Re: UNUSED URANIUM, PLUTONIUM, etc.

puppet_sock_at_hotmail.com
Date: 07/16/04 

Date: 16 Jul 2004 07:10:50 -0700

"N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T:net@nospam.com> wrote in message news:<erIJc.2536$Wv4.1832@okepread03>...
[snip]
> The first time plutonium was tested as fuel in a nuclear reactor, they did
> not jacket it in any other material. As plutonium goes from "room
> temperature" to "operating temperature" it goes through six different
> atomic structures. After a few cycles, the fuel rod had changed dimensions
> by up to 600%, and could not be removed from the core, without severe
> disassembly (involving some cutting, as I heard it told). I understand
> they package it in Zirconium now... ;>)

That's a good fairy story. Now tell us the one where pink unicorns
bring the dew in the morning.

Plutonium was part of the fuel cycle of the very first reactor ever
built, and part of all Uranium reactors. It gets produced during the
normal operation of the reactor. That's where we get Plutonium. A
non-trivial portion of the energy released is produced by reactions
involving Plutonium.

Metalic Plutonium does not go through "six different atomic structures"
in heating to normal temperatures in a reactor. And it certainly does
not expand any 600 percent. (Interesting confluence of 6's there.)

Metalic forms of fuel are not the usual form of reactor fuel.
This is because hot Plutonium has this nasty habit of sucking oxygen
out of water. So does Uranium. So they don't use metalic forms in
most designs. (A few do, but those are usually research systems with
very special purposes.)

Plutonium oxide, the usual form of fuel, is a ceramic. So is Uranium
oxide. These are usually jacketed in some alloy of zirconium in order
to give them strength, and to deal with the fact that the ceramic is
brittle. It is fairly usual for oxide reactor fuel to crack during
normal operation. In the oxide form, these materials are quite stable
until they start to get close to their melting point. (I spent a very
tedious couple weeks a few years ago, typing in the data for
measurements of the change of density, thermal capacity, and thermal
conductivity of these oxides, as a function of temperture, oxygen
content, and isotopic content. Then I used half that data to build
a computer subroutine to predict these quantities, and the other half
to validate the code.)

It's truly amazing how stories get picked up and inflated in the
nuclear biz. As an example, some few years ago, at one of the nukes
in Ontario, a tech left a tool in a fuel channel. The tool was a
sort of round file, and it's name was a "plumber's weasel." At some
later time, the channel was inspected, and this tool was discovered.
The story was passed around and mutated until people were claiming
that herds of dead rats had been found in a fuel channel.

There really is no need or value in passing such unsubstantiated
rumours. There's enough interest in nuclear physics without adding
a lot of fairy stories and false rumours.
Socks

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