SP Uthayakumar, coordinator of the People's Movement Against Nuclear Energy(PMANE), his associates Pushparayan, Mukilan and some others have been booked under different sections of IPC and Explosive Substances Act, top police sources said.
Cases were registered for offences including culpable homicide not amounting to murder and criminal conspiracy among others, they added.
Two live bombs were also recovered from the explosion site even as police formed a special team to probe the incident and stepped up security in and around the controversy-ridden Indo-Russian joint venture whose first unit started generating power last month.
A Department of Atomic Energy(DAE) official said the plant is running fine and is safe.
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Uthayakumar denied any role in the explosion.
"The people of Idinthakarai or members of (anti-nuclear) struggle committee have nothing to do with this explosion. We will cooperate with police and other government officials," he said.
A country-made bomb had gone off "accidentally" at around 6.40 PM yesterday when some suspected miscreants were making the explosive at their hut in Idinathakarai Tsunami colony, about 15 km from the KNPP. Among the dead were a woman and three children, all aged below five, while two persons were injured.
PMANE has been spearheading protests for more than two years against the nuclear project in Tamil Nadu's Tirunelveli district demanding its closure, citing safety concerns following the Fukushima disaster in Japan in 2011.
Unit-1 had attained criticality on July 13 this year.