Le 2011/04/15 13:00, Orchid XP v8 a écrit :
>>> That doesn't mean that the cooling system can't overload and explode.
>>
>> Right. But if you knock down a thorium salt reactor, it just gets cold.
>> It's basically a big stack of pool-ball sized balls that heat up if you
>> get a bunch of them close enough. So if something goes wrong and knocks
>> down the wall, it cools off and you send in people in lead-lined
>> bulldozers to scoop the stuff up.
>
> If it's so simple and easy, why isn't everyone doing it?
>
>>> Uranium-235 has a halflife is 700 million years.
>>
>> U-235 isn't that dangerous, tho, unless you pile up enough to interact.
>>
>> What it also means is that if you spill 100 pounds of U-235 somewhere,
>> it's going to take 700 million years for even 50 pounds of it to have
>> emitted radiation. That's a very low level of radiation.
>
> How do you work that one out?

Halflife is defined as "the time it takes for half of the original 
amount to degrade". So, it takes 700 millions years for half of your 
uranium's atoms to deckay, and thus, emit radiation. After 1400 millions 
years, 75% of the original amount will have deckayed.
It apply to radioactive materials. It also apply to medication in your 
body, and many other things.

>
>> The actual chemical properties are probably more dangerous than the
>> radioactive properties if you spread it out widely enough.
>
> Well, yeah, that's probably true enough.
>
>>> That's /halflife/, not the
>>> time it takes to degrade completely, just the time for *half* of it
>>> to go
>>> away. 700 million years is longer than that oil has been in the
>>> ground. ;-)
>>
>> Which tells you that it isn't *that* dangerous or there wouldn't be any
>> life in the ground.
>
> It's also an extremely rare element. Not like a reactor core, which is
> make out of pure Uranium...
>

A reactor core is NEVER "pure uranium".
The uranium is contained in "fuel canisters" incerted into fuel 
channels, then there is the moderator medium, then the cooling system, 
then the controll rods channels.



Alain

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