Japan Earthquake: nuclear plants


by gmax137
Tags: earthquake, japan, nuclear
oldsloguy
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#37
Mar12-11, 09:58 PM
P: 35
Quote Quote by Reno Deano View Post
Excerpt: 3.1.3 Release of Fission Products from Fuel Contaminant
Even though the reactor core may contain no defective fuel, natural uranium contamination of core construction materials and Zircaloy cladding, as well as enriched uranium contamination of the external cladding surfaces, could be the source of fission products in the coolant during power operations. The recoil range of a fission product is approximately 10 microns; therefore, only the fissions that occur within ≈10 microns of the outer surface of the Zircaloy cladding can introduce fission products into the coolant. It is safe to assume that half of the recoils from the fissioning nuclei will escape to the coolant and the other half will be embedded in the host material.

More Info: [url=http://www.nap.edu/openbook.php?record_id=9263&page=35
[/url]
Quote Quote by Astronuc View Post
If there was some corrosion of the cladding, or the fuel rods overheated, then the softer cladding balloon to the point of perforation. That is not core melting, and in general, core melting is something of a misnomer.

It's not clear what temperatures are reached in the core - whether the cladding got to 100 deg C or 1000 or more, or somewhere in between. While there is water boiling, then the cladding temperature is near the saturation temperature of the boiling water - at 4 atm or 8 atm or whatever the ambient pressure is.

In the steam region, the temperature would be higher because of the poor heat transfer in the steam, especially without forced convection.

One only needs a small breach in the cladding to release Xe, Kr and a little I. Iodine is water soluble, and it is more likely in the coolant.

An infrared thermometer could be used to gauge the temperature of the exposed drywell and inner containment.
Thanks, very interesting, that would explain why releases are observed but small.

When you say, “core melting is something of a misnomer“ are you meaning to imply that as a practical matter it would be difficult to actually achieve temperatures high enough to melt the fuel pellets? If so, does that mean that even in the worst case, release of fission products to the outside world would be pretty much limited to minor amounts due to the pellets remaining solid and thus sequestering the fission products? Can the noble gasses diffuse out of the pellets at rates what would be of any practical significance?
DR13
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#38
Mar12-11, 10:07 PM
P: 210
I'm too tired to summarize this but here is a link to the ANS updates:

http://ansnuclearcafe.org/

and a summary from ANS:

https://docs.google.com/viewer?a=v&p...p5Q2I04CnmM-aQ
vanesch
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#39
Mar13-11, 12:16 AM
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Quote Quote by Astronuc View Post
Drastic in the sense that seawater would not normally be introduced directly into the core. Salt water would corrode the stainless steel in the core. It's probably safe to say that unit 1 will not be restarted, but decommissioned. In theory though, it's life could have been extended another 20 years.
Maybe they will extend its life as the very first BSWR: Boiling Sea Water Reactor
marwood
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#40
Mar13-11, 12:59 AM
P: 9
update from WNN at
http://www.world-nuclear-news.org/RS...3_1303111.html
FlyingEng
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#41
Mar13-11, 06:07 AM
P: 8
How strong might be the impact to all the new builds? Does this influence OL3 and all the Chinese reactors? China planned to pour the concrete for the 1st commercial HTR end of this month... Maybe a delay?

Speculations only? What are your thoughts about it? Is there the next nuclear winter coming up soon?

FE
FishmanGeertz
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#42
Mar13-11, 06:17 AM
P: 190
I certainly hope it wasn't the reactor vessel itself that exploded....
DrDu
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#43
Mar13-11, 07:17 AM
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Quote Quote by FlyingEng View Post
How strong might be the impact to all the new builds? Does this influence OL3 and all the Chinese reactors? China planned to pour the concrete for the 1st commercial HTR end of this month... Maybe a delay?

Speculations only? What are your thoughts about it? Is there the next nuclear winter coming up soon?

FE
Well, at least the German government announced to stop the use of nuclear technology after the events although they wanted before to prolong the time older reactors could still be used.
Angry Citizen
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#44
Mar13-11, 07:53 AM
P: 867
Quote Quote by DrDu View Post
Well, at least the German government announced to stop the use of nuclear technology after the events although they wanted before to prolong the time older reactors could still be used.
A shame, because this is shaping up to be a textbook example of nuclear safety. Most of the backups and emergency procedures failed, yet it looks like little radiation has been or will be released. Considering this is a forty year plant that happened to be very near one of the largest earthquakes ever recorded, I'd say nuclear power is vindicating itself. Of course, I don't expect the ignorant masses to understand what's really going on. I swear, some people hate nuclear power just because it's got ATOMS.
Reno Deano
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#45
Mar13-11, 08:28 AM
P: 128
As I told a member of the public at a meeting concerning start-up of the Diablo Canyon plant, when ask, "what would be the consequences of the coastal area being hit by a 9.0 or larger earthquake". I replied that the nuclear plant would be the least of their worries, since they would be dead or swiming for their life in the sea anyway.
Astronuc
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#46
Mar13-11, 08:52 AM
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ANS has put out a brief which describes events at Unit 1:
  • The plant was immediately shut down (scrammed) when the earthquake first hit. The automatic power system worked.
  • All external power to the station was lost when the sea water swept away the power lines.
  • Diesel generators started to provide backup electrical power to the plant’s backup cooling system. The backup worked.
  • The diesel generators ceased functioning after approximately one hour due to tsunami induced damage, reportedly to their fuel supply.
  • An Isolation condenser was used to remove the decay heat from the shutdown reactor.
  • Apparently the plant then experienced a small loss of coolant from the reactor.
  • Reactor Core Isolation Cooling (RCIC) pumps, which operate on steam from the reactor, were used to replace reactor core water inventory, however, the battery-supplied control valves lost DC power after the prolonged use.
  • DC power from batteries was consumed after approximately 8 hours.
  • At that point, the plant experienced a complete blackout (no electric power at all).
  • Hours passed as primary water inventory was lost and core degradation occurred (through some combination of zirconium oxidation and clad failure).
  • Portable diesel generators were delivered to the plant site.
  • AC power was restored allowing for a different backup pumping system to replace inventory inreactor pressure vessel (RPV).
  • Pressure in the containment drywell rose as wet well became hotter.
  • The Drywell containment was vented to outside reactor building which surrounds the containment.
  • Hydrogen produced from zirconium oxidation was vented from the containment into the reactor building.
  • Hydrogen in reactor building exploded causing it to collapse around the containment.
  • The containment around the reactor and RPV were reported to be intact.
  • The decision was made to inject seawater into the RPV to continue to the cooling process, another backup system that was designed into the plant from inception.
  • Radioactivity releases from operator initiated venting appear to be decreasing.
Since they can't see into the core, they cannot confirm the state of the core. The list is subject to revision/correction as more is learned. They could monitor the air and water for certain isotopes to get an idea if there is fuel release from the fuel.

It appears that the EDGs got knocked out by a tsunami, despite the fact that they should have ensured the EDGs would not be affected by a seiche or tsunami. The containment maybe intact, but it's not clear concerning the integrity of the pipes, primarily those of the recirculation system.

It now appears there is a similar problem at Unit 3.
Reno Deano
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#47
Mar13-11, 09:08 AM
P: 128
•Hydrogen in reactor building exploded causing it to collapse around the containment.

The reactor building for a BWR is nothing more than a thin weather protection building and all other components of major concern are within hardened structures within it.
Astronuc
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#48
Mar13-11, 09:16 AM
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Quote Quote by Reno Deano View Post
•Hydrogen in reactor building exploded causing it to collapse around the containment.

The reactor building for a BWR is nothing more than a thin weather protection building and all other components of major concern are within hardened structures within it.
It also houses the crane(s) to lift the containment cover and vessel components. I haven't seen pictures of the crane.
PietKuip
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#49
Mar13-11, 10:45 AM
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Quote Quote by Angry Citizen View Post
A shame, because this is shaping up to be a textbook example of nuclear safety. Most of the backups and emergency procedures failed, yet it looks like little radiation has been or will be released.
Members of the public got contaminated, so there must have been a significant release of radioactive material. The incredibly horrible logs at http://www.nisa.meti.go.jp/english/ show that in Futaba-machi half of the people tested had counts between 18 000 and 40 000 counts per minute. Unclear whether a pancake detector was used for that, or a whole body counter. One person's shoes had over 100 000 cpm - maybe that made the detector max out. It seems that these people got contaminated why waiting in a school yard for buses to evacuate them.

Some radioactive material on your shoes is not dangerous at all, but these numbers show that an area well outside the power plant perimeter got severely contaminated.
Astronuc
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#50
Mar13-11, 11:02 AM
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Quote Quote by PietKuip View Post
Members of the public got contaminated, so there must have been a significant release of radioactive material. The incredibly horrible logs at http://www.nisa.meti.go.jp/english/ show that in Futaba-machi half of the people tested had counts between 18 000 and 40 000 counts per minute. Unclear whether a pancake detector was used for that, or a whole body counter. One person's shoes had over 100 000 cpm - maybe that made the detector max out. It seems that these people got contaminated why waiting in a school yard for buses to evacuate them.
What exactly is the source of those numbers? The link provides several pdfs.

Normal background btw is about 1-2 cps (60-120 cpm). Background comes from normal solar/cosmic radiation, and natural sources such as granite, and long-lived isotopes like K-40.
Angry Citizen
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#51
Mar13-11, 11:09 AM
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And I would further ask, "What exactly is the significance of those numbers?" Is that even a significant quantity of radiation?
eXorikos
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#52
Mar13-11, 11:09 AM
P: 249
Last time I checked with a proportional counter (friday) background (indoors) was 5-10cps...

The significance of those number also depends on the type of radiation and the place where the contamination is on/in the body. Just cps or cps says nothing really.
alxm
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#53
Mar13-11, 11:18 AM
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Quote Quote by Astronuc View Post
The upper level of containment, the metal walls and roof, was destroyed. That structure is over the inner containment, which is reinforced concrete. I believe the reinforced containment had the pressure increase, which was vented. The venting would be through those stacks (towers) that one sees behind (to the west of) the units. Venting into the upper containment would not be the case as far as I know.
Well, it does seem to be where the explosion occured though. I just found this cutaway which at least seems to say as much. Although there seems to be a lot of conflicting information out there; one report claimed it occurred between the outside wall and a steel containment wall, which I'd interpreted as a Mark-III kind of containment, which isn't correct for the Fukushima reactor.

In theory though, it's life could have been extended another 20 years.
Yup, it'd require heavy investments though. A friend of mine was until recently involved in the upgrades in-progress at Oskarshamn, which is a BWR contemporary to Fukushima (although it's a different, ASEA design)
promecheng
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#54
Mar13-11, 11:42 AM
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Quote Quote by Astronuc View Post
It also houses the crane(s) to lift the containment cover and vessel components. I haven't seen pictures of the crane.
The structure that was destroyed does contain the crane to lift the containment cover and is used during fueling operations. I'm not sure if it is considered secondary containment, but I do believe that it is a bit more secure than a simple metal enclosure. During refueling operations there is a small amount of radioactivity present and I believe the environment within the top portion of the building is controlled and not freely vented to the outside.

Another concern with the loss of the top part of the building is the spent fuel pool. I believe that the SPF is within the structure that was destroyed. If the water in the SPF was lost during the blast, the spent fuel can overheat and potentially melt. With no structure to contain the environment above the SPF any release of radiation would be freely vented to the outside.

Also, I believe that the unit-1 reactor is a BWR/4 design by GE with a MK-1 containment design. I believe this is typical with the wet-well torus design used to suppress a Loss of Coolant Accident (LOCA) within the primary containment. Any steam would be directed to the wet well where it would exit the venting system submerged, and thus condense and relieve any pressure buildup.


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