I've also found these interesting articles/posts on Core Dump files that I would like to share to help others who might run into the same problem:

https://stackoverflow.com/questions/59672173/what-are-the-core-xxxxx-files-created-by-tensorflow

https://en.wikipedia.org/wiki/Core_dump

I have checked the date those Core dumps were created and I remember working on the server that day. Few stuff went wrong then crashed the server. But I managed to fix it and get it back running again. I suspect that that was what crashed my UNA installations creating those Core dump files in the /periodic/ folder. After getting the server back, no more core.xxxx files were generated (I have checked the date). It wasn't a UNA-related problem but instead a server issue.

So, I have just deleted those core files (I have killed'em all 😊) to free disk space on the server. I think there is no need to download them. They are big, they will take time to downalod and I will not need them. Thanks for helping.