<p>If you cannot major in nuclear engineering (there are about 20 universities in the US that offer that as an undergraduate major, and a few more that have a nuclear subspecialty under some other engineering major), then it is likely that some other field of engineering or physics is the best preparation, though chemistry may work as well (but note that chemistry has the worst job and career prospects by itself if you do not continue on to a graduate or professional degree with better prospects).</p>
<p>The Berkeley nuclear engineering department says this about undergraduate preparation:
[Admissions</a> | Department of Nuclear Engineering](<a href=“http://www.nuc.berkeley.edu/grads/admissions]Admissions”>Admissions)
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<p>Berkeley’s undergraduate nuclear engineering curriculum is described here:
[Curriculum</a> | Department of Nuclear Engineering](<a href=“http://www.nuc.berkeley.edu/undergrad/curriculum]Curriculum”>Curriculum)
You may want to see if courses similar to those listed are offered at your school, if it does not offer a nuclear engineering major, so that you can take them.</p>