Measurements of Liquid AISI 304L Steel Density and Surface Tension, and Influence of Surface‐Active Elements at High Temperatures

Abstract

The tungsten inert gas (TIG) welding process is widely used in various industrial fields to achieve high-quality metallic welds. In particular, this process is used for the assembly of primary circuit components in pressurized water reactors. The main limitation of this process is the weak penetration of the welding pool, which does not allow for the welding of large components in one pass, altering its efficiency. [1] Besides, welding operations contribute to modifying material properties and residual stress, both of them constituting input data for the risk analysis of nuclear safety demonstration concerning fatigue degradations, stress corrosion cracking, or mechanical rupture. Numerical simulations are used to characterize, among others, residual stress. Increasing the penetration of the welding pool is thus a major industrial issue requiring the improvement of numerical tools modeling the fundamental phenomena that are involved in the TIG welding process.Among the different physical mechanisms influencing welding pool dynamics, Marangoni flows generated by surface tension gradients at the free surface may play a significant role in the wetting or penetrating behavior of the weld under consideration. [2] As introduced in Section 2, state of the art, the simulation of Marangoni flows requires the knowledge of liquid steel thermophysical properties, such as density ρ and surface tension σ, as a function of temperature. In particular, existing models in the literature have demonstrated their capacities to predict a melt pool if reliable and accurate surface tension data are provided for the steel grade under consideration. [3] These data at liquid state are scarce, and even not available above a temperature threshold around 1800 C, due to technological issues, particularly for austenitic vessel steel AISI 304 L. Moreover, as emphasized hereafter, the strong influence of minor components, such as sulfur and oxygen, on surface tension values, makes such measurements even more challenging.Within this context, the VITI facility is used to provide new data at high temperature T--from melting point up to 2100 C-for the density and surface tension of two grades of AISI 304 L steel, namely 304LP1-low sulfur content-and

High-Temperature Characterization of Melted Nuclear Core Materials: Investigating Corium Properties Through the Case Studies of In-Vessel and Ex-Vessel Retention

“…The reproducibility between different samples is quite satisfying within experimental uncertainty. Additional details-such as original correlations ρ(T)-can be found in Chikhi, et al (2019); Korobeinikov, et al (2021); Delacroix, et al (2022), in the framework of welding pool modeling.…”

“…Elemental analyses-that are not detailed here-confirm the impact of impurities. Recent articles (Korobeinikov, et al, 2021;Delacroix, et al, 2022) highlight the decisive role played by both sulfur and oxygen, acting similarly to surface active agents or surfactants. They tend to favor the decrease of surface tension values and may also influence the sign of dσ/dT at a given temperature T. Additional details-such as original correlations σ(T)-can be found in Korobeinikov, et al, (2021); Delacroix, et al, (2022) as well.…”

“…More recently, a transient approach to the stratified corium pool (Seiler, et al, 2007;Zhang, et al, 2011;Le Tellier, et al, 2015) and a benchmark between different severe accident scenario codes (Sangiorgi, 2015) pointed out that the use of conservative assumptions may result in heat fluxes exceeding the CHF, in link with the focusing effect. If now, we focus on the thermal-hydraulics of the upper metallic layer, recent Computational Fluid Dynamics (CFD) simulations showed that bulk convection is mainly driven by the Rayleigh-Bénard instability and lateral recirculation along the cooled vessel wall (Delacroix, et al, 2022). 1: liquid pool; 2: crucible; 3: susceptor support; 4: capillary tube; 5: thermal shield; 6: inductor; 7: windows; 8: confinement vessel; 9: supporting system; 10: generator; 11: pyrometers; 12: µm translation stage; 13: µ-flow meter; 14: µ-pressure sensor; 15: data bus; 16: acquisition PC; 17: imaging PC; 18: monitoring.…”

“…Mass uncertainty is negligible, given the weighing accuracy. Following JCGM 100 ( 2008), and according to Delacroix, et al (2022), the relative systematic uncertainty associated with VITI-SD density measurements is about 1% when the experimental setup is carefully prepared.…”

“…According to the Young-Laplace equilibrium, the main sources of systematic uncertainty for surface tension measurements at different temperatures are linked to geometry-capillary radius r and immersion depth h, pressure p, density ρ, and temperature T. Once again, following JCGM 100 (2008), and according to Delacroix, et al (2022), the relative systematic uncertainty associated with VITI-MBP surface tension measurements is about 2.5%.…”