X-Message-Number: 29237
Date: Sun, 04 Mar 2007 15:13:06 -0500
From: Keith Henson <>
Subject: Unrecognized problem with nuclear power reactors

It is widely thought that the North Korean bomb test was much smaller than 
intended.

If they used plutonium reprocessed from a reactor that might be the 
reason.  U 238 absorbs a neutron and becomes plutonium 239 in 
reactors.  But the Pu 239 *also* absorbs a neutron becoming Pu 240.

That turns out to be a major problem for making plutonium bombs because Pu 
240 has a high rate of spontaneous fission.  I.e., it releases neutrons to 
start a chain reaction.

For making bombs (this is all in a Clancy novel) you have to compress the 
plutonium and then set it off with a shot of neutrons.  This becomes hard 
to do when there is a lot of Pu 240 spitting out neutrons.

Bomb grade plutonium is upwards of 90% Pu 239.  You can raise the 
percentage by shortening the exposure to neutrons but you also reduce the 
amount being made.

There might be a way to have your cake and eat it too.  The idea is to use 
U 238 in solution, expose it briefly to neutrons by pumping it through a 
reactor and sort the plutonium out of the solution before it has picked up 
a second neutron.

What this means is that any power reactor with a bit of added plumbing and 
a few tanks can be used to make exceptionally good bomb grade plutonium.

This is a bummer since large numbers of power reactors are one of the few 
ways to cope with global warming and peak oil problems.

Keith Henson 

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