Why this is ???

Current laws in India does not allow private sector participation in nuclear power generation. 

Then why Reliance Industries Ltd (RIL) led by Mukesh Ambani has ventured into nuclear sector ? RIL has picked up minority stake in Terra LLC, a US based firm, which is engaged in nuclear power generation business. 

I recommend the reading of featured article from Economic Times which throws more light and information in this subject. 

https://economictimes.indiatimes.com/news/news-by-industry/energy/power/reliance-to-fund-new-generation-nuclear-reactor-along-with-gates-vinod-khosla-ex-ms-honcho/articleshow/11198896.cms