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.