[ RadSafe ] Physics of UO3 gas

[John R Johnson]

Dale

Thanks for this. 

Unfortunately I never learnt much chemistry when I studied physics so I coundn't be one of the "other physicists". 

Also, I would have "ran out of energy" long before the UO3 melted-:).

John
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-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl]On
Behalf Of Dale Boyce
Sent: January 27, 2007 12:21 PM
To: radsafelist
Subject: [ RadSafe ] Physics of UO3 gas


To get atoms (I think you mean molecules) bouncing into things you have to 
form them first. In order for UO3 gas to exist you first have to input 
enough energy to vaporize it.

Let me set up the calculation, and hopefully a couple of other physicists 
will do the calculation independently to see if we get the same result. I'll 
let them look up the inputs.

You have two available energy sources. The kinetic energy of the bullet, and 
the heat of formation from the burning uranium.

You have several energy sinks. You have the heat capacity of the uranium 
and/or oxide. This soaks up a little energy raising the temperature. to the 
melting point. Then you have to supply a lot energy to melt the material. 
This is known as the heat of fusion. Note that you also have to replicate 
these energy sinks for the steel/whatever that gets zapped in the collision.

You then have to heat the liquid to the vaporization point (more heat 
capacity). After that you have to supply the heat of vaporization to form 
the gas.

Now when I plugged in the numbers from my CRC Handbook. I ran out of energy 
before the UO3 even melted, much less became a gas. Moreover, I believe I 
used conservative numbers.  I overestimated the heat of formation and 
underestimated the heat of fusion.

The heat of fusion of uranium metal is about an order of magnitude greater 
than the heat of formation of UO3. The heat of formation is as large or 
larger than the kintic energy of the bullet. Moreover, the heat of fusion of 
UO3 should be a few times that of uranium metal.

I picked 1000 m/sec as the velocity of the round. Probably not too far off.

BTW a long time ago I saw a small uranium fire.  You get a nice bright 
sparkel somewhat white,but that still has a noticible yellow cast. The smoke 
falls instead of rises. This indicates two things. Because of the color the 
temperature is probably around 1000C. Consistent with it being at or near 
its melting point temperature. BTW A substance will remain at its melting 
point temperature until enough energy is added to go through the transition 
to liquid.  Again this energy is substantial. Second the falling smoke 
indicates cooled particulates. If it was in a vapor phase there would be a 
glowing plume well up into the blue or hotter color range.

Bottom line is the stuff is going to be very hot and hold a lot of energy as 
heat, but gas isn't physically plausible.

Noises Off!

Dale



----- Original Message ----- 
From: "James Salsman" <jsalsman at gmail.com>
To: "Otto Raabe" <ograabe at ucdavis.edu>
Cc: "radsafelist" <radsafe at radlab.nl>
Sent: Thursday, January 25, 2007 10:36 AM
Subject: Re: [ RadSafe ] Salsman's uranium trioxide gas proof


> Dr. Raabe,
>
> I find this very difficult to believe:
>
>> Cooling is virtually instantaneous even near the combustion process and
>> results in all (not half) of the vapor being converted to solid oxide
>> particles.
>
> How do "all" of the diffusing gas molecules know to turn around and
> head toward a surface?
>
> Did you actually measure this?  You say that Carter and Stewart
> supports your assertions, as does your own work, but Carter and
> Stewart contains no such mass measurements.
>
> What are the actual numbers upon which you base this absolute claim,
> and where are they documented?
>
> Sincerely,
> James Salsman
> _______________________________________________
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