Alternate Isotopes in RTGs? - Reply

[Charles Willis <CAW@nrc.gov>]

Don, 

As you can imagine, quite a number of nuclides have been seriously considered and
actually used in RTGs.  Considerations include cost (and fesibility) of production,
power density, shielding requirements, half life and safety.  For example, back
when I was involved in these issues, U-232 looked attractive, despite the problems
of having to deal with the daughter products, but the feasibility of production in the
quantities needed had not been fully demonstrated.  Every nuclide presents
problems of one sort or another.  Pu-238 consistantly has come out on top for a
variety of applications.

Be assured that people keep looking for something better, but this is not new
ground to be broken.

Do you suppose that the critics would have been less vocal if the fuel had been
U-232?  I have my doubts.

Charlie Willis
caw@nrc.gov