Simulation of Reactor Pressure Vessel Internals Thermal Stress Due to Internal Heat Generation and Environmental Boundary Conditions Using Stress Transfer Functions

Abstract

The internal heating rates from the capture and scatter of neutrons and primary gamma radiation represent one of the most significant loadings acting on the reactor pressure vessel internal structures. The nuclear heating effects on the internal structures are mitigated by the flow of the primary coolant removing heat energy from these structures. This paper discusses the use of transfer functions to predict the time-dependent thermal stresses in the lower core plate of reactor vessel internals. Numerous stress analysis applications have employed the transfer function approach to obtain thermal stresses from fluid transients in reactor pressure vessel and piping locations. These solutions have been utilized in both design analysis applications and in stress and fatigue monitoring roles for evaluation of pressure vessels subjected to fluid transients and mechanical loads such as pressure and piping loads. This paper presents a further extension of the technology to address heat generation loads. The evaluation of stress and fatigue produced in a reactor vessel internals lower core plate due to multiple loadings, including heat generation, using the stress transfer function approach was investigated for reducing analysis process time and conservatism when compared to conventional analysis methods. Reduced conservatism provides margin that may be beneficial in life extension studies.