From: dietz@cs.rochester.edu (Paul Dietz)
Newsgroups: sci.environment
Subject: Re: plutonium arrives in Japan
Date: 7 Jan 93 19:46:05 GMT
Organization: University of Rochester

In article <82351@ncratl.AtlantaGA.NCR.COM> mwilson@ncratl.AtlantaGA.NCR.COM (Mark Wilson) writes:

>| more complicated.   For example, other countries in Asia have
>| expressed suspiciion about Japanese intentions about nuclear weapons.
	
> For the umpteenth time.  The plutonium in question is not suitable for
> making bombs.


This is simply wrong.  The material is not as good as weapons grade,
but it can be used to make weapons.  From H. A. Feiveson,
"Proliferation Resistant Nuclear Fuel Cycles", in Ann. Rev. Energy,
1979, pages 357-394:

------------------------------

   It is true that reactor grade plutonium is not ideal for weapons
   purposes because of its typically high concentration of the isotope
   plutonium-240.  (See table 1)
   --------------------
			Pu-239	Pu-240	Pu-241	Pu-242
   Weapons Grade	 93.5	  6	  0.5	  -
   Nominal PWR		  57	25.5	 12.5	  5

		Table 1:  Isotopic composition of Plutonium (%)
   --------------------
   There is, however, now an authoritative view that an entirely
   credible national nuclear weapons capability could be constructed
   with use of only reactor-grade material.

   Table 2 presents and compares the aspects of reactor-grade
   plutonium important for explosives.

   --------------------
				Weapons Grade		Reactor Grade

   Bare Sphere Critical
	Mass*			   11 kg		  13 kg
   Specific Activity		   3 curies/gm		  10 curies/gm
   Heat Generation		   3 watts/kg		  10 watts/kg
   Neutron Background		 100 n/(sec gm)		 500 n/(sec gm)

   * Compare bare-sphere critical masses: U-233, 16 kg; highly
     enriched U-235, 56 kg; Pu-240, 40 kg.

   --------------------

   ... [It] is clear that none of these factors represents
   a significant barrier to a determined country.  To wit:

   Reactivity.  All plutonium isotopes are fissionable by fast
   neutrons.  The critical mass for any type of reactor-grade
   plutonium is substantially smaller than the critical mass
   for highly enriched uranium (90% U-235).

   Handling.  Reactor-grade material does have a higher specific
   activity and heat generation than weapons-grade material.  But
   the differences are less than an order of magnitude.  Controls
   required to handle the more radioactive reactor-grade material
   are easily available.

   Neutron background and pre-initiation.  The neutron background
   ... is substantially greater in reactor-grade plutonium, a fact
   that increases the statistical uncertainty of explosive yield
   for this material because of "pre-initiation".  Increasing
   technological sophistication can reduce this uncertainty, and,
   in any event, minimum yields in the low kiloton range could be
   assured with high confidence.  For many, probably most, military
   and political purposes the remaining uncertainties in yield appear
   to be far less significant than the multitude of uncertainties
   that would surround any actual or threatened use of nuclear weapons.

------------------------------

	Paul F. Dietz
	dietz@cs.rochester.edu
Newsgroups: sci.environment