Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[meadowlark]

A couple of speculative questions:
1) Could the "explosion" reported within the #2 containment possibly be similar to a steam hammer event? Rapidly condensing steam vapor in the torus or elsewhere within the containment could have rocked the walls and resulted in a pressure drop. This would not necessarily mean containment was breached.
2) If fuel rods melt or crumble and drop to the bottom of containment or the spent stoage pools, could the fuel mass regain criticality because there would no longer be control rod moderation?

 

[Bob S]

1) Could the "explosion" reported within the #2 containment possibly be similar to a steam hammer event? Rapidly condensing steam vapor in the torus or elsewhere within the containment could have rocked the walls and resulted in a pressure drop. This would not necessarily mean containment was breached.

Gaseous hydrogen mixed with air is a very violent explosive. A hydrogen explosion blew part of the reinforced concrete roof off the experimental area at the Cambridge Electron Accelerator in July 1965. A few liters of spilled liquid hydrogen mixed with the air in the experimental hall, about 30 meters wide by 60 meters long, and was ignited by a spark. One person died, and another seriously injured. See photo in

http://www.sciencemag.org/content/150/3698/866.full.pdf

Bob S

 

[bondboy]

Generally the racks in which spent fuel is stored contain neutron absorbing materials, so if for some reason, the pool was flooded by pure water, the SFP would not go critical. The spent fuel is generally depleted - but each assembly could have some residual positive reactivity, especially as Xe-135 decay. Xe-135 is one of the strongest neutron absorbers, which during operation is in equilibrium - at steady-state, it's production rate = depletion rate.

http://en.wikipedia.org/wiki/Xenon-135

I believe when Unit 4 was shutdown, they did a full-core offload, which means that there is some fuel which still has considerable life left. That would compound the heat burden on the pool, and it would add positive reactivity in the pool.

If TEPCO is concerned, then I'd be concerned too. However, I am not familiar with the practices or their current SFP configuration.

Reactivity is a measure of how a material can contribute to criticality. The multiplication factor, k, is a way to measure criticality. k = 1 means critical (constant power), k < 1 means subcritical (neutrons (neutron flux) and power decreases), and k > 1 means supercritical (neutrons (flux) and power increases).

Positive reactivity increases k, while negative reactivity decreases k.

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

In the spent fuel pool, we want k < 1, always!

http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/u235chn.html#c4
http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/u235chn.html
http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/fiscon.html

See chapter 18 of this book
Nuclear engineering handbook By Kenneth D. Kok
http://books.google.com/books?id=EMy2OyUrqbUC&pg=PA596&lpg=PA596
https://www.amazon.com/dp/1420053906/?tag=pfamazon01-20

Thank you for the response, i'll look up the information you attached shortly.

As a follow up, keep in mind I have no formal training on the material so please excuse my ignorance and I'm sorry if the answers are in the link you provided.
If unit 4 was in shutdown, they did a full-core offload after only one or two cycles and the cells where properly stored within the SFP (subcritical); can you guesstimate (given the fuel used and time since the shutdown) the amount of fuel left in the cells and what the consequences are during the different stages of the coolant failure they are experiencing given that the SFP is outside of the reactor containment unit? What happens when the pool "runs dry" as is now being reported? How fast does the fuel go from subcritical>critical>supercritical? What are the environmental impacts during each stage?
Simple logic tells me that the SFP is totally exposed to the environment given the latest attempts to refill the SFP (their dropping water from helicopters and spraying with water cannons). They started this at roughly 9am their time. This seems like a last ditch effort to me to try and cool the fuel within the SFP and that they are facing a worst case scenario (exposed SFP that is bone dry) yet the radiation levels being reported don't seem to be catastrophic.

Thanks,
Mike

 

[Astronuc]

Let's take unit 2 for example. It is rated at 784 MWe (MegaWatt electric). Let's say that it is 30% efficient, that would mean it is rated at just over 2,600 MWt (MegaWatt thermal). 0.5% of 2,600 is 13 MWt, or 13 million Watts of thermal energy. This is still a considerable amount of energy that needs to be removed via heat transfer.

Ideally water is present, as water is superior to air or steam when it comes to removing heat from an object it comes in contact with. If water is not present, the fuel cannot remove the heat as fast as it produces it, which causes its temperature to rise until it finds equilibrium of heat produced to heat transferred, (energy balance), or it reaches melting point of the material.

This might help.

       BWR  
Unit  Type      Assys   MWt (original)
  1      3       400     1381
  2      4       548     2381
  3      4       548     2381
  4      4       548     2381
  5      4       548     2381
  6      5       764     3293

Based on available data, TEPCO did not uprate those units from the original capacity.

 

[Thermalne]

This question might have been addressed before. I didn't see it though.

What do you (Astronuc and other professions in the Nuclear Power field) believe is the future of the Fukushima Daiichi units that are affected by this incident?

Such as do you believe they will be decommissioned? Or repaired for future operation?

 

[AtomicWombat]

I think that makes sense. I'm rough guessing here as I don't have any tech. specs. in front of me, and no calculator, (sorry for any gross errors). Assuming a 10 ft. diameter x 25' tall vessel, the volume is approximately 15,000 gallons. 1.5 gallons/sec = 5,400 gallons/hr. I think I read earlier on that they thought the RPV would boil down in a few of hours if no water was added. 15,000 / 5,400 = < 3hrs.

This article from the Union of Concerned Scientists explains the boild off rate well.http://allthingsnuclear.org/post/3859682324"

 

[Angry Citizen]

What do you (Astronuc and other professions in the Nuclear Power field) believe is the future of the Fukushima Daiichi units that are affected by this incident?

This has been answered too. The seawater+boric acid combo used to cool 1-3 has essentially eliminated any chance for their future use. 4-6 are anyone's guess though.

 

[Astronuc]

Thank you for the response, i'll look up the information you attached shortly.

As a follow up, keep in mind I have no formal training on the material so please excuse my ignorance and I'm sorry if the answers are in the link you provided.
If unit 4 was in shutdown, they did a full-core offload after only one or two cycles and the cells where properly stored within the SFP (subcritical); can you guesstimate (given the fuel used and time since the shutdown) the amount of fuel left in the cells and what the consequences are during the different stages of the coolant failure they are experiencing given that the SFP is outside of the reactor containment unit? What happens when the pool "runs dry" as is now being reported? How fast does the fuel go from subcritical>critical>supercritical? What are the environmental impacts during each stage?
Simple logic tells me that the SFP is totally exposed to the environment given the latest attempts to refill the SFP (their dropping water from helicopters and spraying with water cannons). They started this at roughly 9am their time. This seems like a last ditch effort to me to try and cool the fuel within the SFP and that they are facing a worst case scenario (exposed SFP that is bone dry) yet the radiation levels being reported don't seem to be catastrophic.

Thanks,
Mike

We will hopefully get the technical details for the fuel and SFP.

The fuel assemblies have some positive reactivity based on their enrichment, burnup and configuration. However, it's the combination of the spent fuel racks (which contain a neutron absorber) and the fuel. I would expect that the fuel offload includes once-burned fuel, twice-burned, and I would guess some thrice-burned for discharge. I'll have to do some basic guesstimates, but I'd really need batch sizes.

 

[Thermalne]

This has been answered too. The seawater+boric acid combo used to cool 1-3 has essentially eliminated any chance for their future use. 4-6 are anyone's guess though.

Thank you

 

[Astronuc]

This question might have been addressed before. I didn't see it though.

What do you (Astronuc and other professions in the Nuclear Power field) believe is the future of the Fukushima Daiichi units that are affected by this incident?

Such as do you believe they will be decommissioned? Or repaired for future operation?

Boiling saltwater in SS304 is not a good idea. Basically, I expect those units are history. The fuel and control rods in Unit 1, 2 and 3, are likely damaged, and therefore waste. The stainless steel internals and control rod drive systems are likely compromised. They will have to be decontaminated, and then disposed of properly.

The other big question is the contamination around and in the units that could preclude any meaningful recovery work.

Those units could be mothballed for years, and at some point there will be a big decomissioning project.

 

[Thermalne]

I think a better question is then,

Do you think the plant site could be reused for future reactors?

 

[Astronuc]

I think a better question is then,

Do you think the plant site could be reused for future reactors?

We shall see.

There were plans for Unit 7 and 8, both being ABWRs. I suspect those plans are suspended indefinitely until the current crisis is resolved.

TEPCO has probably lost credibility with the government and public. The release of fission products to the environment has violated the obligation to the protect the public from exposure to radiation. The sacred trust is broken.

 

[Thermalne]

We shall see.

There were plans for Unit 7 and 8, both being ABWRs. I suspect those plans are suspended indefinitely until the current crisis is resolved.

Again thank you for your information. It's just concerning seeing how this might kill the progress we are making in the states towards a nuclear revival.

 

[Astronuc]

Again thank you for your information. It's just concerning seeing how this might kill the progress we are making in the states towards a nuclear revival.

It certainly makes it more difficult.

 

[turbo]

I think a better question is then,

Do you think the plant site could be reused for future reactors?

There are still lots of facilities and equipment at that site, even if the reactors are toast and are entombed or monitored until they can be dismantled.

There is a strong rejection of any coal-based power here in Maine - especially along the coast where tourism is king. Still, after Maine Yankee was decommissioned, there were plans floated (one just ~2-3 years ago) to establish a coal-fired power plant in Wiscassett and use as much of the Maine Yankee infrastructure as possible.

Given the recent history of that installation, I'd personally offer low odds on any new reactors on that site. And hauling coal to Japan is not going to be cheap.

 

[Bob S]

Given the recent history of that installation, I'd personally offer low odds on any new reactors on that site. And hauling coal to Japan is not going to be cheap.

Looks like Japan will be getting Siberian coal, LNG, and maybe even electricity from Russia, according to Prime Minister Dmitry Medvedev:

"Our moral duty is to help [Japan] in this situation," Mr. Medvedev said Monday as he ordered Deputy Prime Minister Igor Sechin to look into ways of redirecting up to 6,000 megawatts of electrical power from Russia's far east, and arrange delivery of an additional 200,000 tons of liquified natural gas (LNG) plus unspecified amounts of Siberian coal over the next two months.

See http://www.csmonitor.com/World/Europe/2011/0315/Japan-gets-coal-gas-from-historic-rival-Russia

Bob S

 

[myth_kill]

thats really helpful coming from a country like russia who generally are well known for keeping to themselves

 

[Maclomer]

Let's take unit 2 for example. It is rated at 784 MWe (MegaWatt electric). Let's say that it is 30% efficient, that would mean it is rated at just over 2,600 MWt (MegaWatt thermal). 0.5% of 2,600 is 13 MWt, or 13 million Watts of thermal energy. This is still a considerable amount of energy that needs to be removed via heat transfer.

Ideally water is present, as water is superior to air or steam when it comes to removing heat from an object it comes in contact with. If water is not present, the fuel cannot remove the heat as fast as it produces it, which causes its temperature to rise until it finds equilibrium of heat produced to heat transferred, (energy balance), or it reaches melting point of the material.

Promecheng - Thanks for the good answer - taking the BBC figures, the rate of decay is extremely fast in the beginning and then it slows down - I assume because it is the sum of several exponentials. Given that it is .5% at the end of Day 1, I therefore assume it will still be a significant number at Day 6; using your numbers and a guess I suppose we can't count on a decline of significant heat production for quite a few days yet?

 

[MadRocketSci2]

The Japanese have started operations to re-fill the spent fueling pools. Radiation levels over the pools at 1000ft are in the milliSv/hr range.

I'm beginning to wonder though if this is unnecessary: The spent fuel shouldn't be able to get hot enough to cause any damage - certainly not enough to melt.

Vanadium melts at 2183K
The fuel is cladded and encased in neutron absorbing substances.

Even if we assumed that they had a 50cm cubic block of material in one place, and radiation was the only means of balancing the heat produced, the equilibrium temperatures shouldn't be anywhere near that:

Back of the envelope calcs:
50cm cubic block of spent fuel, 40 days old

LaMarsh, pg 415 suggests a rough exponential relationship for the power ratio in fuel over infinite cooldown time: y = 1.0023E-02exp(-2.3049E-07*x) y is power ratio, x is seconds



0.5 emissivity (pulled out of ***)

reactor operating at 50W/cm^3 initially, 0.225 W/cm^3 in fuel after 40 days.

Equilibrium temp: 900K

That's hot, but I don't see how it is hot enough to do anything other than light fuel oil on fire. It shouldn't be enough to melt the cladding. NEI is of the opinion that vanadium fires are impossible to start, requiring even higher temperatures than melting down the vanadium.


I have to wonder if people aren't risking their lives right now due to an overreaction. If these calcs produce anything resembling reality, they should probably just leave it sit.

 

[TCups]

Sorry, can't immediately quote the reference, but in addition to the spent fuel rod assemblies in the SFP at unit 4 there were "Hot" fuel rod assemblies taken from the core when they shut down the reactor for maintenance in 2010.

I also read somewhere that the helicopter water drop tried initially was aborted perhaps because the roof was still covering the SFP at unit 4.

Again, I post this picture with my personal interpretation of what I am seeing at unit 4. I now notice a subtle, but definite faint cloud of darker, sooty smoke coming from the square hole or perhaps the ground below, and rising diagonally across the tower at the right. And if there is still water, boiling, then where is the steam? And if not, could it get hot enough to crumble concrete, melt structural steel, and start secondary fires in things like the oil in the generators? What else might cause a square hole in the side of the building with smoke coming out of it? Inquiring minds want to know.

all is not well at unit 4, IMO

 

[AtomicWombat]

Promecheng - Thanks for the good answer - taking the BBC figures, the rate of decay is extremely fast in the beginning and then it slows down - I assume because it is the sum of several exponentials. Given that it is .5% at the end of Day 1, I therefore assume it will still be a significant number at Day 6; using your numbers and a guess I suppose we can't count on a decline of significant heat production for quite a few days yet?

This image from the UCS site shows the cooling rate settles to a simple exponential after about 1 day:

Here is the accompanying text:
"Figure 2 shows the typical rate at which heat from a shut-down reactor core boils away water when the cooling systems are not functioning. The vertical axis shows the boil-off rate in gallons per minute. The horizontal axis shows the time, in days, since the reactor was shut down. Even a week after being shut down, the heat from a reactor core boils water at a rate of nearly 60 gallons per minute. The boil-off rate declines with time while the rate of radioactive release decreases.

The reactor core resides in the lower portion of the reactor pressure vessel (see Figure 3). The normal water level inside the reactor vessel is roughly 196 inches, or 16 feet, above the top of the reactor core. The nuclear fuel is protected against damage caused by overheating as long as it remains covered with water. A rough rule of thumb is that it takes 200 gallons of water to raise or lower the level inside the reactor pressure vessel by 1 inch.

For the boil-off rate of 60 gallons per minute a week after shut down, it takes around 200 seconds for the water level inside the reactor pressure vessel to drop an inch. If the reactor cooling system fails one week after the reactor was shut down with the water level inside the reactor vessel is at its normal level, it would take approximately 11 hours for boil-off to reduce the water level down to the top of the reactor core."

Source:
http://allthingsnuclear.org/post/3859682324/reactor-core-cooling"

 

[AtomicWombat]

Vanadium melts at 2183K
The fuel is cladded and encased in neutron absorbing substances.

Even if we assumed that they had a 50cm cubic block of material ...

Back of the envelope calcs:
50cm cubic block of spent fuel, 40 days old

LaMarsh, pg 415 suggests a rough exponential relationship for the power ratio in fuel over infinite cooldown time: y = 1.0023E-02exp(-2.3049E-07*x) y is power ratio, x is seconds
...


0.5 emissivity (pulled out of ***)

reactor operating at 50W/cm^3 initially, 0.225 W/cm^3 in fuel after 40 days.

Equilibrium temp: 900K

That's hot, but I don't see how it is hot enough...

Firstly its Zirconium NOT Vanadium.

Unfortunately for now I'll have to match your BOTE calculation with my own BOTE calculation.

From:
http://allthingsnuclear.org/post/3859682324/reactor-core-cooling
Assume the fuel heat is equivalent to a boil-off rate of 50 gal/min (approx 10-20 days after removal from reactor).
This is equivalent to about 8 MW.
Using the stefan-Boltzman Law: Power = 5.67E−8*T^4, one square metre of Zironium will give off about 1.15 MW of heat (as a black body) at its melting T = 2128K. That requires about 8/1.15 say 6 m^2 of unobstructed radiation area to dissipate.

But we don't need to reach 2128K, we only need to reach 1500 K where zirconium reacts exothermically in air or steam. (Note zirconium is protected by a passivating layer that breaks down at this temperature.) The oxygen-Zr reaction gives off 12MJ/kg; the H2O-Zr reaction gives off 5.8MJ/kg.

One square meter of Zr at 1500K radiates 5.67E−8*(1500)^4 = 0.28 MW. 8/0.28 ~ 28 metres squared to get rid of 8MW. To maintain the spent fuel at this temp it would have to have an effective unobstructed radiation area to a black body receiver of 28 square metres. I don't know for sure how tightly the bundles are packed (what is the external area), but I doubt there is enough heat transfer. It is possible that convection could solve this but only after an explosion blowing a hole in the external wall and allowing enough air flow.

 

[TCups]

This image from the UCS site shows the cooling rate settles to a simple exponential after about 1 day:

Here is the accompanying text:
"Figure 2 shows the typical rate at which heat from a shut-down reactor core boils away water when the cooling systems are not functioning. The vertical axis shows the boil-off rate in gallons per minute. The horizontal axis shows the time, in days, since the reactor was shut down. Even a week after being shut down, the heat from a reactor core boils water at a rate of nearly 60 gallons per minute. The boil-off rate declines with time while the rate of radioactive release decreases.

The reactor core resides in the lower portion of the reactor pressure vessel (see Figure 3). The normal water level inside the reactor vessel is roughly 196 inches, or 16 feet, above the top of the reactor core. The nuclear fuel is protected against damage caused by overheating as long as it remains covered with water. A rough rule of thumb is that it takes 200 gallons of water to raise or lower the level inside the reactor pressure vessel by 1 inch.

For the boil-off rate of 60 gallons per minute a week after shut down, it takes around 200 seconds for the water level inside the reactor pressure vessel to drop an inch. If the reactor cooling system fails one week after the reactor was shut down with the water level inside the reactor vessel is at its normal level, it would take approximately 11 hours for boil-off to reduce the water level down to the top of the reactor core."

Source:
http://allthingsnuclear.org/post/3859682324/reactor-core-cooling"

Perhaps. But as a radiologist, I make my living with my eyes, interpreting what I see. Here is a picture from the net of the Fukushima (nomen, omen?) of units 3 and 4, dated October 3, 2008. Note the location of the berm (X).

another view, after unit 3 has exploded, but before the explosion and fire at unit 4:

http://media.kansas.com/smedia/2011/03/14/20/495Japan_Earthquake.sff.slideshow_main.prod_affiliate.80.jpg

Some brave soul peeked out from behind that berm (X) in the first photo to take this picture (annotated with my personal interpretations).

Presuming the access tunnel (1) in the diagram below is coming from the building next to the reactor in the first photo, which seems reasonable, that square hole in the side of unit 4 is, in fact, precisely where the diagram puts the SFP's location (3).

Do you think the roof of the Unit 4 building still looks intact? If there is still (boiling?) water in the SFP, where is the steam? Instead, I see a faint cloud of dark, sooty smoke wafting from the square hole with the red dots inside at an angle across the tower to the right, in the last photo. I hope I am wrong, but my eyes tell me something different from the official reports you quote.

 

[AtomicWombat]

Hi TCups

Perhaps. But as a radiologist, I make my living with my eyes, interpreting what I see.[/PLAIN]

Presuming the access tunnel (1) in the diagram below is coming from the building next to the reactor in the first photo, which seems reasonable, that square hole in the side of unit 4 is, in fact, precisely where the diagram puts the SFP's location.

Agree - I originally posted that picture asking if that was where the SFP is located. The best interpretation I can make is that the missing panel is where the SPF was located, although behind another wall deeper in the building. The hydrogen was sourced from the zirconium-steam reaction and was most concentrated above the SPF. Not surprisingly the building was breached next to the SFP during the subsequent explosion. I believe interpretation of this phoito is what underlies Gregory Jaczko's testimony to congress that "there was now little or no water in the pool storing spent nuclear fuel at the No. 4 reactor of the Fukushima Daiichi Nuclear Power Station, leaving fuel rods stored there exposed and bleeding radiation into the atmosphere."
http://www.nytimes.com/2011/03/17/world/asia/17nuclear.html?hp

I've put in a subsequent post where I suggest there is enough heat for the fuel assemblies to melt, particularly if there is not enough convection cooling.

Do you think the roof of the Unit 4 building still looks intact? If there is still (boiling?) water in the SFP, where is the steam? Instead, I see a faint cloud of dark, sooty smoke wafting from the square hole with the red dots inside at an angle across the tower to the right, in the last photo. I hope I am wrong, but my eyes tell me something different from the official reports you quote.

Whilst I don't believe anyone can be sure, the tongue of material coming out of the large hole has the appearance of a molten metal-slag mix. Once it started leaking from the building it was exposed to convective cooling which solidified the "crust". Was it you who first suggested this?

I'm less convinced about the red dots. However I am far more concerned about reactor 3 than the authorities. I suspect the steam cloud is coming from what remains of the reactor core. The explosion last Monday was directed strongly vertically suggesting to me it originated from deep within the containment structure. It clearly carried substantial solid material to a height of 400-500 metres. Whilst I can't be sure this may have been due to a melt-down of the fuel rods in reactor 3. They melted through the reactor floor (1500 Celsius) and fell into the flooded "dry-well" below. This triggered a large steam- zirconium-water-hydrogen explosion. I suspected this not only blew the concrete top off the containment, it also blew most of the reactor contents out of the reactor.

These are my best visual interpretations based on what I know of the reactor chemistry (I'm a former chemical engineer) and careful observations. In the absence of honesty from TEPCO and the Japanese government what else can you do?

 

[AtomicWombat]

Some brave soul peeked out from behind that berm (X) in the first photo to take this picture (annotated with my personal interpretations).

This appears to be a wide-angle picture taken from the same location at the same time. The photographer was even further than the berm:

 

[kfmfe04]

If the reactors are assumed to be lost, can some material be dumped on top of the entire site so that should explosions occur, the spread of radioactive contamination can be limited?

From my layman's viewpoint, it seems to me that officials are just reacting to what is happening rather just assuming the worst and doing what they can to limit a worst possible outcome, but maybe there are no better solutions? (I'm certainly not an expert in this area).

 

[Pythagorean]

I haven't read through all 20 pages here, but I'm hoping that b) is a unique question:

what are the chances of both a) and b) or a) an c) happening if:

a) a significant meltdown occurs
b) radiation taking the Kuro Siwo (an ocean current) to Alaska
c) significant levels making it to Alaska via atmospheric transport

I would think the ocean currents are much slower, more violently diffusive carriers and wouldn't effectively deliver radiation doses to Alaska's coast.

Would half-lives even be long enough for the journey in either case in post-meltdown?

 

[marwood]

Informative article on the activities to control the reactor accidents at the Japanese nuclear plants:

Below is a summary [for the general public] on the Fukushima situation prepared by Dr Josef Oehmen, a research scientist at MIT, in Boston.

He is a PhD Scientist, whose father has also extensive experience in Germany ’s nuclear industry.

~~~~~~~~~~~~~~~~~~
What happened at Fukushima
I will try to summarize the main facts. The earthquake that hit Japan was 7 times more powerful than the worst earthquake the nuclear power plant was built for (the Richter scale works logarithmically; the difference between the 8.2 that the plants were built for and the 8.9 that happened is 7 times, not 0.7). So the first hooray for Japanese engineering, everything held up...

Informative? or opinion piece? Dr. Josef Oehman is not trained nor an expert in nuclear plant operation or technology. His academic biography states:

''The main research interest of Dr. Josef Oehmen is risk management in the value chain, with a special focus on lean product development. Risk management allows companies to design and achieve the optimal risk-return balance in their portfolio of activities, successfully take entrepreneurial risks, increase their performance, and focus their attention on where it is needed most.

Josef is also involved in the cooperation project between the King Fahd University in Saudi Arabia and MIT, focusing on research in product development and risk management. He is a member of the supervisory board of Climate InterChange, a company developing and implementing projects for the reduction of carbon emission. Before joining LAI, he was the Director for Supply Chain Management at the ETH Center for Enterprise Sciences (BWI) at the Swiss Federal Institute of Technology (ETH Zurich).

He wrote his PhD thesis at the ETH Zurich on the topic of Supply Chain Risk Management with a focus on China. In his research, he investigated and optimized the integration and cooperation between Swiss companies and their Chinese suppliers.

Josef worked as Assistant to the CTO of SIG Holding AG and in parallel pursued an international MBA at the Collège des Ingénieurs in Paris. He was intensely involved in corporate-wide Technology and Innovation Management and was responsible for technology projects. He studied mechanical engineering at the Technical University of Munich, majoring in Product Development and Production Management. He wrote his diploma thesis at LAI on Risk Management in Product Development.''

http://lean.mit.edu/about/lai-structure/faculty-researchers-and-staff/oehmen-josef

 

[CAC1001]

Could this event be worse than Chernobyl, or is that scaremongering?

 

[AtomicWombat]

If the reactors are assumed to be lost, can some material be dumped on top of the entire site so that should explosions occur, the spread of radioactive contamination can be limited?

From my layman's viewpoint, it seems to me that officials are just reacting to what is happening rather just assuming the worst and doing what they can to limit a worst possible outcome, but maybe there are no better solutions? (I'm certainly not an expert in this area).

Agree kfmfe04,

There are obvious practical difficulties. The sheer magnitude of the clean-up task is incredible but unavoidable.

I haven't really thought through the best way to go about it, but I suspect that once the Japanese get their act together (& stop listening to TEPCO & start being honest with their own people), we will see a typically Japanese response. I expect that will involve large robotic Earth moving and construction machinery.

By way of example, Rio Tinto in Australia is already using Komatsu 930E trucks with autonomous control (290 tonne capacity) for iron ore mining - these are controlled remotely from Perth (>1000 km away). They also have other autonomous equipment, such as drills and trains.
http://www.womp-int.com/story/2010vol01/story026.htm"

This will take months to do and the difficulties are enormous - not least being the need to harden such vehicles against radiation. It will be incredibly expensive.

Disclaimer: I have no association with Rio Tinto or Komatsu.

 

[Borek]

Could this event be worse than Chernobyl, or is that scaremongering?

While the situation is serious, so far there is no reasons to believe radioactive contamination of similar scale is possible. Situation is dynamic, so it may change, but as of now such comparisons are scaremongering, I have no doubts about it.

 

[Borek]

the need to harden such vehicles against radiation

That will be a serious problem, high levels of ionizing radiation render electronics useless. From what I remember they were trying to use some early robots in Chernobyl, at least to send cameras for a situation assessment, it didn't work as planned.

 

[AtomicWombat]

Could this event be worse than Chernobyl, or is that scaremongering?

Yes it is quite possible in my view.

There are obvious differences. The most notable is that the Chernobyl reactor used a graphite moderator. Once the initial explosion exposed the graphite to the outside air it burned (for many days) and lofted radioactive material into the air. It would be hard to find a more efficient method of spreading radioactive material from a damaged reactor. It is quite unlikely (in my view) that the radiation at Fukushima will spread as rapidly as in Chernobyl.

On the other side of the ledger. Four reactors have potentially been breached and much more nuclear material is exposed in the spent fuel rods. (I can find no reference to spent fuel rods at Chernobyl - can someone help?) So, it would appear much more nuclear material is involved. Also in this region the population density is much higher than near Chernobyl. The world's largest city is only 250 km away. In time the wind and rain will spread the radiation and create a huge area of contamination.

I dearly hope this is not the outcome.

 

[mattm2]

I am scientifically impaired; however, I have the following questions:

1. Was there no one thinking ahead in this crisis in that: someone had to know that exposing the spent fuel rods to air was not good; and, that the SFP water was increasing in temperature. I believe hot water evaporates faster than cold water. At any rate, it should be easy to calculate/estimate (based on surface area, ambient air temperature/humidity, and temp. of water) how fast the SFP water would evaporate. Additionally, before radiation got real bad: they could have been sending someone to check on the number 4 SFP water level. If the water level started to get low: run a 2 or 3 inch hose(s) to the tank and add sea water to it. It sounds like there were not enough people putting their minds on the problem and not enough workers to carry out the proper tasks. Now the radiation is too high to run a hose to the number four tank. I guess it is easy to be an after-the-fact armchair critic.

2. How many gallons of water do the SFPs hold? If they are quite large; then, I do not think that a bambi bucket helicopter drop would do much good. 7.5 metric tons of water is only about 2000 gallons--and most of that missed.

3. Given the present situation, what are all the ways to get water into the Spent Fuel Pools (SFPs) besides having a volunteer suicide mission?

 

[dave2004]

Here is some information about the spent fuel stored in TEPCO facilities:
http://www.zerohedge.com/sites/default/files/Containment%20Pools.pdf
Maybe this helps you to make a better guess at what is going on right now.