A trooper gunned down three security personnel and injured two at the Kalpakkam nuclear complex following an altercation Wednesday morning, an official said."There was an altercation between some security personnel posted at the Kalpakkam nuclear complex. "One of them started shooting the others. Three persons died on the spot while two got injured. One of the injured is in a serious condition," an official of Nuclear Power Corporation of India Ltd told IANS, preferring anonymity.According to the official, the shoot-out happened at around 5.30 a.m. at the spot where the Central Industrial Security Force (CISF) personnel are camping.He said the police have arrested the trooper who shot the five people.