Under the worst possible conditions, a meltdown can occur in a nuclear submarine. It is an event of low probability, however.
coz if nuclear meltdown it can explode
USA has the most nuclear submarines
a nuclear reactor had a nuclear meltdown
Argentina had diesel-electric submarines while the British had nuclear-powered submarines.
A nuclear meltdown is an informal term for a severe nuclear reactor accident that results in core damage from overheating. A meltdown occurs when the heat generated by a nuclear reactor exceeds the heat removed by the cooling systems to the point which at least one nuclear fuel plate exceeds its melting point.
Chernobyl, Russia
Russia
a meltdown
This sounds like a nuclear core meltdown, reactor meltdown, or just a meltdown.
A number of nuclear submarines sank, and the circumstances vary from accident to accident. Wikipedia has a list, and by going there and entering "List of sunken nuclear submarines" you can review that list.
Nuclear submarines are powered by a nuclear reactor and they are completely independent of air, so there is no need to surface frequently.
The US, Russia, Great Britain, France, China and (recently) India have nuclear submarines.