MCNP Guide
MCNP — Windows Installation
Building and configuring MCNP on Windows with Visual Studio and Intel Fortran
System Requirements
Hardware
CPU: 2+ cores, 2.0 GHz minimum
RAM: 4 GB minimum, 16 GB recommended
Storage: 20 GB free space
Network: Internet access for downloads
Software
OS: Windows 10 / 11 (64-bit)
Visual Studio: 2019 or newer (Community edition sufficient)
Intel Fortran: Intel oneAPI HPC Toolkit
Microsoft MPI: For parallel execution
Windows SDK: Latest version
Required Software
Install the following tools before building MCNP. Links are to official Microsoft and Intel download pages.
Visual Studio 2019+ (Community)
During installation select the "Desktop development with C++" workload. The Community edition is free for academic and personal use.
Intel oneAPI HPC Toolkit (Intel Fortran)
Provides ifort, required for compiling MCNP's Fortran source. The free oneAPI edition is sufficient.
Required for parallel execution. Install both the runtime and the SDK package.
Build Process
Open the Intel oneAPI Command Prompt (or the Visual Studio Developer Command Prompt with the Intel Fortran environment sourced), then navigate to the MCNP source directory and run nmake.
Compile and install
REM Navigate to the MCNP source directory
cd C:\MCNP6.2\Source
REM Set compiler environment variables
set FC=ifort
set CC=cl
set CXX=cl
REM Build using nmake
nmake -f Makefile.win
REM Install to Program Files (or any directory)
nmake -f Makefile.win installAdd to PATH
After installation, add the MCNP bin directory to your system PATH so mcnp6 can be called from any command prompt. Open System Properties → Environment Variables → edit the Path variable and add the path to your MCNP binary (e.g., C:\MCNP6.2\bin).
Cross-Section Data
Nuclear data libraries are distributed separately by RSICC. The most common libraries are:
Essential Libraries
ENDF/B-VIII.0: Latest US evaluation — library suffix .80c
ENDF/B-VII.1: Well-validated library — library suffix .71c
Thermal Data: S(α,β) scattering libraries for bound moderators
Photon Data: Atomic relaxation data for photon transport
Setup data path
Extract the cross-section archive to a directory (e.g., C:\MCNP6.2\data), then set the DATAPATH environment variable to that directory so MCNP can find the xsdir file.
REM Set via command prompt (session only)
set DATAPATH=C:\MCNP6.2\data
REM Or set permanently via System Properties → Environment Variables
REM Variable name: DATAPATH
REM Variable value: C:\MCNP6.2\data
REM Verify the xsdir file is present
dir C:\MCNP6.2\data\xsdirVerify the Installation
Create a simple test input file and run it to confirm MCNP and the cross-section data are both working correctly.
Test input (test.i)
Simple sphere test
1 1 -1.0 -1 imp:n=1
2 0 1 imp:n=0
1 so 10
m1 1001.70c 1
sdef
nps 1000Run the test
REM Run MCNP with the test input
mcnp6 i=test.i o=test.o
REM Search the output for the completion message
findstr "run terminated normally" test.oA successful run prints run terminated normally in the output file.
Test parallel execution
mpiexec -n 4 mcnp6 i=test.i o=test_parallel.o tasks 4Common Issues
Intel Fortran not found
Open the Intel oneAPI Command Prompt rather than a standard command prompt — it sets all compiler environment variables automatically.
nmake errors
Verify that FC, CC, and CXX are set correctly and that the Visual Studio C++ tools are installed alongside Intel Fortran.
MPI problems
Install both the Microsoft MPI runtime and SDK. Ensure mpiexec is in your PATH before running parallel jobs.
Cross-section errors
Check that DATAPATH is set as a system environment variable (not just for the current session) and that it points to the directory containing xsdir.
Permission errors
Run the command prompt as Administrator when installing to C:\Program Files or other protected directories.
For additional troubleshooting, see the MCNP Troubleshooting guide. Keep your RSICC account credentials secure — MCNP licenses typically require annual renewal.