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Japan Earthquake: nuclear plants

by gmax137
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Astronuc
#199
Mar15-11, 10:22 PM
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Quote Quote by Speedo View Post
Assuming that the generators had functioned normally, what kind of process would the reactors have gone through after the quake before they were brought back online?

I'm mainly wondering why it wasn't/isn't feasible to bring one reactor online at a low power setting to provide enough power to sustain cooling for the complex.
They tripped based on the seismic signals. But then they lost the grid - perhaps the local station.

Large equipment like turbines and generators don't like getting shaken very hard - so they would have to inspect 'all' major components. That would take days, especially if they had to compare the data with the design bases.

Because they lost the grid (connection to off-site, and perhaps the local swithyard or distribution system) - the emergency diesel generators came online. They worked! However, a tsunami destroyed the fuel system and apparently some electrical equipment. The slowly lost the ability to the reactor(s). There was no time to even think about a restart - and probably no way to use the electrical power if one did.

Some of that is conjecture because the detailed sequence of events and equipment failure is unknown. While Units 1, 2 and 3 seem to be suffering from the same common mode failure (tsunami damage), there are unique issues with each unit. We won't know for months.


BTW - I want to thank all the contributors for their thoughtful comments and questions.
tkny123
#200
Mar15-11, 10:57 PM
P: 1
I'm a humanities guy but I've been doing some reading and have some questions that maybe posters could answer.

1. I heard that the quick path to cold shutdown at Daiini was restoration of grid power then use of its normal pump systems. I heard that grid power was restored to Daiichi but none of the plant's primary and backup feedwater and injection systems are back up or seem to have any chance. Does anyone know why not? Could every single pumping system be disabled? Doesn't that seem unlikely?

2. Is there absolutely no scenario in which the reactor vessel or drywell could be breached? Some in media insist on that. Could someone put some figures to it?
2A. Temperature angle. I read that the melting point of steel is 2800 Faren and zircaloy 2200 F. Also that concrete starts to crumble at 1800 F. Does that mean there is no way a molten core could reach and sustain a temp of > 2800 F? If it could, why couldn't it melt through the vessel?
2B. Pressure angle. Seems like pressure must be able to present a problem and that is the reason for the current "feed and bleed" method. Is there a critical pressure level for the vessel? What has to happen for that level to be reached (i.e., rods totally exposed for x hours with no water?)?

3. Spent fuel rods. If a group of them get totally uncovered by cooling water, what could happen?
3A. Everyone agrees the rods could heat up, then zircaloy cladding melt, then what? If zircaloy melts at 2200 F, wouldn't the concrete under it start to at crumble at 1800 F? Could they sponteously combust, have a conventional fire, that could disperse radioactive material?
3B. I read different things on whether these rods could go "critical", which I understand to means "to restart fission" (but not explode like a bomb). Most in media say "no way" but TEPCO just said it can't rule it out in the case of Unit 4, and it seems like it may have already. See these articles. So can they go "critical" or not?
http://english.kyodonews.jp/news/2011/03/78403.html
http://online.wsj.com/article/SB1000...newsreel_world
3C. If fresh fission is possible, that's really bad bc it is outside of containment. Freshly fissioned uranium could disperse by fire or explosion (say by hydrogen).

Thanks in advance! I pray for the people of Japan and especially the heros at Daiichi who are sacrificing themselves.
Reno Deano
#201
Mar15-11, 11:25 PM
P: 128
The Mark I containment design consists of several major components, many of which can be seen on
page 3-16. These major components include:
The drywell, which surrounds the reactor vessel and recirculation loops,
A suppression chamber, which stores a large body of water (suppression pool),
An interconnecting vent network between the drywell and the suppression chamber, and
The secondary containment, which surrounds the primary containment (drywell and suppression
pool) and houses the spent fuel pool and emergency core cooling systems.

Technically the Mark 1 torus is outside the Primary containment, but connected by vent ducts.

See the following BWR systems description study guide:http://www.nrc.gov/reading-rm/basic-ref/teachers/03.pdf
AntonL
#202
Mar16-11, 01:14 AM
P: 521
That Nuclear power plants have heated swimming pools (spent fuel storage tanks)
and that the swimming pool heaters can start a meltdown process or catch fire
is news to me. Fukoshima I no 4 reactor fuel rods are all in this indoor swimming pool!

Any discussion on containment primary or secondary is now superfluous

What sort of safety is this!
And that the plant was designed by USA's General Electric the question to ask now is:
How many USA nuclear power plants have heated swimming pools?
AtomicWombat
#203
Mar16-11, 01:59 AM
P: 150
Quote Quote by AntonL View Post
That Nuclear power plants have heated swimming pools (spent fuel storage tanks) and that the swimming pool heaters can start a meltdown process or catch fire is news to me. Fukoshima I no 4 reactor fuel rods are all in this indoor swimming pool!

Any discussion on containment primary or secondary is now superfluous
Yes that is pretty much what the Union of Concerned Scientists is saying:
http://allthingsnuclear.org/post/389...s-at-fukushima
In particular, "If mechanisms to fill the pool at Unit 4 are broken, or if there is a need to repair the pool, it will be difficult to get workers close enough to do this. If spent fuel has been in the pool for a relatively short time, even if the water level is at the top of the fuel rods, the radiation dose to someone at the railing of the pool would give them a lethal dose in well under a minute. "

I am curious. Is anyone familiar enough with the Mark 1 BWR design to tell me whether the spent fuel pool will drain directly through the gaping hole in the reactor building.

http://www.abc.net.au/reslib/201103/r735227_5964756.jpg
snoopies622
#204
Mar16-11, 04:00 AM
P: 611
When they speak of radiation leaks, do they mean only neutrons, alpha, beta and gamma particles - or also other big atomic nuclei that are smaller than uranium nuclei but which will themselves break down and emit more neutrons, alpha, beta and gamma radiation?

Thanks.
Borek
#205
Mar16-11, 04:11 AM
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I believe in this context radiation leak means leak of a radioactive substance, not fact that radiation (be it alpha, beta, gamma) is detectable outside. Sure, when the radioactive substances leak there is a spike in the detected radiation, but it is an effect of the radioactive substances being present outside. As long as the radioactive material is present in the containment at least beta and alpha are almost completely stopped.
AntonL
#206
Mar16-11, 04:12 AM
P: 521
Quote Quote by snoopies622 View Post
When they speak of radiation leaks, do they mean only
neutrons, alpha, beta and gamma particles - or also other big atomic nuclei that are smaller than uranium nuclei but which will themselves break down and emit more neutrons,
alpha, beta and gamma radiation?

Thanks.
radiation leak is a very simple and misleading description
One should speak of radioactive contamination which
contain the original material Uranium as well as the
fission products like Caesium-137 and Iodine-131 both
again highly radioactive and to be avoided.

These fission products have been detected offshore and on-shore
myth_kill
#207
Mar16-11, 05:56 AM
P: 17
In the worst-case scenario, one or more of the reactor cores would completely melt down, a disaster that could spew large amounts of radioactivity into the atmosphere.
TCups
#208
Mar16-11, 06:13 AM
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Quote Quote by AtomicWombat View Post
Yes that is pretty much what the Union of Concerned Scientists is saying:
http://allthingsnuclear.org/post/389...s-at-fukushima
In particular, "If mechanisms to fill the pool at Unit 4 are broken, or if there is a need to repair the pool, it will be difficult to get workers close enough to do this. If spent fuel has been in the pool for a relatively short time, even if the water level is at the top of the fuel rods, the radiation dose to someone at the railing of the pool would give them a lethal dose in well under a minute. "

I am curious. Is anyone familiar enough with the Mark 1 BWR design to tell me whether the spent fuel pool will drain directly through the gaping hole in the reactor building.

http://www.abc.net.au/reslib/201103/r735227_5964756.jpg
Yikes!!!

The fuel rods are stored at (3) -- see:
larrymoencurl
#209
Mar16-11, 06:44 AM
P: 1
Can nuclear plants be built so excess pressure can be vented without so much risk of hydrogen explosions?
Astronuc
#210
Mar16-11, 07:01 AM
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Quote Quote by larrymoencurl View Post
Can nuclear plants be built so excess pressure can be vented without so much risk of hydrogen explosions?
Yes. TMI-2 successfully contained the hydrogen. Some plants have hydrogen recombiners to safely control of the combustion hydrogen.
AntonL
#211
Mar16-11, 07:23 AM
P: 521
Quote Quote by Astronuc View Post
Yes. TMI-2 successfully contained the hydrogen. Some plants have hydrogen recombiners to safely control of the combustion hydrogen.
and can these cope with the vast amount of hydrogen produced in an emergency situation? Why not just flood the building with CO2 in an emergency?
Astronuc
#212
Mar16-11, 07:45 AM
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Quote Quote by tkny123 View Post
I'm a humanities guy but I've been doing some reading and have some questions that maybe posters could answer.

1. I heard that the quick path to cold shutdown at Daiini was restoration of grid power then use of its normal pump systems. I heard that grid power was restored to Daiichi but none of the plant's primary and backup feedwater and injection systems are back up or seem to have any chance. Does anyone know why not? Could every single pumping system be disabled? Doesn't that seem unlikely?
It appears that the damage at the Daiichi site is much more extensive than at Daini. The damage seems to be due to a combination of seismic activity (?) and tsunami.

2. Is there absolutely no scenario in which the reactor vessel or drywell could be breached? Some in media insist on that. Could someone put some figures to it?
2A. Temperature angle. I read that the melting point of steel is 2800 Faren and zircaloy 2200 F. Also that concrete starts to crumble at 1800 F. Does that mean there is no way a molten core could reach and sustain a temp of > 2800 F? If it could, why couldn't it melt through the vessel?
Melting pt of UO2 2800C (5070F)
Melting pt of Zr-2 1850C (3362F)
Melting pt of SS304 1400-1455C (2550-2650F)

The oxidation of Zr-2 takes places at temperatures less than melting. A 'line in the sand' number is 1204C (2200F). However, it is expected that the cladding won't remain at that temperature for more than so many seconds. As the temperature increases, the oxidation rate increases exponentially.

At the base of a BWR fuel assembly is a cast steel tie-plate or nozzle. Under each fuel assembly is a steel pad which supports 4 fuel assemblies. The pad is supported by a large steel support plate. Under the support plate in a BWR, are various pieces of hardware supporting the control rod drive mechanism.

The core is inside a steel pressure vessel, and the pressure vessel sits in a steel-reinforced concrete chamber. It is expected that the damage fuel would be retained in the core supported by the various steel components. They should have the pressure vessel and containment flooded with water.

With the control rods interspersed between the fuel assemblies, the reactor is not expected to regain criticality.

2B. Pressure angle. Seems like pressure must be able to present a problem and that is the reason for the current "feed and bleed" method. Is there a critical pressure level for the vessel? What has to happen for that level to be reached (i.e., rods totally exposed for x hours with no water?)?
The critical pressure is based on the weakest part that would give way. The design pressure for containment is 4 atm based on what's been published so far. Usually there is some margin in design, so it could be a lot higher. In FK-I, a pressure of approximately 8.4 atm was recorded, and as far as we know, it's primary containment held. Not sure about the other units.

3. Spent fuel rods. If a group of them get totally uncovered by cooling water, what could happen?
3A. Everyone agrees the rods could heat up, then zircaloy cladding melt, then what? If zircaloy melts at 2200 F, wouldn't the concrete under it start to at crumble at 1800 F? Could they sponteously combust, have a conventional fire, that could disperse radioactive material?
3B. I read different things on whether these rods could go "critical", which I understand to means "to restart fission" (but not explode like a bomb). Most in media say "no way" but TEPCO just said it can't rule it out in the case of Unit 4, and it seems like it may have already. See these articles. So can they go "critical" or not?
3C. If fresh fission is possible, that's really bad bc it is outside of containment. Freshly fissioned uranium could disperse by fire or explosion (say by hydrogen).
The spent fuel pools would not go critical, especially if water is removed. The concern is that the fuel rods would get too hot, the Zr-2 cladding would breach and leak radioactive Xe and Kr gases, and maybe some I, Br, or worse the Zr-2 rapidly oxidizes (some are concerned about burning) which would release those aforementioned elements and Cs, and other volatile radioisotopes. That would add to the contamination at the unit, in the plant, but the gases and some volatiles, perhaps some small particulates would be carried into the atmosphere where they are carried on the wind.

I pray for the people of Japan and especially the heros at Daiichi who are sacrificing themselves.
We all do.
TCups
#213
Mar16-11, 08:34 AM
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Quote Quote by Astronuc View Post
The spent fuel pools would not go critical, especially if water is removed. The concern is that the fuel rods would get too hot, the Zr-2 cladding would breach and leak radioactive Xe and Kr gases, and maybe some I, Br, or worse the Zr-2 rapidly oxidizes (some are concerned about burning) which would release those aforementioned elements and Cs, and other volatile radioisotopes. That would add to the contamination at the unit, in the plant, but the gases and some volatiles, perhaps some small particulates would be carried into the atmosphere where they are carried on the wind.

We all do.
Astronuc:

IF the rods in the pool were perhaps not fully spent. . . for example, Unit 4 were shut down for maintenance, and all the fuel rod assemblies removed from the reactor core (and therefore removed from the primary containment) and IF, instead, they were in the SFP outside of the primary containment . . .

THEN, could loss of circulating coolant surrounding the rods in the SFP result in heat sufficient to boil off the remaining water, oxidize the Zr-2 cladding, generate steam + hydrogen + fires, burn through the floor and sidewall of the "dry" SFP, and "blow out" the side of the Unit 4 building?

Look where the photo (I hope it was a remote robotic taking the picture) is centered. What do you think they were assessing? Does it look to you like there is a "slag-like" tongue of something hanging out of a relatively square hole in roughly the location that might correspond to the SFP, and that a sideways blast has taken out some of the structures external to the building as well as the roof of the building?

http://www.abc.net.au/reslib/201103/r735227_5964756.jpg

The damage from explosion at Unit 4 is fundamentally different than that at Unit 3, where all the structures seem to be blown out away from the primary containment.
Astronuc
#214
Mar16-11, 08:54 AM
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Quote Quote by TCups View Post
Astronuc:

IF the rods in the pool were perhaps not fully spent. . . for example, Unit 4 were shut down for maintenance, and all the fuel rod assemblies removed from the reactor core (and therefore removed from the primary containment) and IF, instead, they were in the SFP outside of the primary containment . . .

THEN, could loss of circulating coolant surrounding the rods in the SFP result in heat sufficient to boil off the remaining water, oxidize the Zr-2 cladding, generate steam + hydrogen + fires, burn through the floor and sidewall of the "dry" SFP, and "blow out" the side of the Unit 4 building?
The spent fuel pool (3) is outside of primary containment. It sits on top of the concrete structure. Each fuel assembly sits in a square tube in a rack. The rack has neutron absorber material to prevent criticality. The water covering the fuel provides cooling and shielding. The concern is that the water evaporates, and exposes the fuel to air. The oxgyen in the air then oxidizes the Zr-2 cladding, which produces hydrogen. The question then is what caused the fire at unit 4? If it was hydrogen deflagration (not an explosion) - then what is the source of the hydrogen? If there is no fuel in the reactor vessel - it may be that it is coming from the SFP, which has already dried out. Could there have been other sources of hydrogen? Perhaps if the plant uses hydrogen water chemistry. Could there have been other sources of fuel? If so, what?

If fuel is taken from the spent fuel pool and shipped out of the reactor building, it would be do so in a shielded cask, which is shown in the picture. The cask contains several assemblies (~28 perhaps), and it is filled with He for cooling. Even so, the casks can get pretty hot. Smaller shipping casks, which hold fewer assemblies, do not get as hot as storage casks. The oldest, coolest fuel is put in storage casks if there is insufficient room to store all discharged fuel + a full core's worth.

Look where the photo (I hope it was a remote robotic taking the picture) is centered. What do you think they were assessing? Does it look to you like there is a "slag-like" tongue of something hanging out of a relatively square hole in roughly the location that might correspond to the SFP, and that a sideways blast has taken out some of the structures external to the building as well as the roof of the building?

http://www.abc.net.au/reslib/201103/r735227_5964756.jpg

The damage from explosion at Unit 4 is fundamentally different than that at Unit 3, where all the structures seem to be blown out away from the primary containment.
Units 1 and 3 had significant explosions, whereas unit 4 may have had a smaller explosion or fire. Or, was it damaged by the explosion and fire of unit 3?

I expect they are trying to assess the damage to unit 4 and how they might get water to the spent fuel pool.
Borek
#215
Mar16-11, 09:00 AM
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If memory serves me well unit 4 fire was explained as burning leaking oil - either lubricant or hydraulic. I can't locate source right now, besides, I read it in Polish.
Astronuc
#216
Mar16-11, 09:04 AM
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Quote Quote by AntonL View Post
That Nuclear power plants have heated swimming pools (spent fuel storage tanks)
and that the swimming pool heaters can start a meltdown process or catch fire
is news to me. Fukoshima I no 4 reactor fuel rods are all in this indoor swimming pool!

Any discussion on containment primary or secondary is now superfluous

What sort of safety is this!
And that the plant was designed by USA's General Electric the question to ask now is:
How many USA nuclear power plants have heated swimming pools?
The spent fuel pools are actually cooled. They are designed for interim storage of discharged fuel, and they are heated by the decay heat from the spent fuel. Every plant has them. In Mk I containment systems, they are at top of the reactor building under the metal housing atop the concrete structure. More modern plants have SFP locates in separate structure adjacent to the reactor building.

With respect to the spent fuel pool, clearly the Mk I containment is inadequate in the Fukushima event.


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