Virtual Simulation in Tokamaks and the Nuclear Sector

By Jacques Delacour, CEO and founder of OPTIS

April 26th, 2018 | Partnership

Article nucléaire

Nuclear fusion is an essential energy source for future generations. A coalition of 35 nations is collaborating on ITER, the world’s most ambitious energy project, and working to create a tokamak twice the linear size and 10 times the volume of Joint European Torus (JET), the world’s largest operational magnetic confinement plasma physics experiment, located at Culham Centre for Fusion Energy in Oxfordshire, UK. ITER is currently under construction in Saint-Paul-lez-Durance, in the South of France, and is designed to deliver 10 times more power than it consumes. The ITER project will lead to an industry-ready prototype that is expected to be the first nuclear fusion facility to provide electricity to the grid.


In nuclear fusion experiments, plasma-facing components are exposed to high heat fluxes, and infrared (IR) imaging diagnostics are routinely used for surveying surface temperatures to prevent damage. However, the use of metallic components in the ITER tokamak will complicate the temperature estimation, as the metal walls create a highly reflective environment.


As René Magritte said in his famous painting, The Treachery of Images, a picture is not the reality. For engineers working with nuclear fusion machines, a similar concept is noted in their work measuring the temperatures of the walls of experimental fusion reactors. Nuclear fusion machines’ tungsten walls are highly reflective, making the interpretation of temperature measurement by IR thermography difficult. The bright colors of an IR image are not necessarily associated with a real hot spot, but may be the result of reflections. While measuring these hotspots is an essential safety tool for the machine, the integrity and correct operation of the machine depends on the interpretation of the IR measurements.


Simulation acts as a complementary tool to model the transport of photons in the environment and thus is able to differentiate reflections from true hot spots. OPTIS, a company that has worked with CEA, the Atomic Energy and Alternative Energies Commission since 2010, uses its simulation software to create an accurate simulation of these infrared images. The collaboration aims to measure the temperature of the walls of experimental fusion reactors, such as ITER, using simulation technology.


A spectral simulation software, for UV, IR and visible simulation, can simulate and measure the temperature of the walls of fusion machines by determining the difference between the proper temperature of the walls and the temperature resulting from the reflection of the infrared radiation on the wall’s materials. Using the complex vessel geometry and the thermal and optical properties of the surfaces, the simulation recreates the complex interactions between photons and materials to predict the global response of the complete infrared surveillance system.


The CEA has chosen to use the OPTIS Virtual BSDF Bench VBB to precisely define the materials to be used for tokamak projects like ITER. The virtual laboratory for measuring materials makes it possible to simulate the use of materials under realistic conditions. It provides the CEA with precise and informative images, modeling complex physical phenomena involved in the interaction of photons with matter.


The CEA can carry out a virtual control of the quality of the materials and anticipate the influence of their aging on the reactors, especially the degradation of their surface state and the consequences on the interpretation of the infrared measurement. This tool contributes to a better control of the performance of IR measurements, which is essential to optimize the operation of future reactors while ensuring their safe operation.


In addition, the Institute for Magnetic Fusion Research (IRFM) teams at the CEA center in Cadarache can now, for the first time, more precisely model the plasma radiation and study the polarization phenomena and their possible impact on the simulation results. OPTIS’s product SPEOS allows them to review and analyze the results as a function of the polarization of the properties of this plasma. This advance is a great first, made possible by the use of physically realistic numerical simulation, and the CEA will compare OPTIS’s simulations with the experimental results obtained in its WEST tokamak.


These simulations are very demanding in terms of computation time, and the CEA uses OPTIS HPC, which guarantees a higher calculation efficiency. The CEA has reduced its simulation time from one day to less than one hour, significantly increasing the number of simulations carried out on a yearly basis. Another significant advantage of the SPEOS software is that it is possible to conduct all these studies in a single environment - Dassault Systèmes' Catia V5 CAD software - and the digital model of the entire thermonuclear reactor.


Looking forward in regard to IR simulation for similar projects, the temperature measurement in other parts of the tokamak, e.g. for the colder target, requires reflections compensation to have realistic temperature measurements. Several methods are being considered to compensate for the reflected flux. Active photo-thermal method using pulse or modulated sources may be an answer to measure locally the surface temperature independently of the reflected flux. Another approach may be the exploitation of possible polarization of the reflected flux in order to minimize its contribution on the sensor plane. Finally, the photonic modeling itself could help to get the surface temperature by inverting the signals collected by the camera taking into account the contribution of the reflected flux.


Building further on simulation capabilities, other solutions are being developed to support other levels of the nuclear development. Immersive virtual reality tools, based on physical simulation, now assist in the handling of nuclear installations.


Initially a joint project developed by AIRBUS and OPTIS and dedicated to aerospace material and installations, the solution has been refined in a version dedicated to the nuclear industry. It consists of a fully immersive virtual reality tool, allowing the user to simulate various operations in a life-size environment. In real-time, operators virtually interact with the future installations, supervising maintenance, use, assembling and dissembling operations. Teams have two different points of view to get an understanding of the human interactions with the installations: a first-person view for a fully immersive experience, and the interactive manipulation of a human mannequin within the system, for collaborative reviews.


This direct human experimentation on a digital prototype has two, complementary, primary purposes for the nuclear industry.


The first one is a pre-step, to improve the global design of the nuclear infrastructure before it is built. From the initial design phase, it gives an understanding of the space, proportions and reachability of the elements in the nuclear plant. Users can evaluate the installation’s overall accessibility and comfort envelopes, required efforts to perform specific tasks and fields of view for the operators, in order to validate the global ergonomics and optimize the building of the installations to ease the operations of the teams on-site.


The second purpose is the training of operators. They can use systems as in real life, even though they are not available yet or critical to easy manipulation. Operators can simulate interventions, even in harsh environments, to be ready for actual interventions, while improving their safety, both during the training and during the operations. It also simulates radiations inflicted to operators during maintenance or dismantlement, to determine the most strategic actions to perform in case of emergency.


It appears that this new accurate and predictive physical simulation software enables the ability to justify the design of reactors, as it is now able to model innovative and complex design features. The objectives of the use of simulation are to guarantee the safety of the analysis, operation, and design. Simulation addresses the engineering aspects of both nuclear development and security. As such, it is a paramount solution for the further development of the nuclear industry.