Lokanathan, an Electrical and Electronics Engineering diploma holder and employed as onsite contract worker at the MPAS complex at nearby Kalpakkam, was arrested yesterday, police said.
He was detained based on the interrogation of Sharif Ali, arrested on August 6 for allegedly possessing 400 photos of the BHAVINI Prototype Fast Breeder Reactor (PFBR) in pendrives and a mobile phone, they said.
Ali, also a contract workers, has been remanded in judicial custody last week at the end of the interrogation.
Police sources said the National Intelligence Agency (NIA) had been kept informed about the progress of the probe.
The case might be handed over to the NIA, which has shown keen interest in it after the police filed the chargesheet, they added.