I have never touched Fortran, but my wife worked on 50 years old code for atmospheric physics / boundary layer modelling. I have no idea how stable it is, and m

I have never touched Fortran, but my wife worked on 50 years old code for atmospheric physics / boundary layer modelling. I have no idea how stable it is, and my wife is not cs but a physicist, so wouldn't tell me, but I have a feeling that it's pretty mature. What do US nukes use? Anyone?