Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Astronuc]

News sites are reporting now that unit#2 core has melted through the bottom of the pressure vessel down to the floor of the drywell .

Based on what evidence?

Please be careful about making such claims, and please avoid making unverified or unsubstantiated claims.

Please cite one's source.


See also - http://www.world-nuclear-news.org/RS_Trench_water_under_investigation_2903111.html

 

[timeasterday]

News sites are reporting now that unit#2 core has melted through the bottom of the pressure vessel down to the floor of the drywell .

What "news sites?"

Please provide a link to the source. I am not seeing anything out there.

 

[Joe Neubarth]

Based on what evidence?

Indeed!

I have the television on in the background and have not heard that story.

I Google News stories and there is no mention there.

 

[shogun338]

Based on what evidence?

Here is a link to one of the stories . http://www.guardian.co.uk/world/2011/mar/29/japan-lost-race-save-nuclear-reactor

 

[|Fred]

google gave me:
Richard Lahey, who was head of safety research for boiling-water reactors at General Electric when the company installed the units at Fukushima, told the Guardian workers at the site appeared to have "lost the race" to save the reactor ../..
the indications we have, from the reactor to radiation readings and the materials they are seeing, suggest that the core has melted through the bottom of the pressure vessel in unit two, and at least some of it is down on the floor of the drywell

to be noted:
Richard Lahey in an other interview http://live.washingtonpost.com/fukushima-nuclear-expert.html said on the 21th regarding melting:
"It is not likely as long as there is water in the reactor pressure vessels. The only concern that i have is long term cooling using salt water, since after a while the salt may plug up the fuel. Anyway, if the lower head of the vessels does melt the corium released will interact with the concrete basemat and radioactivity will be released to the environment (not likely in this accident)."

=> Did he get unreleased evidence regarding water level in the RPV ? I do not think so , in the Guardian article he formulate a speculation "I hope I'm wrong etc"

 

[divmstr95]

Yes - it's about the nature of the fire and dispersion. However, a fire is not necessary for dipersion of gases or volatiles. Gases escape on their own, and volatiles can be carried by steam or air currents.

A Zr-fire would imply a significant exothermic reaction with temperatures of about 3000 K or greater - white hot - like a welder's arc. That would have lit up the containment and area. I don't think we saw that.

I believe the hydrogen explosion was over the containment - above the pool. The hydrogen was attributed to the core, not the SFP in Units 1, 2, and 3. In Unit 4, it has been assumed that the hydrogen did come from SFP - and probably the fuel that was offloaded last November from the core.

Er, I guess I wasn't clear in my earlier post - I was speaking strictly about Unit 4 SFP.

Some believe the way the building appears to be damaged that it is sagging from high temperatures. I guess only time will tell.

Thanks for the insight. This is a great forum. Wish I had known about it before this event.

 

[rhody]

Decide for yourselves using http://www.google.com/#hl=en&sugexp...1&bav=on.2,or.r_gc.r_pw.&fp=ccb61cac0dc95407": core breach march 29

I think this is not based on official information, but information picked up and spread like the wind. I will leave it for you to decide.

http://www.google.com/url?sa=t&source=web&cd=1&sqi=2&ved=0CB8QFjAA&url=http%3A%2F%2Fblog.alexanderhiggins.com%2F2011%2F03%2F29%2Fjapan-maximum-alert-radiation-levels-plant-signal-meltdown-lethal-4-hours-12182%2F&ei=9Q6STa3nO6LA0QGNwOnMBw&usg=AFQjCNF4OmbIKy0cWTVlS7cw1AfdQP5gaw&sig2=EmF3qt2Imc2pZGsFVcqd8g"

Seems to be the trouble maker, but I could be wrong. Everything else I could find is before March 29th.

Rhody...

 

[M. Bachmeier]

Here is a link to one of the stories . http://www.guardian.co.uk/world/2011/mar/29/japan-lost-race-save-nuclear-reactor

This video from US expert is a little more balanced...

http://www.cbsnews.com/video/watch/?id=7360761n

 

[Joe Neubarth]

I had supposed that the massive explosion in reactor building number three was due to core melt down and melting through the reactor vessel to the containment area which was filled with cooler water. When the lava dripped through it created that massive steam explosion that scattered bit and pieces of Uranium and Plutonium around the site.

If Reactor Number Two had eaten through the bottom of the reactor why wasn't there a similar massive steam explosion? If the containment vessel was dry there probably would not have been any explosion. So when did this breach of the vessel happen?

The fact is we do not know if it has.

 

[AntonL]

Decide for yourselves using Google search: core breach march 29
Rhody...

I did - your post is position 7

 

[RealWing]

What Anton is seeing are not ruptured welds. At least I do not think they are welds. Most of thpse external pipes have lagging on them to prevent people from getting burned or to prevent collection of ambient condensate which can rust the pipes. The lagging is usually covered by a thin metalic foil of some sort, most likely aluminum or thin stainless steel. It would be subject to shock wave wrinkling.

I agree - looks like simple insulation/lagging blown off to me.

 

[rhody]

I did - your post is position 7

I don't think it is reliable, because his blog site lists quotes with no dates, and everything else I can find says nothing new (and verifiable) as best as I can tell.

Some of the google links I clicked with "additional dates of March 29th in header" text would not load for me so I couldn't dig any further. A bit frustrating.

Rhody...

 

[alexhiggins]

I don't think it is reliable, because his blog site lists quotes with no dates, and everything else I can find says nothing new (and verifiable) as best as I can tell.

Some of the google links I clicked with "additonal dates of March 29th in header" text would not load for me so I couldn't dig any further. A bit frustrating.

Rhody...

Dates are at the top of the page right beneath the headlines.

The video is a verifiable news source.

I don't understand what is not verifiable... All quotes from mainstream media with links to the original source along with the video which clearly has the headline "Nuclear Reactor Core Breached"

 

[NUCENG]

And what caused the welds on these pipes to break and unfurl? (https://www.physicsforums.com/showthread.php?p=3198789&highlight=pipes#post3198789") as arrowed and you can see fuel service tunnel panels been blown out to the right of the arrow

received no answers to #589 yet

I apologize if this shows up twice, Had a computer hiccup when I tried to post on this.

I believe what you are seeing is damage to pipe insulation. Woud be fewer welds in a long straight pipe run like that, but metal strapped insulation is applied in short sections. Since a pipe rupture would happen at a weak point I wouldn't expect to see a failure that appears to run the full length of the pipe.

 

[shogun338]

I had supposed that the massive explosion in reactor building number three was due to core melt down and melting through the reactor vessel to the containment area which was filled with cooler water. When the lava dripped through it created that massive steam explosion that scattered bit and pieces of Uranium and Plutonium around the site.

If Reactor Number Two had eaten through the bottom of the reactor why wasn't there a similar massive steam explosion? If the containment vessel was dry there probably would not have been any explosion. So when did this breach of the vessel happen?

The fact is we do not know if it has.

An explosion was heard after 06:14 JST on 15 March in unit 2, possibly damaging the pressure-suppression system, which is at the bottom part of the containment vessel.The radiation level was reported to exceed the legal limit and the plant's operator started to evacuate all non-essential workers from the plant. Only a minimum crew of 50 men, also referred to as the Fukushima 50, was left at the site. Soon after, radiation equivalent dose rates had risen to 8.2 mSv/h around two hours after the explosion and again down to 2.4 mSv/h, shortly after.Three hours after the explosion, the rates had risen to 11.9 mSv/h. What else would have caused this explosion in the bottom of the reactor ?

 

[DosEnbier]

@AntonL @NUCENG @...



http://img.ibtimes.com/www/data/images/full/2011/03/15/74343-an-aerial-view-of-tokyo-electric-power-co-s-fukushima-daiichi-nuclear-.jpg

look at the pipes

 

[NUCENG]

I assume the ultimate temperature of the melt would depend on the mass of the molten material and the equilibrium between internal heat generation and conduction/radiation of heat away from the melt. I presume it could get awfully hot - enough to easily melt steel and even concrete with which it is said to react chemically.

So many detailed practical questions and a lot of very smart people here putting out very ingenious conjecture here - all of which I find extremely valuable. This is one of the best sites for information at present.

My own question: imagine a suspended fuel rod undergoing partial melt - the cladding melts on one place - does the lower end of the rod then drop to the bottom of the containment? It seems the cladding alone gives the rod structural integrity?

Reactor cooling is presently being achieved by 'injection' using fire pumps and others -considering the required volume of water one must assume that this is a closed, albeit leaky, loop. How does this mode of cooling differ from the one which failed after the tsumami and which we are told they are trying desperately to restore?

Fuel assemblies are only suspended while they are moving to or from the reactor via the refueling platform. In the reactor they sit on a nozzle on the core support plate. In the fuel pool they rest on the bottom of a fuel rack.

Probably the best idea of fuel assembly melting can be found in drawings about the TMI-2 accident. The hottest points are at the top of the bundle when the water drops below the Top of Active Fuel (TAF). Melting is preceded by Zr-H2O reactions which weaken the clad. This reaction is strongly exothermic and adds even more heat. As melting begins, it will dribble down the remainder of the rod, further damaging fuel and potentially blocking coolant flow past the adjacennt rods. This accelerates heating and fuel damage. Eventually corium can form a puddle at the bottom of the reactor vessel or the fuel pool. Once the core begins to relocate it loses the necessary core, control rod geometry that is guaranteed to keep the reactor subcritical. That is why they are adding boron.

If coolant is added to hot fuel it can shatter the rods causing unmelted fuel pellets to fall out of the rods. This left a "granola"-like rubble in the cavity at TMI-2.

 

[AntonL]

@AntonL @NUCENG @...
http://img.ibtimes.com/www/data/images/full/2011/03/15/74343-an-aerial-view-of-tokyo-electric-power-co-s-fukushima-daiichi-nuclear-.jpg

look at the pipes

That settles the issue - cladding it is

 

[shogun338]

@AntonL @NUCENG @...



http://img.ibtimes.com/www/data/images/full/2011/03/15/74343-an-aerial-view-of-tokyo-electric-power-co-s-fukushima-daiichi-nuclear-.jpg

look at the pipes

Here is a link to a very good video showing closeups on units and pipes around them.

 

[|Fred]

Documents provided by tepco called Conditions of Fukushima Dai-ichi Nuclear Power Station Unit 1-6 and updated every day or so, give information on Reactor pressure vessel temperature, namely "Feed water nozzle" and "bottom head of the Reactor Pressure vessel"

Some of the value seems to indicate malfunction but not all.. I'm sure that we can make use of some of those data,can't we?

exemple: http://www.nisa.meti.go.jp/english/files/en20110329-7-2.pdf

 

[NUCENG]

Decide for yourselves using http://www.google.com/#hl=en&sugexp...1&bav=on.2,or.r_gc.r_pw.&fp=ccb61cac0dc95407": core breach march 29

I think this is not based on official information, but information picked up and spread like the wind. I will leave it for you to decide.

http://www.google.com/url?sa=t&source=web&cd=1&sqi=2&ved=0CB8QFjAA&url=http%3A%2F%2Fblog.alexanderhiggins.com%2F2011%2F03%2F29%2Fjapan-maximum-alert-radiation-levels-plant-signal-meltdown-lethal-4-hours-12182%2F&ei=9Q6STa3nO6LA0QGNwOnMBw&usg=AFQjCNF4OmbIKy0cWTVlS7cw1AfdQP5gaw&sig2=EmF3qt2Imc2pZGsFVcqd8g"

Seems to be the trouble maker, but I could be wrong. Everything else I could find is before March 29th.

Rhody...

I have seen quite a bit of speculation that there is a large vertical crack in thereactor pressure vessel (RPV), but cannot figure out how they could tell. There has been no entry of the Dryell (Primary Containment) due to rad levels and I am not aware of cameras that would survive longtime exposure in the drywell during normal operations and they certainly haven't installed cameras since the accident. If pressure was high enough to cause a break it would likely occur in piping or rod penetrations of the RPV. Breaches due to core melt would be on the bottom of the vessel. It just doesn't seem to me that a vertical crack in the RPV can be any more than speculation.

At least I hope so.

 

[NUCENG]

@AntonL @NUCENG @...



http://img.ibtimes.com/www/data/images/full/2011/03/15/74343-an-aerial-view-of-tokyo-electric-power-co-s-fukushima-daiichi-nuclear-.jpg

look at the pipes

I did. There are some areas where the piping is broken. In one shot it looks like the pipe is disconnected at the building. This is probably due to the blast damage to the building.

In another shot a section of the piping is lying loose on a building roof. Again, from the destruction around it, it appears to be due to the explosion of the reactor building next to it (I believe it is Unit 3). The brief shots of the double run of the pipes in the video look like the were roughed up but I still don't see indications that they burst from overpressure insidee those pipes.

Some of these lines appear to be common vent lines from turbine and other buildings. Others may be offgas lines to the stacks. I worked for 15 years as an engineer at a single unit BWR-4 Mk I power plant in the States and am not certain how those systems are routed in a multi-unit site in Japan.




,

 

[DosEnbier]

..[/url]

indeed
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/v8/Main.html

 

[RealWing]

Fuel assemblies are only suspended while they are moving to or from the reactor via the refueling platform. In the reactor they sit on a nozzle on the core support plate. In the fuel pool they rest on the bottom of a fuel rack.

Probably the best idea of fuel assembly melting can be found in drawings about the TMI-2 accident. The hottest points are at the top of the bundle when the water drops below the Top of Active Fuel (TAF). Melting is preceded by Zr-H2O reactions which weaken the clad. This reaction is strongly exothermic and adds even more heat. As melting begins, it will dribble down the remainder of the rod, further damaging fuel and potentially blocking coolant flow past the adjacennt rods. This accelerates heating and fuel damage. Eventually corium can form a puddle at the bottom of the reactor vessel or the fuel pool. Once the core begins to relocate it loses the necessary core, control rod geometry that is guaranteed to keep the reactor subcritical. That is why they are adding boron.

If coolant is added to hot fuel it can shatter the rods causing unmelted fuel pellets to fall out of the rods. This left a "granola"-like rubble in the cavity at TMI-2.

I agree- TMI gives some very good clues as to what is happening in these reactors.

There have been several posts about cooling of the fuel rods after the core is partially uncovered. There have been many, many theoretical and experimental projects (some using heated rods and some using actual fuel in test reactors) since the first reactors were designed to first understand things like Critical Heat Flux (CHF) and Boiling Transition (BT) and Film Boiling and Dryout etc. All of this work has gone into sophisticated safety analysis programs that are used by the utilities as part of their formal Safety Reports to the regulators.
All of this can be somewhat simplified (I'm a simple minded engineer) by thinking of a water droplets dropped onto a hot frypan. They jump and dance due to a thin layer of insulating vapor between the droplets and the plate. The plate is not cooled in this process in the short term.
Now back to very hot exposed fuel elements. Injection of cooling water starts a "rewetting" phase (you can Google this and CHF and BT and spend years reading!) and it takes considerable time to cool any fuel due to this insulating film effect.
If we assume the core remained partially uncovered, the water will boil at some point in the bottom of the core, but the steam being generated will not be sufficient to cool the exposed rods at the top of the core. The water vapour (steam) will not get anywhere near the surface of the hot fuel rods to impart any cooling. (This is totally different than saturated steam cooling (at a defined void fraction)when the reactor is at power and this high velocity steam is passing by the fuel rods.)
The exposed rods will continue to heat up and finally melt - just like they did at TMI.
Only when you reflood the whole core will this stop.

It will probably be several years before we get a look inside (assuming they regain core cooling), but in my humble opinion, it will look very similar to the pictures of the TMI reactor core - except for the salt deposits!

 

[Cire]

Did he get unreleased evidence regarding water level in the RPV ? I do not think so , in the Guardian article he formulate a speculation "I hope I'm wrong etc"

Richard Lahey is wildly speculating, which I suspect has more to do with getting paid to show up on news channels then it does to actually advance the understanding of what's happening.

A few points which I believe are correct would tend to disprove his assertion.

1. History has shown via three mile island that its very difficult to melt through a reactor vessel. In the case of three mile island 70% of the core slagged to the bottom of the reactor vessel and heated it to the point where the entire vessel was glowing red. In that case only 5/8" of inch out of 9" was ablated.

2. A reactor pressure vessel is a massive heat sink. I believe the drywell on both reactor 1 and 2 where flooded early on in the process; providing addition temperature relief. This doesn't include the water that has been injected since the start of the accident.

3. In three mile island the molten corium destroyed the temperature probes that measure the reactor pressure vessel, which is expected when you heat the sensors to this level. The temperature sensors are still functioning at the bottom of the reactor vessel on Unit 2. If the corium melted through the reactor vessel we would not have temperature data from the bottom of the reactor. I have yet to see a temperature measurement for the bottom of any of the reactor pressure vessels that comes anywhere near the melting point of steel.

4. Three mile islands coolant loss event occurred much earlier in the reactor shutdown process then did at Fukushima. This implies the fuel rods at three mile island suffered exponentially higher heat loads then the core at Fukushima.

finally, Richard Lahey states "The indications we have, from the reactor to radiation readings and the materials they are seeing, suggest that the core has melted through the bottom of the pressure vessel in unit two..."

What indications from the reactor? The radiation readings can be explained by the known damage suffered to the fuel storage pools.

Just my thoughts on the subject. I reserve the right to be mistaken.

 

[DosEnbier]

@NUCENG

That settles the issue - cladding it is

that's all, i hope

let's go ahead

 

[NUCENG]

Richard Lahey is wildly speculating, which I suspect has more to do with getting paid to show up on news channels then it does to actually advance the understanding of what's happening.

A few points which I believe are correct would tend to disprove his assertion.

1. History has shown via three mile island that its very difficult to melt through a reactor vessel. In the case of three mile island 70% of the core slagged to the bottom of the reactor vessel and heated it to the point where the entire vessel was glowing red. In that case only 5/8" of inch out of 9" was ablated.

2. A reactor pressure vessel is a massive heat sink. I believe the drywell on both reactor 1 and 2 where flooded early on in the process; providing addition temperature relief. This doesn't include the water that has been injected since the start of the accident.

3. In three mile island the molten corium destroyed the temperature probes that measure the reactor pressure vessel, which is expected when you heat the sensors to this level. The temperature sensors are still functioning at the bottom of the reactor vessel on Unit 2. If the corium melted through the reactor vessel we would not have temperature data from the bottom of the reactor. I have yet to see a temperature measurement for the bottom of any of the reactor pressure vessels that comes anywhere near the melting point of steel.

4. Three mile islands coolant loss event occurred much earlier in the reactor shutdown process then did at Fukushima. This implies the fuel rods at three mile island suffered exponentially higher heat loads then the core at Fukushima.

finally, Richard Lahey states "The indications we have, from the reactor to radiation readings and the materials they are seeing, suggest that the core has melted through the bottom of the pressure vessel in unit two..."

What indications from the reactor? The radiation readings can be explained by the known damage suffered to the fuel storage pools.

Just my thoughts on the subject. I reserve the right to be mistaken.

TMI-2 was a PWR. Damage scenarios for fuel in a PWR begin at the Onset of Nucleate Boiling (ONB). A BWR doesn't make any power until boiling occurs. They are concerned with a departure form Nucleate Boiling or dryout. A PWR may be closer to its limits, but anytime water level drops below the top of active fuel the fuel heatup is rapid and leads to damage in a very short time.

Unlike Fukushima TMI makeup water was blocked at the beginning of the event. Fukushima reactors probably used RCIC as long as they had steam and battery power. That could have delayed the onset of damage for several hours, depending on how they controlled the event. Once the reactor depressurized or the suppression pool reached its temperature limit, they were forced to vent containment to keep it below its limits, without having any makeup available for the RPV water level. That is the point where heatup and damage began.

TMI-2 was able to restore flow in the vessel and halt the meltdown before it reached significant damage to the reactor vessel. I amm not sure they have reached that point yet in Japan, so the reactor vessel could still be at risk. They have performed containment flooding, from the updates I have read, so that increases the heat sink for the reactor vessel.

If the vessel had been breached by corium melt-through it would likely result in a massive steam explosion due to the flooded containment. I haven't seen evidence of that yet. Further at that point you would start to see different isotopes due to interaction with concrete.

 

[jensjakob]

With the latest measurements - what can we then estimate the radiation to be in #2?

I.e. does the calculations below still hold meaning that there is +20 Sv/h inside #2?

Greetings, this is my first post and I'm not that good with english language, i apologize in advance.

I have a question regarding the radioactivity measurements in reactor #2 :

in this document (http://www.nisa.meti.go.jp/english/files/en20110327-1-5.pdf ) i understand there has been mistakes about I-134 and possibly other elements. But even without these I-134 and Co-56 numbers, something troubles me.

As i understand, they can only measure up to 1 sieverts with current equipment there (press reports worldwide are 1 sieverts per hour but original documents show MORE than 1 sievert per hour without more details. In this pdf, measurements inside Unit 3 are at 750 msv/h).

Knowing that for example :
I-131 - Unit 2 : 1.3×10E7 vs Unit 3 : 3.2×10E5
Cs-137 - Unit 2 : 2.3×10E6 vs Unit 3 : 5.6×10E4
the list goes on, but from what i see most elements are about 50 times higher in Unit 2 compared to Unit 3.

My question is : is there a way to calculate (approximately) the real number of Sv/h in Unit 2 (and outside Unit 2 probably now...), as we know Unit 3 water surface is at 750 msv/h ?

Oh, and thank you all for a very useful topic to help us understand the situation

 

[jensjakob]

When the activity of the water is 50 times higher, the dose rate above the water is also 50 times higher, because it is the same brew of isotopes. Edit: assuming equal depth.

So yes, the dose rate in the turbine hall of unit 2 is about 30 sievert per hour.

Which makes it impossible to do work there.

Has anyone rechecked these calculations - on basis of the latest sample analysis from the water of #2 basement?

30 Sv/h sounds like quite a lot (even though 3 SV/h is also a lot) - but it will be very interesting to get a second opinion

 

[Joe Neubarth]

Has anyone rechecked these calculations - on basis of the latest sample analysis from the water of #2 basement?

30 Sv/h sounds like quite a lot (even though 3 SV/h is also a lot) - but it will be very interesting to get a second opinion

30 Sv per hour sounds very frightening, almost as if there was a small fission process taking place somewhere in that pool of water. Since that is unrealistic, the measurements must be off, someway or somehow.