The NRC references for guidance on ASME Code applicability are:
NUREG-1609 (625K) "Standard Review Plan for Transportation Packages for Radioactive Material"
and, NUREG/CR-3019, Table 1.

The best DOE reference is the "Packaging Review Guide for Reviewing Safety Analysis Reports for Packagings" which can be downloaded (575K) from the "RAMPAC" site.

Note: each of the above links will open a new browser window.

NUREG-1609: http://www.nrc.gov/NRC/NUREGS/SR1609/SR1609.html

DOE Review Guide:   href=http://www.rampac.com/pcn/PRG99_Final.pdf

DOE RAMPAC Site:   http://www.rampac.com/