Safety analysis of thermal equipment and piping systems in the CANDU nuclear power plant subjected to thermal shocks

Abstract

Due to the complexity of nuclear power plants and the risks of damage that may occur during their existence, it is necessary to pay more attention to the safety features. An important influence is the operational temperature of thermal equipment and pipes, especially within the primary circuit, as the coolant is radioactive and in case of damage would cause natural disasters. An assessment of thermal reliability of nuclear power plant equipment and systems is necessary for optimization in the design stage. High thermal shocks with severe and sudden drop in coolant temperature represent a high potential for damage, especially in propagation of existing cracks, under stress due to high pressures. On the other hand, vibrations produced by variable fluid flow conditions or of mechanical origin may induce vibratory fatigue, which combined with thermal fatigue may influence the system’s safety. This study aims to develop computational models for thermal fatigue in pipelines in nuclear power plants, highlighting pressurized thermal shock analysis, temperature distribution diagram along the wall thickness, stress distribution diagram by wall thickness, factor distribution diagram stress intensity, critical crack size diagram, critical reference temperature of nil ductility transition (RTNDT) diagram. Evaluation of these diagrams were performed using the calculation programs Nuclear Piping Integrity Expert System (NPIES) and Reactor Vessel Integrity Evaluation System (RVIES).