The four-year reimbursable framework contract has a potential value range of between £240m-£336m with the JV partners splitting the financial terms equally.
Work is scheduled to begin immediately.
BEP is designed to treat Magnox reactor waste currently stored at Sellafield by containing it in concrete and getting it ready for long term storage.
The joint venture will be responsible for the complete life cycle of the scheme from design, engineering, procurement, installation and construction management through to commissioning and handover.
Balfour Beatty’s Major Projects business will provide a broad range of expertise including civil engineering, construction and mechanical and electrical capabilities, and supply chain management.
Building Information Modelling will support accelerated delivery by integrating design and construction information within the construction programme to optimise planning and co-ordination.
The joint venture has pledged to engage local small and medium sized businesses in the supply chain and employing local apprentices and trainees.
Balfour Beatty UK construction chief executive officer Nicholas Pollard said: “Balfour Beatty has a strong heritage in the nuclear sector including a 35 year presence at Sellafield.
“This is an important project to reduce hazardous waste across the Sellafield site and Balfour Beatty and our partners will draw upon and share our extensive experience of safely delivering major nuclear facilities. This latest award underscores Balfour Beatty’s success and capability in the UK power sector. “