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A study has been carried out on the foaming effect which occurs during the calcination of MTR-type waste materials, in order to improve the in-pot vitrification technology. Foaming is accompanied by swelling and growth expansion phenomena, and is influenced by the initial composition of the waste and by the operating parameters in the applied vitrification process, in particular the heating conditions. The waste studied was made of a mixture of alkaline sludges and zeolites coming from the treatment of simulated high aluminium content nitric liquid waste (the so-called "alkaline declassification" process), and the vitrifying additives. During the heat treatment of the samples, attention was focussed on: - softening temperature, - thermal decomposition, examined by differential thermogravimetric analysis, - residual nitrate ion and released gas composition, and - iron oxidation state after heat treatment in air and in nitrogen. The foaming effect on the calcined material occurred in the temperature range 923-1023 K and was due to gas release at temperatures higher than the softening temperature of the calcined material. The most effective remedy to minimise foaming was found to be the addition of organic substances, such as sugar, to the material to be calcined. A weight ratio of 1.5:1 between sugar and the nitrate content was found to be sufficient to eliminate the foaming effect. During the waste heating process in the presence of sugar, nitrates are totally destroyed at temperatures much lower than the bulk softening point of the material. In addition, below 1273 K in nitrogen, only a partial reduction of iron occurs.

Additional information

Authors: FACCHINI A, Politecnico di Milano, Milano (IT);NANNICINI R, ENEA, Ispra (IT);SERRINI G, JRC Ispra (IT);ZAMORANI E, JRC Ispra (IT)
Bibliographic Reference: Paper presented: 3rd International Conference on Nuclear Fuel Reprocessing and Waste Management, Sendai (JP), April 14-18, 1991
Availability: Available from (1) as Paper EN 36159 ORA
Record Number: 199110754 / Last updated on: 1994-12-02
Original language: en
Available languages: en