Honestly, I do not think that India stands to gain much in the long term by expanding its nuclear power program.
But here are the points used by many to support the expansion of the nuclear power program.
India's economic development has led to a large increase in its power consumption. This is expected to grow at 6.3% per annum and by 2050 is expected to reach an annual consumption of 5000 - 6000 kWh per capita.
Most of India's electricity generation is done through coal-powered thermal power plants. As the reserves of coal are limited and non-renewable it would not be possible to expand power generation to the required levels and maintain them.
It is also difficult to expand renewable hydroelectric power as India's high population makes it impossible to find land to create the huge reservoirs that are needed for hydroelectric power plants.
No large expansion in the field of renewable sources of power like solar or wind is expected that may be able to replace the present power generation using fossil fuels.
Nuclear energy which presently provides just 2.5% of India's electricity requirements can easily be expanded now. This is mainly due to the fact that India now has access to advanced technology required to build the reactors and there are also no restrictions on the import of nuclear fuel from other nations.