Hydrothermal Treatment of Radioactive Waste: Solidification of High-Level Radioactive Waste by Hydrothermal Hot-Pressing

  • Kazumichi Yanagisawa
  • Mamoru Nishioka
  • Nakamichi Yamasaki


Simulated high-level radioactive waste was immobilized into a silica matrix by hydrothermal hot-pressing. The optimum conditions to produce a waste form with high mechanical strength and low leachability were determined as follows; starting composition: 21.8wt% waste, 10wt% A1(0H)3, 47.7wt% low-quartz and 20.5wt% amorphous aluminosilicate with the addition of 10N NaOH solution (2.5 cm3/20g of starting powder), reaction temperature: 350 °C, reaction pressure: 66 MPa, reaction time: 6 hours.

The waste form produced under the optimum conditions was mainly composed of low-quartz of the matrix and the waste components (Fe2O3, CeO2, ZrO2). It was porous, apparent density 2.3 g/cm3, porosity over 20%, and BET specific surface area m2/g. It had high mechanical strength, compressive strength 200MPa. The leach rate of the waste form, determined by static leach tests at 90°C in distilled water for 28 days, was much lower than a concrete waste form and was comparable with glass and ceramic waste forms. The waste form was stable under hydrothermal conditions in comparison with a glass waste form. It had high thermal and thermal shock resistance. Its thermal conductivity was about 0.01 J/cm·sec·K, a value similar to that of a glass waste form.


Compressive Strength Hydrothermal Condition Silica Matrix High Compressive Strength Waste Form 
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Copyright information

© Elsevier Science Publishers Ltd. 1990

Authors and Affiliations

  • Kazumichi Yanagisawa
    • 1
  • Mamoru Nishioka
    • 1
  • Nakamichi Yamasaki
    • 1
  1. 1.Research Laboratory of Hydrothermal Chemistry, Faculty of ScienceKochi UniversityKochi-shiJapan

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