ИСТИНА

Nuclear waste management and long-term disposition of current and legacy nuclear wastes remain an open issue in the movement to a true renaissance of nuclear power generation. The physical and chemical durability of oxide glasses combined with their high tolerance to compositional changes make them irreplaceable materials for the immobilisation of highly toxic substances, such as nuclear waste, to ensure safe long-term storage, transportation and disposal. Nuclear waste vitrification is attractive because of technological and compositional flexibility, the large number of elements which can be safely immobilised, high corrosion resistance, mechanical and radiation durability, as well as the reduced volume of the resulting wasteform. Borosilicate and to a lesser extent phosphate glasses are the overwhelming world-wide choice for the immobilization of high level radioactive wastes (HLW) resulting from nuclear fuel reprocessing and low- and intermediate level radioactive wastes such as those from operation of nuclear power plants and legacy waste. Vitrification is a mature technology which has been used on an industrial scale for more than fifty years. Continued advances in glassy wasteforms and nuclear waste vitrification technologies will be keys in enabling widespread deployment of nuclear energy [1]. This paper focuses on In-Can Melting (ICM) and In-Can Vitrification (ICV) technologies applied to immobilisation of nuclear legacy waste [2,3]. This waste is mainly from nuclear fuel fabrication utilities and research organisations. It may contain organics (PVC, PE, neoprene, wipes, glovebox windows), metals (Fe, Cu, Al, wires, tools, various products, tools…), filtering materials (HEPA, prefilters, laboratory samples, …), fiberglass, ceramics pieces and so on. It is characterised by a varying composition and is typically an intermediate level radioactive waste (ILW) containing long-lived radionuclides e.g. alpha emitters such as U, Pu, Am in oxide forms. Because of long-lived nature it requires a reliable immobilisation where glasses and vitrification are of primary choice. The ICM and ICV processes developed currently mainly in France [2,3] can accommodate this kind of waste producing waste packages that contain vitreous and metallic wasteforms inside of same package. Metallic parts of waste are melted at temperatures reaching 1450 C, whereas glasses which immobilise the oxide part of waste are typically melted at lower temperatures about 1250 C. However, the ICM/ICV processes require refractory crucibles able to withstand action of corrosive melts during processing at these high temperatures. Refractory crucibles are containers for melting and holding of non-ferrous metals. According to their very good thermal and/or electrical conductivity they can be readily used in different types of furnaces like electrical resistance, fuel fired and induction furnaces. A specific clay bonded graphite crucible from Morgan MMS was chosen after long time laboratory tests by a French company to melt a mix of glass and metal at 1450°C in an induction furnace. The dimensions of the actual cylindrical clay-graphite crucible are about 550 mm in the outside diameter and in the height. It demonstrated a good performance in experiments with simulant ILW and is considered for actual legacy waste use. The report will provide details on crucibles and operational performance. References 1. J.C. Marra, M.I.Ojovan. Vitrification of Radioactive Wastes. Glass International, 37 (4), 19-21 (2014) 2. P. Gruber, S. Lemonnier, J. Lacombe Y. et.al. Development of In-Can Melting Process Applied to Vitrification of High Activity Waste Solutions (HAWS): Glass characterizations and process tests results – 12442. Proc. WM2012 Conference, February 26-March 1, 2012, Phoenix, AZ, USA. 3. C. Girold, P. Charvin, I. Hugon et.al. Mixed Metallic and Organic Transuranic Waste Incineration / Vitrification – 17539. Proc. WM2017 Conference, March 5-9, 2017, Phoenix, Arizona, USA.