"The nuclear reactor on-board the INS Arihant would be made critical (activated) in next two to three weeks," DRDO chief V K Saraswat told PTI here today.
Nuclear triad is the ability to fire nuclear-tipped missiles from land, air and sea.
He said after the nuclear reactor is activated, the agencies concerned can work towards readying the warship for operational deployments soon.
INS Arihant has been undergoing trials at Navy's key submarine base in Vishakhapatnam and would be launched for sea trials after the nuclear reactor goes critical.
The nuclear submarine will help India achieve the capability of going into high seas without the need to surface the vessel for long durations.
Conventional diesel-electric submarines have to come up on surface at regular intervals for charging the cells of the vessel.