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

  • Kazumichi Yanagisawa
  • Mamoru Nishioka
  • Nakamichi Yamasaki

Abstract

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.

Keywords

Compressive Strength Hydrothermal Condition Silica Matrix High Compressive Strength Waste Form 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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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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