Design of a Model of Liquid Feeder to an Incinerator of Hazardous Waste and its Optimization from the Cooling Point of View: Part II
Abstract
A series of articles aimed at the cooling of the liquid radioactive waste feeder into the incinerator space optimization. The second part examines ion-exchange resins used in the nuclear industry and the possibilities of their combustion. A 3D model of a radioactive waste feeder with different variants of cooling pipes is proposed. Using numerical simulation, the cooling efficiency of individual variants is compared.
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Introduction
The first part of the article discussed individual types of radioactive waste and the possibility of their incineration. However, ion-exchange resins (IONEX) are also used in various nuclear power plant systems for the purpose of removing specific contaminants. For example, Amberlite IRN78 with a maximum operating temperature of 60 °C is used to remove traces of chlorine contamination from the reactor cooling system and to control the boron level in the primary system of the power plant. It is also used for exhaust cleaning of the steam generator. Due to its high stability and purity, Amberlite IRN150 with a maximum operating temperature of 60 °C can also be used for cleaning the cooling water of the primary circuit. Amberlite IRN97 H with a maximum operating temperature of 120 °C is used to regulate the pH of the reactor coolant, to remove fission products and to remove Caesium-137 from water vapor.
The main function of IONEXes is the ability to bind ions contained in the liquid on their surface, which are subsequently exchanged for positively charged ions. They therefore serve as a medium for ion exchange. These are usually small porous balls with a diameter in the range of 0.3 – 1.2 mm. The porous surface provides a larger area for ion exchange. According to the size of the pores, IONEXes are divided into macroporous and gel. Gel IONEXes have a smaller pore size and are mechanically less resistant.
There are natural or synthetic IONEXes of organic or inorganic origin. Since the IONEXes used in nuclear power plants are mostly of organic origin, burning them in a dry state is not problematic. Combustion of IONEXes in a dry state is possible through fluidic combustion devices with problem-free transport of IONEXes in the form of pellets and at the same time with good air access, which is essential for high efficiency combustion. Feeding IONEXes with a high water content of approximately 40% into the furnace is problematic due to the formation of large clumps and very rapid settling of particles in a liquid transport medium. A suitable medium capable of transporting these particles is, for example, foam (liquid - gas) with sufficient thermal and temporal stability. The advantage is undemanding production directly at the place of consumption with acceptable energy requirements. Among the disadvantages is the negative impact of water on the energy balance of combustion.
Conclusion
The production of electricity in nuclear power plants requires a high technical level of many devices for safe and continuous operation, including the RAW and IONEX feeders to the furnace premises. Considering the environment of the furnace with high temperatures and the limited operating temperatures of individual IONEXes, it is necessary to ensure effective cooling of these devices. When considering the mass flow of water determined by the calculation in Part I at the level of Qm = 0.779 kg·s-1 , all 3 proposed variants are satisfactory in terms of operating temperature, while the best results in the field of cooling are provided by variant no. 3 with a curved end of the tube with a maximum temperature of 48.9 °C. Further reduction of temperatures in the feeder can be achieved, for example, by increasing the cooling water flow to the level of 1.17 kg·s-1 . With this increased flow, it would be possible to additionally reduce the maximum temperature by 11 °C.