Treatment of active concrete waste arising from the dismantling of nuclear facilities

This report describes an investigation into a method of immobilizing dust following demolition of a concrete structure. It considers a number of materials that could be used for this purpose and selects sodium silicate for detailed assessment as a first choice, based on various practical factors. Part A dealing with the chemical aspects shows that sodium silicate will successfully encapsulate dust in bulk and will affix that left attached to rubble and which is not easily removable. It determines the technology of use of sodium silicate and its properties in relation to dust encapsulation paying attention to the effect of the silica/alkali ratio on the properties of sodium silicate solutions. Part B, dealing with the engineering and process aspects, examines how the dust may be collected and stabilized with silicate. The preferred process from operational considerations is to pelletize the dust, so that it can be held in a harmless form. The pellets can be packed economically with more active material. A study of pneumatic conveying shows that the feasibility of collection by suction nozzle, conveying and separation from the air stream is not in doubt. Pelletizing machines are selected from those in use on other materials. The most successful machines are a pan agglomerator and various forms of briquetting roller compaction machines. A comparison is made of the properties of pellets made in these trials. This leads to recommendations of the most suitable pelletizing machine and process parameters for a pilot plant. For a remotely controlled pelletizing process the proportions of dust in different particle size ranges has to be controlled, particularly to ensure the presence of a sufficient quantity of fine particles. The strength of binder solution and the dustbinder ratio must also be controlled to optima established to suit the dust