5 ms·

An Engineer's Explanation of the Fukushima Incident

Probably the clearest technical explanation of what occurred at Fukushima after the recent earthquake and resulting tsunami.

pasbesoin 16y ago
All right. The Google URL's are different, so I'll assume this isn't just another copy/pasta karma endeavor. http://news.ycombinator.com/item?id=2400790 http://news.ycombinator.com/item?id=2400790 I don't particularly care about my own karma (or lack thereof; and after all I was reformatting someone else's URL, albeit to avoid the PowerPoint dependency (and risk)), but I do care about the contribution of repetition to the increasing volume of noise on HN. That aside, it is an interesting slide deck.
hubb 16y ago
although not submitted separately, this was discussed a bit yesterday on HN, when plux posted it: http://news.ycombinator.com/item?id=2411141 http://news.ycombinator.com/item?id=2411141 it looks like the attribution is different for each presentation, though the content is identical
- uvdiv 16y ago
  The attribution here is correct (Matthias Braun, Areva); the name and logos were stripped when it was released, apparently for some kind of legal reason. This is discussed at the end of this article: http://www.nytimes.com/2011/04/03/science/03meltdown.html?pagewanted=all http://www.nytimes.com/2011/04/03/science/03meltdown.html?pa...
  - Tom_Chippendale 16y ago
    Beat me to it :-)
- Tom_Chippendale 16y ago
  It appears the Stanford presentation was given by an Areva executive, and the branding / sources on this copy were removed: "On March 21, Stanford University presented an invitation-only panel discussion on the Japanese crisis that featured Alan Hanson, an executive vice president of Areva NC, a unit of the company focused on the nuclear fuel cycle." Source here: http://www.nytimes.com/2011/04/03/science/03meltdown.html?pagewanted=2 http://www.nytimes.com/2011/04/03/science/03meltdown.html?pa...
TryThinking 16y ago
Areva is a company that sells nuclear reactors. It's important to realize that there are enormous political and financial interests on both sides of the "nuclear debate" in framing the "reality" of what happened and continues to happen. How the accident is presented and which details are highlighted depends very strongly on who is doing the presentation. In this case, let's have a healthy dose of skepticism about certain value statements in the presentation, knowing full well that there are unquantifiable financial implications for the presenter, Areva.
nitrogen 16y ago
It seems that it might be a good idea to design future nuclear reactors with pneumatic-powered robots in mind; purpose-built shafts and ramps could allow robots with minimal electronics into areas unsafe for humans. I say pneumatic instead of hydraulic, as based on my very limited understanding of nuclear physics, lightweight gases are less likely to become neutron activated for extended periods of time.
- klbarry 16y ago
  I believe radiation messes with machines a bit too, though.
  - nitrogen 16y ago
    I could see neutrons activating the parts of a robot, but what physical mechanism would prevent a pneumatic motor from driving some wheels or moving an arm in the presence of radiation, other than the parts heating up and expanding?
    - hga 16y ago
      A robot that can't see isn't very useful.... One problem I've read in these sorts of situations is the robot eventually or unexpectedly gets killed by the ambient radiation ... and now you have to get humans to dash in there to pull it out of the way.
- bdonlan 16y ago
  Getting robots in wouldn't help with the Fukushima incident much; the real problem there is getting energy out, not getting robots in.
  - nitrogen 16y ago
    They could have been used for monitoring inaccessible locations earlier in the disaster, possibly by using fiber optic cameras and lighting.
VladRussian 16y ago
i'm wondering about the main design principle of the reactor cores - by default they are "hot", ie. producing heat/energy, so one needs to make effort to keep them "cold", ie. non-producing heat/energy. This hot-by-default principle was the main reason of Chernobyl catastrophe and here as well. Why not reverse the principle and design the cold-by-default core? For example, instead of inserting graphite rods into the core to calm it down, one would need to insert additional uranium rods (or pump molten uranium salt, or move the 6-8-12 pieces of core close enough, etc...) for the reactor to activate and become "hot".
- bdonlan 16y ago
  There's a difference between sub/super critical (producing energy via fission) and "hot" (producing energy _at all_). Chernobyl became more reactive (= more fission) as the water boiled away, leading to a runaway criticality, and explosive disassembly of the core. Fukushima, however, has a negative void coefficient. Moreover, the fission reaction was stopped immediately after the earthquake successfully by the automatic insertion of control rods. The heat that is being generated is from short-lived fission products (ie, nuclear waste) undergoing spontaneous decay events, thus producing heat (but only a small fraction of the heat of an active reactor). It is physically impossible to design a reactor in which such spontaneous decay can be stopped. You can only remove the energy actively until these short-lived products decay to the point where air cooling is sufficient to keep them at a safe temperature. You can, however, design a reactor in which the passive containment structures can withstand the temperatures of fresh waste material with no active cooling; however such technology was not available at the time the Fukushima plants were built.
  - Tobias42 16y ago
    Do you know if new plants are generally built with containments that work without cooling?
    - Tuna-Fish 16y ago
      No. The new reactors under construction are mostly very conservative and traditional Gen III+ PWR designs, with some added safety features. The reactors that can survive complete loss of cooling are all Gen IV designs, that are currently under discussion, not construction.
derrickpetzold 16y ago
I am certainty no expert on nuclear engineering or containment design but it seems odd to me that the spent fuel rods are stored in above ground pools. I wouldn't even let my kids play in one much less store radioactive materiel that requires active cooling in one.
- nanidin 16y ago
  I feel bad for your kids
- hga 16y ago
  I've read It's an issue with manipulating the fuel: to do so, you unbolt the containment cap on the top of the reactor pressure vessel and fill the entire path from on top of it to the initial spent fuel pool with water. That allows you to safely transfer hot (thermally as well as radiatively) rods and it's pretty hard to get around if you're using this sort of reactor geometry (I understand it holds for both PWRs as well as these BWRs).

Probably the clearest technical explanation of what occurred at Fukushima after the recent earthquake and resulting tsunami.

pasbesoin 16y ago

All right. The Google URL's are different, so I'll assume this isn't just another copy/pasta karma endeavor. http://news.ycombinator.com/item?id=2400790 http://news.ycombinator.com/item?id=2400790 I don't particularly care about my own karma (or lack thereof; and after all I was reformatting someone else's URL, albeit to avoid the PowerPoint dependency (and risk)), but I do care about the contribution of repetition to the increasing volume of noise on HN. That aside, it is an interesting slide deck.

hubb 16y ago

although not submitted separately, this was discussed a bit yesterday on HN, when plux posted it: http://news.ycombinator.com/item?id=2411141 http://news.ycombinator.com/item?id=2411141 it looks like the attribution is different for each presentation, though the content is identical

uvdiv 16y ago
The attribution here is correct (Matthias Braun, Areva); the name and logos were stripped when it was released, apparently for some kind of legal reason. This is discussed at the end of this article: http://www.nytimes.com/2011/04/03/science/03meltdown.html?pagewanted=all http://www.nytimes.com/2011/04/03/science/03meltdown.html?pa...
- Tom_Chippendale 16y ago
  Beat me to it :-)
Tom_Chippendale 16y ago
It appears the Stanford presentation was given by an Areva executive, and the branding / sources on this copy were removed: "On March 21, Stanford University presented an invitation-only panel discussion on the Japanese crisis that featured Alan Hanson, an executive vice president of Areva NC, a unit of the company focused on the nuclear fuel cycle." Source here: http://www.nytimes.com/2011/04/03/science/03meltdown.html?pagewanted=2 http://www.nytimes.com/2011/04/03/science/03meltdown.html?pa...

TryThinking 16y ago

Areva is a company that sells nuclear reactors. It's important to realize that there are enormous political and financial interests on both sides of the "nuclear debate" in framing the "reality" of what happened and continues to happen. How the accident is presented and which details are highlighted depends very strongly on who is doing the presentation. In this case, let's have a healthy dose of skepticism about certain value statements in the presentation, knowing full well that there are unquantifiable financial implications for the presenter, Areva.

nitrogen 16y ago

It seems that it might be a good idea to design future nuclear reactors with pneumatic-powered robots in mind; purpose-built shafts and ramps could allow robots with minimal electronics into areas unsafe for humans. I say pneumatic instead of hydraulic, as based on my very limited understanding of nuclear physics, lightweight gases are less likely to become neutron activated for extended periods of time.

klbarry 16y ago
I believe radiation messes with machines a bit too, though.
- nitrogen 16y ago
  I could see neutrons activating the parts of a robot, but what physical mechanism would prevent a pneumatic motor from driving some wheels or moving an arm in the presence of radiation, other than the parts heating up and expanding?
  - hga 16y ago
    A robot that can't see isn't very useful.... One problem I've read in these sorts of situations is the robot eventually or unexpectedly gets killed by the ambient radiation ... and now you have to get humans to dash in there to pull it out of the way.
bdonlan 16y ago
Getting robots in wouldn't help with the Fukushima incident much; the real problem there is getting energy out, not getting robots in.
- nitrogen 16y ago
  They could have been used for monitoring inaccessible locations earlier in the disaster, possibly by using fiber optic cameras and lighting.

VladRussian 16y ago

i'm wondering about the main design principle of the reactor cores - by default they are "hot", ie. producing heat/energy, so one needs to make effort to keep them "cold", ie. non-producing heat/energy. This hot-by-default principle was the main reason of Chernobyl catastrophe and here as well. Why not reverse the principle and design the cold-by-default core? For example, instead of inserting graphite rods into the core to calm it down, one would need to insert additional uranium rods (or pump molten uranium salt, or move the 6-8-12 pieces of core close enough, etc...) for the reactor to activate and become "hot".

bdonlan 16y ago
There's a difference between sub/super critical (producing energy via fission) and "hot" (producing energy _at all_). Chernobyl became more reactive (= more fission) as the water boiled away, leading to a runaway criticality, and explosive disassembly of the core. Fukushima, however, has a negative void coefficient. Moreover, the fission reaction was stopped immediately after the earthquake successfully by the automatic insertion of control rods. The heat that is being generated is from short-lived fission products (ie, nuclear waste) undergoing spontaneous decay events, thus producing heat (but only a small fraction of the heat of an active reactor). It is physically impossible to design a reactor in which such spontaneous decay can be stopped. You can only remove the energy actively until these short-lived products decay to the point where air cooling is sufficient to keep them at a safe temperature. You can, however, design a reactor in which the passive containment structures can withstand the temperatures of fresh waste material with no active cooling; however such technology was not available at the time the Fukushima plants were built.
- Tobias42 16y ago
  Do you know if new plants are generally built with containments that work without cooling?
  - Tuna-Fish 16y ago
    No. The new reactors under construction are mostly very conservative and traditional Gen III+ PWR designs, with some added safety features. The reactors that can survive complete loss of cooling are all Gen IV designs, that are currently under discussion, not construction.

derrickpetzold 16y ago

I am certainty no expert on nuclear engineering or containment design but it seems odd to me that the spent fuel rods are stored in above ground pools. I wouldn't even let my kids play in one much less store radioactive materiel that requires active cooling in one.

nanidin 16y ago
I feel bad for your kids
hga 16y ago
I've read It's an issue with manipulating the fuel: to do so, you unbolt the containment cap on the top of the reactor pressure vessel and fill the entire path from on top of it to the initial spent fuel pool with water. That allows you to safely transfer hot (thermally as well as radiatively) rods and it's pretty hard to get around if you're using this sort of reactor geometry (I understand it holds for both PWRs as well as these BWRs).