Nuclear technology is key to enabling the establishment of scientific bases on the Moon or Mars, or for exploring deep space. Its use relies on two different physical principles for producing heat: radioactive decay of a heavy nucleus and the nuclear fission chain reaction. In the second case, the heat produced by a nuclear reactor can be either directly used for propulsion (Nuclear Thermal Propulsion, NTP), or converted into electricity. The generated electricity can be used to power a lunar base, or an ion propulsion engine. This latter technology is called Nuclear Electric Propulsion (NEP), which is the focus of this thesis. These systems have been studied in the past, within the US PROMETHEUS project and the Russo-European MEGAHIT and DEMOCRITOS projects – typically for exploring Jupiter's satellites – while currently, design studies are underway at CEA for a 100 kWe electronuclear system.

The system under study combines several specific technology and material choices, including: uranium nitride fuel, direct gas cooling (helium-xenon mixture), energy conversion system based on a Brayton cycle, and waste heat evacuation by radiation, the only heat transfer mode available in space. Moreover, the design is guided by requirements to minimize mass and volume, and to ensure performance and reliability for the duration of the scientific mission. Analyzing the dynamic behavior of the electronuclear system is therefore crucial for the project's success. However, the issue of transient modeling of a complete spatial electronuclear system is poorly addressed in the state of the art, especially for NEP.

The thesis objectives are therefore to research and develop physical models adapted to an NEP system, propose a validation approach, and finally implement these to analyze the reactor's dynamic behavior and contribute to improving its design. Several mission phases can be studied: reactor startup in space, power variation transients for the ion propulsion engine, reactor response in case of failure, and its potential shutdown with the problem of safely evacuating the decay heat.

The thesis will be conducted at CEA's Cadarache site, in a stimulating scientific environment, and integrated into a team designing innovative nuclear reactors. CNES will also be involved in monitoring the work, particularly to define the ion propulsion engine characteristics and exploration missions of interest for the electronuclear system. The thesis topic, combining modeling, fluid mechanics, thermodynamics, neutronics, and space mechanics, will lend itself to scientific communication and allow the development of key skills for an academic or industrial career.

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For more Information about the topics and the co-financial partner (found by the lab!); contact Directeur de thèse - frederic.bertrand@cea.fr

Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online  before March 13th, 2026 Midnight Paris time!