Impact of power histories on the decay heat of spent nuclear fuel
Decay heat is the energy released by the disintegration of radionuclides present in spent fuel. Precise knowledge of its average value and range of variations is important for the design and safety of spent fuel transport and storage systems. Since this information cannot be measured exhaustively, numerical simulation tools are used to estimate the nominal value of decay heat and quantify its variations due to uncertainties in nuclear data.
In this PhD, the aim is to quantify the variations in decay heat induced by reactor operating data, particularly power histories, which are the instantaneous power of fuel assemblies during their residence in the core. This task presents a particular challenge as the input data are no longer scalar quantities but time-dependent functions. Therefore, a surrogate model of the scientific computing tool will be developed to reduce computation time. The global modeling of the problem will be carried out within a Bayesian framework using model reduction approaches coupled with multifidelity methods. Bayesian inference will ultimately solve an inverse problem to quantify uncertainties induced by power histories.
The doctoral student will join the Nuclear Projects Laboratory of the IRESNE institute at CEA Cadarache. He/she will develop skills in neutron simulation, data science, and nuclear reactors. He/she will be given the opportunity to present his/her work to various audiences and publish it in peer-reviewed journals.
Development of an X-ray detection system for particle ID of superheavy nuclei
The synthesis and study of the superheavy nuclei (SHN) is still one of the major challenges of modern nuclear physics. Experimental studies of hitherto unknown nuclei depend crucially on their identification in terms of atomic charge Z and nuclear mass A. To complete particle ID capabilities of the separator-spectrometer set-up S3 at GANIL-SPIRAL2, already providing a mass resolution sufficient to resolve the A of SHN, its focal plane detection system SIRIUS will be provided with X-ray detection for Z identification of the species of interest. The development of an X-ray detection system array, employing thin germanium crystals with thin entrance windows (based on so-called Low-Energy Photon Spectrometers (LEPS)), its integration in the SIRIUS set-up as well as its in-beam test and use for SHN decay spectroscopy will be the main tasks of the Ph.D. thesis. The Ph.D. student will be involved in SHN spectroscopic studies at GANIL and international accelerator laboratories like ANL, which serve as efficient preparation of the experiment campaigns planned at S3 which is scheduled to come online in 2024. This Ph.D. thesis work is an important ingredient for the preparation of the detection instrumentation needed for the S3 operation.
Study of reaction mechanisms for the synthesis of super-heavy elements
One of the main activities in nuclear physics is the study of the properties of the exotic nuclei up to the limits of the nuclear chart, in regions with extreme proton-neutron ratios (proton/neutron driplines) and at the highest masses A and atomic numbers Z. The so-called super-heavy nuclei (SHN) are expected to exist beyond the liquid drop limit of existence defined by a vanishing fission barrier, thanks to the quantum mechanical shell effects. These nuclei are particularly interesting because they are at the limit between few-body and large n-body physics: the magic proton and neutron numbers, Z and N, are replaced by a magic region or island extended in Z and N.
The synthesis of these very and super-heavy nuclei by fusion-evaporation reactions is an experimental challenge due to the extremely low cross-sections. Modelling the complete reaction in order to guide the experiments is also a difficult challenge, as models developed for lighter nuclei cannot simply be extrapolated. Fusion reactions are hindered compared to what is observed with light nuclei, because the very strong Coulomb interaction is enhanced by the strong repulsion caused by the large number of positive charges (protons) in the system in competition with the attractive strong (nuclear) force in a highly dynamic regime. The predictive power of the models needs to be improved, although the origin of the hindrance phenomenon is qualitatively well understood. The quantitative ambiguities are large enough to observe a few orders of magnitude differences in the fusion probabilities calculated by different models. A small change in the cross-section could result in many months being required to perform successful experiments.
At GANIL, in collaboration with other institutes, we have developed a model that describes all the three steps of the reaction to synthesise super-heavy nuclei. Future developments will focus on finding ways to assess the models in order to improve their predictive power, including the design of dedicated experiments to constrain the so-called fusion hindrance. Of course, a careful uncertainty analysis, which is new in theoretical nuclear physics, will be necessary to assess the different ideas. Standard methods as well as state-of-the-art data analysis methods such as Bayesian analysis may be used.
This PhD work will be done in collaboration with the experimental group at GANIL and a research team in Warsaw (Poland). Depending on the skills of the student, the thesis will be more oriented towards formal developments or towards the experiments at the new S3 facility at Spiral2. Participation in experiments is possible.
Experimental and theoretical studies of the fission fragment excitation energy and angular momentum generation
The discovery of nuclear fission in 1939 profoundly changed our understanding of nuclear physics. The fission reaction is the splitting of heavy nuclei, such as uranium 235, into two lighter nuclei, together with the release of a large amount of energy. Many years of research have led to the development of nuclear fission models, from which evaluated nuclear data files are derived. These files are essential inputs to reactor simulations; yet, their quality needs to be improved.
This PhD thesis aims to study the generation of angular momentum and the excitation energy of fission fragments from both experimental and theoretical standpoints. These studies will not only improve our understanding of the underlying process and our models, but also enhance the predictive power of simulation tools, particularly those used to predict gamma heating in reactors. Part of the work will involve finalizing the analysis of data acquired as part of a recent thesis. The student will take part in complementary experimental campaigns at the nuclear reactor of the Institut Laue-Langevin (ILL), using the LOHENGRIN spectrometer to measure isomeric ratios and the kinetic energy distributions of fission fragments.
The doctoral student will be based in a nuclear and reactor physics unit. He/she will develop skills in nuclear physics, data analysis, and computer programming. The programming languages used will be C++ and Python. Professional perspectives include academic research, R&D organisations, nuclear industry, and possibly also data scientist positions.
Time reversal invariance test in nuclear beta decay: Analysis of the data of MORA at JYFL
The Matter’s Origin from RadioActivity (MORA) experiment searches for a sign of CP violation in nuclear beta decay, via the precise measurement of the so-called D correlation. An innovative technique of in-trap ion polarization for such a measurement enables attaining unprecedented sensitivity to New Physics, which could explain the matter-antimatter asymmetry observed in the universe. With a goal in sensitivity on a non-zero D of a few 10-4, the measurement that MORA is undertaking at Jyväskylä will be competitive with the best limit obtained so far on a non-zero D correlation in neutron decay [5]. To attain such precision regime several weeks of data taking are required along the coming years (2025-2027) at Jyväskylä, both for 23Mg+ and 39Ca+. The data analysis has to be undertaken in parallel. Crosschecks and adaptation of existing simulations of individual detectors of MORA, performed with GEANT4 and PENELOPE Monte Carlo codes, are required to pursue the investigation of systematics effects potentially affecting the final sensitivity on D. Dissemination of the results of the data analysis at national and international conferences will be asked to the PhD student.
Innovative modeling for multiphysics simulations with uncertainty estimates applied to sodium-cooled fast reactors
Multiphysics modeling is crucial for nuclear reactor analysis, yet uncertainty propagation across different physical domains—such as thermal, mechanical, and neutronic behavior—remains underexplored due to its complexity. This PhD project aims to address this challenge by developing innovative methods for integrating uncertainty quantification into multiphysics models.
The key objective is to propose optimal modeling approaches tailored to different precision requirements. The project will explore advanced techniques such as reduced-order modeling and polynomial chaos expansion to identify which input parameters most significantly impact reactor system outputs. A key aspect of the research is the comparison between "high-fidelity" models, developed using the CEA reference simulation tools, and "best-estimate" models designed for industrial use. This comparative analysis will highlight how these errors propagate through different models and simulation approaches.
The models will be validated using experimental data from SEFOR, a sodium-cooled fast reactor. These experiments provide valuable benchmarks for testing multiphysics models in realistic reactor conditions. This research directly addresses the growing need for reliable, efficient modeling tools in the nuclear industry, aiming to improve reactor safety and performance.
The candidate will work in a dynamic environment at the CEA, benefiting from access to advanced simulation resources and opportunities for collaboration with other researchers and PhD students. The project offers the possibility of presenting results at national and international conferences, with strong career prospects in nuclear reactor design, safety analysis, and advanced simulation.
Development of a dosimetry system to track alpha particles in in vitro assays for Targeted Alpha Therapy
Targeted Alpha Therapy (TAT) is a promising new method of treating cancer. It uses radioactive substances called alpha-emitting radioisotopes that are injected into the patient's body. These substances specifically target cancer cells, allowing the radiation to be concentrated where it is needed most, close to the tumors. Alpha particles are particularly effective because of their short range and ability to target and destroy cancer cells.
As with any new treatment, TAT must undergo preclinical studies to test its effectiveness and compare it to other existing treatments. Much of this research is done in laboratory, where cancer cells are exposed to these radioactive substances to observe their effects, such as cell survival. However, assessing the effects of alpha particles requires special methods because they behave differently than other types of radiation.
Recently, a method for measuring the radiation dose received by cells in laboratory experiments has been successfully tested. This method uses detecto
Study of radiative decay of the nucleus using a technic like Oslo-method
Radiative neutron capture is a nuclear reaction forming a compound nucleus which decays by emitting gamma-rays at excitation energy around the neutron binding energy. This well-known reaction which we known how to accurately measure its cross section at low incident neutron energies for most stable and few unstable nuclei close the stability valley, remains difficult to measure for exotic nuclei like fission fragments. Nuclear reaction models based essentially on stable nuclei, also struggle to provide reliable predictions of cross sections for these exotic nuclei. However, in the recent years, progress made related to the models and the measurements for the radiative capture show that significant improvements in including microscopic ingredients studies. These micoscopic ingredients: gamma strength function and nuclear level density, remain accesible to the experiment. These ingredients which respectively manage the way of how the gamma cascade occurs and the nuclear structure at high excitation energy can also be measured and calculated to be compared and suggest ways to improve the predictability of models. This kind of improvements have a direct impact for instance on the cross sections for these exotic nuclei which are produced in the stellar nucleosynthesis. The subject of thie thesis is to measure these quantities for a nucleus involved in the nucleosythesis using a new setup called SFyNCS.
Physics & control of dissipative divertor regime in WEST tokamak experiments
The success of the magnetic confinement fusion program relies on the control of the interaction between the hot confined plasma, where the fusion reactions take place, and the wall of the vacuum vessel in which this plasma is maintained. Currently, this interaction is managed by a hardware and magnetic configuration called the divertor, which aims to concentrate the lost plasma fluxes through a dedicated volume (the divertor volume) towards high flux components (surface components of the divertor). The control of dissipative phenomena in this divertor volume is a critical objective that shall allow maintaining high confinement performances in the core (hot plasma) while maintaining fluxes to the components below technological limits. The WEST tokamak, currently operated at CEA Cadarache, has as its main objective the control of this interaction, in close support with the ITER project. The thesis project aims to improve the physical understanding of the control experiments started on WEST, through advanced experimental analysis, to the optimization of a robust and generic control model that can be deployed on WEST to conduct scenarios representative of ITER conditions. The project will also be part of a very active international context on the subject, both in Europe (EUROfusion Activities), in Asia and in the United States, offering a wide spectrum of visibility and possibilities for collaborations and developments. The results will be published in peer-reviewed journals with possibly high impact factors, and may be presented at international conferences.
Transport in runaway electron companion plasmas: impact on mitigation and extrapolation to ITER
Disruptions are abrupt interruptions of plasma discharges in tokamaks. They are due to instabilities leading to the loss of thermal energy and magnetic energy of the plasma over periods of the order of a few tens of milliseconds. Disruptions can generate so-called relativistic runaway electron beams reaching energies up to several MeV and potentially carrying a large part of the initial current. It is crucial to control or stop them to ensure a reliable operation of future tokamaks such as ITER. The proposed thesis project focuses on the mitigation of runaway electrons by massive injection of deuterium or hydrogen into the beam. This scenario leads to a drastic decrease in the energy deposited on the wall by the runaway electrons, through two phenomena: a magnetohydrodynamic instability and the absence of regeneration of the runaway electrons in the final loss of the plasma current. These two conditions are obtained when the plasma created by the interaction between the runaway electron beam and the neutral gas remains cold enough to recombine. The recombination mechanism relies on energy transport processes by the neutrals and a decrease in the interaction between the runaway electrons and the background plasma. Limits to this scheme were found on current tokamaks; they must be understood in order to extrapolate to future machines. The first part of the thesis will focus on the characterization of the cold plasma: density profiles, deuterium/hydrogen or heavy impurity concentration, current profile. We will be particularly interested in the quantities related to transport phenomena in the plasma: heat conduction, particle diffusion or radiation transport. This experimental characterization will quickly call upon numerical modelling to confirm the role of the various transport mechanisms in keeping the conditions required for the dissipation of the beam without damage. An extrapolation towards ITER will then be considered via simulations.