Lowering of the huge stainless steel main vessel -- 12.9 metres in diameter and 12.94 metres in height, weighing 206 tonnes -- is considered a major step in completing the 500 MW power project by the September 2011 deadline.
The sodium-cooled fast reactor designed by the Indira Gandhi Centre for Atomic Research (IGCAR) has three vessels - a safety vessel, a main vessel and an inner vessel.
Outermost is the stainless steel safety vessel, which was lowered into the reactor vault last June - the first milestone.
The third and smallest of the three vessels is the inner vessel -- 11 metres tall. It houses pumps, heat exchangers and other equipment. Together, they all go inside the main vessel.
Kumar said the 11-metre-tall cone-shaped inner vessel, thermal baffle, grid plate and primary pipe were ready. The reactor control rods were being tested.
'By March next year the roof slab of the nuclear reactor vault will be erected,' Kumar said.
The other major project activities completed are the erection of four 12.5-metre-tall argon buffer tanks and the transfer of around 825 tonnes of sodium to the sodium storage tanks.
Last word on Japan's Monju fast breeder reactor is for a Feb 2010 restart