الفهرس 
Chapter 1: IntroductionOnly 14 pages are availabe for public view
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Abstract
In the light of the numerous projects, it is important to generate electricity from a variety of sources. One of the most important of these sources is the generation of electric power using nuclear energy. Most nuclear power plants rely on the use of pressurized water reactors. This type of the reactors is divided into a primary cooling circuit, which we refer to, and a secondary cooling circuit.
In the primary cooling circuit, the primary cooling water (PCW) could be contaminated with different radionuclides, which can be released from fracture of fuel rods or for other reasons. The most important types of radionuclides generated are fissile like strontium, active like nickel, and corrosive products such as cobalt.
This contaminated water is treated by the chemical volume control system unit (CVCS). This unit depends on two or four ion exchangers. Within these exchanges, organic resins are used, which have flaws resulting in the use of inorganic alternatives. Applying these inorganic substances also has problems.
Therefore, the aim of this study is to find a safe and inorganic alternative used in the treatment of the primary cooling water. In addition to, the safety standards that should be enhanced in the various stages of the radioactive waste management. We though in a science that proved its efficiency in many practices which is nanotechnology. Using natural raw materials such as kaolinite (K), bentonite (B) and rice straw ash (RSA), nano materials were synthesized and applied in the treatment of primary coolant.
The prepared nano materials were applied in the removal of chemical elements from contaminated water. Various batch experiments were performed; selection of efficient sorption nano-material, Optimum operational weight ratio (element/nano material, selection of the nano material for elements used, determination of the equilibrium curve of sorption process, and desorption behavior of nano material with pH and temperature variation. The samples were analyzed by using the inductively coupled plasma emission spectrometer. Nano materials provided high removal rates of the chemical elements from contaminated water.
Nano materials presented approximately the same capacity of sorption for the three elements; 88 to 90% for Sr, 74 to 77% for Ni and Co. Nano material from rice straw ash (RSA) was selected as nano-treated materials for economic reasons and avoiding environmental pollution. Therefore, it was proposed as an alternative treatment material than organic resin beds in CVCS. In case of Sr element, the best ratio of 97.4% was reached by the addition of 1g Silica 3 and 329 mg/l Sr (high weight of silica and low concentration of element). In case of Ni and Co, no obvious difference can be detected during the variation of weight ratio. The removal percentage changed from 60% to 70%.
The sorption process reached equilibrium after 30 min approximately. Through the experimental data, the sorption reaction of element by the nano material was irreversible reaction with the change of temperature and pH. Objectively, the findings of these experiments using the nano material increased the safety margin of the treatment stage in the multi barrier concept.
It is important to analyze the sorption process of nano material from RSA with these chemical elements. The analysis was conducted by studying kinetic factors, adsorption isotherms and thermodynamic parameters. The kinetic of the sorption process was studied by applying the pseudo-first order, pseudo-second order and intraparticle diffusion models. The isotherms of the sorption process were assigned using Langmuir, Freundlich and Dubinin–Radushkevich (D-K-R) isotherms. The key parameters of thermodynamic were calculated.
from experiments, the adsorption capacity values for elements with concentration of 400mg/l were 19128, 18270 and 19728mg/g respectively. from the data of experiments, the amount of elements adsorbed by nano materials (qe cal ) was the same for three elements and equal 20000 mg/g in the pseudo second order model. By the intraparticle diffusion model, the qe cal values were equal 19024, 18006 and 19131mg/g respectively. It meant a very strong chemical adsorption process. In Freundlich isotherm, the calculated correlation factors of three elements were 0.979, 0.992 and 0.990 respectively. These results confirmed the heterogeneity of nano-silica surface and that the adsorption was multilayer process. from D-K-R isotherm, the calculated energies were 316.23, 316.23 and 353.55 kJ mol-1 respectively. from the thermodynamic results, the reaction for the three elements was spontaneous. These results confirmed that the nano material from RSA could be good adsorbent material for removing R.Ns.
The nano materials from RSA, B and K were analyzed by using EDX, TEM and XRD to assure that these were inorganic materials in nano scale. The analyses were qualitative elemental analysis, crystallinity, phase form, morphology and particle size. EDX results exhibited the different atomic percentages of Si in the three nano materials: 47.9%, 63.3% and 51.8% from RSA, B and K respectively. The range of particle size obtained from both analyses of XRD and TEM were (17- 33 nm), (12-38 nm), (20-25 nm) for RSA, B and K respectively. The results demonstrated the responsibility of silicon (Si) not silica, according to low percentage of oxygen, for the adsorption process. Silicon element, nano scale of particle size, was the essential factor contributing to the high chemical adsorption process of the nano materials.
The information obtained from this phenomenon was used to formulate the schematic design of the treatment unit and to some extent looks like the CVCS. In addition, mass balance and heat balance were calculated for the whole unit. The “Aspen Hysys” software code was used as a tool to perform the studies and the design under considerations. The proposed design of the treatment unit was depending on the optimum conditions which obtained from the experiments such as temperature, pH, equilibrium time and purification ratios. In addition, a generic scenario, in case of accident in some valves, was undertaken to check the suitability of the equipment and to prove the safety assessment in the proposed unit.