Introduction

Space Nuclear Electric systems such as Nuclear Electric Propulsion (NEP) are expected to play a pivotal role in the new space era by providing a flexible power source for propulsion, as well as for electric and thermal supply in manned, scientific, and commercial missions. NEP and related nuclear space technologies have been studied in the USA and Russia almost continuously since the dawn of the nuclear era, though with varying success, while receiving far less attention and budget in Europe. Over the past three years, however, European interest has grown significantly driven by Exploration roadmaps and cooperation perspectives, and several exploratory studies have been launched, including the ESA RocketRoll studies, one of whose projects has been led by our Reactor Physics Group at LPSC-Grenoble/IN2P3/CNRS (2023–2025). The CNRS-RocketRoll project aimed to identify promising technologies, perform a preliminary NEP design for commercial space applications, and develop a European roadmap. This effort improved our understanding of how to integrate mission requirements with nuclear and electric propulsion technologies within a coherent design framework.

Since 2019, our team has worked on designing a microreactor for NEP and developing numerical tools (NepFOAM and PRESTO) tailored for modeling such systems. In 2023, we established a collaboration with CNES through a co-funded PhD (2023–2026: Thèse Francisco Szmandiuk) dedicated to advancing PRESTO, a conceptual design tool for evaluating and comparing NEP configurations. PRESTO is central to the design process, supporting decisions on the most promising system concepts and determining optimal parameters (e.g., size, materials, enrichment, temperature, flow), which are later refined through high-fidelity multiphysics simulations with NepFOAM.

During the ongoing PhD, PRESTO has been significantly enhanced with a new reactor technology: the Heat Pipe Reactor (HPR), one of the main systems currently investigated in the USA and Europe. Three HPR concepts have been modeled (with and without neutron moderation, using monolithic fuel or fuel rods). Additional subsystems have been integrated, including a Stirling converter, reactor shielding, space radiators (passive and heat-pipe), and the thermal transport network. PRESTO will soon enable optimization studies considering subsystem interactions, and by the end of the PhD, these features will be linked with Molten Salt Reactor (MSR) models, allowing comparisons with both technologies and considering an added Potassium Rankine Cycle.

The proposed new joint PhD project will further enhance PRESTO’s capabilities and conduct trade-off analyses to address key design questions. It will also include new experimental activities to improve model reliability and contribute to the broader project objectives.

PhD project

The proposed PhD project will extend PRESTO’s capabilities to cover the full spectrum of reactor technologies for Nuclear Electric Propulsion and Surface Power applications. New reactor concepts will be incorporated: Liquid Metal Reactors (LMRs) and Gas-Cooled Reactors (GCRs). A new power conversion system, the Brayton cycle, will also be modeled in PRESTO. Although particularly suitable for GCRs, this cycle has also been proposed for HPRs, MSRs, and LMRs. In the later phase, PRESTO will be modified to enable preliminary design optimization for Surface Power systems, such as those envisioned for Moon or Mars bases.

With these capabilities, PRESTO will help address key design questions for these reactors concepts beyond performance comparisons, such as: What is the optimal reactor power for a given mission? What fuel enrichment (HALEU<20% or HEU) is preferable? Under which conditions should a fast reactor be favored over a moderated one? Are there power ranges where one technology outperforms another? What is the practical upper power limit for each concept? Which subsystem in the NEP engine has the lowest design margin? More broadly, which technologies should be prioritized in a European NEP roadmap? By integrating design constraints for surface power reactors, the tool will help to assess the potential adaptability of NEP technologies to lunar or Martian applications.

To achieve these goals, the PhD project will be structured as follows:

1. Development and implementation of the GCR model and Brayton cycle in PRESTO (Y1).

2. Development of the LMR model, specifically a sodium-cooled reactor (Year 2).

3. Comparative performance studies of the four main NEP technologies: LMR, GCR, HPR, and MSR (Y2–3).

4. Integration of new design constraints and models (notably shielding) to enable optimization for Surface Power applications (Y3).

5. PhD manuscript preparation (Y3).

Depending on progress and funding, the PhD may also include experimental work (Y2) at the FEST platform (LPSC), focusing on power conversion and heat transport. The PhD candidate will participate in ongoing international collaboration.

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For more Information about the topics and the co-financial partner (found by the lab !); contact Directeur de thèse - Pablo.rubiolo@lpsc.in2p3.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!