Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Astronuc]

Do you get radioactive Cesium and Iodine released without melting of the core? I thought not. And if there were an internal explosion followed by a drop in pressure in the coolant and a rise in radiation levels, can that imply some other more likely scenario?

Yes - Cs and Iodine are volatile at fuel operating temperatures, and if the ceramic fuel gets hot enough, the Cs and I can come out into the gap between pellet and cladding. If the cladding is breached - i.e., cracks - then Cs and I can be carried out into the coolant. Xe and Kr obviously come out.

In normal operation, when fuel fails - cladding is breached - the coolant can enter the fuel rod. The UO2 oxidizes which reduces the thermal conductivity, which increases temperature, which causes Xe, Kr, Cs, I and some other volatile elements to migrate out of the cermamic. Oxidation of UO₂ also increases the diffusivity of some fission products - particularly noble gases.

So once can release Cs and I without melting the fuel.

Also - I beta decays to Xe, which beta decays to Cs, so Cs, in addition to being a direct fission product, is also a daughter product of Xe decay.

 

[falcon32]

No, the radiation source is independent of geometry, and only dependent on the fission products or nature of the radionuclides decaying.

But wouldn't the neutron intensity increase by changing from spaced rods to an agglomerated molten puddle?

 

[Reno Deano]

It is sad state of affairs that the news media hypes the reactor problems when thousands are dead and missing, and 10 of thousands people homeless in Japan and suffering. If all three BWRs had a full core melt the carnage would not be a tenth as bad what is already facing those currently trying to survive.

 

[Astronuc]

If so, this seems to be the main danger.. that as the fuel melts, they would pool in one area and become critical again. But Astronuc said the rods have to be arrange in some symmetrical configuration to become critical.. so I wonder if the melted pooling fuel at the floor can fission again (with the control rods left above). Astronuc?

I doubt the fuel will melt - but it might break into pieces - which will be trapped by the channels and bottom tie plate. The control rods may still be intact.

However, even if the fuel did melt though the bottom tie plate - then the steel pad - it would fall between the control rod drive guide system and still not achieve criticality.

The term 'core melting' is used losely by some in the industry, and certainly by those outside of industry. According to my understanding of the term, core melting may not have happened - it has been very limited. If cooling is achieved, then further core melting is prevented.

However, there is still the matter of the fission products in containment and how much will be released and how.

 

[Astronuc]

But wouldn't the neutron intensity increase by changing from spaced rods to an agglomerated molten puddle?

No. And in fact, as far as I can tell - there will not be a molten puddle.

If the ceramic fuel melted, then the steel would melt sooner and it would dilute the fuel, displace the water, and there would be no moderation to make the system critical. The enrichment is too low for a fast fission system.

 

[lapsedgeo]

Thank you all for calm and informed analysis, as a member of Joe Public this has been such a helpful place to visit. Every day it seems to get a little worse and I detect a note of resignation in all your posts now. Hearing that the spent fuel pond is on fire has made my heart sink. As a geographer I want to people to realize that we are not sitting on an inanimate lump of rock but this is one heck of a reminder.

 

[rogerl]

So if what Astronuc saying is accurate. The worse is over. Even if worse case scenerio no water were added anymore and the fuel rods just dry up. They won't melt at all. And even if they melted, fission wouldn't be restarted. They would be just molten mixture of many stuff that nullify the reactions. So we expect the crisis to be over in a few days with some emission of small radiations that is not dangerous to health, the emissions lasting perhaps for a couple of days or so and then everything will be back to normal. Right guys? Many people are evacuating Tokyo now and wish Astronuc can share with them technical stuff so as to lessen the panic. Thanks to him for answering all technical questions.

 

[rogerl]

I just heard from CNN that the heat in nearby reactors could have evaporated the water that soaked the spent fuel in reactor #4 and the rods caught fire and release radioactive debris about 400 milliSiv inside the compound.

So how dangerous are spent fuel? If they are "spent", there should be few live nuclei left that can fission, isn't it. Or the decayed project is acting up and still radioactive? What elements?

Also about Reactors 1-3. Isn't it if you leave cyanide powder in the trash can with no wind in the room, it would stay there. If you instead blow it with air, it will spread. What I'm saying is that the fuel rods in reactors 1 to 3 are no longer live and just left over decay heat. So why don't they just stop putting water and releasing steam outside the plants which can spread radiation all over the country and instead just let the fuel rods rot or melt and let the mixture stay safely in the bottom of the containment shell just like cyanide power left in the bottom of the trash can and basically quarantined there? Stupid questions but this nuclear incident is unprecendented. Sorry and thanks/

 

[falcon32]

No. And in fact, as far as I can tell - there will not be a molten puddle.

If the ceramic fuel melted, then the steel would melt sooner and it would dilute the fuel, displace the water, and there would be no moderation to make the system critical. The enrichment is too low for a fast fission system.

Astronuc, many thanks for answering my questions. It does sound hopeful, in that we only have to wait for the byproducts to decay, with the main uranium fission reaction inhibited.

One more question did come to mind...suppose in the unlikely event that the core did melt -- wouldn't the mixture separate by density, with uranium on the very bottom, and everything else floating on top?

 

[promecheng]

When posting activties, please cite the source and/or link.

Sorry, I got this information from watching the live broadcast of a press conference on HNK television in Japan. They were giving English translation of what the government spokesman was saying about the situation.

 

[Astronuc]

I just heard from CNN that the heat in nearby reactors could have evaporated the water that soaked the spent fuel in reactor #4 and the rods caught fire and release radioactive debris about 400 milliSiv inside the compound.

I'd like to confirm that. Unit 1-3 should not affect unit 4. Unit 4's upper containment seems intact - but I haven't confirmed that.

So how dangerous are spent fuel? If they are "spent", there should be few live nuclei left that can fission, isn't it. Or the decayed project is acting up and still radioactive? What elements?

Spent fuel is pretty dangerous! That's why it is normally handled with 30 feet of water or several feet of steel and/or concrete between spent fuel assemblies or rods and people. The objective is to retain the fission products in the fuel rods (enclosed by the ceramic fuel and Zr-alloy cladding tube), but that clearly is not the case at Fukushima.

Also about Reactors 1-3. Isn't it if you leave cyanide powder in the trash can with no wind in the room, it would stay there. If you instead blow it with air, it will spread. What I'm saying is that the fuel rods in reactors 1 to 3 are no longer live and just left over decay heat. So why don't they just stop putting water and releasing steam outside the plants which can spread radiation all over the country and instead just let the fuel rods rot or melt and let the mixture stay safely in the bottom of the containment shell just like cyanide power left in the bottom of the trash can and basically quarantined there? Stupid questions but this nuclear incident is unprecendented. Sorry and thanks

It seems they may be contemplated something like that - which is pretty much how Chernobyl ended up, with the possible exception that it is not yet clear the fuel actually 'melted', as opposed to simply breached or cracked (typical vertical or longitudinal cracks), and it is not clear that it will necessarily melt - assuming there is some form of coolant inventory.

The questions are not stupid. And yes - this event is unprecedented!


To give better or more definitive answers, I'd need better information. I'm working on that.

This is still not detailed enough, but . . .
http://www.world-nuclear-news.org/RS_Possible_damage_at_Fukushima_Daiichi_2_1503111.html

 

[ZapperZ]

Not sure if this has been posted here, but this could be an informative article.

http://tech.mit.edu/V131/N13/yost.html

Zz.

 

[rogerl]

Reactor #3 is said to use MOX, "a controversial fuel made with reprocessed plutonium and uranium oxides". Does it have larger thermal properties?

http://search.japantimes.co.jp/cgi-bin/nn20100823a7.html

"Fukushima reactor receives MOX

FUKUSHIMA (Kyodo) Tokyo Electric Power Co. on Saturday loaded a nuclear reactor in Fukushima Prefecture with MOX, a controversial fuel made with reprocessed plutonium and uranium oxides, as it prepares to become the leading power utility's first facility to go pluthermal.

The No. 3 reactor at Tepco's Fukushima No. 1 plant will be the nation's third pluthermal facility, but only the first to be refurbished since the plant was built 34 years ago.

Tokyo Electric plans to activate the reactor on Sept. 18 and let it start generating electricity on Sept. 23."

 

[TCups]

Regarding fuel rods, including the MOX fuel rods:

Is it known if the spent fuel rods from reactor units 1, 2, and 3 stored in the containment pool for unit 4 or not?

If so, might there more danger from the contaminated steam coming off the "boiling" containment pool and fire at unit 4 than otherwise might be the case (ie, from plutonium release)?

If not, are there additional spent fuel rods from units 1, 2, and 3 stored in each of the reactor facilities? Where would fuel rod storage be located in a GE Mark I type reactor facility? Are they at risk?

Might contamination arising from the problems associated with failed cooling of the spent fuel rod storage sites yet be a bigger problem than cooling the reactor cores?

 

[Astronuc]

Regarding fuel rods, including the MOX fuel rods:

Is it known if the spent fuel rods from reactor units 1, 2, and 3 stored in the containment pool for unit 4 or not?

If so, might there more danger from the contaminated steam coming off the "boiling" containment pool and fire at unit 4 than otherwise might be the case (ie, from plutonium release)?

If not, are there additional spent fuel rods from units 1, 2, and 3 stored in each of the reactor facilities? Where would fuel rod storage be located in a GE Mark I type reactor facility? Are they at risk?

Might contamination arising from the problems associated with failed cooling of the spent fuel rod storage sites yet be a bigger problem than cooling the reactor cores?

Each unit has it's own spent fuel storage pool, so the spent fuel for one unit is stored in it's own pool. The SFP is located near the top of the primary containment.

The SFPs could be at risk. We are lacking the details on their status.

 

[Naty1]

Here's an example of one crazy media report: there are several obvious inaccuracies...

they seem to have "reactor" mixed up with "fuel storage pond" for one thing...

Can spent fuel in separate storage even "catch fire" if exposed from underwater ?


Japanese officials told the International Atomic Energy Agency that the reactor fire was in a fuel storage pond — an area where used nuclear fuel is kept cool and that "radioactivity is being released directly into the atmosphere." Long after the fire was extinguished, a Japanese official said the pool might still be boiling, though the reported levels of radiation had dropped dramatically by the end of the day.

...Late Tuesday, officials at the plant said they were considering asking for help from the U.S. and Japanese militaries to spray water from helicopters into the pool.

(Here the article apparently shifts from fuel storage to reactor discussion:)

That reactor, Unit 4, had been shut down before the quake for maintenance.

If the water boils, it could evaporate, exposing the rods. The fuel rods are encased in safety containers meant to prevent them from resuming nuclear reactions, nuclear officials said. But they acknowledged that there could have been damage to the containers. They also confirmed that the walls of the storage pool building were damaged.

Experts noted that much of the leaking radiation was apparently in steam from boiling water. It had not been emitted directly by fuel rods, which would be far more virulent, they said..."

http://news.yahoo.com/s/ap/as_japan_earthquake

 

[Naty1]

Japan rocked by fresh blast at Fukushima nuclear plant• New explosion at Fukushima's second reactor
• Partial meltdown 'may be underway' (How was this conclusion made??)
• Tokyo asks international community for help


Share887 Justin McCurry in Tokyo, Tania Branigan in Beijing and Ian Sample The Guardian, Tuesday 15 March 2011

Non-essential technicians were evacuated from the facility after radiation levels around the Fukushima No 1 power plant briefly rose four-fold in the wake of the blast, which appears to be the most serious to date.

The plant operators said its reading had reached 8,217 microsieverts per hour – described by broadcaster NHK as equivalent to eight times the radiation a person would usually experience in a year. It later fell sharply, the broadcaster said. The peak was still far below the level which would cause immediate damage to health.

http://www.guardian.co.uk/world/2011/mar/14/japan-nuclear-fukushima-third-reactor

 

[Reno Deano]

High radiation levels in and around the plant can be partially caused due to the use of seawater to cover the RX core and the production of short lived thermal neutron Sodium activation. Activated Sodium gives off a healthly gamma. Some can be carried off in the off-gasing from the Dry Well or leaks from the Torus. Fission fragments and noble gases will be the primary source of radiation.

 

[Drachma]

Dear Astonuc:

"The SFPs could be at risk. We are lacking the details on their status."

Try an educated guess. Didn't Building #1 and #3 completely explode? Where are the spent fuel rod pools? Are they in the core container or outside of it? We know they are just below the roof, which incidentally has been vaporized. After these massive explosions, we are to believe that these pools are intact. How many rods in each pool, 3000 maybe? We are also to believe that there has been no loss of containment but somehow we are detecting increases in ambient radiation levels. So which one is it? Where is the radiation coming from? Where are the elevated levels of cesium and iodine measured outside the containment coming from?

In the larger explosion of Unit #3 the smoke is clearly dark and there are massive chunks of debris (core perhaps) flung 3000 ft. in a couple seconds. The initial explosion at #3 is an orange and black cloud (doesn't look like hydrogen combustion to me). The building is gone, but we are to believe that there is no damage to containment or any of the machinery that would allow for emergency response. Didn't the problems start with the impact of the tsunami? Do you think the containment vessels were tested for a 7.0 or an 8.0 earthquake, let alone a 9.0? I don't know of any of these tests from GE or the Japanese themselves on the Mark-I design. Do you? What was the Richter equivalent to the core containment of a massive building explosion all around it?

No amount of technical word play semantics can diminish the seriousness of what is going on. All this talk about low levels of radioactive contamination is irrelevant. The problem will get much, much worse before it gets better, if ever. Our governments will continue to downplay this disaster even when people are puking in the streets and cancer rates 10-15 years from now explode.

We had the same word play around the Chernobyl disaster, and to this day we are still finding out the massive health effects from that. It will be the same if not worse with Fukushima.

Expect full meltdown of all reactors at Fukushima. It's game over for Fukushima.

 

[Reno Deano]

Sure would like to see the radiochemistry results from the reactor vessel, drywell, torus, and secondary containment. Hope their reactor accident and core coolant sampling system perform as designed. My hat really goes off to the operators in that they must have nearly soiled themselves during the violent explosions that surely rippled through the control rooms and remote control stations. Truly an unprecedented occurrence that is not in the reactor operator training mock ups.

 

[Astronuc]

Try an educated guess. Didn't Building #1 and #3 completely explode? Where are the spent fuel rod pools? Are they in the core container or outside of it? We know they are just below the roof, which incidentally has been vaporized. After these massive explosions, we are to believe that these pools are intact. How many rods in each pool, 3000 maybe? We are also to believe that there has been no loss of containment but somehow we are detecting increases in ambient radiation levels. So which one is it? Where is the radiation coming from? Where are the elevated levels of cesium and iodine measured outside the containment coming from?

Xe, Kr, Cs (radioisotopes of Xe decay to Cs), and I would be coming from the fuel; they are fission products as well as decay products. According to the limited schematics, the spent fuel pools are in top the reinforced containment structure, but the water is exposed to at the surface or floor of the metal structure that was damaged in the explosions. If the water remains, it's not a problem. If the water evaporates then there could be additional release of gaseous and volatile fission products. The concrete containment is intact, but they have been venting steam with fission products to relieve pressure in containment, so that the containment doesn't fail.

In the larger explosion of Unit #3 the smoke is clearly dark and there are massive chunks of debris (core perhaps) flung 3000 ft. in a couple seconds. The initial explosion at #3 is an orange and black cloud (doesn't look like hydrogen combustion to me). The building is gone, but we are to believe that there is no damage to containment or any of the machinery that would allow for emergency response. Didn't the problems start with the impact of the tsunami? Do you think the containment vessels were tested for a 7.0 or an 8.0 earthquake, let alone a 9.0? I don't know of any of these tests from GE or the Japanese themselves on the Mark-I design. Do you? What was the Richter equivalent to the core containment of a massive building explosion all around it?

The orange flame would be the case where combustion wasn't stoichiometric - i.e., it's not a pure mix of hydrogen and oxygen. There is nitrogen and water vapor as well, and maybe some Xe and Kr. The massive chunks of debris was the sheet metal and insulation, and whatever has accumulated on top of the roof - e.g., dust.

The containment held in the quake - as far as we know. The reactors scrammed. The EDGs operated for one hour. However, the problem arose when the fuel system was compromised and the EDGs lost their fuel supply, or water was transferred into the EDGs. They stopped. Then the batteries ran for sometime, but were depleted. I lack the details of what happened after that.

No amount of technical word play semantics can diminish the seriousness of what is going on. All this talk about low levels of radioactive contamination is irrelevant. The problem will get much, much worse before it gets better, if ever. Our governments will continue to downplay this disaster even when people are puking in the streets and cancer rates 10-15 years from now explode.

No one here is playing semantics or diminshing the seriousness of the situation.

We had the same word play around the Chernobyl disaster, and to this day we are still finding out the massive health effects from that. It will be the same if not worse with Fukushima.

Expect full meltdown of all reactors at Fukushima. It's game over for Fukushima.

The Russians certainly minimized Chernobyl. I have not heard anyone here minimizing the Fukushima event. However, you've made unsubstantiated conjectures.

How bad it could or will get depends on the source term (which is currently unavailable to those of us outside the plant) and what happens between the core and the environment.

It is a very serious situation. However, we can do without the sensationalism and unsubstantiated conjecture.

 

[Naty1]

the spent fuel pools are in top the reinforced containment structure...,

Ah, now I see how the media got things mixed up...I thought they would be outside...

Is storage within the containment structure pretty standard??

 

[Reno Deano]

No amount of technical word play semantics can diminish the seriousness of what is going on. All this talk about low levels of radioactive contamination is irrelevant. The problem will get much, much worse before it gets better, if ever. Our governments will continue to downplay this disaster even when people are puking in the streets and cancer rates 10-15 years from now explode.

Truly statements from someone that is "uneducated" at best, and exceptionally in nuclear operations, plant design or health physics, and has no factual idea of what really is going on or the future consequences for the people of Japan. Fear mongering is best left to CNN, FOX, etc., but maybe you can get on full time with them to spout your nonsense.

BTW, just how much worse can it get considering the state of affairs in the other parts of Japan? Answer: Minuscule when compared to the destruction and carnage in the other quake and tsunami stricken areas of Japan.

Dean Chaney, CHP

 

[DR13]

I got an email from the Nuclear Engineering department at my University. They forwarded a message from NEI:

UPDATE AS OF 8:30 A.M. EDT, TUESDAY, MARCH 15:
Fukushima Daiichi

Units 1 and 3 at Fukushima Daiichi are stable and cooling is being maintained through seawater injection. Primary containment integrity has been maintained on both reactors.
The Japan Atomic Energy Agency reported an explosion in the suppression pool at Fukushima Daiichi Unit 2, at 19:14 EDT on March 14. Reactor water level was reported to be at 2.7 meters below the top of the fuel. The pressure in the suppression pool decreased from 3 atmospheres to 1 atmosphere. Radiation readings at the site increased to 96 millirem per hour.

Dose rates at Fukushima Daiichi as reported at 21:22 EDT on March 14 were:
Near Unit 3 reactor building 40 rem/hr
Near Unit 4 reactor building 10 rem/hr
At site boundary 821 millirem/hr.
Kitaibaraki (200 km south of site) 0.4 millirem/hr.

We are working on getting updated information on radiation and dose rates at and near the plant. Station personnel not directly supporting reactor recovery efforts have been evacuated, leaving approximately 50 staff members at the site. Operators are no longer in the main control room due to high radiation levels. Safety relief valves were able to be re-opened and seawater injection into the reactor core was restarted around 1 a.m. EDT on March 15 and is continuing. At Unit 4 on March 14 at approximately 8:38 p.m. EDT, a fire was reported in the reactor building. It is believed to have been from a lube oil leak in a system that drives recirculation water pumps. Fire fighting efforts extinguished the fire. The roof of the reactor building was damaged.

Fukushima DainiAll four reactors at Fukushima Daini are being maintained with normal cooling using residual heat removal systems.

 

[TCups]

Astronuc:

Do I have this right -- I believe so. The cutaway shows an access tunnel where fuel rods can be transported into the reactor (1), lifted by the crane (2) and either transported to one of two pools of water (3), (4), or dropped into/taken out of the reactor vessel when refueling.

In principle, then, if the cooling pools were low on water or dry, either from boiling off water that wasn't being replaced, or from damage and leakage secondary to the explosion(s), the stored fuel rods (are they pictured in (3)?), could overheat in much the same way that the rods in the reactor are overheating -- not at a "critical" level of a sustained chain reaction, but hot enough to potentially damage the metal casings of the fuel rods and release, along with steam, the same contaminants that might be released when steam is vented from the reactor vessel?

It appears from the pictures of Unit 1, that the superstructure damaged was all above the level of the storage pools. I can't find any picture of unit 4 that might indicate whether the pools and rods stored therein are still intact or potentially scattered about.

Edit: Actually, as I look at the rails on the floor for the crane, they don't seem to extend over (4), so that may be a coolant storage reservoir.

 

[DR13]

Here is a nice table that summarizes what is happening

 

[Homer Simpson]

this morning when there were reports of 40 Rem/h at the station, and 800 mR/h at the station boundary... what kind of radiation/isotopes might cause that? Short-lived stuff that will decay away quickly? Noble gas cloud type radiation, or particulates? Obviously the levels have come down drastically since then, so does this mean at this point there is a low probability of long-lived ground contamination existing after the emergency subsides?

ie; as it stands now, should people be able to move back home or will there likely be an exclusion boundary long term?

 

[aamrwc]

I'm just a dumb economist and would love to have someone lay out three scenarios and implications: Best case, Most Likely and Worst Case. So far, it seems like this is a recoverable event and financially manageable but all the reporting I'm hearing makes me want to run screaming to the exits. Thanks. this would be greatly appreciated.

 

[DrDu]

I got an email from the Nuclear Engineering department at my University. They forwarded a message from NEI:

UPDATE AS OF 8:30 A.M. EDT, TUESDAY, MARCH 15:
Fukushima Daiichi


Dose rates at Fukushima Daiichi as reported at 21:22 EDT on March 14 were:
Near Unit 3 reactor building 40 rem/hr
Near Unit 4 reactor building 10 rem/hr
At site boundary 821 millirem/hr.
Kitaibaraki (200 km south of site) 0.4 millirem/hr.

We are working on getting updated information on radiation and dose rates at and near the plant. Station personnel not directly supporting reactor recovery efforts have been evacuated, leaving approximately 50 staff members at the site. Operators are no longer in the main control room due to high radiation levels. Safety relief valves were able to be re-opened and seawater injection into the reactor core was restarted around 1 a.m. EDT on March 15 and is continuing. At Unit 4 on March 14 at approximately 8:38 p.m. EDT, a fire was reported in the reactor building. It is believed to have been from a lube oil leak in a system that drives recirculation water pumps. Fire fighting efforts extinguished the fire. The roof of the reactor building was damaged.

Fukushima DainiAll four reactors at Fukushima Daini are being maintained with normal cooling using residual heat removal systems.

I can't believe that Japanese authorities still use units like rem and Roentgen. Are you sure these infos are not from Burkina Faso?

 

[promecheng]

I'm just a dumb economist and would love to have someone lay out three scenarios and implications: Best case, Most Likely and Worst Case. So far, it seems like this is a recoverable event and financially manageable but all the reporting I'm hearing makes me want to run screaming to the exits. Thanks. this would be greatly appreciated.

Do yourself a favor and shut off your TV. NEI has been posting good updates here, http://nei.cachefly.net/newsandevents/information-on-the-japanese-earthquake-and-reactors-in-that-region/ which seem to contain the latest, most accurate information without any of the grossly incorrect, purely speculative, sensational and fear-mongering reporting that you'll find on the major network "news" outlets.

 

[andyr]

I'm just a dumb economist and would love to have someone lay out three scenarios and implications: Best case, Most Likely and Worst Case. So far, it seems like this is a recoverable event and financially manageable but all the reporting I'm hearing makes me want to run screaming to the exits. Thanks. this would be greatly appreciated.

Unfortunately the media decided to tell a Hollywood blockbuster story at a time when they could reassure and educate the masses. Just read through this entire thread, it will quickly change your perspective.

In future though, take mainstream populist news channels with a pinch of salt.

 

[PietKuip]

NEI has been posting good updates here, http://nei.cachefly.net/newsandevents/information-on-the-japanese-earthquake-and-reactors-in-that-region/ which seem to contain the latest, most accurate information without any of the grossly incorrect, purely speculative, sensational and fear-mongering reporting that you'll find on the major network "news" outlets.

Which is very scary reading. Operators have abandoned the control room: nobody in the driving seat anymore.

 

[marwood]

DrDu doesn't seem very impressed with the ''scientific data'' being presented on the nei.cachefly.net site.

The reported decline in radiation levels to 60millirems/hr is over 2000 x background radiation levels, suggesting ?? ongoing emissions from the No.2 reactor steam venting? or from a leak in the No.2 reactor containment? or contamination of the ground area by emissions from the No.4 spent fuel pool fire? According to http://english.kyodonews.jp/news/2011/03/78352.html

''The utility firm said later in the day the massive radiation amount of 400 millisievert per hour, or 400,000 microsievert, was recorded around debris in front of the No. 3 reactor and that the material may have come from the nearby No. 4 reactor.''

As far as best, most likely, and worst case scenarios, as economic theory claims, accurate information is costly, especially when agents have incentives to conceal it (http://www.guardian.co.uk/world/2011/mar/14/japan-radiation-leak-cover-up?CMP=twt_gu), so there is not sufficient information to make anything but speculations about most likely scenarios. For best case check the nuclear engery promoters opinions eg http://bravenewclimate.com/2011/03/12/japan-nuclear-earthquake/ and for the worse case scenario see the anti-nuclear environmentalists opinions eg http://www.ucimc.org/content/meltdowns-grow-more-likely-fukushima-reactors .

Seems that the No.1 and No.3 reactors are toast and will have to be de-constructed and recycled. The No.2 reactor may be recoverable after a 3 or 5 year down period for inspection and repair. Haven't seem much about the likely costs ...

 

[aamrwc]

The advice to ignore populists news channels is what I am trying to do. Hence, this is why I am here. I have read this complete thread and have not found a concise Best case, Most likely and Worst case outcome in layman's terms. Responses so far have not been useful. There is a lot of interesting info here but its is fragmented. Could really use the help. Thanks

 

[marwood]

Summary of each Fukushima Daiichi NPP reactor as of late Tue 15th Tokyo time.

http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1300189582P.pdf

Looks like No.2 is being cooled with seawater -- so will be non-recoverable.