The US and Vietnamese governments reached the agreement in October, 2013. Congress now has 90 days to review it. If lawmakers do nothing, the deal will take effect.
The "123 agreement", approved by Obama on Monday, allows US firms into Viet Nam's civilian nuclear power market. Russian and Japanese companies are already planning to build reactors there.
Under the agreement, Viet Nam is committed to relying on the international market for its nuclear fuel supply rather than enriches uranium or reprocesses plutonium itself.
By Thuy Dung