With the decreased cost and increased capabilities of computers, Nuclear Engineering has implemented computer software into all facets of this field. There are a wide variety of fields associated with nuclear engineering, but computers and associated software are used most often in design and analysis. Neutron Kinetics, Thermal-hydraulics, and structural mechanics are all important in this effort.
The codes can be separated by use and function.
Monte Carlo Radiation Transport
Deterministic Radiation Transport
Spatial Kinetics
Thermal-Hydraulics
Computational Fluid Dynamics
Severe Accident
Many codes are supported by the U.S. Nuclear Regulatory Commission (NRC). The include SCALE, PARCS, TRACE (Formerly RELAP5 and TRAC-B), MELCOR, and many others.
http://www.nrc.gov/about-nrc/regulatory/research/safetycodes.html