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• W99153321 abstract "The decommissioning of Salaspils research reactor is connected with the treatment of 2200 tons different materials. The largest part of all materials ({approx}60 % of all dismantled materials) is connected with low level radioactive wastes conditioning activities. Dismantled radioactive materials were cemented in concrete containers using water-cement mortar. According to elaborated technology, the tritiated water (150 tons of liquid wastes from special canalization tanks) was used for preparation of water-cement mortar. Such approach excludes the emissions of tritiated water into environment and increases the efficiency of radioactive wastes management system for decommissioning of Salaspils research reactor. The Environmental Impact Assessment studies for Salaspils research reactor decommissioning (2004) and for upgrade of repository 'Radons' for decommissioning purposes (2005) induced the investigations of radionuclides release parameters from cemented radioactive waste packages. These data were necessary for implementation of quality assurance demands during conditioning of radioactive wastes and for safety assessment modeling for institutional control period during 300 years. Experimental studies indicated, that during solidification of water- cement samples proceeds the increase of temperature up to 81 deg. C. It is unpleasant phenomena since it can result in damage of concrete container due to expansion differences for mortar and concrete walls. Another unpleasantmore » factor is connected with the formation of bubbles and cavities in the mortar structure which can reduce the mechanical stability of samples and increase the release of radionuclides from solidified cement matrix. The several additives, fly ash and PENETRON were used for decrease of solidification temperature. It was found, that addition of fly ash to the cement-water mortar can reduce the solidification temperature up to 62 deg. C. Addition of PENETRON results in increasing of solidification temperature up to 83 deg. C. Experimental data shows, that water/cement ratio significantly influences on water-cement mortar's viscosity and solidified samples mechanical stability. Increasing of water ratio from 0.45 up to 0.65 decreases water-cement mortar's viscosity from 1100 mPas up to 90 mPas. Significant reduction of viscosity is an important factor, which facilitates the fulfillment all gaps and cavities with the mortar during conditioning of solid radioactive wastes in containers. On the other hand, increase water ratio from 0.45 up to 0.65 decreases mechanical stability of water-cement samples from 23 N/mm{sup 2} to the 12 N/mm{sup 2}. It means that water-cement bulk stability significantly decreases with increasing of water content. Technologically is important to increase the tritiated water content in container with cemented radioactive wastes. It gives a possibility to increase the fulfillment of container with radioactive materials. On the other hand, additional water significantly reduces bulk stability of containers with cemented radioactive wastes, which can result in disintegration of radioactive wastes packages in repository during 300 years. Taking into account the experimental results, it is not recommended to exceed the water/cement ratio more than 0.60. Tritium and Cs{sup 137} leakage tests show, that radionuclides release curves has a complicate structure. Experimental results indicated that addition of fly ash result in facilitation of tritium and cesium release in water phase. This is unpleasant factor, which significantly decreases the safety of disposed radioactive wastes. Despite the positive impact on solidification temperature drop, the addition of fly ash to the cement-water mortar is not recommended in case of cementation of radionuclides in concrete containers. In conclusion: The cementation processes of solid radioactive wastes in concrete containers were investigated. The influence of additives on cementation processes was studied. It was shown, that the increasing of water ratio from 0.45 up to 0.65 decreases water-cement mortar's viscosity more than 10 times. Mechanical stability of samples decreases 2 times, which reduces the bulk stability of cemented radioactive wastes package. It is not recommended to increase water ratio more than 0.60 in cement-water mortar. Addition of flay ash to the water-cement mortar decreases the solidification temperature from 83 deg. C to 62 deg. C. However, it was found, that the addition of fly ash to the water-cement mortar facilitate the radionuclides leakage from solidified water-cement matrix. Therefore fly ash is not recommended for radioactive wastes cementation. It was shown that tritiated water can be used for cementation of solid radioactive wastes in concrete containers.« less" @default.
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• W99153321 date "2008-01-15" @default.
• W99153321 modified "2023-10-07" @default.
• W99153321 title "Low Level Radioactive Wastes Conditioning during Decommissioning of Salaspils Research Reactor" @default.
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