The US, Russia, Great Britain, France, China and (recently) India have nuclear submarines.
The PLA navy has more than 225,000 personnel and is thought to have as many as 70 submarines, 10 of them nuclear-powered
From Wikipedia: Today, six countries deploy some form of nuclear-powered strategic submarines: the United States, Russia, France, the United Kingdom, People's Republic of China, and India Several other countries, including Argentina and Brazil, have ongoing projects in different phases to build nuclear-powered submarines.
15
ONE
USA has the most nuclear submarines
230
170
nearly 155
Argentina had diesel-electric submarines while the British had nuclear-powered submarines.
Reactors power submarines and many surface ships. Nuclear weapons.
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.