PhD Thesis: “Modeling and Design of Nuclear Systems for Space Electric Propulsion: A Study of Gas-Cooled Reactor (GCR) and Liquid Metal Reactor (LMR) Technologies (M/F)

Job Description

Thesis Subject

Since 2019, the Reactor Physics Group at LPSC has been working on the design of microreactors for Nuclear Electric Propulsion (NEP) as well as on the development of dedicated numerical tools (NepFOAM and PRESTO) for modeling such systems. PRESTO plays a central role in the design process by helping identify the most promising concepts and determine the optimal parameters (size, materials, fuel enrichment, operating temperature, flow rate, etc.) for all NEP subsystems. These preliminary designs are subsequently refined through high-fidelity multiphysics simulations using NepFOAM.
During the ongoing PhD project, co-funded by the French National Centre for Space Studies (CNES), PRESTO has been significantly enhanced through the integration of a new reactor technology: the Heat Pipe Reactor (HPR). The present PhD project aims to continue and extend this development in order to cover the full range of reactor technologies envisioned for Nuclear Electric Propulsion while also accounting for surface power applications.
Two additional reactor concepts will be incorporated into PRESTO: Gas-Cooled Reactors (GCRs) and Liquid Metal Reactors (LMRs). In parallel, a new power conversion system based on the Brayton cycle will be implemented. Although the Brayton cycle is particularly well suited to GCRs, it is also a relevant option for HPRs, Molten Salt Reactors (MSRs), and LMRs. In a later phase of the PhD project, PRESTO will be further extended to enable the preliminary optimization of surface power systems, such as those envisioned for permanent lunar or Martian bases.
These new capabilities will allow PRESTO to address fundamental design questions that go far beyond simple performance comparisons between technologies. By incorporating the specific design constraints associated with surface power systems, the tool will also make it possible to assess the extent to which technologies developed for Nuclear Electric Propulsion can be adapted for applications on the Moon or Mars.

Key activities:
To achieve the objectives described above, the PhD project will be structured into four main stages:
1. Development and implementation of a Gas-Cooled Reactor (GCR) model and the Brayton power conversion cycle in PRESTO (Year 1).
2. Development of a Liquid Metal Reactor (LMR) model, considering reactor concepts cooled by sodium (Na), sodium-potassium alloy (NaK), or lithium (Li) (Year 2).
3. Comparative performance studies of the four main Nuclear Electric Propulsion technologies—LMRs, GCRs, HPRs, and MSRs (Years 2–3). Existing models will be improved and refined whenever necessary.
4. Depending on the progress of the project, integration of additional design constraints and models—in particular radiation shielding models—to enable the optimization of systems intended for surface power applications (Year 3), together with the preparation of the PhD dissertation.
The design of the GCR and LMR concepts, carried out during Stages 1 and 2, will require the development of neutronic, thermal-hydraulic, and mechanical numerical models specifically adapted to these reactor technologies. These models will account for different materials for the fuel, cladding, coolant, reflector, and, where applicable, moderator. They will be used to evaluate operating conditions (power, temperature, pressure, mass flow rate, etc.), as well as the dimensions, masses, and design and safety limits of the main reactor components.
The neutronic models used to calculate the reactor critical mass will be built from Monte Carlo simulations performed with the SERPENT code. These calculations will also provide the neutron and gamma source terms required for radiation shielding design, as well as estimates of the maximum neutron fluence experienced by structural materials. In addition, the models will enable the assessment of different fuel enrichment levels and both thermal and fast neutron spectrum reactor concepts.
For GCRs, TRISO fuel will be considered, whereas LMRs will rely on a more conventional fuel pin design using UN or UO₂ fuel pellets. The thermal-hydraulic models, aimed at evaluating temperatures, heat fluxes, and flow rates throughout the reactor core, will be developed using lumped-parameter approaches or one-dimensional formulations based on the conservation equations for mass, momentum, and energy. Reactivity control systems will be designed by accounting for reactivity feedback coefficients, fuel burnup over the mission lifetime, variations in operating temperatures, and reactor start-up and shutdown procedures.
All these numerical models will be used to build the database required by PRESTO for the conceptual design optimization process.
During the third stage, a comprehensive comparison of the performance of the different NEP concepts will be carried out over a wide range of electrical power levels representative of various space mission profiles. This analysis will help identify the technologies best suited to specific mission requirements.
During the fourth stage, and depending on the progress of the work, the design constraints—particularly those related to radiation shielding—will be adapted to account for the specific requirements of reactors intended for surface power applications, such as permanent lunar bases. The final part of the project will be devoted to the preparation and writing of the PhD dissertation.
Finally, depending on project progress and available funding, the PhD may also include an experimental component during the second year on the FEST platform at LPSC. This work will focus on comparative experiments related to power conversion and heat transport, with the objective of validating and improving the models implemented in PRESTO. Throughout the PhD, the candidate will also participate in the international collaborations currently conducted by the research team.

Your Work Environment

The Grenoble Laboratory of Subatomic Physics and Cosmology (LPSC) (http://lpsc.in2p3.fr) is a joint research unit operated by the CNRS-IN2P3, Université Grenoble Alpes (UGA), and Grenoble INP, employing approximately 230 staff members. The PhD candidate will join the Reactor Physics Group, which comprises ten researchers and engineers at LPSC. The research will be carried out within the FEST (Fluids Experiments and Simulations in Temperature) experimental platform, under the direct supervision of the Head of the Reactor Physics Group.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

The research professions