R&D on Surrogate Kernel Fabrication in Support of Reaktor Daya Eksperimental (RDE) Project

Abstract

Abstract R&D program on HTGR fuel to support the RDE project has been outlined and is aimed to develop national capabilities on nuclear fuel technology. The external sol-gel technology has been adopted for the fabrication of kernels. Laboratory scale work has been ongoing at the Center for Nuclear Fuel Technology (PTBBN) BATAN to study various parameters involved in the process of kernel fabrication including tuning of parameters related to droplet formation (feed flow rate, vibrator frequency, NH3 gas flow rate), optimizing chemical formulation in broth preparation, various treatments in aging, washing, drying process, and thermal treatment for densification of kernels. In this early stage, zirconium precursors were used to manufacture surrogate kernels of ytrria-stabilized zirconia. The steps for kernel fabrication include chemical formulation of broth and droplet casting, aging-washing-drying of gel microspheres, calcination and sintering, and characterization of sintered kernels (surface morphology, density, diameter/sphericity, solid phase). Stable cast of droplets from 1 mm nozzle diameter was optimized by adjusting feed flowrate at 30 ml/min, viscosity at 45-60 cP, and vibrating frequency at 100 Hz. Presolidification of gel skin was optimized at a working NH3 flow rate of 3.5 - 4 L/min. Addition of urea with mole ratio urea/metal 2.5/1.0 gave the most preferable results based on SEM examination for crack and morphological structure. Control the opaqueness of the sol can be done by portioning addition of urea, where a portion of urea was added at decomposing temperature around 85°C, while another portion was added at a lower temperature. Addition of urea has a desirable effect on crack reduction during heat treatment of gel microspheres. Increase in metal concentration results in an increase in kernel diameter when other sol-to-gel conversion parameters were kept unvaried. Phase determination by X-Ray Diffractometer indicates that solid phase for ceria-stabilized zirconia prepared with precursor composition of 16% yttrium in zirconium-yttrium sol results in yttria-stabilized zirconia 8YSZ with cubic phase.