Cement Based Encapsulation Experiments of Low-Radioactive Phosphate Effluent
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Cement Based Encapsulation Experiments of Low-Radioactive Phosphate Effluent Atsushi Sugaya, Kenichi Horiguchi, Kenji Tanaka and Shigeru Akutsu Tokai Reprocessing Research and Development Centre, Japan Atomic Energy Agency (JAEA), 4-33 Muramatsu, Tokai-Mura, Naka-Gun, Ibaraki, 319-1194, Japan ABSTRACT The Tokai Reprocessing Plant produces a phosphate effluent consisting of NaH2PO4 at an approximate concentration of 440 gℓ-1, with only very minor quantities of other species. JAEA intends to encapsulate this waste in cement. Results are presented from non-active trials that demonstrate that it is possible to encapsulate this waste using ground granulated blastfurnace slag or Super-Cement. It was found that to achieve a stable wasteform it was necessary to pretreat the phosphate effluent with lime before encapsulation. The optimum pre-treatment and cement formulations were investigated. Compressive strengths of grouted waste simulant exceeded 10 MPa after 28 days curing and a waste loading exceeding 13 wt% was achieved. INTRODUCTION The operation of a nuclear fuel reprocessing plant generates a number of different types of effluent treatment wastes. It is necessary for all these wastes to be disposed of in a safe, sustainable and economic manner. In Japan these wastes must be disposed of on land, and not at sea, using either deep or shallow burial depending on the radioactive inventory of each waste type. Following the strategy adopted widely by a number of countries, effluent wastes from JAEA nuclear fuel reprocessing operations will be immobilised in solid matrices that convert the waste into a safer and more convenient form for transportation, storage, and ultimate disposal. Until 1997 low level radioactive liquid wastes such as solvent washing effluent, radionuclide analysis waste, off-gas scrubber wastes, and decontamination wastes were concentrated by evaporation and then bituminisation. However, this process was discontinued in 1997 after a fire in the bituminisation facility. A cementation facility is now being designed with construction starting during 2012 and operation from 2014. Here we focus on research into the encapsulation of effluent waste containing phosphate salts that is generated during the solvent extraction processes at the Tokai Reprocessing Plant. This phosphate waste consists principally of an aqueous solution of monosodium phosphate of typical concentration 440 gℓ-1, with additional minor species. The phosphate effluent has a pH of ~ 4. Therefore, it is necessary to ‘pre-treat’ the waste before mixing to increase the pH to make it compatible with the cement powder. An option within the process is also available to evaporate the waste to reduce the water content of the phosphate effluent. For this option to be used the phosphate waste must first be treated to increase the pH to ~ 7 to prevent corrosion and damage of the evaporator. The work presented here gives the results of an investigation into the pre-treatment of the phosphate waste and its subsequent encapsulation in cement
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