Nuclear Industry

Fluid dynamics for the nuclear industry

The nuclear industry is an important one for OptiFluides, especially in view of its collaboration with EDF on R&D and innovation projects. And what could be more natural, given that fluid dynamics and heat transfer are fundamental to the understanding and analysis of phenomena at work on various scales, or to the design and safety of new installations.

Here are just a few examples of CFD applications in the nuclear industry.

Cooling of nuclear reactors

• Design of cooling towers: Cooling towers are used to cool the water in the cooling circuit. The complex heat exchanges taking place between the rising air stream and the rain shower can be numerically simulated to optimize the design and operating parameters of these essential components of pressurized water reactors.
• Heat transfer analysis: CFD simulation provides a precise view of heat transfer in reactor components, such as the reactor vessel or fuel assemblies. The challenge here is to provide adequate models to take into account all the phenomena that have an impact on heat transfer. By modeling the dissipation of heat generated by the fission reaction, engineers can assess the operating boundary conditions of materials and improve their design to prevent thermal failures such as hot spots, thus optimizing reactor durability and reducing risks.
• Quantifying the impact of load variation on thermal-hydraulics: Nuclear power plants were initially designed to operate at full power. With the development of intermittent energy sources, nuclear power plants are increasingly being used as an adjustment variable for electricity production, with the result that some units are periodically reduced in power to varying degrees. These alternative operating regimes can lead to the appearance of local thermohydraulic phenomena that generate thermal fatigue for components, which can be quantified using CFD simulation.

Analysis of heat exchange in steam generators

Steam generators (alsoreferred to as boilers) play a crucial role in heat transfer between the primary circuit, where the water is heated, and the secondary circuit, where the steam is used to propel the turbines.

• Heat exchanger optimization: Steam generators are designed to efficiently transfer heat from the hot water in the primary circuit to the water in the secondary circuit without direct mixing. CFD is used to model the complex flow of water in these heat exchangers, taking into account phenomena such as boiling and condensation. Thanks to this simulation, it is possible to optimize heat exchange conditions, improve overall plant performance and identify possible areas of fouling, which could reduce system efficiency.
• Characterization of thermal fatigue: variations in the operating regime of the unit will subject the steam generators to significant variations in temperature, and therefore to highly variable levels of thermal expansion that can generate fatigue, or wear, which is calculated with the Usage Factor. CFD will make it possible to precisely determine the temperature fields associated with each operating regime, and even to evaluate them in scenarios of clogging or unusual operation, providing valuable input data for thermomechanical calculations.

Design of ventilation and containment systems

Ventilation systems are essential to ensure a safe environment in sensitive areas of nuclear power plants. They maintain adequate air quality and limit the spread of contaminants in the event of a leak.

• Simulation of air flows in containment areas: CFD can be used to model air flows inside confined areas such as control rooms. This ensures optimum ventilation, enabling controlled pressure to be maintained and avoiding the build-up of hazardous gases. Simulations are also used to model emergency extraction systems to safely evacuate radioactive contaminants.
• Cooling of electronic equipment in the reactor building: electronically equipped measuring devices can be installed in the reactor building, to monitor operation or acquire valuable measurement data. In order to prevent malfunctions or even incidents (such as localized fire outbreaks), it is necessary to check that this equipment is properly cooled, which can be done using CFD simulation.

Optimization of advanced and modular reactors

Advanced reactors, such as fast neutron reactors, and small modular reactors (SMRs), present complex technical challenges requiring detailed analysis of fluid and thermal phenomena.

• Simulation of fast-neutron reactors: These reactors use metallic liquids as coolants, such as sodium, which are of particular interest due to their thermal properties. CFD can be used to model flows and heat transfers under extreme conditions, taking into account the complex interactions between the fluid and the reactor structures, thus contributing to their design and optimization to ensure safe and efficient operation. During dismantling, for example, to design suitable draining systems, simulation can be used to prototype customized equipment to guarantee operator safety.
• SMR design: Small modular reactors need to maximize safety and efficiency within compact envelopes. CFD can be used to simulate integrated cooling systems and optimize the design of primary circuits, which is essential to ensure efficient heat dissipation while meeting stringent safety requirements.

Conclusion

CFD simulation is a key technology for the nuclear industry. By enabling detailed and accurate analyses of thermodynamic and fluid phenomena, CFD provides an in-depth understanding of the complex behavior of nuclear systems, helping to improve their safety, energy performance and long-term reliability.

Contact us for more information or to discuss your project in the nuclear industry.