When we were planning my late husband's funeral, I referred to the interment of his ashes. The funeral director gently told me that, when it's ashes rather than a whole body, the correct term is 'internment'.
I had never heard this before but, when the manager of the burial site also referred to 'internment', I accepted that they must be correct.
I've not given the subject another thought in the intervening years until I saw this thread and started Googling. Interesting: no references to internment meaning anything except a form of imprisonment.
Well, we buried his ashes in a lovely woodland site which was what he wanted and he probably wouldn't have worried too much about the words used.