You've broken the first three rules of the [OpenMC style guide](http://mit-crpg.github.io/openmc/devguide/styleguide.html), section 2.1:

1. Conform to the Fortran 2008 standard.
2. Make sure code can be compiled with most common compilers, especially gfortran and the Intel Fortran compiler. This supercedes the previous rule — if a Fortran 2003/2008 feature is not implemented in a common compiler, do not use it.
3. Do not use special extensions that can be only be used from certain compilers.