HOWTO Build a Nuclear Device

[Eric Cordian]

F. Marc de Piolenc wrote: 

> Consider that nuclear weapons could not be built if the fissiles had
> high rates of spontaneous decay - the stuff would detonate prematurely,
> resulting in a fizzle. That, incidentally, is why plutonium cannot be
> used in a gun-type device - two isotopes are inevitably present, one of
> which (forgot the mass number, but you can look that up, too) has a
> spontaneous decay rate that is too high for the (relatively) slow
> assembly rate of a gun.

Weapons grade plutonium contains less than 7% of the non-fissile isotope
plutonium-240.  This is created if you leave the plutonium-239 in the
reactor after it is formed, and it manages to absorb an additional
neutron.  Small amounts of higher numbered plutonium isotopes are also
created by the same process.

For this reason, spent fuel from power reactors is not a suitable source
of weapons grade plutonium, although it is theoretically possible to build
a bomb from reactor grade plutonium if you use enough of it.  Bear in mind
you will have big thermal problems from short-lived plutonium isotopes if
that you employ plutonium from spent fuel, as well as problems from
neutrons getting soaked up by non-productive species.

-- 
Eric Michael Cordian 0+
O:.T:.O:. Mathematical Munitions Division
"Do What Thou Wilt Shall Be The Whole Of The Law"