erature is progressively increased up to 1100 to 1500 C and then is maintained for several hours so to allow the glass to elaborate. The third step is 'Glass casting'. The glass is cast in a special container. The heating of the output of the vitrification pot causes the glass plug to melt, thus allowing the glass to flow into containers which are then transferred into the storage. Although part of the waste is transformed into a solid product there is still treatment of gaseous and liquid wastes. The gases that escape from the pot during feeding and calcination are collected and sent to ruthenium filters, condensers and scrubbing columns. The ruthenium filters consist of a bed of glass pellets coated with ferrous oxide and maintained at a temperature of 500 C. In the treatment of liquid wastes, the condensates collected contain about 15% ruthenium. This is then concentrated in an evaporator where nitric acid is destroyed by formaldehyde so as to maintain low acidity. The concentration is then neutralized and enters the vitrification pot. Once the vitrification process is finished, the containers are stored in a storage pit. This pit has been designed so that the number of containers that may be stored is equivalent to nine years of production. Powerful ventilators provide air circulation to cool down glass. The glass produced has the advantage of being stored as solid rather than liquid. The advantages of the solids are that they have almost complete insolubility, chemical inertias, absence of volatile products and good radiation resistance. The ruthenium that escapes is absorbed by a filter. The amount of ruthenium likely to be released into the environment is minimal. Another method that is being used today to get rid of radioactive waste is the 'placement and self processing radioactive wastes in deep underground cavities'. This is the disposing of toxic wastes by incorporating them into molten silicate rock, with low permea...
