The nuclear materials process begins with fueling a nuclear
reactor. Uranium ore is processed to remove most of the
contaminants and built into fuel rods. These rods can be clad in
several types of metal, one being a type called Magnox, which is found
in older reactors produced out of the U.K. For instance, this is
the type of reactor that was installed in North Korea.
The rods are inserted in the core and fuel the nuclear effects in the
reactor for about three years at which time they must be removed and
disposed of. However, the material that is left over can be
combined with depleted uranium to create MOX -- Mixed Oxide -- a new
type of fuel that has a bit more energy than the processed uranium
ore. MOX rods are then inserted into the reactor core.
At the end of the fuel cycle, the rods will contain U-238, and two
types of Plutonium, P-236 and P-238. These isotopes are also
found in the MOX. However, the plutonium can be placed into a
"breeder" reactor which transforms the plutonium isotopes into P-239
and P-241, both of which are highly fissile and make excellent weapons
grade material. Thus the nuclear fuel cycle produces three
weapons grade materials, U-238, P-239 and P-241.
P-241 decays at a rate of about 0.5 % per year into Am-241. The
Amercanium is extremely dangerous, even more so than the highly
radioactive plutonium or uranium isotopes. Am-241 presents
a horrible occupational health hazard to workers defueling a nuclear
reactor and its disposal presents challenges to nuclear waste
engineers.
The bigger risk, should it occur, is the diversion of Am-241 into toxic
weapons such as a Radiological Dispersal Weapon or RDW -- the so called
"dirty" bomb. The RDW is not intended (and cannot) "go nuclear",
that is, it cannot create a kiloton or more of explosive power like a
nuclear weapon. The idea behind a RDW is to use conventional
explosives to disperse -- spread around -- a whole bunch of toxic and
radioactive material onto people, places and things. People
attacked with the material die from the toxic properties (these
isotopes are poison) or radioactive poisoning (radiation
sickness). Places and things become radioactively contaminated
and people can no longer be near them, rendering places uninhabitable
or things unusable. The effects can last many decades.
Note that nuclear weapons material that is waiting to be crafted into a
nuclear weapon can be "burned" in new fuel rods as nuclear fuel, and
indeed it produces more energy than a standard fuel rod. However,
no one would be foolish enough to create weapons grade material
specifically for use in a nuclear reactor -- the extraction process
alone would make the nuclear fuel extremely expensive per rod. However
a country which is prevented from producing fuel from ore (i.e. has no
resources or has been blacklisted and cannot purchase and import ore)
might choose to "kill two birds with one stone" - produce weapons grade
material to build a nuclear weapon and then if needed, use that
material in their reactors if they had excess or decommissioned weapons.
