The analysis of diversification of nuclear fuel for the Water-Water Power Reactors
Students Name: Tanasiichuk Karyna Pavlivna
Qualification Level: magister
Speciality: Nuclear Рower Еngineering
Institute: Institute of Power Engineering and Control Systems
Mode of Study: full
Academic Year: 2020-2021 н.р.
Language of Defence: англійська
Abstract: Tanasiichuk K., Kuznetsova M.(supervisor), Analysis of diversification of nuclear fuel at WWER power units. Master’s thesis. – Lviv Polytechnic University, Lviv, 202. Extended abstract. An actual and priority issue for Ukraine’s nuclear energy is the diversification of nuclear fuel, which is replacing structural fuel assemblies (FA) with alternative ones. At Ukrainian nuclear power plants (NPPs) has begun the introduction of an alternative fuel of the American company Westinghouse Electric Company. Diversification of nuclear fuel is the expansion of the market for nuclear fuel suppliers, which allows other companies’ fuel to compete with the supplier company that was conditioned by the project. Currently, there are 33 WWER reactors in the European Union (EU) and Ukraine. Russia is the main supplier of nuclear fuel to these nuclear power plants. However, the experience of other nuclear markets shows that the monopolization of the supply and storage of nuclear fuel has a negative effect on safety and competition for the improvement of technology. In addition, there is a positive experience of mixed core fuel loading with different fuels [1]. Mixed core loading is the simultaneous units of fuel assemblies, which differ in design and / or fuel component [4]. The multinational company Westinghouse Electric has many years of experience in supplying nuclear fuel for various types of reactors and is a promising supplier of alternative fuels for WWER type reactors (including Ukraine). Study object is fuel assemblies of WWER units. Scope object is a diversification of nuclear fuel of WWER units. Goal of research: analysis of diversification of nuclear fuel, its characteristics and safety of operation at WWER reactors in Ukraine. Research results. The design of fuel assemblies of each manufacturer at the stage of development undergoes a number of specialized project (tests, only a comprehensive analysis will justify the safety of joint operation of fuel assemblies of different types, considering their mutual influence and differences in parameters - thermohydraulic, neutron-physical and structural. In the first section of the master’s thesis, a comparative characteristic between the Russian fuel used by TVEL and the alternative fuel of the American company Westinghause was considered and carried out. The design features and advantages of Westinghause fuel, quality and safety of its use, important for operation characteristics are given and the characteristic design of FA and fuel rods (FL) is described. The second section describes the experience of operation of FA-W in WWER type reactors in the EU and Ukraine. The main problems using new nuclear fuel are considered, namely 1) incomplete introduction of control rods due to the change in the size of the FA-W; 2) bending of fuel assemblies and fuel elements; 3) leakage from fuel rods and increase in coolant activity. Methods of finding and solving these problems are analyzed. An important condition for the diversification of nuclear fuel is the safety of its use. In the third section of the Master’s thesis, an analysis of the safety of operation of mixed fuel loads and the problem of handling spent nuclear fuel with FA-W was conducted. Based on the existing research, the safety of using FA-W was analyzed according to the following criteria: - thermohydraulic analysis of the use of mixed fuel loading; - analysis of the isotopic composition of spent nuclear fuel. For the full thermohydraulic analysis the accidents most unfavorable concerning criteria of reliable cooling of fuel assemblies are chosen. The consequences of such accidents can be a violation of the integrity of the shells of fuel rods - a physical barrier between radioactive substances and the coolant of the primary circuit, in case of destruction of which radioactive substances enter the coolant and spread through the primary circuit [2]. In the calculations of transient emergency processes - jamming of the Main circulating pump and bilateral rupture of the Main circulating pipeline - the authors checked the failure of the shell of the fuel element at a temperature of 1200 ° C, which is the maximum project limit of damage [5]. The results of the analysis prove that at any initial event, which is determined for design basis accidents, reliable cooling of fuel assemblies will be provided, and therefore the maximum temperature of fuel assemblies will not be reached. When introducing a new type of fuel, it is important not only to use it, but also to handle it properly after operation. Important for safety characteristics of spent nuclear fuel are due primarily to the isotopic composition, which was formulated in the process of fuel combustion. Determination of isotopic composition is necessary for accounting and control of nuclear hazardous materials; identification of sources for thermal and radiation safety analysis; the use of burnout as a parameter of nuclear safety in the substantiation of nuclear safety of spent fuel management systems [3]. Based on the analysis of the study of the isotopic composition of spent fuel, it can be concluded that from the point of view of safety of storage and handling of spent nuclear fuel at WWER reactors of new fuel from Westinghause does not require changes in existing conditions and procedures. Key words - nuclear fuel, fuel assembly, fuel rod, core, diversification of nuclear fuel, safety of nuclear fuel using References: 1. Kirst, M., Benjaminsson, U., Onneby, C. (2015). 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