I used MCNP to do some modelling for my Masters. I got quite annoyed with the lack of highlighting for its source files, so I wrote a highlighting file. It works well, although it's filled with a pile of RegExs, so it's rather slow (it sure beats nothing though).

To the highlighting file for Kate, place the mcnp.xml file in your ~/.kde/share/apps/katepart/syntax directory.

Enjoy!

MCNP home:
http://mcnp-green.lanl.gov/index.html