“Chernobyl Diaries” is an original story from Oren Peli, who first terrified audiences with his groundbreaking thriller, “Paranormal Activity.” The film follows a group of six young vacationers who, looking to go off the beaten path, hire an “extreme tour” guide. Ignoring warnings, he takes them into the city of Pripyat, the former home to the workers of the Chernobyl nuclear reactor, but a deserted town since the disaster more than 25 years ago. After a brief exploration of the abandoned city, however, the group soon finds themselves stranded, only to discover that they are not alone…