasterday]

News sites are reporting now that unit#2 core has melted through the bottom of the pressure vessel down to the floor of the drywell .

What "news sites?"

Please provide a link to the source. I am not seeing anything out there.

 

[Joe Neubarth]

Based on what evidence?

Indeed!

I have the television on in the background and have not heard that story.

I Google News stories and there is no mention there.

 

[shogun338]

Based on what evidence?

Here is a link to one of the stories . http://www.guardian.co.uk/world/2011/mar/29/japan-lost-race-save-nuclear-reactor

 

[|Fred]

google gave me:
Richard Lahey, who was head of safety research for boiling-water reactors at General Electric when the company installed the units at Fukushima, told the Guardian workers at the site appeared to have "lost the race" to save the reactor ../..
the indications we have, from the reactor to radiation readings and the materials they are seeing, suggest that the core has melted through the bottom of the pressure vessel in unit two, and at least some of it is down on the floor of the drywell

to be noted:
Richard Lahey in an other interview http://live.washingtonpost.com/fukushima-nuclear-expert.html said on the 21th regarding melting:
"It is not likely as long as there is water in the reactor pressure vessels. The only concern that i have is long term cooling using salt water, since after a while the salt may plug up the fuel. Anyway, if the lower head of the vessels does melt the corium released will interact with the concrete basemat and radioactivity will be released to the environment (not likely in this accident)."

=> Did he get unreleased evidence regarding water level in the RPV ? I do not think so , in the Guardian article he formulate a speculation "I hope I'm wrong etc"