For the dirty weapon that you're talking about, you'd need the radioactivity to be spread via the air...since the sub would be underwater (or even mostly underwater when surfaced), I doubt it. I also doubt that this is something that you'd have to worry about though. Very few nations operate nuclear submarines (US, Russia, Britain, France, China) and all of them have decent security measures in place.
__________________
Thor:
Intel Core i7 4770K|ASUS Z87Pro|32GB DDR3 RAM|11GB EVGA GeForce RTX 2080Ti Black|256GB Crucial M4 SSD+2TB WD HDD|4X LG BD-RE|32" Acer Predator Z321QU 165Hz G-Sync (2540x1440)|Logitech Z-323 2.1 Sound|Win 10 Pro
Explorer (MSI GL63 8RE-629 Laptop):
Intel Core i7 8750H|16GB DDR4 RAM|6GB GeForce GTX 1060|128GB SSD+1TB HDD|15.6" Widescreen (1920x1080)|Logitech R-20 2.1 Sound|Win 10 Home
|