CHAMBER OF CHILLS (1972) #13

Reprint of the 2nd story from World of Suspense #7 A sea creature is captured and brought to an atomic testing facility. It attempts to communicate telepathically with the man who brought it there, but the man thinks it is evil and resists it. When it gets out of the tank, the man acquires a gun and hunts it down to kill it. After he does so, he encounters scientists who tell him that the creature shut down an out of control atomic pile saving all of their lives.