What's been going on with the sunken nuclear powered submarines?

What has been going on with the nuclear powered submarines that sunk years ago - from the United States, and the former Soviet Union, and from Russia? Have they been leaking radioactive material? Is it possible that more radioactive material could get into oceans and/or the waterways? Should we make an effort to recover the sunken subs. to prevent future radioactive leaks, and to properly dispose of the rest of the nuclear material still on-board the subs? Is anyone looking into this?