Cold Crucible Vitrification of NPP Operational Waste
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COLD CRUCIBLE VITRIFICATION OF NPP OPERATIONAL WASTE Feodor A. Lifanov1, Michael I. Ojovan2, Sergey V. Stefanovsky1, Rudolf Burcl3, 1 State Unitary Company SIA ‘Radon’, Moscow, RUSSIA 2 Department of Engineering Materials, University of Sheffield, UK 3 International Atomic Energy Agency, Vienna, A-1400, AUSTRIA ABSTRACT Operational radioactive waste is generated during routine operation of nuclear power plants (NPP). This waste must be solidified in order to ensure safe conditions of storage and disposal. Vitrification of NPP operational waste is a relative new solidification option being developed for last years. The vitrification technology comprises a few stages, starting with evaporation of excess water from liquid radioactive waste, followed by batch preparation, glass melting, and ending with vitrified waste blocks and some relative small amounts of secondary waste. Application of induction high frequency cold crucible type melters facilitates the melting process and significantly reduces the generation of secondary waste. Two types of glasses were designed in order to vitrify operational waste depending on the reactor type at the NPP. For the NPP with RBMK-type reactors the glass 16.2Na2O 0.5K2O 15.5CaO 2.5 Al2O3 1.7Fe2O3 7.5B2O3 48.2SiO2 1.1 Na2SO4 1.2NaCl (5.7 others) was produced. For NPP with WWER reactors the glass 24.0Na2O 1.9K2O 6.2CaO 4.3Al2O3 1.8Fe2O3 9.0B2O3 46.8SiO2 0.8Na2SO4 0.9NaCl (4.3 others) was produced. The melting temperatures of both glass formulations were 1200-1250 C, specific power consumption was 5.2 ± 0.8 kW h/kg, 137Cs loss was within the range 3 - 4 %. The specific radioactivity of glass reached 7.0 MBq/kg. Glass blocks obtained were studied both in laboratory and field conditions. Long-term studies revealed that vitrified NPP operational waste has the minimal impact onto environment. Since the glass has excellent resistance to corrosion it gives the basic possibility of maximal simplification of engineered barrier systems in a disposal facility. The simplest disposal option for vitrified NPP waste is to locate the packages directly into earthen trenches provided the host rock has the necessary sorption and confinement properties. INTRODUCTION Vitrification currently becomes the most perspective for NPP operational low and intermediate level radioactive waste (LILW) [1, 2]. Two main advantages of vitrification attract attention: the best retention of radionuclides and the maximum volume reduction of waste. The safety requirements to waste storage and disposal facilities become by time more and more stringent. Glass as an immobilising material has the advantage of almost maximum reliability of radionuclide retention among reasonable applicable technologies. The minimal impact to environment of vitrified product can be crucial for reduced possibilities on constructing large complex and costly repositories. In this respect the glass requires minimal containment properties of a storage facility. Vitrification opens up real possibilities of storage and disposal in the simplest
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