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Insightful reporting on the scale of the problem from NYT: http://www.nytimes.com/2011/03/14/world/asia/japan-fukushima-nuclear-reactor.html?hp http://www.nytim

Insightful reporting on the scale of the problem from NYT: http://www.nytimes.com/2011/03/14/world/asia/japan-fukushima-nuclear-reactor.html?hp http://www.nytimes.com/2011/03/14/world/asia/japan-fukushima... The major issue seems to be that the power equipment is in a room that is flooded, so regular cooling is impossible. They're pumping in seawater, but they have to release pressure as it builds up and this released steam is irradiated. Until some kind of regular cooling system is rebuilt, this process to prevent meltdown will continue for the forseeable future.

waterlesscloud 16y ago
How long does this post-shutdown cooling process take? I thought I'd read something like 48 hours in the immediate aftermath of the quake, but that's obviously not correct.
- redthrowaway 16y ago
  I'd read that the problem was residual heat, as the control rods should have dropped as soon as coolant flow halted. This means that no new heat is being added to the system, but that the reactor will experience a gradual decline from its 3000 MW operating capacity. All of that energy is stored as irradiated steam, which can be forced into pools of seawater beneath the plant to cool it, but only so much.
  - skybrian 16y ago
    My understanding is that new heat continually gets added because the nuclear byproducts decay. It's exponential decay with a long half-life. I hadn't thought of this, but it makes sense, considering that normally the cooling rods are kept in ponds for years after being removed from the reactor.
  - jeza 16y ago
    I don't think it's true to say no new heat is being added. The uranium fission process has stopped, but there are secondary radioactive elements created by the decay of uranium. These elements will continue to decay, as such the core is still producing the heat. Though eventually this heat will decline to a safe level, provided there isn't a meltdown beforehand. The design oversight seems to be that they depend on external AC power or diesel generators for backup. Surely there should be an emergency generator that can run off the heat that the core still produces in order to at least partially operate the cooling system. Much like aeroplanes have a small dynamo that runs off a tiny wind emergency wind turbine so they can still operate the hydraulics with no engines running. A saving grace in the case of Gimli Glider (http://en.wikipedia.org/wiki/Gimli_Glider http://en.wikipedia.org/wiki/Gimli_Glider).
    - redthrowaway 16y ago
      Ah, thanks for the explanation. As I said, that was just what I had read. I appreciate the further info. What you said makes sense, and explains why steam pressure is still building.
      - jeza 16y ago
        No problem. Further to my comments about the design, I read in another story linked to on HN that generation III reactors now use convection based cooling. I gather this means the water is taken elsewhere as steam to cool then returns via gravity to the core. Therefore you wouldn't have this same kind of issue with a modern reactor.
        redthrowaway 16y ago
        Interesting. That seems like a smart way of doing it.
- DrStalker 16y ago
  I saw a figure earlier today (can't recall where sorry) that once the control rods are in and the reactor is shutdown it still produces 6% of the usual amount of heat, which is enough to still require some cooling.
  - beefman 16y ago
    The decay heat is about 5% of full reactor power at shutdown, but decreases exponentially thereafter, to about 1% at 4 hours, etc. Daiichi units 1 & 3 are about 1.4 and 2.4 MW(th) respectively.
RK 16y ago
this released steam is irradiated Just as a pedantic point, irradiated steam would not be hazardous. Steam with radioactive particles mixed in, on the other hand, would be.
- radicaldreamer 16y ago
  Thanks, my mistake! Irradiation is the process of exposing to radiation while in this case the steam actually contains radioactive particles.
  - ars 16y ago
    Yah, the steam itself is perfectly safe. It's only what is mixed in that is a problem. I can't imagine there is very much mixed in though, water boils at much lower temperatures than the other things there. And I assume they are venting from the top, so it should be pretty pure. (Worlds most expensive steam distillation :)
paganel 16y ago
> and this released steam is irradiated I wonder where this steam is going to end up. All those lambasting us about how this is "not another Chernobyl" seem to forget mentioning this, as if all this mess isn't serious enough if it's not on par with Chernobyl.

waterlesscloud 16y ago

How long does this post-shutdown cooling process take? I thought I'd read something like 48 hours in the immediate aftermath of the quake, but that's obviously not correct.

redthrowaway 16y ago
I'd read that the problem was residual heat, as the control rods should have dropped as soon as coolant flow halted. This means that no new heat is being added to the system, but that the reactor will experience a gradual decline from its 3000 MW operating capacity. All of that energy is stored as irradiated steam, which can be forced into pools of seawater beneath the plant to cool it, but only so much.
- skybrian 16y ago
  My understanding is that new heat continually gets added because the nuclear byproducts decay. It's exponential decay with a long half-life. I hadn't thought of this, but it makes sense, considering that normally the cooling rods are kept in ponds for years after being removed from the reactor.
- jeza 16y ago
  I don't think it's true to say no new heat is being added. The uranium fission process has stopped, but there are secondary radioactive elements created by the decay of uranium. These elements will continue to decay, as such the core is still producing the heat. Though eventually this heat will decline to a safe level, provided there isn't a meltdown beforehand. The design oversight seems to be that they depend on external AC power or diesel generators for backup. Surely there should be an emergency generator that can run off the heat that the core still produces in order to at least partially operate the cooling system. Much like aeroplanes have a small dynamo that runs off a tiny wind emergency wind turbine so they can still operate the hydraulics with no engines running. A saving grace in the case of Gimli Glider (http://en.wikipedia.org/wiki/Gimli_Glider http://en.wikipedia.org/wiki/Gimli_Glider).
  - redthrowaway 16y ago
    Ah, thanks for the explanation. As I said, that was just what I had read. I appreciate the further info. What you said makes sense, and explains why steam pressure is still building.
    - jeza 16y ago
      No problem. Further to my comments about the design, I read in another story linked to on HN that generation III reactors now use convection based cooling. I gather this means the water is taken elsewhere as steam to cool then returns via gravity to the core. Therefore you wouldn't have this same kind of issue with a modern reactor.
      - redthrowaway 16y ago
        Interesting. That seems like a smart way of doing it.
DrStalker 16y ago
I saw a figure earlier today (can't recall where sorry) that once the control rods are in and the reactor is shutdown it still produces 6% of the usual amount of heat, which is enough to still require some cooling.
- beefman 16y ago
  The decay heat is about 5% of full reactor power at shutdown, but decreases exponentially thereafter, to about 1% at 4 hours, etc. Daiichi units 1 & 3 are about 1.4 and 2.4 MW(th) respectively.

RK 16y ago

this released steam is irradiated Just as a pedantic point, irradiated steam would not be hazardous. Steam with radioactive particles mixed in, on the other hand, would be.

radicaldreamer 16y ago
Thanks, my mistake! Irradiation is the process of exposing to radiation while in this case the steam actually contains radioactive particles.
- ars 16y ago
  Yah, the steam itself is perfectly safe. It's only what is mixed in that is a problem. I can't imagine there is very much mixed in though, water boils at much lower temperatures than the other things there. And I assume they are venting from the top, so it should be pretty pure. (Worlds most expensive steam distillation :)

paganel 16y ago

> and this released steam is irradiated I wonder where this steam is going to end up. All those lambasting us about how this is "not another Chernobyl" seem to forget mentioning this, as if all this mess isn't serious enough if it's not on par with Chernobyl.