Nuclear subs are nuclear powered. The German made subs are not nuclear powered. They use batteries underwater or snorkel using diesels. They have to snorkel to recharge batteries. That makes noise. Nuclear powered subs can stay underwater for months and don't run diesel engines for as long as food exists aboard. Iran has subs, too. And they, too are diesel & battery subs.
Knesset approves 2015-16 state budget in first reading (Haaretz)
from the article: Report: Israel to deploy nuclear-armed submarines off Iran coast