NEW DELHI: The indigenous nuclear submarine INS Arihant is set to be launched for sea trials in a "month or two" and it will testfire the submarine-launched nuclear capable ballistic missile BO-5 DRDO said today.The nuclear reactor on board the INS Arihant was activated last year in August taking it closer towards sea trials after which the vessel would be inducted into operational service in the Navy."Arihant is going through the power-up cycle (in its nuclear reactor). It is the first time that we are doing the power-up cycle on a nuclear submarine. So, we are very cautious and going step by step. It will take a month or two more before it goes to the sea (for trials)," DRDO chief Avinash Chander told PTI.He was asked about the present status of the indigenous nuclear submarine programme under which at least three Arihant-Class nuclear underwater vessels would be built for the Navy."During the trial phase, the Arihant will testfire the fully-developed BO-5 missile as part of the sea trials," he said.Once inducted, the submarine will help the country complete its nuclear triad giving it the capability to respond to nuclear strikes from sea, land and air-based systems. Nuclear triad is the ability to fire nuclear-tipped missiles from land, air and sea-based weapon platforms.INS Arihant has been undergoing trials at Navy's key submarine base in Vishakhapatnam and has cleared most of its harbour acceptance trials. The medium-range nuclear missile BO-5 has a range of over 700km-range. The nuclear submarine will help India achieve the capability of going into high seas without the need to surface the vessel for a long duration . Conventional diesel-electric submarines have to come up on surface at regular intervals for charging the cells of the vessel.