NSA provides nuclear safety, design engineering, and professional security services.
Atkins chief executive officer Dr Uwe Krueger said: "This acquisition is another step towards our strategy to be one of the world’s leading energy consultancies.
"NSA will enhance our presence in North America, the world’s largest nuclear market, and its safety and security skills will strengthen our international nuclear offering."
Atkins Energy nuclear business managing director Chris Ball said: "NSA’s highly qualified workforce and its people and client focused culture are a perfect fit for Atkins.
With the acquisition, Atkins will expand in the US nuclear commercial (operation of existing stations, new build and power upgrades), and government, (ongoing activity at national laboratories and decommissioning of the legacy defense sites) markets.
"Atkins’ nuclear business is also supporting countries that are building nuclear for the first time, and those countries are establishing US-style regulatory regimes.
"NSA’s expertise in the US Nuclear Regulatory Commission (NRC) regulatory environment will be of great value in delivering these projects."
