Thermal Fatigue Analysis of a PWR NPP Steam Generator Injection Nozzle Model Subjected to the Thermal Stratification Phenomenon

Abstract

This work is related to an experimental thermal stratification study aiming to quantify thermal fatigue damages in the pipe material. Thermal fatigue damages appear as a consequence of non-linear longitudinal and circumferential loads and thermal stripping present in pipes whit thermal stratified flows. In this work an experimental section, simulating the injection nozzle of a NPP steam generator, was subjected to the effects of thermal fatigue due to thermal stratification. The experimental section was made of stainless steel pipe type AISI 304L and its geometric characteristics allowed the same range of Froude numbers of a Pressurized Water Reactor (PWR) NPP. Temperatures were measured externally and internally in three positions and deformations just externally in seven positions. Up-and-down fatigue tests were done to assess the amount of damage induced in the material experimental section. Preliminary numerical simulations were done using a coupled analysis in the ANSYS code with temperatures and pressure inputs taken from thermo hydraulic experimental results. The objectives in this work are quantify the thermal fatigue intensity imposed to the pipe material by thermal stratification experiments, verify the agreement between numerical and experimental thermal stratification results and obtain the material fatigue limit testing specimens made of pipe experimental section and from the virgin pipe. In this work is possible to conclude that stratified flows could be developed in the experimental section, thermal stratification induces considerable thermal stresses and strains in the experimental section pipe material, thermal stratification reduces the material fatigue limit, numerical and experimental results agreed appropriately in some pipe region and disagreed in others.