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Re: Why Hafnium?

On 29 Apr 1997 TOM WALKIEWICZ ASKED:

A student of mine that went through a nuclear training program while
in the Navy mentioned that Naval reactors use Hafnium as control rods
instead of Cadmium. It was interesting to then find that several
consecutive stable isotopes of Hafnium have a fairly high cross section
for neutron capture. However, elemental Cadmium has a cross section
of 2,450 barns while elemental Hafnium has a cross section of only
about 100 barns.
Question: Why is Hafnium used instead of Cadmium?

Unlike civilian reactors some navy reactors operate on fast neutrons.
Your high cross sections refer to thermalized neutrons, not a dominant
part in a fast reactor. This is only an "educated guess"; I never heard
about using Hafnium to control criticality. Will be happy to hear what
other phys-L-ers will say.
Ludwik Kowalski