SCOPE

Due to their high specific heat, low viscosity, and good diffusivity, supercritical fluids have the potential to be ideal coolants. In addition, the supercritical heat transfer properties are shown to result in up to 45% efficiency in nuclear power generation, which operates nearly at 550°C. However, understanding the heat transfer for fluids under supercritical conditions has been a challenge. In this regard, a wide range of experiments with different parameters has been performed to understand the peculiar heat transfer characteristics. The generated experimental database could serve as a reference to assess the prediction capabilities of the Reynolds-Averaged Navier-Stokes (RANS) based computational fluid dynamics (CFD) approach under supercritical conditions. RANS is the most widely used modeling approach and has been an industrial workhorse for decades. This work aims to study the heat transfer characteristics of supercritical Carbon Dioxide (sCO2) in horizontal tubes using different RANS models. Various flow conditions are modeled to study the impact on the heat transfer coefficient. A large-temperature variation is also expected in some conditions due to stratification. In such cases, the impact of buoyancy on the heat transfer coefficient is also explored. The prediction capabilities of selected RANS models will be assessed against the experimental reference data and will be presented in a full-length article.

Turbulent heat transfer is an extremely complex phenomenon and is critical in scientific and industrial applications. It becomes much more challenging in a buoyancy-influenced flow regime, particularly for non-unity Prandtl number (Pr) fluids. In this article, an effort has been put forward to assess the prediction capabilities of different Reynolds-Averaged Navier-Stokes (RANS) based turbulence models for a mixed convection flow regime. In this regard, a fixed Richardson number (Ri = 0.5) case is considered at three different Prandtl number fluids (Pr= 1, 0.1, and 0.01). The considered flow configuration is a parallel plate arrangement with differentially heated top and bottom walls. Two different classes of turbulent heat flux models, i.e., based on Simple Gradient Diffusion Hypothesis and Algebraic formulations, are compared with the available reference DNS (Direct Numerical Simulation) database. The prediction capabilities for these modeling approaches are assessed and will be extensively discussed in this full-length paper.

"Since the beginning of nuclear industry, corrosion issues have been a major concern. Less than two years after start-up, stress corrosion cracking occurred on the stainless steel tubing of the steam generator of the prototype for the Nautilus in USA (1953); more recently, last year in 2022, several French Pressurised Water Reactors were shut down due to stress corrosion cracking of stainless steels pipes in a safety injection circuit. We propose to underline the complex corrosion mechanisms linked to the aggressive environments (high temperature and high pression water environments) and to present briefly the three main corrosion phenomena occurring in Light Water Reactors (LWRs), after a short overview of the basic designs and materials of the boiling water reactors (BWRs) and pressurized water reactors (PWRs):
- general corrosion of zirconium cladding which limits the life-time of fuel elements to generally 3 cycles;
- flow-accelerated corrosion (FAC) of carbon steel components, which is the only corrosion phenomenon that has led to several deaths in PWRs;
- stress corrosion cracking (SCC) of nickel base alloys (“the Coriou effect”) and of stainless steels including irradiation-assisted stress corrosion cracking (IASCC); SCC phenomena has led to the replacement of major components like steam generators or pressurised vessel heads.
Finally, the corrosion future will be discussed as BWRs and PWRs are extending their period of operation up to 60 and 80 years, and even more."

The Digital Twin (DT) is the most advanced paradigm to
create a virtual representation of a real world multi-physical system
for the sake of designing, monitoring, and supporting the decision
making throughout its whole lifecycle. Therefore, DT requires a
flexible ecosystem made of a variety of engineering tools and services
that need to be highly interoperable and enable knowledge
management and traceability. However, the major challenges that
slows down the emergence of DT environment are the inherent
incompatibility of engineering tools with the absence of a unified
standard for interoperability, and the human change aversion to new
technologies, tools and paradigms. For this purpose, we have
developed an evolutive environment that answers the main
requirements of Interoperability, Traceability, Flexibility, and
Knowledge management. In this paper, we introduce a general
overview of DT ecosystem with the limitation of some state-of-art
existing implementations with respect to four metrics. Then we will
introduce our solution applied to a nuclear case study to demonstrate a
highly evolutive implementation of a DT ecosystem.