Prime Minister Theresa May has defended the delay on whether to give the go-ahead to Hinkley Point.
Mrs May said it was down to "the way I operate", and she wanted to look at the evidence for the £18bn nuclear plant in Somerset.
The review comes amid concerns about the high cost of energy from the proposed plant and security implications of Chinese involvement.
A decision is expected to be announced later this month.
Mrs May was speaking at the G20 summit in the Chinese city of Hangzhou.
The prime minister is due to discuss the project with China's President Xi Jinping amid heightened diplomatic tensions over her perceived concerns about Chinese involvement in Hinkley Point.
Asked whether the National Security Council would be examining the project, in which the state-owned China General Nuclear would take a one-third stake, Mrs May said: "I'm going to be looking at all the evidence around this issue. The way I look at this, I don't just take an instant decision.
"I actually look at the evidence, take the advice, consider it properly and then come to a decision.
"I have been very clear that I will be doing that and taking a decision some time this month."
Mrs May will meet Chinese president Xi Jinping after the G20 summit in Hangzhou concludes on Monday.