

An Engineer's Explanation of the Fukushima Incident - Tom_Chippendale
https://docs.google.com/leaf?id=11RJz6KCYjVa6M8urvzO0tYq1SjbgqQwW5zw8nquMshzBqSNxn2n3leC_O8hP&hl=en
Probably the clearest technical explanation of what occurred at Fukushima after the recent earthquake and resulting tsunami.
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hubb
although not submitted separately, this was discussed a bit yesterday on HN,
when plux posted it:

<http://news.ycombinator.com/item?id=2411141>

it looks like the attribution is different for each presentation, though the
content is identical

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uvdiv
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?pa...](http://www.nytimes.com/2011/04/03/science/03meltdown.html?pagewanted=all)

~~~
Tom_Chippendale
Beat me to it :-)

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VladRussian
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".

~~~
nathanhammond
Control rod insertion is designed to be an entirely passive operation,
effectively making the default state one where the fission reaction is not
active. Your proposals are all different ways to stop the fission reaction but
do not address residual heat.

What you're really asking for is a system wherein the cooling of the fuel
after fission has stopped (this is where the problems occurred at the
Fukushima plants) is entirely passive.

I'm sure somebody could get clever with siphons to make this happen but you'll
need an absolutely massive amount of water to do so and/or a way to do the
cooling such that the water itself is not exposed to radiation. This would
allow you to, for example, safely take it from one side of the dam to the
other.

An active solution instead allows recirculation of the same water (often
borated) and can generally be a closed-loop (and radiation apathetic) system.

~~~
Tuna-Fish
> What you're really asking for is a system wherein the cooling of the fuel
> after fission has stopped (this is where the problems occurred at the
> Fukushima plants) is entirely passive.

This can be achieved by designing the safe core temperatures to be much
higher, which makes cooling easier. The very interesting small molten salt
breeder design FUJI MSR <http://en.wikipedia.org/wiki/Fuji_MSR> is designed to
survive complete external cooling loss by shutting down fission (either under
control, or by the heat physically destroying the neutron mirrors required for
it's operation), and then dealing with the decay heat by conductive transfer
to the environment and simply letting the reactor heat up.

The fact that the core is molten in normal operation, under no pressure and
entirely chemically inert even at elevated temperatures makes passive safety
somewhat easier.

~~~
nathanhammond
And that was a fun way to spend an evening: new reactor designs are quite cool
:). It seems like a lot of the innovation is occurring in parallel with both
fuel types and containment approaches.

I too look forward to having completely passive shutdown of reactors, but from
what I can tell (outside of a few small-scale test reactors) we're just not
there yet. Someday...

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nitrogen
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.

~~~
bdonlan
Getting robots in wouldn't help with the Fukushima incident much; the real
problem there is getting energy out, not getting robots in.

~~~
nitrogen
They could have been used for monitoring inaccessible locations earlier in the
disaster, possibly by using fiber optic cameras and lighting.

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derrickpetzold
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.

~~~
hga
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).

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pasbesoin
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>

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.

