Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[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.

 

[promecheng]

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

I wonder how much function they actually lose by abandoning the control room. It seems the site is still in "blackout", with no off-site or on-site electricity available to power any RHR or ECCS pumps or systems. Additionally, from reports it seems that their instrumentation is questionable as well, (RPV/containment level vs. pressure vs. radiation not agreeing). I am guessing that their current priorities are to make sure they keep the portable fire pumps fueled, ensure adequate seawater in the suction pit for the pumps and make sure they vent containment/RPV so as to prevent an overpressure situation and keep pressure low enough to be able to keep on pumping into those areas. On top of this they maybe trying to figure out how to get water back into one, or several spent fuel pools to prevent overheating. What's really concerning is unit 2 and the extent of the damage to the primary containment.

God bless the operators and workers still at the site. These people are heroes!

 

[aamrwc]

Thanks Marwood. These weren't of much use. I'm looking for rational analysis not emotion.

 

[promecheng]

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

The problem is there is not enough information on what has happened or what is currently happening at the site to make any useful predictions.

Additionally, there is no video feed into the reactor. Operators determine the state of the reactor through measurements of temperature, pressure, fluid flow, surrounding area radiation, etc. This information feeds into the control room.

Edited incorrect and speculative comments.

 

[Reno Deano]

If they abandon the control room it is for a good reason. They then go to the emergency remote control room. Most of the fuel within the spent fuel pool has been cooling for 1.5 to 3 years or more. The spent fuel pool does also contain fuel rods that have been removed from fuel bundles due to damage detected during a previous refueling, and reconstituting of a fuel bundle.

Here is a time line html of some interest: http://online.wsj.com/article/SB100...project=JREACTOR0311&articleTabs=interactive"

 

[Reno Deano]

US NRC issues analysis of Japanese actions:

http://www.nrc.gov/reading-rm/doc-collections/news/2011/11-049.pdf"

 

[promecheng]

Is the suppression pool torus on the MK-1 design considered part of primary containment?

 

[Reno Deano]

NEI WEB UPDATE AS OF 2:15 P.M. EDT, TUESDAY, MARCH 15:

Excerpt: An explosion at Unit 2 of the Fukushima Daiichi plant earlier today has damaged the suppression chamber, which holds water and steam released from the reactor core. Personnel not directly supporting recovery efforts have been evacuated from the plant, with about 50 employees remaining, principally to restore cooling water in the reactors.

Later in the day, water level inside the Unit 2 reactor was measured at 1.7 meters below the top of the fuel rods, but it was rising as workers pumped sea water into the reactor, reports said.

Tokyo Electric Power Co. said that an oil leak in a cooling water pump at Unit 4 was the cause of a fire that burned for approximately 140 minutes. The fire was not in the spent fuel pool, as reported by several media outlets. Unit 4 was in a 105-day-long maintenance outage at the time of the earthquake and there is no fuel in the reactor.

 

[Astronuc]

Is the suppression pool torus on the MK-1 design considered part of primary containment?

Yes - it is in the volume that contains the pressure vessel and recirculation system.

If there is no fuel in the core of Unit 4, it means they did a full core offload - and the fuel resides in the SFP or other pool. I've seen thermals coming off older fuel.


This gives a pretty decent explanation of what got the plant in its present situation.
http://blogs.forbes.com/christopher...hat-caused-the-incident-at-fukushima-daiichi/

I don't necessarily agree with the conclusion/remedy regarding fluoride salt fueled reactors.

 

[Texan99]

Suppose a nuclear reactor were successfully shut down with control rods, but then the cooling system immediately failed and no one managed to do a single thing to get it running again. Does anyone really know whether the containment vessels currently in use should be expected to contain the whole meltdown without any significant release of contamination? In other words, I guess steam would build up in there like crazy, but is the vessel up to that task? Or is that just untested territory? In Three Mile Island, for instance, I've read that the core melted down about halfway without breaching the vessel, but I don't know how well the cooling system was functioning.

Special thanks to Reno Deano and Promechang, among others, for your very helpful posts for us laymen.

 

[Texan99]

What is the impact, if any, of a breach of the suppression pool torus on the ability of the containment vessel to hold in all the fissile materials? I mean, suppose you hacked a big hole in the torus. Could melted fuel run out there?

 

[Astronuc]

Suppose a nuclear reactor were successfully shut down with control rods, but then the cooling system immediately failed and no one managed to do a single thing to get it running again. Does anyone really know whether the containment vessels currently in use should be expected to contain the whole meltdown without any significant release of contamination? In other words, I guess steam would build up in there like crazy, but is the vessel up to that task? Or is that just untested territory? In Three Mile Island, for instance, I've read that the core melted down about halfway without breaching the vessel, but I don't know how well the cooling system was functioning.

Special thanks to Reno Deano and Promechang, among others, for your very helpful posts for us laymen.

Some background on TMI-2's accident.
http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/3mile-isle.html

IF the Fukushima plant was able to cool the core, i.e., IF the EDGs had not failed and been able to cool the plants - we wouldn't be having this conversation.

But the ability to cool the cores of Units 1, 2 and 3 failed! That's the critical matter. One unit by itself is bad enough, but three units is three times as bad.

In a normal plant - all the fuel rods could fail. It doesn't matter outside of the utility, as long as the activity is contained in the primary system, and plants are so designed - with the assumption that they have cooling capability so that they primary systems doesn't build up pressure which has to be released. At Fukushima, they lost the cooling capability and that forced the release of fission products into the environment.

Now all other LWR (PWR and BWR) operators must ensure that their own plants will not suffer the same fate.

 

[Astronuc]

What is the impact, if any, of a breach of the suppression pool torus on the ability of the containment vessel to hold in all the fissile materials? I mean, suppose you hacked a big hole in the torus. Could melted fuel run out there?

It depends on where the breach leads to. As long as the breach doesn't lead to the environment, that doesn't affect the public - only the staff that have to deal with whatever part of containment is directly affected by the breach.

Ideally, the fission products stay within the pressure vessel - except for those that have been vented. Otherwise, any fission product in the cooling water that ends up in the torus, will either stay in the torus, or within the primary containment.

Contamination of containment would be a complication of further operation - or complication for decommissioning.

 

[Texan99]

I'm sorry, Astronuc, I'm still not understanding. I do see that the cooling was inadequate, which was why this problem started developing. With normal cooling, the reactor would shut down and gradually cool off. What we got instead was not "zero cooling," but some interruptions or inadequacies in cooling, and some resulting problems with steam and possibly degradation of the fuel rod cladding. At a result we also got explosions here and there that may have put firetrucks out of operation or done some damage to the torus, which might mean that whatever cooling we'd managed to get going again in there was about to get interrupted again, or at least that the cooling system was degraded enough that it couldn't quite keep up for a while. I'm trying to figure out whether it's a huge concern that the cooling might get interrupted or degraded again. Obviously, it's a bad thing for the plant and its owners, but I mean, at this point, assuming that reactor's toast anyway, would a complete loss of the cooling system mean anything more than a lot of slagged-down fuel rods in an intact vessel? And does that answer change when you consider that there may or may not have been a breach in the torus?

 

[Drakkith]

Texan, if we just let the fuel heat up, we would get more Hydrogen buildup. And in addition to the explosive risk from that, the pressure buildup from the evaporating coolant could rupture the containment vessel and building, releasing large amounts of radioactive material into the air.

 

[Texan99]

I realize it's about what's probable. I guess I was just wondering whether it was possible to quit worrying about whether the alternative cooling systems will continue to work, because we continue to get disheartening news about the cooling systems failing, one after the other. I was hoping that we could say, in the end, that no matter what happens with the cooling systems, the vessel will hold, but you're saying no. Rats. Well, I know they're still moving heaven and Earth to continue to provide all the cooling they can, and so far even the compromised cooling has proved adequate to the task of preventing a vessel rupture.

 

[Astronuc]

I'm sorry, Astronuc, I'm still not understanding. I do see that the cooling was inadequate, which was why this problem started developing. With normal cooling, the reactor would shut down and gradually cool off. What we got instead was not "zero cooling," but some interruptions or inadequacies in cooling, and some resulting problems with steam and possibly degradation of the fuel rod cladding. At a result we also got explosions here and there that may have put firetrucks out of operation or done some damage to the torus, which might mean that whatever cooling we'd managed to get going again in there was about to get interrupted again, or at least that the cooling system was degraded enough that it couldn't quite keep up for a while. I'm trying to figure out whether it's a huge concern that the cooling might get interrupted or degraded again. Obviously, it's a bad thing for the plant and its owners, but I mean, at this point, assuming that reactor's toast anyway, would a complete loss of the cooling system mean anything more than a lot of slagged-down fuel rods in an intact vessel? And does that answer change when you consider that there may or may not have been a breach in the torus?

I expect that they are trying to accomplish 2 things: 1) prevent further degradation of the fuel, and 2) prevent pressurization of the containment that would mean venting more steam and/or hydrogen, and more fission products.

In theory, the cooling prevents further degradation, and in fact, less fission gases as the Xe and Kr decay: I -> Xe -> Cs -> Ba and Br -> Kr -> Rb -> Sr. I and Br are volatiles (low boiling/sublimation points), Xe and Kr are noble gases, Cs and Rb are alkali metals (with relatively low melting points), and Ba and Sr are alkaline Earth metals with higher m.p. the corresponding alkali metals.

Ref: http://www.webelements.com/ and http://www.nndc.bnl.gov/chart/ (Zoom 1 or 2 to see details on particlular radionuclides)

The idea is too cool the fuel so that no more fuel fails/degrades, and retain (contain) the fission products in the containment so that they decay away to less radioactive or inert isotopes, which are more manageable. The longer they can keep the fuel cool (and intact) the better, since the expectation is that release of fission products to the environment will be minimized.

 

[DR13]

My roommate was watching the local news (yeah...he does that). They were doing a story on Fermi 2 (in SE Michigan). The news anchor was talking about how dangerous the reactor is since it's 20 years old. Then they go to some intervew with the head of an anti-nuke group leader here in Michigan and he is talking about how Fermi 2 is kinda the same reactor as the one having problems in Japan and how the same thing could easily happen to us. Then the news anchor confirms that she thinks that the plant is also a hazzard (because local news anchors obviously have nuclear engineering degrees).

This was bad enough but then it got worse. They started talking about what would happen if what happened in Japan happened here. YEAH, BECAUSE MAGNITUDE 8.9 EARTHQUAKES AND TSUNAMIS OCCUR IN MICHIGAN ALL THE TIME. I MEAN SERIOUSLY PEOPLE!

This is the problem with the media. Little facts, lots of BS. They don't even talk to someone who is knowledgeable on the subject!

I had to force my roommate to mute the tv until the segment was over.

 

[WatermelonPig]

Hi, not to interrupt conversation but I like would to ask a question: I heard that there was partial exposure of the fuel rods within I believe the third reactor. What exactly does this mean? Did the zircaloy melt? Also, how significant is the height of the fuel rods above the ground in a possible attack on the facility? And do you think this incident will severly affect future power plant construction?

 

[Astronuc]

Hi, not to interrupt conversation but I would to ask a question: I heard that there was partial exposure of the fuel rods within I believe the third reactor. What exactly does this mean? Did the zircaloy melt? Also, how significant is the height of the fuel rods above the ground in a possible attack on the facility? And do you think this incident will severly affect future power plant construction?

There was a headline that indicated that the third reactor at Fukushima experienced partial exposure [to steam] of the fuel rods. The article referred to Unit 3 (the third reactor built, not the third reactor affected). However, a third unit was affected.

The order in which three units experienced cooling problems is Unit 1, Unit 3 and then Unit 2.

The Zircaloy didn't necessarily melt, but it could have reacted (oxidized or corroded rapidly) to the point where it breached. The breaching released the fission gases and volatile fission products into the steam or water as salt water was introduced into the core.

The core sits in a pressure vessel (inches of steel), which is surrounded by several walls (layers) of steel-reinforced concrete.

I expect that designs and construction will receive additional scrutiny in light of the current event at Fukushima Daiichi.

 

[Speedo]

Assuming that the generators had functioned normally, what kind of process would the reactors have gone through after the quake before they were brought back online?

I'm mainly wondering why it wasn't/isn't feasible to bring one reactor online at a low power setting to provide enough power to sustain cooling for the complex.

 

[Drakkith]

Assuming that the generators had functioned normally, what kind of process would the reactors have gone through after the quake before they were brought back online?

I'm mainly wondering why it wasn't/isn't feasible to bring one reactor online at a low power setting to provide enough power to sustain cooling for the complex.

Probably would have remained offline as the waste heat gradually died down. Once the grid was reconnected and everything was verified safe and operational I'm sure they would have started them back up. I don't know how much actual damage the plants sustained from the earthquake, so who knows when they would have been brought back online.

 

[promecheng]

Assuming that the generators had functioned normally, what kind of process would the reactors have gone through after the quake before they were brought back online?

I'm mainly wondering why it wasn't/isn't feasible to bring one reactor online at a low power setting to provide enough power to sustain cooling for the complex.

It's moot at this point since units 1-3 appear to be permanently disabled, and units 4-6 were in outage mode, (not fit for operation), when the earthquake hit. However, even if there was a unit that was fueled and potentially ready to go. There was a 8.9 or 9.0 earthquake that shut the units down for a reason. I think someone said that the plant DBE, (Design Basis Event). earthquake was 7.0 or 7.5. This means that the plant was only designed to withstand up to this event. Being that a 8.9 earthquake is 14 times a 7.5 magnitude one, I'm sure they would have serious reservations about starting a unit back up without a thorough inspection, (which would probably take months or years). For all they know the earthquake could have disabled a number of critical systems necessary for the safe operation of the reactor. This would be too large of a gamble. Additionally I thought I read somewhere that they had significant electrical damage at the plant, so even if they could start a unit and produce steam, (which takes some time to bring up to power), the turbine and switching systems may have been damaged. The bottom line is that you just don't flip a switch to start a plant back up, especially after such a significant earthquake!

 

[Drakkith]

Hi, not to interrupt conversation but I like would to ask a question: I heard that there was partial exposure of the fuel rods within I believe the third reactor. What exactly does this mean? Did the zircaloy melt? Also, how significant is the height of the fuel rods above the ground in a possible attack on the facility? And do you think this incident will severly affect future power plant construction?

1. The partial exposure means that the coolant had dropped so low that parts of the fuel rods had NO coolant high enough to cover them. This is bad obviously.

2. I don't think there is any significance to the height of the fuel rods in the event of an attack.

3. In my opinion it will most definitely affect future nuclear power plant construction, and not in a good way. But mostly because people are ignorant and have zero idea about what radiation and nuclear power really means.

 

[Astronuc]

Assuming that the generators had functioned normally, what kind of process would the reactors have gone through after the quake before they were brought back online?

I'm mainly wondering why it wasn't/isn't feasible to bring one reactor online at a low power setting to provide enough power to sustain cooling for the complex.

They tripped based on the seismic signals. But then they lost the grid - perhaps the local station.

Large equipment like turbines and generators don't like getting shaken very hard - so they would have to inspect 'all' major components. That would take days, especially if they had to compare the data with the design bases.

Because they lost the grid (connection to off-site, and perhaps the local swithyard or distribution system) - the emergency diesel generators came online. They worked! However, a tsunami destroyed the fuel system and apparently some electrical equipment. The slowly lost the ability to the reactor(s). There was no time to even think about a restart - and probably no way to use the electrical power if one did.

Some of that is conjecture because the detailed sequence of events and equipment failure is unknown. While Units 1, 2 and 3 seem to be suffering from the same common mode failure (tsunami damage), there are unique issues with each unit. We won't know for months.


BTW - I want to thank all the contributors for their thoughtful comments and questions.

 

[tkny123]

I'm a humanities guy but I've been doing some reading and have some questions that maybe posters could answer.

1. I heard that the quick path to cold shutdown at Daiini was restoration of grid power then use of its normal pump systems. I heard that grid power was restored to Daiichi but none of the plant's primary and backup feedwater and injection systems are back up or seem to have any chance. Does anyone know why not? Could every single pumping system be disabled? Doesn't that seem unlikely?

2. Is there absolutely no scenario in which the reactor vessel or drywell could be breached? Some in media insist on that. Could someone put some figures to it?
2A. Temperature angle. I read that the melting point of steel is 2800 Faren and zircaloy 2200 F. Also that concrete starts to crumble at 1800 F. Does that mean there is no way a molten core could reach and sustain a temp of > 2800 F? If it could, why couldn't it melt through the vessel?
2B. Pressure angle. Seems like pressure must be able to present a problem and that is the reason for the current "feed and bleed" method. Is there a critical pressure level for the vessel? What has to happen for that level to be reached (i.e., rods totally exposed for x hours with no water?)?

3. Spent fuel rods. If a group of them get totally uncovered by cooling water, what could happen?
3A. Everyone agrees the rods could heat up, then zircaloy cladding melt, then what? If zircaloy melts at 2200 F, wouldn't the concrete under it start to at crumble at 1800 F? Could they sponteously combust, have a conventional fire, that could disperse radioactive material?
3B. I read different things on whether these rods could go "critical", which I understand to means "to restart fission" (but not explode like a bomb). Most in media say "no way" but TEPCO just said it can't rule it out in the case of Unit 4, and it seems like it may have already. See these articles. So can they go "critical" or not?
http://english.kyodonews.jp/news/2011/03/78403.html
http://online.wsj.com/article/SB100...76201643613498376.html?mod=WSJ_newsreel_world
3C. If fresh fission is possible, that's really bad bc it is outside of containment. Freshly fissioned uranium could disperse by fire or explosion (say by hydrogen).

Thanks in advance! I pray for the people of Japan and especially the heros at Daiichi who are sacrificing themselves.