Re: fission question

From: Steven Sharp (sharp_at_cadence.com)
Date: 07/22/04 

Date: 21 Jul 2004 17:02:00 -0700

sbharris@ix.netcom.com (Steve Harris sbharris@ROMAN9.netcom.com) wrote in message news:<79cf0a8.0407041402.163437c7@posting.google.com>...
>
> Now, having said that, the second interesting thing about the Slotin
> and Daghlian incidents is what DIDN'T happen. The cores didn't melt
> and give a mini-China syndrome, burning globs of liquid plutonium into
> the floor. I've seen a picture of the core after the Daghlian
> accident, and it's perfectly intact.

That should be "core", not "cores", since both accidents involved the
exact same core. Both times the nickel canning was still intact. The
estimated yields were 10**16 and 3*10**15 fissions. For comparison, that
corresponds to the energy of an ounce or two of high explosives (though
the fission energy would mostly be released as heat, not kinetic energy).

> Now, obviously, that didn't happen in either of these accidents. From
> discriptions, it sounds as though the reaction went up to some ungodly
> high power output very fast, but then quit increasing. And didn't go
> past the limit where things melted or vaporized. So where was the
> brake.

As noted elsewhere, the dominant quenching mechanism was thermal
expansion of the core itself.

> Inquiring minds want to know. I wonder if they had the balls to repeat
> these accidents under control "dragon" type conditions, just to see
> what really DID happen? I'll bet not. If they did, it's still
> classified.

Well, the unclassified document that I have has a footnote that says:

 "The Los Alamos National Laboratory archives include some data and comments
 about a rerun performed 2 October 1945 to determine the radiation dose
 received in the accident of 21 August 1945. The yield of the rerun was
 about 6x10**15 fissions, but the prompt critical state was not reached.
 The maximum reactivity of the system during this experiment was about
 60 cents above delayed criticality."

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