MODELLING AND SIMULATION OF THERMAL STRESS DYNAMICS IN A STEAM GENERATOR

Abstract

Enormous price increases and limited reserves of fossil fuels have resulted in increased use of nuclear power plants for the base load of electricity supply. Consequently, conventional steam power plants have been used in variable and peak load ranges in the dailly load curves of electricity generation. Economical control of nonstationary operations (start-up, shut-down, fast and large load changes) is possible only by approaching and maintaining the maximum allowable material stresses at the critical points of power plants. These points occur during the steam generator operation, on the inside surface of the insulated thick wall components containing high temperature and high pressure steam. The rate of load change of a steam generator is mainly limited by thermal stresses occuring in the thick wall elements in which the working fluid flows. The appropriate design and effective application of a new control system for the nonstationary operating conditions require knowledge of the dynamic behaviour of the thermal stresses at the critical points in the system. Thermal stress dynamics in steam generator components depend on the dynamics of the working fluid as well as on the design data of the component concerned. Extension of the working fluid dynamics to the thermal stress dynamics in steam generators is investigated in this study. The study comprises modeling and simulation of working fluid dynamics and their extension to thermal stress dynamics of an actual once-through steam generator. The mathematical model developed for the thermal stress dynamics can be used for developing and optimization of new control and measurement systems used for the control of power plants under nonstationary operating conditions.