The analysis of emergency processes in the gas-cooled fast neutron reactors
Students Name: Haidash Vladyslav Andriiovych
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: Haydash V.A., Lys S.S. (supervisor). The analysis of emergency processes in the gas-cooled fast neutron reactors. Master’s thesis. - Lviv Polytechnic National University, Lviv, 2020. Nuclear reactors on fast neutrons with gas cooling are in many respects similar to those in reactors with liquid metal cooling. This applies to such parameters as neutron-physical characteristics, properties of materials, etc. As for the design of NR and safety problems, there are a number of fundamental differences between nuclear reactors on fast neutrons, cooled by liquid metal and gas. Therefore, the paper considers the design features and safety issues of nuclear reactors on fast neutrons with gas cooling. In the development of gas-cooling nuclear reactors on fast neutrons in general, preference is given to the helium option. The main advantage of helium is the smaller effect of deceleration and absorption of neutrons than in the case of sodium or other coolants. Disadvantages of helium cooling - weak in comparison with sodium, the interaction of neutrons with helium has a negative side, which is to increase neutron leakage. This is especially evident in NR of relatively low electrical capacity (about 300 MW and below). Therefore, nuclear reactors on fast neutrons with helium cooling become economical at a significant electrical power (1000 MW and above), when the size of the AZ is large and the relative role of leakage decreases. The object of research is gas-cooled fast neutron reactors. The subject of research is the design features and safety issues of gas-cooled fast neutron reactors. The purpose and objectives of research. The aim of this work is to analyze the emergency processes in fast neutron reactors with gas cooling. To achieve this goal it was necessary to perform the following tasks: - perform thermohydraulic calculations, which are especially important in the design of gas-cooled NRS; - consider the heat exchange of the gas coolant flowing through the internal channels; - to develop an algorithm for calculating the coefficient of friction and heat transfer coefficient in the transient mode of NRS with gas cooling; - to establish typical operating characteristics of the assembly of NRS with helium cooling; - conduct a risk analysis of possible sequences of accidents; - to develop the concept of safety of NRS with gas cooling; - to calculate the equilibrium state of the combined liquid metal bath. In this master’s qualification work the analysis of emergency processes in reactors on fast neutrons with gas cooling is carried out. The risk analysis of possible sequences of accidents showed that among the frequent transients, such sequences predominate, which can lead to violations of the cooling of the AZ. In this regard, the assessment of the reliability of gas-cooled nuclear reactors on fast neutrons is considered especially as an integral part of activities to ensure their safety. This activity influences the choice of the reactor structure as a whole even at the stage of elaboration of the safety concept itself. The calculation of regulatory and recording systems is done in the detailed design of NR, and at the final stage measures are determined to check and test all systems. The concept of safety of nuclear reactors on fast neutrons with gas cooling provides for the presence of two main barriers that prevent the spread of radioactive substances: high-pressure housing made of prestressed concrete and protective shell. The latter consists of an inner sealed shell and an outer concrete cover. Such a protective environment is designed based on certain safety requirements for an accident without destroying the AZ. Thus, the design of the high-pressure housing is calculated so that when the helium circuit ruptures, the maximum rupture area does not exceed a certain value. This limits the maximum rate of pressure drop in advance. Another requirement concerns the pressure in the housing cavity: it should not exceed the maximum design limits. Typical requirements for protective shell are as follows. It must provide an internal helium pressure sufficient to cool the AZ when the pressure in the main circuit drops. Enter the maximum allowable value of helium leakage. Finally, protective shell serves as a barrier that prevents the spread of radioactive products in the event of their release from the AZ. In the economic part, the feasibility study of decisions on decontamination and the cost of processing radioactive waste was carried out. In this master’s thesis, a control system for the turbine condenser at a nuclear power plant is developed. Any object, including a capacitor, is calculated at the design stage for nominal values, the value of which depends on the features of the technological process. In any case, energy facilities require automatic regulation of their work by developing and improving the technological units of the NPP in addition to improving the operation of the equipment itself, as well as modifications of the automatic control system using the device. Keywords: emergency processes, fast neutron reactors, gas cooling, liquid metal cooling, safety issues.