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Japan Earthquake: nuclear plants

by gmax137
Tags: earthquake, japan, nuclear
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kloptok
#271
Mar16-11, 05:55 PM
P: 188
So according to Reno Denos post things appear to have calmed down at reactors 1-3, am I right in concluding that?

What about the exposed fuel rods in the reactor 4 building? I hear that the water could be completely evaporated ( http://www.nytimes.com/2011/03/17/wo...r.html?_r=1&hp ), something denied by TEPCO though it seems. In case this is true, would it possible that the fuel rods could ignite or melt in some way? Is cooling of these rods in progress?
Drakkith
#272
Mar16-11, 06:33 PM
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Quote Quote by JohanSjoman View Post
How come that they did not in some way let the hydrogen gas out of the building before it exploded. Could they not simply make holes in the reactor building?
COULD you? Yes. But thats generally a bad idea, If they KNEW hydrogen was building up they might have, but I'm guessing they had no idea it would explode like it did. In something like this you don't want to do anything to reduce the integrity of the reactor and surrounding structure. Don't want any radioactive materials released of course.
Homer Simpson
#273
Mar16-11, 07:01 PM
P: 191
However, if they had the design (someone said earlier they do) to vent via stacks to the outside, it would seem ridiculous to CHOOSE to vent inside, as the H2 Zr/steam reaction is well known. If it was chosen to vent inside just to allow decay of radiation before emitting outside, you might question the motives behind that choice, no?
Maclomer
#274
Mar16-11, 07:04 PM
P: 6
Snippet from BBC:

16 March 2011 Last updated at 16:16 ET
By Richard Black Environment correspondent, BBC NewsReactors

"Once a reactor is turned off, radioactivity and heat generation in the rods die away quickly; down to 7% of the original power within a second of switch-off, 5% within a minute, 0.5% within a day."

If this is true, where is all the heat coming from?
snoopies622
#275
Mar16-11, 07:06 PM
P: 611
Quote Quote by AntonL View Post
radiation leak is a very simple and misleading description
Indeed! It's been frustrating to hear so many TV anchors and reporters speak of "radiation leaks", "radiation exposure", "radiation levels", etc. without bothering to be specific about it.
promecheng
#276
Mar16-11, 07:32 PM
P: 22
Quote Quote by Maclomer View Post
Snippet from BBC:

16 March 2011 Last updated at 16:16 ET
By Richard Black Environment correspondent, BBC NewsReactors

"Once a reactor is turned off, radioactivity and heat generation in the rods die away quickly; down to 7% of the original power within a second of switch-off, 5% within a minute, 0.5% within a day."

If this is true, where is all the heat coming from?
Let's take unit 2 for example. It is rated at 784 MWe (MegaWatt electric). Let's say that it is 30% efficient, that would mean it is rated at just over 2,600 MWt (MegaWatt thermal). 0.5% of 2,600 is 13 MWt, or 13 million Watts of thermal energy. This is still a considerable amount of energy that needs to be removed via heat transfer.

Ideally water is present, as water is superior to air or steam when it comes to removing heat from an object it comes in contact with. If water is not present, the fuel cannot remove the heat as fast as it produces it, which causes its temperature to rise until it finds equilibrium of heat produced to heat transferred, (energy balance), or it reaches melting point of the material.
Bob S
#277
Mar16-11, 07:49 PM
P: 4,663
Quote Quote by promecheng View Post
Let's take unit 2 for example. It is rated at 784 MWe (MegaWatt electric). Let's say that it is 30% efficient, that would mean it is rated at just over 2,600 MWt (MegaWatt thermal). 0.5% of 2,600 is 13 MWt, or 13 million Watts of thermal energy. This is still a considerable amount of energy that needs to be removed via heat transfer.
The heat of vaporization of boiling water is 2260 joules per gram, or 8.55 MJ (megajoules) per gallon. To remove 13 MWt would require boiling about 1.5 gallons of water per second.

Bob S
promecheng
#278
Mar16-11, 07:54 PM
P: 22
Quote Quote by Bob S View Post
The heat of vaporization of boiling water is 2260 joules per gram, or 8.55 MJ (megajoules) per gallon. To remove 13 MWt would require boiling about 1.5 gallons of water per second.

Bob S
I think that makes sense. I'm rough guessing here as I don't have any tech. specs. in front of me, and no calculator, (sorry for any gross errors). Assuming a 10 ft. diameter x 25' tall vessel, the volume is approximately 15,000 gallons. 1.5 gallons/sec = 5,400 gallons/hr. I think I read earlier on that they thought the RPV would boil down in a few of hours if no water was added. 15,000 / 5,400 = < 3hrs.
SredniVashtar
#279
Mar16-11, 08:18 PM
P: 96
Quote Quote by kloptok View Post
What about the exposed fuel rods in the reactor 4 building? I hear that the water could be completely evaporated ( http://www.nytimes.com/2011/03/17/wo...r.html?_r=1&hp ), something denied by TEPCO though it seems. In case this is true, would it possible that the fuel rods could ignite or melt in some way? Is cooling of these rods in progress?
This comes from CNN, quoting the IAEA

Temperatures recorded at spent fuel pools at the Fukushima plant Tuesday reached 84.0 degrees Celsius (183 Fahrenheit) at Unit 4; 60.4 degrees C (141 F) at Unit 5 and 58.5 degrees C (137 F) at Unit 6, the International Atomic Energy Agency said.

The agency said on Wednesday that "no data" registered for Unit 4, and Unit 5 had risen to 62.7 degrees C (145 F) and Unit 6 had risen to 60.0 degrees C (140 F). The temperature of these pools is normally kept below 25 degrees Celsius (77 degrees F)

"no data"...
Thermalne
#280
Mar16-11, 08:19 PM
P: 263
Here is a link to the original IAEA article.

http://www.iaea.org/newscenter/news/...iupdate01.html

Also,

Injuries or Contamination at Fukushima Daiichi Nuclear Power Plant

Based on a press release from the Japanese Chief Cabinet Secretary dated 16 March 2011, the IAEA can confirm the following information about human injuries or contamination at the Fukushima Daiichi nuclear power plant.

Please note that this list provides a snapshot of the latest information made available to the IAEA by Japanese authorities. Given the fluid situation at the plant, this information is subject to change.

Injuries
2 TEPCO employees have minor injuries
2 subcontractor employees are injured, one person suffered broken legs and one person whose condition is unknown was transported to the hospital
2 people are missing
2 people were ‘suddenly taken ill’
2 TEPCO employees were transported to hospital during the time of donning respiratory protection in the control centre
4 people (2 TEPCO employees, 2 subcontractor employees) sustained minor injuries due to the explosion at unit 1 on 11 March and were transported to the hospital
11 people (4 TEPCO employees, 3 subcontractor employees and 4 Japanese civil defense workers) were injured due to the explosion at unit 3 on 14 March

Radiological Contamination
17 people (9 TEPCO employees, 8 subcontractor employees) suffered from deposition of radioactive material to their faces, but were not taken to the hospital because of low levels of exposure
One worker suffered from significant exposure during ‘vent work,’ and was transported to an offsite center
2 policemen who were exposed to radiation were decontaminated
Firemen who were exposed to radiation are under investigation

The IAEA continues to seek information from Japanese authorities about all aspects of the Fukushima Daiichi nuclear plant.
Taken from the IAEA facebook page.

http://www.facebook.com/notes/intern...02364423126685
meadowlark
#281
Mar16-11, 08:28 PM
P: 1
A couple of speculative questions:
1) Could the "explosion" reported within the #2 containment possibly be similar to a steam hammer event? Rapidly condensing steam vapor in the torus or elsewhere within the containment could have rocked the walls and resulted in a pressure drop. This would not necessarily mean containment was breached.
2) If fuel rods melt or crumble and drop to the bottom of containment or the spent stoage pools, could the fuel mass regain criticality because there would no longer be control rod moderation?
Bob S
#282
Mar16-11, 09:06 PM
P: 4,663
Quote Quote by meadowlark View Post
1) Could the "explosion" reported within the #2 containment possibly be similar to a steam hammer event? Rapidly condensing steam vapor in the torus or elsewhere within the containment could have rocked the walls and resulted in a pressure drop. This would not necessarily mean containment was breached.
Gaseous hydrogen mixed with air is a very violent explosive. A hydrogen explosion blew part of the reinforced concrete roof off the experimental area at the Cambridge Electron Accelerator in July 1965. A few liters of spilled liquid hydrogen mixed with the air in the experimental hall, about 30 meters wide by 60 meters long, and was ignited by a spark. One person died, and another seriously injured. See photo in

http://www.sciencemag.org/content/150/3698/866.full.pdf

Bob S
bondboy
#283
Mar16-11, 09:08 PM
P: 6
Quote Quote by Astronuc View Post
Generally the racks in which spent fuel is stored contain neutron absorbing materials, so if for some reason, the pool was flooded by pure water, the SFP would not go critical. The spent fuel is generally depleted - but each assembly could have some residual positive reactivity, especially as Xe-135 decay. Xe-135 is one of the strongest neutron absorbers, which during operation is in equilibrium - at steady-state, it's production rate = depletion rate.

http://en.wikipedia.org/wiki/Xenon-135

I believe when Unit 4 was shutdown, they did a full-core offload, which means that there is some fuel which still has considerable life left. That would compound the heat burden on the pool, and it would add positive reactivity in the pool.

If TEPCO is concerned, then I'd be concerned too. However, I am not familiar with the practices or their current SFP configuration.

Reactivity is a measure of how a material can contribute to criticality. The multiplication factor, k, is a way to measure criticality. k = 1 means critical (constant power), k < 1 means subcritical (neutrons (neutron flux) and power decreases), and k > 1 means supercritical (neutrons (flux) and power increases).

Positive reactivity increases k, while negative reactivity decreases k.

http://en.wikipedia.org/wiki/Neutron...ication_factor

In the spent fuel pool, we want k < 1, always!

http://hyperphysics.phy-astr.gsu.edu...235chn.html#c4
http://hyperphysics.phy-astr.gsu.edu...e/u235chn.html
http://hyperphysics.phy-astr.gsu.edu...ne/fiscon.html

See chapter 18 of this book
Nuclear engineering handbook By Kenneth D. Kok
http://books.google.com/books?id=EMy...A596&lpg=PA596
http://www.amazon.com/Nuclear-Engine...dp/1420053906/
Thank you for the response, i'll look up the information you attached shortly.

As a follow up, keep in mind I have no formal training on the material so please excuse my ignorance and i'm sorry if the answers are in the link you provided.
If unit 4 was in shutdown, they did a full-core offload after only one or two cycles and the cells where properly stored within the SFP (subcritical); can you guesstimate (given the fuel used and time since the shutdown) the amount of fuel left in the cells and what the consequences are during the different stages of the coolant failure they are experiencing given that the SFP is outside of the reactor containment unit? What happens when the pool "runs dry" as is now being reported? How fast does the fuel go from subcritical>critical>supercritical? What are the environmental impacts during each stage?
Simple logic tells me that the SFP is totally exposed to the environment given the latest attempts to refill the SFP (their dropping water from helicopters and spraying with water cannons). They started this at roughly 9am their time. This seems like a last ditch effort to me to try and cool the fuel within the SFP and that they are facing a worst case scenario (exposed SFP that is bone dry) yet the radiation levels being reported don't seem to be catastrophic.

Thanks,
Mike
Astronuc
#284
Mar16-11, 09:23 PM
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Quote Quote by promecheng View Post
Let's take unit 2 for example. It is rated at 784 MWe (MegaWatt electric). Let's say that it is 30% efficient, that would mean it is rated at just over 2,600 MWt (MegaWatt thermal). 0.5% of 2,600 is 13 MWt, or 13 million Watts of thermal energy. This is still a considerable amount of energy that needs to be removed via heat transfer.

Ideally water is present, as water is superior to air or steam when it comes to removing heat from an object it comes in contact with. If water is not present, the fuel cannot remove the heat as fast as it produces it, which causes its temperature to rise until it finds equilibrium of heat produced to heat transferred, (energy balance), or it reaches melting point of the material.
This might help.
       BWR  
Unit  Type      Assys   MWt (original)
  1      3       400     1381
  2      4       548     2381
  3      4       548     2381
  4      4       548     2381
  5      4       548     2381
  6      5       764     3293
Based on available data, TEPCO did not uprate those units from the original capacity.
Thermalne
#285
Mar16-11, 09:27 PM
P: 263
This question might have been addressed before. I didn't see it though.

What do you (Astronuc and other professions in the Nuclear Power field) believe is the future of the Fukushima Daiichi units that are affected by this incident?

Such as do you believe they will be decommissioned? Or repaired for future operation?
AtomicWombat
#286
Mar16-11, 09:28 PM
P: 150
Quote Quote by promecheng View Post
I think that makes sense. I'm rough guessing here as I don't have any tech. specs. in front of me, and no calculator, (sorry for any gross errors). Assuming a 10 ft. diameter x 25' tall vessel, the volume is approximately 15,000 gallons. 1.5 gallons/sec = 5,400 gallons/hr. I think I read earlier on that they thought the RPV would boil down in a few of hours if no water was added. 15,000 / 5,400 = < 3hrs.
This article from the Union of Concerned Scientists explains the boild off rate well.http://allthingsnuclear.org/post/3859682324
Angry Citizen
#287
Mar16-11, 09:30 PM
P: 867
What do you (Astronuc and other professions in the Nuclear Power field) believe is the future of the Fukushima Daiichi units that are affected by this incident?
This has been answered too. The seawater+boric acid combo used to cool 1-3 has essentially eliminated any chance for their future use. 4-6 are anyone's guess though.
Astronuc
#288
Mar16-11, 09:34 PM
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Quote Quote by bondboy View Post
Thank you for the response, i'll look up the information you attached shortly.

As a follow up, keep in mind I have no formal training on the material so please excuse my ignorance and i'm sorry if the answers are in the link you provided.
If unit 4 was in shutdown, they did a full-core offload after only one or two cycles and the cells where properly stored within the SFP (subcritical); can you guesstimate (given the fuel used and time since the shutdown) the amount of fuel left in the cells and what the consequences are during the different stages of the coolant failure they are experiencing given that the SFP is outside of the reactor containment unit? What happens when the pool "runs dry" as is now being reported? How fast does the fuel go from subcritical>critical>supercritical? What are the environmental impacts during each stage?
Simple logic tells me that the SFP is totally exposed to the environment given the latest attempts to refill the SFP (their dropping water from helicopters and spraying with water cannons). They started this at roughly 9am their time. This seems like a last ditch effort to me to try and cool the fuel within the SFP and that they are facing a worst case scenario (exposed SFP that is bone dry) yet the radiation levels being reported don't seem to be catastrophic.

Thanks,
Mike
We will hopefully get the technical details for the fuel and SFP.

The fuel assemblies have some positive reactivity based on their enrichment, burnup and configuration. However, it's the combination of the spent fuel racks (which contain a neutron absorber) and the fuel. I would expect that the fuel offload includes once-burned fuel, twice-burned, and I would guess some thrice-burned for discharge. I'll have to do some basic guesstimates, but I'd really need batch sizes.


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