[Gerben42]

On request of Gonzalo, here's a fact check of the Fukushima incident.

Fukushima 1 is a Boiling Water Reactor built by GE-Hitachi. Unfortunately, the quake with strength 8.9 was well beyond the loads the plant was designed to handle. Not only off-site power supply was lost, but also the emergency power supply (normally by diesel engines) was damaged and as such unavailable.

The reactor was successfully shut down, but since the fission products in the core still produce several megawatts of energy in this state, continuous cooling is necessary. This cooling now was only possible using battery power, which then soon was depleted.

Without the cooling, the water level in the reactor pressure vessel (RPV) began to fall dangerously and it is my suspicion that partial core damage occurred. The explosion that occurred this morning is a likely witness of this. The most likely cause of the explosion is in my opinion a hydrogen combustion in the reactor building, caused by a zirconium oxidation (Zr + 2 H2O -> ZrO2 + 2 H2) after a heating up of part of the core.

As we are already more than a day after the reactor was shut down, the core degradation will progress relatively slowly, so that the cooling with sea water that is currently undertaken is promising. As only a small amount of water will be able to do the trick (5 litres per second will more than suffice) hopefully soon the reactor will have reached a controlled state and a melt-through of the RPV will be avoided, as it was in Three Mile Island.

The crisis team is taking the right steps at the moment and seems to be in control of this situation. Given that they were close to the centre of one of the strongest earthquakes ever recorded, one should not underestimate this feat. It shows that the hard work to be prepared for such events saves lives.

In contrast, in Chernobyl, which was basically a plutonium factory that could also be used for power generation, had a graphite-cooled core without a containment. When the graphite caught fire there was no barrier between the core and the environment, and the result was a catastrophe without equal. Worse: there was no outside cause of the accident - it was human failure after knowingly putting some safety systems out of work.

Even the worst-case-scenario for Fukushima, or for that matter any western nuclear reactor, cannot be compared with what happened almost exactly 25 years ago.

It is my job to know about these things, as in my daily work I investigate the likelihood and progression of severe accidents in nuclear power plants, and help to improve on existing and future designs from this perspective. I hope this information is helpful for you.

[Aberlour10]

Gerben42, on 2011-March-12, 11:22, said:

On request of Gonzalo, here's a fact check of the Fukushima incident. Fukushima 1 is a Boiling Water Reactor built by GE-Hitachi. Unfortunately, the quake with strength 8.9 was well beyond the loads the plant was designed to handle.

It is strange even for the pure amateur like me. The maginitude 8.9 has been registered in the epicentre of the earthquake, Fukushima was about 170 km away from it, so the magnitude there had to be lower ( how much? ) If so, every nuclear plant design in such active seismic region like Japan had to consider a quake of this strongness or?

[hotShot]

Aberlour10, on 2011-March-12, 12:17, said:

It is strange even for the pure amateur like me. The maginitude 8.9 has been registered in the epicentre of the earthquake, Fukushima was about 170 km away from it, so the magnitude there had to be lower ( how much? ) If so, every nuclear plant design in such active seismic region like Japan had to consider a quake of this strongness or?

It should have withstand a magnitude of 8, but you should remember that the scale is logarithmic.

[Gerben42]

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It should have withstand a magnitude of 8, but you should remember that the scale is logarithmic.

It's even more than logarithmic, 1 point on the Richter scale is a factor 32.

In 1978 there was an earthquake with 7.7 near Sendai, and the first four Fukushima reactors were already operational at this time.

Still, this earthquake released about 100 times more energy.
I'm used to big numbers, but I cannot grasp this amount of energy, which is 40.000 Hiroshima bombs...

[shintaro]

Just Curious

As the Power Plant appears to be on the edge of the Ocean

Why cannot they merely pump Water onto the reactor direct??

[PassedOut]

shintaro, on 2011-March-12, 15:24, said:

Just Curious

As the Power Plant appears to be on the edge of the Ocean

Why cannot they merely pump Water onto the reactor direct??

Looks like that's what they did: Japan Floods Nuclear Reactor Crippled by Earthquake to Avert a Full Meltdown

Quote

Japanese officials took the extraordinary step on Saturday of flooding a nuclear reactor with seawater in a last-ditch effort to avoid a nuclear meltdown, after an explosion there escalated the emergency caused by the huge earthquake and tsunami that destroyed parts of the country’s northeastern coast on Friday.

[Fluffy]

Thank you ao much Gerben

[shintaro]

PassedOut, on 2011-March-12, 15:41, said:

Looks like that's what they did: Japan Floods Nuclear Reactor Crippled by Earthquake to Avert a Full Meltdown

oopps cheers missed that news item

[blackshoe]

Good report, Gerben, thank you.

I have a degree in NE, though I never got to use it for anything, unfortunately. Still, I do remember some of what I learned back then, and what you say makes sense to me.

[cherdano]

Thanks!

[jjbrr]

Hi everybody. I'm jjbrr. You might remember me from such threads as the off topic thread and the "what should i have for dinner" thread.

I personally have found it helpful to read about the nuclear situation in Japan in very simple terms, so here are some quotes with information. Gerben seems much more of an expert than me, so he can comment if anything seems erroneous.

Cliffs: Barring some unexplored, sci-fi-esque scenario like you might see in movies, the very worst case scenario at this point seems to be that the land directly around the plant might become uninhabitable for an indeterminate amount of time in the case of a total meltdown. Consensus seems to be that radiation exposure will mostly be held to a minimum, and areas outside of Japan mostly have nothing to worry about.

Quote

Quote

So what happens in a worst-wosrt case scenario total meltdown? How far can the radiation spread by air? Is the radiation released into the water a concern outside the immediate vicinity? I've heard reports that Russia and Korea are preparing for possible evacuations.

Absolute worst case scenario would be a complete meltdown of the core, that melts through the pressure vessel, and also destroys the containment vessel. I really don't see a possibility of a chernobyl like steam explosion that would eject fuel material into the atmosphere. I certainly can't imagine a fire that would rage for 7 days like happened in chernobyl which put alot more radioactive material into the atmosphere. So hopefully you believe me when I say that this is not, even under the worst-worst scenario, going to be as bad as chernobyl.

Some of the fission products that are in the core are gases. Iodine and xenon will be released as radioactive gases. These will spread far and wide obviously, fortunately they will dillute quickly into the atmosphere and shouldn't cause much of a problem.

For the rest, it shouldn't spread very far from the plant. Some will get into the ocean right next door, some will contaminate the area around the plant. I believe that the 12 mile evacuation zone will be sufficient to protect the population.

Of course some crazy ass thing could happen that could cause an explosion, which would spread radioactive particles for potentially several hundred miles

Quote

http://www.reuters.c....72B2UN20110312

The Japanese nuclear safety agency has thus far deemed this accident to be a "four" on the nuclear incident scale. The scale is measured from 1-7. Seven being Chernobyl and a five being 3 mile island. This is an early estimate of course, but there are some things we can assume based solely on this information.

The amount of radiation released has been less than what was released at 3 mile island. The reason this is important is because the long term health effects of 3 mile island have been "statistically insignificant". I put that in quotes because I, like many scientists, assume that there is no such thing as a safe dosage of radiation. I would even go so far as to assume that someone somewhere has had some sort of severe health problem directly caused by three mile island, but that's my personal opinion.

The health effects that may have been caused by three mile island hasn't been widespread enough to increase the occurance rate above what is considered to be standard variance for the size of the population. I'm sure that everyone here on 2+2 can appreciate that.

So aside from the disaster that was Chernobyl, the most devestating nuclear disaster hasn't caused any measureable public health concerns. While I have to concede that there is no such thing as a zero probability of a level 6 or 7 disaster happening again, the chance of that happening gets closer and closer to zero with each incident that happens.

By the way the nuclear incident scale is a standard 10x scale. Each step up is 10x worse than the previous step.

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Salt water is very bad for reactors. This reactor will never operate again. That doesn't mean it's very bad in the sense that all hell breaks loose when you add seawater to a shut down reactor.

This post conflicts with the post above, but this was from early yesterday morning, when there was less information available.

Quote

Worst nuclear disaster with the exception of chernobyl. Three mile island doesn't even come close to this. The good news is, if the reactor pressure vessel remains intact this won't come anywhere near chernobyl. It's kinda like comparing a bowling ball to the moon.

To start you have to understand how many safety systems have failed to get to this point. A plant like this has multiple ways to add water to the reactor plant. It has electric driven pumps which can run off of the main power grid, the backup generators, and the backup backup batteries. It also has steam driven and probably air driven pumps.

For all of this to have failed, the plant would have had to take massive damage to it's support systems. Reports also say there were leaks in the primary cooling water system caused by the earthquake.

It's really hard for me to grasp all the **** that went wrong here. The engineers are basically living every single emergency drill I've ever done in one casualty.

-a reactor coolant leak
-a loss of cooling capacity
-a loss of all electrical power
-an overpressurization and overheating of the reactor plant
-hydrogen buildup in the reactor plant (caused by overheating of the material that holds the uranium fuel in place)
-hydrogen leaking into the secondary containment (the building that surrounds the reactor)
-then a hydrogen explosion (reported not confirmed, it could have been overpressurization due to steam combined with structural damage due to earthquakes) that blew the secondary containment apart.

The fact that the primary pressure vessel has survived this is pretty amazing.

Hope some of this has helped! Credit to will1530@2p2

[jjbrr]

one more re: the explosion that occurred at the facility yesterday (they called it a collapse of a structure; it's pretty obvious from video footage that some sort of explosion (possibly related to pressure built up from hydrogen gas) occurred):

Quote

Is the primary containment made of some indestructible material or something? Can't the explosions have exposed the deadly radioactive material to the air or environment somehow?

Quote

It's made of very thick steel and is pretty hard to breach. Indications are it was not breached due to no rise in radioactivity outside the building subsequent to the explosion. However it's possible it might have been breached or that it will later be breached via a meltdown. The point is that if this does happen, contamination will remain local. Chernobyl involved a reactor explosion and a week-long fire spreading particulate radioactive material into the air. The main vector of concern in the event of a core breach here would be water - groundwater or ocean water - how much of a concern that would be in Japan is anyone's guess, but you're not going to see contamination in China or Korea for instance.

[Gerben42]

Okay, today was my first day at work again after the weekend. Of course, many thoughts were posed to the situation in Fukushima and here is an update for you.

First of all, as some have already commented: The earthquake didn't do the damage, the tsunami did. After the earthquake, all reactors shut down and the emergency diesel generators took over to provide the power needed. Everything was allright up to the point where the tsunami hit and either flooded the diesels or destroyed their cooling. If you Google "Fukushima nuclear power plant" you can see that wave breakers are in place, but apparently the tsunami was too large to be stopped.

The accident progression then went on as I have described in my first post. Both explosions were indeed caused by hydrogen. When hydrogen is produced in the core, the pressure in the containment rises and in the GE Mark I containment which is used for these reactors, the pressure can only be reduced by releasing the atmosphere into the reactor building. This then caused a hydrogen burn and the spectacular-looking explosions. As in both cases at least 100 kg Hydrogen was burnt, it must be assumed that at least in reactor #1 there is significant core damage and probably in reactor #3 as well.

In both cases there was no damage to the containment itself, only to the reactor building. The measured fission product release so far is all from the (necessary) pressure relief of the containment.

At this point it is worth mentioning that this "GE Mark I containment" is a very old design and certainly not state-of-the-art. German BWR reactors, even the oldest ones, have a filtered venting system which holds back 99.9% of all fission products (except noble gases, particularly Xenon). In addition, the filtered containment atmosphere is then led into the chimney and not into the reactor building, so that the reactor building roof will not blow off like it did.

In the mean time, the containment and the RPV have been flooded with sea water. I cannot interpret today's news that the fuel rods are dry again. This would not be good but let's not exclude it.

So what's going to happen next?

Basically, 3 possibilities:

1. The RPV can be flooded with sea water and will not fail. In this scenario, there will be no further release of fission products into the environment. Still the sea water may in the long term damage the RPV and the containment should remain flooded, preferably with fresh water.

2. The RPV cannot be flooded with sea water. In this case, further core damage will occur. As the containment is flooded, there is a good chance that the RPV will not fail and the melt is contained inside the RPV (if not, see #3). In this case, there is still the necessity of further containment pressure releases which will mean some more relatively small release of fission products, most notably noble gases (esp. Xenon).

3. The RPV cannot be flooded and fails due to the heat of the melt. In this case we still have the flooded containment. Because already 3 days have past, the decay heat has now decreased to a level where the melt will no longer attack the underlying concrete when it's under water. So in this case, it's essential to keep water in the containment. For the rest, see #2.

All in all, it seems that there will be no long-term contamination of the area around the plant. The main radiation outside the plant comes from Xenon. This is good news, since as a noble gas it does not react with anything so that it doesn't contaminate the soil or gets incorporated into the body.
The main adverse health effect is caused by Iodine and its release is highly reduced by the measures taken by the crisis team.


Assuming the scenario unfolds as above, one should really credit the Japanese crisis team for its excellent work under extremely difficult conditions.

What can still go wrong?

The main risk is another earthquake and tsunami of similar size of the "big one" that will hit the damaged plants with their cover down. Or that for some unknown reason, it is no longer possible to get water into the containment, something that has already succeeded so far.

[helene_t]

Hi Gerben, could you explain what these "millisievert" numbers mean?

According to wikipedia, a milligray is one millijoule absorbed per kg body mass and a millisievert is something similar, with adjustments for factors other than the amount of energy (for example, type of radiation) that are of biological relevance.

So I can understand what it means that a particular human is exposed to say 100 millisievert during a particular year (or day or hour or w/e).

But the numbers I find in various news sources don't specify a particular location or just say "at the site". I would expect the numbers to many magnitudes larger just outside the reactor than in residential areas a few kilometers from the reactor. Or is that not the case? I could understand if measurements in residential areas have not been made, or if they are difficult to rely on as they change from minute to minute depending on wind directions, but nevertheless it would be necessary to get numbers from residential areas in order to decide on evacuation, wouldn't it?

[xxhong]

The situation got worse on last night as it appears. RPV of reactor 2 might be damaged and there were explosions in both reactor 2 and 4. Also, reactor 5, 6, 7 need to be cool down. Reactor 4, 5, 6 were not operating at the earthquake, but they were said to still have some heat left.
The most serious problem is probably the damage of RPV of reactor 2 I guess.

Gerben42, on 2011-March-14, 12:31, said:

Okay, today was my first day at work again after the weekend. Of course, many thoughts were posed to the situation in Fukushima and here is an update for you.

First of all, as some have already commented: The earthquake didn't do the damage, the tsunami did. After the earthquake, all reactors shut down and the emergency diesel generators took over to provide the power needed. Everything was allright up to the point where the tsunami hit and either flooded the diesels or destroyed their cooling. If you Google "Fukushima nuclear power plant" you can see that wave breakers are in place, but apparently the tsunami was too large to be stopped.

The accident progression then went on as I have described in my first post. Both explosions were indeed caused by hydrogen. When hydrogen is produced in the core, the pressure in the containment rises and in the GE Mark I containment which is used for these reactors, the pressure can only be reduced by releasing the atmosphere into the reactor building. This then caused a hydrogen burn and the spectacular-looking explosions. As in both cases at least 100 kg Hydrogen was burnt, it must be assumed that at least in reactor #1 there is significant core damage and probably in reactor #3 as well.

In both cases there was no damage to the containment itself, only to the reactor building. The measured fission product release so far is all from the (necessary) pressure relief of the containment.

At this point it is worth mentioning that this "GE Mark I containment" is a very old design and certainly not state-of-the-art. German BWR reactors, even the oldest ones, have a filtered venting system which holds back 99.9% of all fission products (except noble gases, particularly Xenon). In addition, the filtered containment atmosphere is then led into the chimney and not into the reactor building, so that the reactor building roof will not blow off like it did.

In the mean time, the containment and the RPV have been flooded with sea water. I cannot interpret today's news that the fuel rods are dry again. This would not be good but let's not exclude it.

So what's going to happen next?

Basically, 3 possibilities:

1. The RPV can be flooded with sea water and will not fail. In this scenario, there will be no further release of fission products into the environment. Still the sea water may in the long term damage the RPV and the containment should remain flooded, preferably with fresh water.

2. The RPV cannot be flooded with sea water. In this case, further core damage will occur. As the containment is flooded, there is a good chance that the RPV will not fail and the melt is contained inside the RPV (if not, see #3). In this case, there is still the necessity of further containment pressure releases which will mean some more relatively small release of fission products, most notably noble gases (esp. Xenon).

3. The RPV cannot be flooded and fails due to the heat of the melt. In this case we still have the flooded containment. Because already 3 days have past, the decay heat has now decreased to a level where the melt will no longer attack the underlying concrete when it's under water. So in this case, it's essential to keep water in the containment. For the rest, see #2.

All in all, it seems that there will be no long-term contamination of the area around the plant. The main radiation outside the plant comes from Xenon. This is good news, since as a noble gas it does not react with anything so that it doesn't contaminate the soil or gets incorporated into the body.
The main adverse health effect is caused by Iodine and its release is highly reduced by the measures taken by the crisis team.


Assuming the scenario unfolds as above, one should really credit the Japanese crisis team for its excellent work under extremely difficult conditions.

What can still go wrong?

The main risk is another earthquake and tsunami of similar size of the "big one" that will hit the damaged plants with their cover down. Or that for some unknown reason, it is no longer possible to get water into the containment, something that has already succeeded so far.

[Gerben42]

Today didn't go at all as I expected. After the problems in blocks 1 and 3 were solved, entirely new problems took the accident at Fukushima to a new dimension:

In block 2, they were trying to avoid the hydrogen explosion that had taken place in blocks 1 and 3 by opening up the roof. Although this succeeded, for some reason the depressurisation of the containment did not work as expected, causing a leak in the pressure suppression pool (part of the containment). The leak in this part of the containment DOES of course make it easier to inject sea water as there is now no longer a pressure difference between the containment and outside. Also, there is no air path between the melting core and the outside. So my reaction to this was: That didn't go very well but the consequences, although larger than for blocks 1 and 3, is not in the area where people need to start a panic.

This picture (source: www.grs.de) shows the radiation measurements at the plant.

http://www.grs.de/si...ima_Daiichi.png

The third peak shows the release due to the explosion in block 2.

To my horror, this was not the only thing that went wrong.

In block 4, which had been under revision, there was a fire in the spent fuel pool and the cooling water was boiling. These spent fuel pools are not normally a problem, as they do not require much cooling and can be left alone for more than 24 hours. However, half a week has past since Friday... When this starts to boil, it means that spent fuel rods which are OUTSIDE the containment may get exposed. And they still have problems filling the water level back up. This is the real disaster now. Never mind the three core melts going on. I can't get out of my mind that this part could have bene avoided. And I have still some hope that this will not lead to high dose levels. But I am worried about this, as this is taking place outside the containment.

All in all, my mood has gone from "don't panic" to "don't panic yet". I hope it moves back in the right direction.

[cherdano]

Gerben, I really appreciate these posts, thanks.

[matmat]

And now Merkel has closed a bunch of plants in Germany.

is it time to panic yet?

[Trinidad]

cherdano, on 2011-March-15, 17:13, said:

Gerben, I really appreciate these posts, thanks.

So do I

Rik

[Aberlour10]

matmat, on 2011-March-15, 20:08, said:

And now Merkel has closed a bunch of plants in Germany. is it time to panic yet?

She set only a three-month moratorium on extension of lifespans the older nuclear plants in Germany. Many see in it an electoral campaign trick. She faces a three important elections in the next fortnight, beginning this Sunday.