The dynamics analysis of severe accidents in water-cooled reactors
Students Name: Matviichuk Dmytro Oleksandrovych
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: ukrainian
Abstract: Matviychuk D.O., Yurasova O.H. (supervisor). The dynamics analysis of severe accidents in water-cooled reactors. Master’s thesis. - Lviv Polytechnic National University, Lviv, 2020. During the accident in the NPP containment, multiphase multicomponent systems with intensive phase transformations under conditions of high-temperature heat and mass transfer are subject to consideration. However, the applications of known models of multiphase systems to determine such important parameters as phase transition and mass transfer intensities, phase interaction forces, local heat fluxes between phases, etc., are significantly limited by the absence of local closing relations, which are obtained only for simplified situations. A small gap in the body can quickly increase in size, as it is exposed to pressure, high temperature and chemical aggressiveness of the jet of corium melt. For relatively thick jets, the most significant factors that determine their behavior are the pressure of the jet, the resistance of the liquid in the pool of jet introduction and gravitational forces. At a relative density of 9.4, the depth of penetration of the jet of finite length almost does not change to about the values of the Freud number of about 200 and then slowly increases with increasing Freud number. The behavior of short jets (H = 5) differs sharply; the depth of penetration into the layer of short jets increases intensively with increasing Froude number. At a relative density of 9.4, the results of calculations of the depth of penetration of a jet of finite length are in the darkened zone (area of reliability) to Freud numbers above 100. With decreasing length, the range of Freud numbers in which satisfactory agreement is reduced ) the results of the calculations do not fall into the realm of reliability, which indicates a significant difference in the laws of the process for the fragments of the jets. However, when the relative density decreases, this phenomenon weakens, and already at ?2/1 = 1.9 (water is about twice as dense as the jet), the results of calculations according to the presented formulas are almost completely in the zone of reliability. The purpose and objectives of research. The aim of the work is to analyze the dynamics of severe accidents in water-cooled reactors. To achieve this goal it was necessary to perform the following tasks: - to analyze the results of modeling the features of the functioning of different systems at the initial and final stages of a serious accident; - to analyze the course of the accident in the NPP containment; - to consider the behavior of large-diameter jets, corresponding to the further destruction of the NR body during the development of the accident; - to create a mathematical model of the behavior of a thick jet of corium melt, which may be suitable for describing the introduction into the pool not only of a liquid jet, but also of cylindrical solids, which can be likened to frozen fragments of the jet. The object of research is water-cooled nuclear reactors. The subject of research is the dynamics of severe accidents in water-cooling reactors. In this master’s qualification work the analysis of dynamics of heavy accidents in water-cooling reactors is carried out. Some known results of modeling the features of the passive nuclear fuel retention system inside the basin in case of rupture of the NR body and leakage of corium melt into the basin at the initial and final stages of a severe accident It is shown that the main way to further increase the economic efficiency of nuclear power plants is to reduce annual production costs by improving the use of nuclear fuel. The scheme of automatic control of chemical water purification is developed, on the basis of which technical means for realization of the formulated functions of control and management have been chosen. Keywords: water-cooling reactors, modeling, small body gap, corium melt jet, sub-reactor pool with water.