Compiling the util/ directory with USE_NOIO=TRUE should make any junk.xxx file to not appear.
Are you sure that NWChem was compiled with USE_NOIO=TRUE?
I didn't do anything specific in util/ directory, just under src/:
make nwchem_config
make
then use ./getmem.nwchem
I put "export USE_NOIO=TRUE" and "export USE_NOFSCHECK=TRUE" in my .bashrc file.