How did they shut down the TMI-2 reactor?

  • #1
If most of the fuel assembly was melted (as shown in the below image) in the three mile island reactor #2, how were they able to insert the control rods? I would imagine the channels in which the rods are inserted through would have bee severely malformed, thus making it impossible to insert the rods all the way.

Are there other ways of permanently shutting down and cooling a nuclear reactor without using the boron control rods, and even if most of the core has been melted?

Off-topic, but is the ruined reactor at the TMI plant still inside it's containment vessel, or did they remove and replace it with another reactor?

http://www.inl.gov/threemileisland/i/core-damage.gif
 

Answers and Replies

  • #2
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At TMI the reactor was scrammed before the core overheated, so there was no problem inserting the control rods.

In general, if you have an accident where the water is removed from the core (like a large pipe break), the fission reaction stops because the water is required (it slows the neutrons, making the reaction possible). The overheating can occur because of the decay heat from the fission products produced during plant operation. This decay heat continues to be produced, though it decreases exponentially with time.

The damaged core at TMI was removed from the site many years ago.
 
  • #3
QuantumPion
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Are there other ways of permanently shutting down and cooling a nuclear reactor without using the boron control rods, and even if most of the core has been melted?
Yes, you dump a bunch of boron in the reactor. At Fukushima they are adding borated seawater to cool the reactor and ensure it remains very subcritical, even if damaged.
 
  • #4
Drakkith
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The Three Mile Island incident, just like the one they are currently battling in Japan, was due to decay heat from waste products of the reaction. In both cases the reactors were all shutdown successfully by inserting control rods. However, the waste products are much more radioactive than the fuel itself is, and just by themselves will produce heat. The TMI incident happened because coolant was unable to flow into the core and cool it after the core shut down. They are trying to avoid a similar situation in Japan.
 
  • #5
The Three Mile Island incident, just like the one they are currently battling in Japan, was due to decay heat from waste products of the reaction. In both cases the reactors were all shutdown successfully by inserting control rods. However, the waste products are much more radioactive than the fuel itself is, and just by themselves will produce heat. The TMI incident happened because coolant was unable to flow into the core and cool it after the core shut down. They are trying to avoid a similar situation in Japan.
So I guess it's just about trying to get water to the core by any means possible..

Is there any structure beneath the reactor vessel to catch the molten fuel if it burns it's way through the bottom of the reactor? Perhaps made from a material which will resist the white-hot 5,000+ degree heat from the molten fuel? So it won't burn it's way through the Earth and into the ground water creating "the china syndrome?"
 
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  • #6
Drakkith
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The core is contained in the reactor vessel which is located in a concrete building I believe. I don't know the details though. I'm pretty sure there is something beneath it.
 
  • #7
The core is contained in the reactor vessel which is located in a concrete building I believe. I don't know the details though. I'm pretty sure there is something beneath it.
Roughly eight feet worth of reinforced steel and concrete. Apparently the containment structure in one of the reactor buildings was badly damaged. I thought these structures were designed to withstand almost anything.
 
  • #8
Drakkith
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Roughly eight feet worth of reinforced steel and concrete. Apparently the containment structure in one of the reactor buildings was badly damaged. I thought these structures were designed to withstand almost anything.
Looks like it withstood the whole thing pretty well to me, given the circumstances.

And honestly, there is a limit to what they can withstand.
 
  • #9
Looks like it withstood the whole thing pretty well to me, given the circumstances.

And honestly, there is a limit to what they can withstand.
Do you think the reactor vessel itself in the below image which appears to have been devastated by an explosion (the one with smoke pouring out of it) has been comprimised?

alg_fukushima-reactor-number-4.jpg
 
  • #10
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Do you think the reactor vessel itself in the below image which appears to have been devastated by an explosion (the one with smoke pouring out of it) has been comprimised?

alg_fukushima-reactor-number-4.jpg
That picture is from Reactor unit 4 I believe. The reactor vessel is believed to be undamaged and here is a picture of what it's suppose to look like.

general-electric-boiling-water-reactor-mark-I.jpg


What happened is the actual vessel is intact and undamaged. The roof blow off.

The reactor that has suspected vessel damage is reactor 2. They believe the Torus (The donut at the bottom of the picture) is cracked somewhere.
 
  • #11
That picture is from Reactor unit 4 I believe. The reactor vessel is believed to be undamaged and here is a picture of what it's suppose to look like.

general-electric-boiling-water-reactor-mark-I.jpg


What happened is the actual vessel is intact and undamaged. The roof blow off.

The reactor that has suspected vessel damage is reactor 2. They believe the Torus (The donut at the bottom of the picture) is cracked somewhere.
I don't trust what the media is saying about the condition of the reactors. I have a feeling the media both in Japan and elsewhere is downplaying the severity of this disaster. There's no way the reactor inside that decimated building (unit 4) isn't severely damaged. The cooling pumps and the pipework which supplies cooling water to the core have probably been destroyed in the hydrogen explosions.

It really isn't the reactors I'm concerned about, it's the some 600,000 spent nuclear fuel rods which are housed at the top floor of the reactor buildings. Apparently these rods pose a FAR greater radiological hazard than the worst thing that could possibly happen to the reactor core.

I believe the smoke pouring out of that reactor building is from the burning spent fuel, and not from the reactor itself.
 
  • #12
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I don't trust what the media is saying about the condition of the reactors. I have a feeling the media both in Japan and elsewhere is downplaying the severity of this disaster. There's no way the reactor inside that decimated building (unit 4) isn't severely damaged. The cooling pumps and the pipework which supplies cooling water to the core have probably been destroyed in the hydrogen explosions.

It really isn't the reactors I'm concerned about, it's the some 600,000 spent nuclear fuel rods which are housed at the top floor of the reactor buildings. Apparently these rods pose a FAR greater radiological hazard than the worst thing that could possibly happen to the reactor core.

I believe the smoke pouring out of that reactor building is from the burning spent fuel, and not from the reactor itself.
The pumps providing cooling for the core is contained around the reactor. It is not in the part that was affected by the Hydrogen explosion. The core was not suspected to be damaged in units 1, 3, and 4. The major containment were not suspected to be damaged.

The smoke pouring out is suppose to be an oil fire from a pump (unrelated to the core) in the top level.
 
  • #13
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I believe the smoke pouring out of that reactor building is from the burning spent fuel, and not from the reactor itself.
Last time I checked, uranium dioxide doesn't burn, nor does Zircaloy.
 
  • #14
The pumps providing cooling for the core is contained around the reactor. It is not in the part that was affected by the Hydrogen explosion. The core was not suspected to be damaged in units 1, 3, and 4. The major containment were not suspected to be damaged.

The smoke pouring out is suppose to be an oil fire from a pump (unrelated to the core) in the top level.
The building with steam pouring out of it has been nearly flattened. There isn't any way the containment structure and reactor vessel have not been severely compromised or even already destroyed. The other damaged reactor buildings are in much better shape, but it's (number 2?) I'm worried about.

[URL]http://images.mirror.co.uk/upl/m4/mar2011/7/7/image-4-for-japan-crisis-close-up-images-of-fukushima-nuclear-power-plant-gallery-227834778.jpg[/URL]
 
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  • #15
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If reactor four was shut down why is it a mess. I think they forgot about the pools of fuel rods while fighting the problems of other reactors and let the water get low. Also if 14 reactors of the same design were effected by the same earthquake and tsunami why is it that only four are effected. I think that they restarted these reactors after the earthquake and before the flood. There were also early reports on the internet only ,that other reactors north of ****inchina were in trouble and now we hear nothing about them. I like to see how they entomb these in a earthquake prone area.
 
  • #16
Drakkith
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If reactor four was shut down why is it a mess. I think they forgot about the pools of fuel rods while fighting the problems of other reactors and let the water get low. Also if 14 reactors of the same design were effected by the same earthquake and tsunami why is it that only four are effected. I think that they restarted these reactors after the earthquake and before the flood. There were also early reports on the internet only ,that other reactors north of ****inchina were in trouble and now we hear nothing about them. I like to see how they entomb these in a earthquake prone area.
It is believe that Hydrogen, either from Unit 3, or from the spent fuel pond accumulated and exploded.

The 4 that were affected were all at the same site. The tsunamai flooded the generator room which caused an eventual loss in power to the core cooling system. The others did not have their generators flooded and had continual power to cool the cores. The most definately did NOT restart the 3 reactors between the quake and the flood. The incident was caused by decay heat generated naturally from the fuel. This is normally removed via the cooling system, but loss of external power, generator power, the eventual failing of the batteries due to use, and an inability to quickly hook up alternate power to the plant due to issues with the switchgear.
 
  • #17
Astronuc
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If reactor four was shut down why is it a mess. I think they forgot about the pools of fuel rods while fighting the problems of other reactors and let the water get low. Also if 14 reactors of the same design were effected by the same earthquake and tsunami why is it that only four are effected. I think that they restarted these reactors after the earthquake and before the flood. There were also early reports on the internet only ,that other reactors north of ****inchina were in trouble and now we hear nothing about them. I like to see how they entomb these in a earthquake prone area.
Unit 4's reactor vessel was undergoing maintenance. The full core had been offloaded into the spent fuel pool. That is unique about Unit 4 at FK. Unit 5 and 6 also shutdown for maintenance, but may have had fuel in the cores.

Units 1, 2, 3 were shutdown upon detection of seismic activity, and loss of grid which would trigger protection systems. The emergencies diesel generators (EDGs) were operating as expected until a tsunami of unanticipated magnitude took them out. Then battery backup was used until that ran out or was damaged. That's when all the safety systems requiring power failed - and the rest is history.
 
  • #18
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Also if 14 reactors of the same design were effected by the same earthquake and tsunami why is it that only four are effected.
They weren't. Only Fukushima Daiiachi 1-6 got flooded since all other NPPs in the tsunami region were built on higher ground.
Daiichi 5 and 6 were already in shutdown state when the Tsunami hit AND they were built higher than Units 1-4, that's why they survived.
 
  • #19
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A water force of extraordinary magnitude. (dr. klan)
 
  • #20
They shouldn't build nuclear power plants in areas which are highly vulnerable to earthquakes and tsunamis. It wasn't the earthquake which caused the ordeal at the Fukashima plant, it was the tsunami which destroyed some of the buildings that housed the cooling pumps for the reactors, and the fact that the plant lost power after the quake/tsunami.
 
  • #21
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Actually no building was destroyed by the tsunami, altough it is very likely that sea water pumps (vital for cooling on the secondary side) were damaged severely and would alone have caused major concerns.

Basements housing emergency diesel generators were simply flooded, truth is Fukushima Daiichi units 1:4 would have experienced the same tragic sequence even if confronted with a much less severe flooding event.

Unit 5 and 6 were saved by a series of factors: 3 meters higher grounds, presence of one "surviving" air cooled diesel generator and the fact that they were not operational when the quake hit.

Fukushima Daiini was saved mainly by the fact that one single line connecting it to the grid survived the quake.
A line the world should be grateful to.

We could go in depth to examine which, if any, other japanese plants as configured on march 11th, would resist the fault of all external lines AND the 15 meters high tsunami wave that hit Fukushima Daiichi.
My suspicion is that none would, altough more careful analysys on a plant to plant basys would be needed to state this conclusively.

The overall picture is one of a total failure of the japanese regulatory and technical framework when confronted with the scale of the phenomenon at hand.

My opinion is that such a scale of event was well within the scope of what could be envisaged as possible and failure to do so is a striking example of a recurrent "black swan" phallacy that our technical and organisational systems are prone to, in many fields.

For nuclear power such a phallacy spells disaster and could spell apocalypse. We went pretty damn close to it.

Regards
 
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  • #22
Actually no building was destroyed by the tsunami, altough it is very likely that sea water pumps (vital for cooling on the secondary side) were damaged severely and would alone have caused major concerns.

Basements housing emergency diesel generators were simply flooded, truth is Fukushima Daiichi units 1:4 would have experienced the same tragic sequence even if confronted with a much less severe flooding event.

Unit 5 and 6 were saved by a series of factors: 3 meters higher grounds, presence of one "surviving" air cooled diesel generator and the fact that they were not operational when the quake hit.

Fukushima Daiini was saved mainly by the fact that one single line connecting it to the grid survived the quake.
A line the world should be grateful to.

We could go in depth to examine which, if any, other japanese plant as configured on march 11th, would the resist the fault of all external lines AND the 15 meters high tsunami wave that hit Fukushima Daiichi.
My suspicion is that none would, altough more careful analysys on a plant to plant basys would be needed to state this conclusively.

The overall picture is one of a total failure of the japanese regulatory and technical framework when confronted with the scale of the phenomenon at hand.

My opinion is that such a scale of event was well within the scope of what could be envisaged as possible and failure to do so is a striking example of a recurrent "black swan" phallacy that our technical and organisational systems are prone to, in many fields.

For nuclear power such a phallacy spells disaster and could spell apocalypse. We went pretty damn close to it.

Regards
Fukashima wasn't "saved" by anything. The four reactors have been severely damaged and are pouring out lethal levels of radiation. It is the worst nuclear catastrophe next to Chernobyl. Most of the plant workers are probably going to die from cancer and radiation-related illness before the end of this year.

Here is an example to help describe the true gravity of the situation at the affected Japanese NPP. Trace amounts of radiation were detected in rainwater as far away as Massachusetts.

http://theintelhub.com/2011/03/27/f...ater-as-bio-robots-fight-to-prevent-disaster/
 
  • #23
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Hi, I share the extreme worry and the severe judgement on the scale and consequences of fukushima daiichi events.

My "saved" word was referred to the Daiini plant, not the Daiichi one that I would never refer to as something saved.
Actually I have been never more worried of any accident before in my life (I am an engineer with 22 yrs experience BTW, for what is worth).

Furtermore with regards to Daiini I was stressing that it was a rather lucky evenience (that fact that just one line did not fail) that saved the plant, otherwise we would be confronted with two disasters, not just one.

Tha fact (you may have seen the pics released a few days ago) that the tsunami wave resulted in a flooding, albeit of a massive scale, and not buldings being swept away as some naive people here in Italy think (imagining an event of truly epic proportions) is in my eyes an element of further negative judgement.
Taking countermeasures to such an evenience is far from impossible and the fact that it was not done in japan, adds to the responsabilities of the nuclear technical and regulatory framework there.

regards again
 
  • #24
I noticed how nothing is being said about the Fukashima disaster on the mainstream media. Probably because of a massive media blackout to prevent people in Japan and elsewhere, from panicking.

That is how bad the situation actually is....
 
  • #25
I noticed how nothing is being said about the Fukashima disaster on the mainstream media. Probably because of a massive media blackout to prevent people in Japan and elsewhere, from panicking.

That is how bad the situation actually is....
I sincerely believe the issue is too technical for the media to be able to report. All we are getting is TEPCO releases here and there of scientific data. The media really wants solid laymans conclusions to run with, and there simply aren't any yet (IMO).
 

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