The job is part of the huge decommissioning programme at the Cumbria site and will allow for the demolition of old silo facilities.
The joint venture will now work with Sellafield Ltd to deliver the concept and preliminary design (phase 1).
This will be followed by phase 2 during which the contractor will be responsible for completing the detailed design and the procurement of any long lead items of plant and equipment.
Phase 3 of the works will see the contractor completing the procurement, manufacture, construction and commissioning of the silo maintenance facility.
This is the second major contract success at Sellafield for the pairing who last year began design work on multi-million pound waste storage facility known as the Box Encapsulation Plant Product Store.