Last updated on March 1, 2013
Uppdate 22:45(UTC) / 23:450(CET) / 07:45(JST)
There has been no further info yet on the status of the exposed workers or the status of the reactors. Only news about the reactors is that both number 1 and number 3 have now switched to fresh water injection into the core and number 2 was supposed to follow promptly. I end todays updates with a few video clips of the explosion in one of the refineries that was hit worst by the earthquake and tsunami. This disaster has struck so many lifes, so many industries and so many towns that it is hard to fathom.
Uppdate 16:30(UTC) / 17:30(CET) / 00:30(JST)
The 2 workes taken to hospital reportedly got a dose to their feet and lower legs between 2-6 Sieverts from beta radiation. They also got close to 200 mSv from gamma and an unknown internal dose.
They have not shown any signs of acute radiation sickness so far. But the dose to the legs are very worrying and in the worst case might mean amputation.
Update 14:15 (UTC) / 13:15 (CET) / 22:15 (JST)
New updates from JAIF and NISA(link 1, link 2, link3). JAIF status is from 15:00 JST and NISA updates from 10:00 and 12:30 JST. As before the first number is from the JAIF update and the number within () is from the older NISA update.
Reactor 1:
Water level in the core: 1.65 (1.65) meters below the top of fuel assemblies
Core pressure: 450 kPa (450 kPa)
Containment pressure: 295 (295) kPa
Core temperature(feedwater nozzle): 197.8 Celsius
Core temperature(bottom head) 153.6 Celsius
Dose rate within containment: 38.9 Sievert/hour
If one looks at the JAIF status updates one can see a very encouraging piece of information, they have switched from seawater to fresh water injection into the pressure vessel! That is one significant step in the direction of stabilizing the reactor since seawater injection could never be a permanent solution. They are still not using the internal pumps however. The temperature of the core seems to have been brought under control and the high containment pressure is on a slowly declining trend. We can only keep our hopes up that they will be able to avoid venting the containment.
Reactor 2:
Water level in the core: 1.20 (1.2) meters below the top of fuel assemblies
Core pressure: unknown
Containment pressure: 120 (120) kPa
Core temperature(feedwater nozzle): 107 Celsius
Core temperature(bottom head) 105 Celsius
Dose rate within containment: 45.6 Sievert/hour
Reactor 3.
Water level in the core: 2.3 m below the top of fuel assemblies.
Core pressure: 139 (139) kPa
Containment pressure: 107 kPa
Core temperature(feedwater nozzle): 42.8 Celsius (probably junk)
Core temperature(bottom head) 111,6 Celsius
Dose rate within containment: 51 Sievert/hour
Preparations are being made to switch from seawater to fresh water for reactor 2 and 3. If it goes as quickly as for number one it should be done within half a day. Work with electrical equipment on going.
We have earlier warned for the possibility that molten material in the core can be lying on the bottom of the vessel and eating its way through, now that seems unlikely considering how low the bottom head temperatures of the vessel are. All of them are below 200 degrees.
Dose rate at main gate around 200 micro sievert per hour.
Update 12:30 (UTC) / 11:30 (CET) / 20:30 (JST)
TEPCO is preparing to switch from salt water to fresh water for the core cooling. From NHK:
TEPCO says it intends to switch over from pumping sea water to pumping fresh water into the 3 reactors, as salt in the sea water could cause corrosion and buildup, hampering the smooth flow of water inside the structures.
The company has been pumping seawater as an emergency measure.
The power company also says preparations to switch to fresh water were completed at the No.1 reactor on Friday afternoon.
Operations to pump fresh water into reactors No.2 and No 3 are expected to start later in the day.
Update 10:00 (UTC) / 11:00 (CET) / 19:00 (JST)
Here are the status tables from the JAIF update described below and summary.
Reactor 1:
Water level in the core: 1.7 meters below the top of fuel assemblies
Core pressure: 465 kPa
Containment pressure: 310 kPa
Core temperature(feedwater nozzle): no new info yet today
Dose rate within containment: no new info yet today
Pressure has decreased by about 60-80 kPa in both vessel and containment since yesterday.
Reactor 2:
Water level in the core: 1.10 meters below the top of fuel assemblies
Core pressure: unknown
Containment pressure: 120 kPa
Core temperature (feedwater nozzle): no new info yet today
Dose rate within containment: no new info yet today
Reactor 3.
Water level in the core: 2.3 m below the top of fuel assemblies.
Core pressure: 139 kPa
Containment pressure: 107 kPa
Core temperature (bottom head): no new info yet today
Dose rate within containment: no new info yet today
Containment damage is again suspected on number 3, otherwise no major changes since yesterday. Let’s hope the containment is not damaged! Luckily the reactors in the possibly damaged containments are behaving more stable than the number one reactor (that has a undamaged containment).
Picture of reactor number 3 building
Update 08:45 (UTC) / 09:45 (CET) / 17:45 (JST)
The 16:00 JAIF update for March 25 has been published. Two changes:
…so far seventeen workers have been exposed to more than 100 mSv of radiation.
100 mSv is the limit where an increase in cancer risk has been proven. At 100 mSv, the lifetime risk of getting cancer increases from about 25-32% to 29-36%.
Keep in mind that this does not say whether or not any of these workers will actually get any cancer, much less die from it. It is safe to assume that just as after Hirosima/Nagasaki, the medical authorities will keep those exposed under very close watch, meaning their chances of getting diagnosed early and thus surviving any cancer will be quite good.
The other change is that the radiation reading at the main gate has gone up again:
The Main Gate: 259.0μSv/h at 11:00, Mar. 25
The pressure in the #1 containment vessel is moving up and down. #2 is stable. The #3 pressure is slowly decreasing. With the worries of a leak from #3, this may have more than one explanation, not all of them good.
Update 07:20 (UTC) / 08:20 (CET) / 16:20 (JST)
The 10:00 (JST) JAIF update for March 25 has the following new entries:
Monitoring results of seawater sampled at the coast near the Fukushima Dai-ichi NPS on Mar. 23rd showed that radioactive Iodine, Cesium, Ruthenium, and Tellurium exceeding the regulatory limit were detected. Also, monitoring results of seawater sampled at coasts within about 16km from the Fukushima Dai-ichi NPS in Mar. 23rd showed that radioactive Iodine and Ruthenium exceeding the regulatory limit were detected.
Nuclear Safety Commission of Japan reported the result of preliminary calculation of exposure dose in the surrounding area of Fukushima Dai-ichi NPS.
The dose rate mesaured at the main gate has dropped slightly, from 209.4μSv/h at 12:00, Mar. 24 to 193.8μSv/h at 06:00, Mar. 25.
The high exposure of three workers in the number three turbine hall suggests that #3 may have a leak after all, says the government’s Nuclear and Industrial Safety Agency.
Water supplies continue to show taints of Iodine-131, but the readings fluctuate and it’s still hard to make out a general trend. Tokyo is no longer under a recommendation not to drink the tap water, but concerned citizens continue to use bottled water to some extent.
Following the latest findings, the Tokyo officials said it will no longer warn against consumption of tap water in the metropolitan area.
”I believe readings will go up and down. But even if levels exceed standards temporarily, it will be no problem as long as they stay (most of the time) within the range throughout the year,” Tokyo Gov. Shintaro Ishihara said at a news conference. ”I hope people in Tokyo would act calmly.”
Still, people in the capital area — located about 220 kilometers from the crippled Fukushima Daiichi nuclear plant — and elsewhere continued to buy up limited supplies of bottled water from shops and vending machines.
The government has asked that people in the 20-30 km zone around the crippled Fukushima plant to evacuate volontarily out of concern for supplies for daily necessities.
The Japanese government has encouraged people living within 20 to 30 kilometers of the troubled nuclear plant in Fukushima Prefecture to leave voluntarily, with concerns over access to daily necessities rather than resident safety prompting the advice, top government spokesman Yukio Edano said Friday.
Länkar:
SvD mycket troligt en läcka i 3an
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DN Kärnan kan vara skadad (den person som valde den här rubriken borde sluta använda google translate….)
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I am quite worried by the combination of some things:
– The used fuel pool at reactor 3 is apparently leaking water so the pool is damaged.
– This fuel contains plutonium (which has a 24 000 y half-life and is also very poisonous).
– The reactor itself may be damaged.
It looks to me that it may come to situations where it is difficult to handle the used fuel here. If for example a new tsunami should hit then perhaps very bad things could happen. Perhaps bad situations could emerge in many other ways.
What are your opinions about this?
Thanks for the comment Lennart,
To be honest(and this might sound a bit callous), I am not worry at all about the plutonium. Plutonium isn’t an issue due to its poor mobility. It’s not water soluble, it doesn’t form dust that easily spreads and there isn’t a whole lot that can happen to spread it. Even in Chernobyl where the entire core exploded and burned for 10 days the plutonium spread is a minor concern compared to, among other nuclides, the cesium emitted.
Things could certainly get worse again, if for instance some kind of leak bad enough to require total evacuation of the site happens. Then they would lose the ability to pump water into the spent fuel pools and also lose the ability to maintain the reasonably stable condition the reactors are in right now. But for every day that they keep the situation manageable the likelihood of something worse happening decreases.
A new tsunami would of course be disastrous, but it seems unlikely for two strong tsunamis to hit the same spot within a couple of weeks of eachother.
I think this chapter from a book by professor Bernard Cohen puts plutonium in a better perspective(scroll down to the part about plutonium toxicity).
http://www.phyast.pitt.edu/~blc/book/chapter13.html
Thanks Johan, I have not followed the debate about plutonium so I was unaware of Bernard Cohens view. Most of it seems reasonable.
We are about as worried as anyone else… the event is not finished yet and troublesome reports of contaminations are starting to appear. The australian report that Fukushima is releasing as much Iodine-131 and Caesium-137 as Chernobyl is deeply worrying. If that report is true we will have to rethink quite a bit when it comes to nuclear safety.
Regaring #3 in particular, let me first kill a myth: plutonium is not very toxic. That is a media hype with not very much truth behind it. The chemical toxicity of plutonium is about that of cadmium.
Also plutonium is a rather “benign” substance when it comes to contamination: it’s pretty much chemicaly inert in its oxide form and rather heavy, so it doesn’t go anywhere. Any release of plutonium will be very localize in, at and very close to the plant.
Also I must point out that a long half-life means less activity. Twice the half-life = half the activity. They are inversely correlated.
The reactor cores in 1, 2 and 3 are all damaged. The activity inside the containment structures are extreme (see yesterday’s update) which doesn’t happen unless the fuel assmeblies have been damaged. The reactor tank and the reactor containment on the other hand seems to be holding the major part of the core inside, and that is good. It is worrying with the possible leak in #3 but plutonium is not the major issue there.
I-131 and Cs-137 are the big worries because they are volatile (meaning they get around easilly) and have much shorter half-lives (meaning they are very much more active).
One small note: it may also be proven that we did think right after TMI/Harrisburg.
Much of the contamination problems that are starting to appear now would not have been an issue if Fukushima I had had proper filters for steam release operations. The Swedish FILTRA silos catches over 99.9% of the contaminants… and you don’t need much for them to work either: basicly a large silo of gravel (grovt grus) and a scrubber sprinkler… possibly a few chemicals.
Michael, the problem with long half-life is of course that the threat is there longer.
Can you please elaborate a bit more about I-131 and why it worries you? It has a half-life of 8 days, which is good because the threat disappears by itself rather quickly. Unfortunately it is also a main product from the fission. What levels are we talking about and what time frames considering this?
If you could do the same for Cs-137 I would be glad. The worries there should be quite different since the half-life is 30 years and the threat therefore does not disappear by itself (in a human life perspective, of course).
I-131 is generally concidered major worry in a nuclear accident becuase:
1) There’s “alot” of it among the fission products, relatively speaking.
2) It’s volatile and moves around in the environment easily
3) It has a short half-life so it’s very active during the time it still exists.
4) It has a nasty tendency to go for the thyroid and accumulate there.
I-131 with its halflife of 8.1 days decays quickly… the time frame is this, counting in half-lives of 8.1 days
1: 50%
2: 25%
3: 12.5%
4: 6.25% (one month)
8: 1 / 256 (two months)
12: 1 / 4096 (three months)
So if you today would have 4096 Bq/kg water, in three months that would be 1 Bq /kg. The big question is of course what you drink until then…
Cs-137 is also concidered a major worry for almost all the same reasons: it’s abundant, it gets around and it is active. It’s not quite active as I-131, but with a half-life of 30 year it hangs around for a long while.
Thanks Michael, but I tried to ask what this may mean practically in the current situation (and similar situations, of course). I guess everyone here is able to do simple calculations.
Aha, I see what you mean.
First of all the reactors will need to be stabilized and a reliable cooling operation established. Until then, noone shall be in the zone.
After that, assuming the situation does not deteriorate much further from what we have now, the practical implication is that Fukushima and possible “hotspots” will need to be evacuated for a bit… in the time frame a couple of weeks to a few months at the most.
After that monitoring of produce and water supplies will have to be made continuously.
A deterioriation of the situation will have implications in that food and water supplies will become strained, which is not good in a country that is already on its knees, bleeding from the beating it took from the earthquake and tsunami. It’s not lethal… people won’t die in droves… but it’ll be a factor that worsens an already bad situation.
From what you say I conclude that the amount of Cs-137 produced must be very small (since it has a half-life of 30 years). Is that true, or?
Michael, this was a continuation of our discussion above. So I am asking you. (And I wonder where I clicked to fall out of the thread 😉
Cs-137 is a right bugger because it combines three bad qualities:
1) It is abundant, i.e. you get alot of it in the reactor
2) It has a short enough half-life to be active enough to notice and be a problem (uranium in comparison has a very long halflife so it’s not very radioactive per unit of weight)
3) It has a long enough half-life to remain in the biosphere for a long period of time (unlike most fission products that disappear within a few days or weeks).
Cs-137 is the worst combination of these qualities in the long run.
– If it had been less abundant, we wouldnt’ care, because there wouldn’t be alot of it.
– If it had had a longer halflife, it wouldn’t be a bother because it wouldn’t be very radioactive, like uranium.
– If it had had a shorter halflife, it wouldn’t be much of a problem because it would disappear quickly, like I-131.
Not necessarily. For each fission there is a greater chance of producing I-131 than Cs-137, but because the I-131 decays during the time the reactor is running you reach an equilibrium level, while Cs-137 is built up in the reactor until the fission process is stopped.
In a school book example you would have roughly the following amounts of a few different radioisotopes in a 1000 MW reactor 30 minutes after shutdown (after a full cycle):
Cobolt-60 (5.3 years) 0.3 kg
Strontium-90 (30.2 years) 28 kg
Iodine-131 (8 days) 0.7 kg
Cesium-137 (30.1 years) 54 kg
Plutonium-239 (9 million years) 340 kg
Sr-90 turned out not to be such a big problem after Chernobyl (it was more dominating after the atmospheric atomic bomb tests when it was freely dispersed in the air).
Co-60 has nasty gamma radiation (two peaks of quite high energy) but is not volatile, and the amount produced is not so much.
And the relatively large amount of Pu-239 was, as explained by Michael, not a big deal in the Chernobyl accident.
As you can see we have plenty of Cesium-137 in the core. We certainly do not want to see it dispersed in large amounts.
As you can see Lennart, there is not alot of I-131 in there… but the short half-life means that even with the small amount there is, it’s a noisy troublemaker. Per amount of matter (i.e. for the same number of atoms), I-131 is approximately 1200 times more active than Cs-137.
So even though there is almost 100 times as much Cs-137 as I-131 at the end of the fuel cycle, the collected amount of I-131 starts off as 12 times as active as the amount of Cs-137.
Thanks Michael for the figures. So except for the first month(s) the most serious is perhaps Cesium-137 and Strontium-90.
In Chernobyl, Sr-90 didn’t move around much. It stayed put at the site. Cesium is more mobile. So for the first month, I-131 and Cs-137 are the major worries.
But can’t Strontium-90 because of it properties enter the food chain? (Where it can replace Calcium.)
Thanks Michael and Lantzelot.
Do we then also not have to worry about the used fuel in the pool above the reactor? I am quite surprised to see that the pool is above the reactor and that it is a common construct. It does not look as an optimal placement to me since if there is a serious leak from the reactor itself it might perhaps prevent control of the used fuel pool. (And in this case we know that the pool is damaged already.)
What are your thoughts about this? What scenarios could lead to damage to the used fuel in the pool such that it starts to leak for example Cesium-137?
On order for substances to escape from the fuel elements, the elements must become damaged in some way. The fuel always comes in a cladding, that is to say it is encased in an outer “skin”. This cladding is a zirconium alloy (unimaginatively named “Zircaloy”).
http://en.wikipedia.org/wiki/Zirconium_alloy
So for as long as the clading holds, the contaminants stay locked inside. The clading needs to be damaged for the contaminants to escape. The different ways in which spent fuel may become damaged is:
– mechanical damage (i.e. the elements become bent, crushed, dented)
– melting/fire damage (i.e. the zircaloy melts or gets burned away)
– bursting from the inside due to run-away fission
Mechanical damage seems unlikely at this point. A minor fraction of the elements may have been damaged this way during the explosions.
The fuel elements still produce some amount of heat. If they are left without cooling, very “fresh” elements may become hot enough for the cladding to be in danger of melting or catching fire. That would be bad.
For reasons all too obvious configurations of fuel pools, where runaway reactions would be possible, is not allowed. They are meant to store the fuel in such a manner this cannot happen. Unless they have completely messed up the configuration of the pools, runaway fission reactions causing bursting is not to be expected.
And yes… spent fuel pools will most likely be hotly debated now. They have already been criticized. We can expect to see changes in policies there.
Why do you think mechanical damage is unlikely at this point? We have already seen explosions from H2. Can’t this happen again? And could not the impact on the already damaged pool be bigger by a new explosion?
How long time do you think a used fuel element without cooling could eventually melt down or catch fire? (How old are the elements in the used fuel pool and that ages are they?)
It looks to me serious accident destroying part of the reactor building have not been taken into account when placing the used fuel above the reactor. Or is there a reason for that placement?
Hasn’t there been other incident in other reactors where this placement has been critisized?
They seem to have water levels under control in all pools now so any renewed hydrogen production should be unlikely. Same with the reactors , the vessel temperatures are quite low and nice so the temperature of the fuel rods cant be to high. Its hard to say if there is a lot of hydrogen within the containments lingering from earlier production that could be released and cause more explosions in case of venting.
But since the number 1 and 3 buildings are gone a venting wont cause a accumulation of hydrogen. It could happen in number 2, but the containment situation there doesnt point towards a need for venting.
I would be surprised if there is not quite large amounts of mechanical damage to the fuel rods in the pool of the number 3 building. All the debries that fell down into it after the explosion is bound to have damaged the rods. They are already quite fragile after the time spent in the reactor.
The pool is placed where it is for easy access during refueling. But using them as a long term storage seems like an exceptionally bad idea after this incident. Changes needs to be made.
Johan, why could not a hydrogen explosion occur during the venting? Can you really control the amount of hydrogen let out in a situation like this so an explosion will not happen?
Maybe a major hydrogen explosion can not occur, I do not know, maybe someone else here has enough knowledge to answer that?
However since the pool appears to be damaged and open perhaps a more minor explosion could damage the fuel rods in the pool?
I am worried too that what we see today might be damage to the fuel rods in the pool. How much protection is there left if they are damaged?
Lennart, for a hydrogen explosion to happen, you need to gather quite a bit of hydrogen. This obviously cannot happen at #1, #3 and #4 now as the buildings have been blown out and the winds moves freely through them. Hydrogen is – as we all know – a very light gas with a low specific weight so it will rise quickly out and away from the wrecked buildings.
At worst right now we might get local hydrogen fires where the gas bubbles out of the water.
As far as damaged fuel cells go… here is what a typical fuel assembly looks like (scroll down to the BWR pictures):
http://www.world-nuclear.org/info/nuclear_fuel_fabrication-inf127.html
As you can see, the elements consists of big bundles of thin rods. In order to release the fission products, you must break a rod and peel away the cladding.
While the hydrogen explosions were violent, the fuel bundles were undoubtedly cusioned by the water, meaning the force on the bundles was evenly distributed. It’s hard to break a fuel bundle that way.
The biggest hazard as far as mechanical damage goes would be from falling material landing in the pool, on top of the bundles, and snapping them under the weight.
“The biggest hazard as far as mechanical damage goes would be from falling material landing in the pool, on top of the bundles, and snapping them under the weight.”
Which just might have happened.
Crack in the reactor confirmed?
“Concerns about Reactor No. 3 have surfaced before. Japanese officials said nine days ago that the reactor vessel may have been damaged.
A senior nuclear executive who insisted on anonymity but has broad contacts in Japan said that there was a long vertical crack running down the side of the reactor vessel itself. The crack runs down below the water level in the reactor and has been leaking fluids and gases, he said.
The severity of the radiation burns to the injured workers are consistent with contamination by water that had been in contact with damaged fuel rods, the executive said.
“There is a definite, definite crack in the vessel — it’s up and down and it’s large,” he said. “The problem with cracks is they do not get smaller.””
http://www.nytimes.com/2011/03/26/world/asia/26japan.html?_r=3&hp
Since the water the workers stepped into contained a bunch of short lived isotopes it can’t be from the spent fuel pools. So there must be a leak path from the containment into the turbine building basement.
But I don’t see why one would draw a conclusion that there is a damage to the vessel from that piece of information. Steam from the vessel of the reactors have been blown into the containments so that is the obvious path for the mentioned radionuclides to have taken. But we don’t know of any event that would have produced cracking of the vessel unless it has been exposed to severe thermal shocks.
Michael, it is not quite clear to me how the buildings look at the moment. Is there anything left of the roof above the used fuel pool?
I agree with your argumentation, if the buildings are totally blown out then the changes of a hydrogen explosion must be much smaller. (But details might be needed to say more.)
You imply that some of the roof might have fallen down on the used fuel rods in the pool. Just as you argue about explosion and water protection, water may have been protecting against falling roof parts too. However if the water had already gone away partly at that time, isn’t there then a much bigger risk that the rods may have been damaged? What was the state of the water at that time?
I think one can say with almost 100% certainty that many fuel rods have been damaged in the number 1 and 3 pools. The devastation of the number 4 building also seems so large that it would be unlikely for fuel rods not to have been damaged. From the pictures it seems like the crane used to move around fuel in the number 3 building is gone, if parts of that went down into the pool there must be quite large scale damage.
But if they manage to keep the water levels over the assemblies in the pools there should’t be much radionuclides escaping. Only if they go dry again and one get oxidation of the zirconium will we see a mechanism for spreading.
Of course if the pools are leaking then the leaking water will bring with it among other things cesium. Luckily that will only be a local problem around the plant.
Johan, why would Cesium-137 leakage be a local problem only? Cesium salts are very soluble in water. Will not Cesium-137 then follow the water sprinkled on the (possibly) leaking pools into the surroundings and futher on?
Thanks for the discussions today. I have some more worries that was made more clear from our discussions here, but I will wait a while with them. (And I am very surprised no one has taken them up yet.)
Thanks yourself! Your welcome to share your other worries as well. It is always interesting to have more points of views on this kind of event and we are all struggling with the lack of information. Most of what one can say is just educated guesses that might turn out wrong due to the lack of information.
About the cesium, due to the close proximity of the ocean I would venture a guess that anything flushed out of the pool will be flushed into the ocean rather than migrate inwards in some fashion. It should not take to long for it to dilute in the ocean and since nobody is drinking that water its not a public health risk.
Here seems to be a rather good overview of the spent fuels pools. At least it gives the amount of fuel and its current activity. I can see now why there has been problem in reactor 4 (which was not on duty at the time of the eathquake).
All Things Nuclear • More on Spent Fuel Pools at Fukushima
http://allthingsnuclear.org/post/4008511524/more-on-spent-fuel-pools-at-fukushima