> On 4/16/2011 12:02 PM, Alain wrote:

>>> On 4/15/2011 5:26 AM, Bill Pragnell wrote:
>>>> Invisible<voi### [at] devnull> wrote:
>>>>> Nuclear power works in theory. In practise, if you make even the
>>>>> tiniest
>>>>> mistake, just once, everything is ruined forever. (Or at least, for
>>>>> several centuries.) And there's nothing you can do to fix it.
>>>>
>>>> That's not really true. Chernobyl was caused by a very long chain of
>>>> mistakes,
>>>> all committed with a reactor design which was already itself a long
>>>> chain of
>>>> mistakes. It should be noted that most other countries have never
>>>> built a
>>>> reactor that could fail as catastrophically as this, even through
>>>> wilful
>>>> sabotage.
>>>>
>>>> TMI was also long chain of mistakes, which resulted in only the
>>>> reactor being
>>>> ruined, and they did fix it.
>>>>
>>>> I suppose you could say that Fukushima was really only one very big
>>>> mistake,
>>>> i.e. how big a tsunami was ever likely to be. However, they show every
>>>> sign of
>>>> being able to fix it eventually.
>>>>
>>> No, the "big" mistakes where:
>>>
>>> 1. Having no way to cool it, or certainty that the power systems would
>>> still work, to do so, if enough failures happened. And, no, battery
>>> backup doesn't work, if it lasts less than 24 hours.
>>>
>>> 2. Placing the old, spent, fuel in something that was ever *less*
>>> effectively cooled.
>>>
>>> And, I would add 3. Presuming that a *big* reactor, which produces
>>> massive amounts of power, but where it would be nearly impossible to
>>> either make it less hazardous, or run battery backup long enough, or
>>> otherwise create a system that *could* compensate for major problems,
>>> remains bloody stupid.
>>>
>>
>> Some more gross mistakes at Fukushima:
>>
>> a. Need *EXTERIOR* power source to run the cooling system when you
>> produce that power localy.
>> The pumps failed when the power lines TO the reactor got damaged by the
>> tsunami. That's a humongously huge mistake!
>>
>> b. NO passive shutdown mechanism. Sanity *demands* that there are
>> several controll rods suspended by electro magnets powered by the
>> reactor itself over the core. If the cooling system fails, the turbines
>> stop, they no longer produce current, shutting down the magnets whitch
>> let the controll rods fall into the core, stoping the nuclear reaction
>> and thus the heat generation. Those rods are usualy made of cadmium
>> because that metal can absorbs huge amounts of neutrons.
>> Those rods must be set and designed so that gravity alone will make them
>> fall completely into position.
>> There where obviously none! Totaly insane!
>>
>> c. NO passive cooling mesures. A passive cooling mesure should be enough
>> to evecuate the residual heat from the shut down reactor.
>>
>> d. Severly skipping on maintenance for over 10 years.
>> The director of the station said so himself...
>>
>>
>>
>> Alain
> Yeah. Those would have been a damn good idea too.
>
> a) makes no damn sense to me at all (even if it was some minimal system,
> enough to just keep pumps going), unless the tsunami took out
> lines/systems in the actual turbine part of the system. I would have
> thought those would be internal to the reactor, but.. Then again, their
> systems reuse a lot of waste heat/energy, so its hard to say how complex
> the whole thing was, and thus "where" those systems where, and thus
> whether it was even feasible to have the turbines in the reactor
> buildings. Its a definite WTF for me, but may go towards the whole, "If
> you make the thing so damn big you can't do *basic* shit to keep it
> working, you may be building them too big." If I where to guess... They
> probably have "internal systems that funnel water to and from the
> reactor, then a "heat exchange" point, with and entirely separate
> system, which is external to the reactors themselves. This would then
> run out to their actual turbine systems, where the heated water produces
> the actual power, is cooled, then pumped back into the exchanger. You
> don't want to run radioactive water through the turbines, or use a
> system where water from one might get into the other. This means that,
> for practical purposes, power isn't generated "in" the reactor itself,
> at all. So...
The reactor heat water in the primary cooling loop.
It circulate between the reactor and a heat exchanger just outside the 
reactor housing.
This water, in turn, turn water in the secondary loop into steam.
That steam powers the turbines.
All of this is housed in a building that contains the reactor housings.

One big buiding that contains the reactors, the primary to secondary 
heat exchangers and the turbines. The transformers are located outside 
and alongside that building, as shown by the satellite and aerial photos 
of the site.
The link from the building to the transformers station are very short 
and shielded from the sea by the large building.
The transforming station was unaffected by the stunami.
The main building did NOT suffer from the stunami at all, but did stop 
it and protected a significan area.
The power lines where cut over 100m BEHIND the plant.
It's the lost of those lines that caused all the problems.

>
> b) not sure any of them have this. Its not enough to just drop in a few,
> in most cases, and.. well, if you can bend the damn things to shit in a
> system that runs them in slowly, you can imagine what sort of mess you
> end up with if some of them jam being "gravity dropped" into place.
> Again, the whole design seems a problem, and most of it due to scale,
> not just this one issue.

Not just a few. Those drop controll rods are realy calles *Stop* rods.

They are present in the Candu reactors and several other models. They 
are also mandatory in several countrys. After Tree Miles Island, they 
became mendatory in the USA. Some older US reactors where shut down 
because they lacked that feature.

At the end of the drop, they are stopped from the top. They can't bend, 
just stretch a little. Think of a big nail shaped rod suspended above 
the core by an electro magnet.

>
> c) Hmm.. This is an interesting problem. How do you make a passive
> cooling system which doesn't move contaminated air, or water, or
> something else, and exchange it often/fast/effective enough to do that?
> We are talking about something heating to temperatures on massive
> scales, pretty damn fast, with a *major* exchange requirement. Again,
> size here matters. Think of it like trying to cool a high end CPU, using
> only a bit of foil taped to the top, because someone had to build the
> case so an actual radiator grill and electric fan wouldn't fit in there.
> You can get by with it if you are using low power, a lower end chip,
> etc., but... scale up to a PC, or, in the case of power plants, a full
> size nuclear reactor... and you "passive" systems are just not going to
> cut it in any practical sense.

No horizontal heat exchanger, you maximize the vertical to horizontal 
proportions of the cooling loops to increase the thermal syphon mechanism.
That way, the heat will greatly help you to circulate the cooling fluids.

Then, once the stop rods are droped, you have MUCH less heat to 
dicipate. This, in turn, makes passive cooling easily feasible and 
practical.

>
> So.. Again, seems to me, once you get past the basics of, "make sure the
> damn thing can run the active systems long enough to matter", everything
> else is, "scale, scale, scale", and the impracticality of doing jack to
> solve such problems at the scales being talked about. And, short of
> building the damn things in Antarctica, and somehow getting the power
> from there to every place else, I don't see "passive" being too viable...

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