X research in nuclear power: Between fusion and fission

March 11, 2021 will mark the 10th anniversary of the Fukushima nuclear accident, which occurred as a result of a tsunami following an earthquake on the same day. This is the second nuclear power plant disaster in history, rated at level 7, the highest on the International Nuclear Event Scale (INES), the same level of severity as the Chernobyl disaster (1986), whose root causes were different.

The Fukushima accident resulted in a halt or reversal in some countries' civilian nuclear programs. However, many others continued to use nuclear energy mainly to safeguard their sovereignty over energy and/or to prepare for the energy transition as part of their commitment to fight global warming.

Some countries have given up or significantly curtailed their nuclear programs - for example Italy or Germany. Others, like France or the United States, remain major operators of nuclear energy plants, or are rapidly expanding their installed nuclear capacity, such as Russia and especially China. Finally, there are a few new entrants. Some like the United Arab Emirates or Belarus are in the process of building their first nuclear reactor while others have expressed a desire to gain access to this energy.

An examination of the number of reactors in operation and under construction by different countries illustrates the transition underway in the nuclear field. While the largest capacities at present are mostly located in developed countries, most reactor construction is taking place in emerging countries, particularly in China, which accounts for a third of the reactors under construction, but also in India, Russia, South Korea and the United Arab Emirates.

The École Polytechnique laboratories do not work directly on nuclear energy currently produced in the power plants. Nevertheless, several researchers are involved in the understanding of phenomena related to nuclear fission and others seek to understand the physics involved in nuclear fusion projects.

Nuclear Fission

Studying materials under irradiation - At the Irradiated Solids Laboratory (LSI*), thanks to the SIRIUS electron accelerator, researchers are able to study the effects of aging and the behavior of materials under irradiation. For example, in the area of waste management, they have worked on the study of phosphate cements used for treatment of acidic effluents contaminated by strontium. They are also studying the modifications induced by irradiation in uranium dioxide that is used as a fuel material for nuclear power.

Modeling reactor cores - Deformations of reactor cores coupling hydraulic, mechanical and high irradiation of materials. Researchers at the Solid Mechanics Laboratory (LMS*) are studying them using a multi-scale approach with the aim of economic optimization of fuel management while guaranteeing operational safety.

Improving the safety of reactor cores - Researchers at the Center for Applied Mathematics (CMAP*) are studying multi-physical coupling (neutronics, fuel thermal, thermo-hydraulics, vibration mechanics) to improve the numerical simulation of safety of nuclear reactor cores.

Uncertainties in accident scenarios - CMAP is also working on problems of quantification of uncertainties in numerical simulations, in particular, for multi-physical simulations of different accident scenarios in nuclear power plants.

Preventing the consequences of accidents - The Laboratory of Condensed Matter for Physics (PMC*) is working with the CEA to model corium, a metallic and mineral magma that can form in the reactor core after a severe accident and that is likely to cause contamination of the external environment if it manages to "escape" through the ground by melting the tank containing it.

Change of fuel - Nobel Prize winner professor emeritus of X Gérard Mourou's ambition is to improve current fission technologies through the use of lasers to reduce the half-life of nuclear waste or to activate the fission reaction of Thorium, a radioactive element whose waste has a half-life time much shorter than that of uranium.

Nuclear Fusion

While current technologies are based on nuclear fission (a large atom that disintegrates into two smaller atoms, emitting energy), great hope is placed in the production of energy by nuclear fusion (two small atoms fuse into one larger atom, producing energy). The theme of plasmas carried by the Institut Polytechnique de Paris allows researchers to contribute to the understanding of the scientific stakes that will allow this technological innovation.

Numerically studying thermonuclear plasmas in tokamak - Researchers of the Theory of Plasmas Group from the Center for Theoretical Physics (CPHT*) are studying plasmas in the context of fusion and in particular the mechanisms of fast magnetic reconnection and tearing instability of the magnetic surfaces. They also study the influence of hot ions on plasma stability and model collision phenomena that influence the ion velocity distribution within plasmas. Finally, CPHT researchers are studying laser-plasma interaction in the context of laser fusion.

Studying the turbulence of magnetically confined fusion plasmas - Researchers at the Plasma Physics Laboratory (LPP*) are studying turbulence in fusion plasmas. The control of these turbulences is a major issue in magnetically confined fusion plasmas research accompanying the construction of ITER. The LPP collaborates closely with the CEA (Cadarache) on the theoretical level and in the construction of diagnostic tools for plasma fluctuations.

Improving the understanding of plasmas - Beyond work specifically related to magnetic confinement, several laboratories are also working on plasmas, their understanding and also the underlying physics such as the equations of state of certain materials for fusion. These laboratories are part of PLASMAScience, an initiative of the Graduate School of the Institut Polytechnique de Paris created in 2020, with the mission to federate plasma activities, to attract the brightest French and foreign students in PhD, Master, internships and to promote plasma research at the international level.

A teaching and research chair

Since 2008 and with the support of EDF, the "Sustainable Energies" Chair has aimed to develop training and research activities in the field of sustainable energies, including nuclear energy. The Chair's professors contribute to courses in this field, mainly in the Polytechnique engineering cycle but also in the Master's program. Led by François Willaime, director of research at the CEA and professor at the École Polytechnique de l'Institut Polytechnique de Paris, the research actions supported by the Chair range from battery and photovoltaic cell improvement to the increase in safety and in operating time of nuclear reactors. The chair also researches tomorrow's nuclear systems.

*LSI: A joint research unit of CEA, CNRS and École Polytechnique - Institut Polytechnique de Paris
LMS: A joint research unit of CNRS and École Polytechnique - Institut Polytechnique de Paris
CMAP: A joint research unit of CNRS and École Polytechnique - Institut Polytechnique de Paris
PMC: A joint research unit of CNRS and École Polytechnique - Institut Polytechnique de Paris
CPHT: A joint research unit of CNRS and École Polytechnique - Institut Polytechnique de Paris
LPP: A joint research unit of CNRS, École Polytechnique - Institut Polytechnique de Paris, Observatoire de Paris, Sorbonne Université and  Université Paris-Saclay