The work is across all 10 sites that are operated by Magnox on behalf of the Nuclear Decommissioning Authority.
The framework is expected to be worth up to £30m a year, initially for five years with options to extend by up to a further five years.
The project work includes the design, construction and maintenance of permanent buildings and structures, infrastructure maintenance and extension works incorporating construction, civil engineering and ground works projects.
Costain is already carrying out work for Magnox. In June 2011 its joint venture with Amec and Jacobs Engineering was included on a framework to retrieve and process both wet and solid intermediate level radioactive waste across all the Magnox sites in the UK.
Costain chief executive Andrew Wyllie said: "Construction, infrastructure and maintenance will form a major part of the work to deliver Magnox sites into a state of care and maintenance. Inclusion on this framework is testament to our growing reputation for providing specialised engineering solutions to customers and industry sectors which have highly complex requirements.
"The contract award also demonstrates the ongoing success of the implementation of our 'Choosing Costain' strategy: providing a broader service offering to blue chip customers who are making significant investment in the UK's national infrastructure needs."
Balfour Beatty chief executive Ian Tyler said: "We are delighted to have been selected by Magnox as part of this important framework. Our role in the framework highlights Balfour Beatty's strengths in the design, delivery and maintenance of infrastructure assets in the power sector. We look forward to working with Magnox."