The contractor will develop a scalable design for facilities to store intermediate-level waste held in ductile iron containers or yellow boxes as they are more commonly known.
Eight specialist stores will then be built at separate sites with variable ground conditions.
The anticipated value of the agreement over the four years plus a possible three-year extension is between £15m and £18m.
Several projects are now online and on their way towards final design solutions.
Throughout the working process, Magnox and Interserve have forged a mutually supportive professional relationship.
John Vieth, Supply Chain Development & Relationship Manager of Magnox, said: “Through Interserve’s consistent delivery we are moving efficiently from project to project and site to site expending minimal effort.
Interserve has a thorough understanding of what is required to make the framework a success and is actively supporting us to make it happen.”
The agreement with Magnox follows on from contracts at Sellafield including the first two of 11 large, prefabricated modules required to build the Evaporator D facility located at the Sellafield nuclear site in Cumbria, the biggest nuclear project underway in the UK.