The use of Wireless Sensor Networks (WSN) is now widespread, with well-documented deployments across a diverse range of sectors including aerospace, agri-science and consumer electronics. In the nuclear industry there have been successful deployments of WSN technologies for instrumentation and control, however, there are significant challenges that need to be addressed before wireless sensing can be used in some nuclear decommissioning extreme environments. This paper presents a concept design for a wireless sensor network capable of delivering wireless remote sensing and control capability through the reinforced concrete structures used in nuclear processing environments. The paper describes the deployment challenges, and how these are being addressed by the design methodology. These challenges include: difficult to reach areas with limited or no power sources; radiation tolerance of sensors and communication systems and delivery of secure and reliable communication in spaces exhibiting highly variable wireless propagation conditions. Following the description of the design methodology, the paper focuses on recent work to characterise the wireless propagation through the reinforced concrete structures found in many decommissioning environments. Preliminary Radio Frequency (RF) propagation measurements undertaken in two buildings on the Sellafield site are presented. The paper demonstrates how analysis of these results enables potential transmission frequencies to be identified and the power budget of the wireless sensor nodes to be modelled.