Characterization of local multi-physics phenomena in the CABRI research reactor

The IRESNE R&D institute at CEA Cadarache invites applications for a post-doctoral position whose aim is first to develop a coupling between the APOLLO3®/THEDI core model at the pin-scale and the CATHARE model of the 3He depressurization system. Then, with the support of this simulation tool, the second objective will be to define core configurations of interest and measurements for characterizing local multi-physics phenomena in CABRI.
The CABRI pool-type research reactor located at CEA Cadarache is dedicated to the analysis of nuclear fuel behavior during Reactivity-Injection Accident (RIA) in Pressurized Water Reactors. The reactor experimentally simulates power pulse transients in the driver zone, which induces a RIA-representative energy deposition in the fuel sample of a water-loop at the core center. The power transients in the CABRI core are initiated by the depressurization of transient rods containing a strong neutron absorber, 3He.
Two models have been recently developed to simulate CABRI power transients. The first model at the assembly scale is a tool called PALANTIR, based on the CATHARE2 system thermal-hydraulics code with additional surrogate models to take into account the reactivity injected by 3He depressurization. The CATHARE2 code includes a neutron point kinetics module, a heat equation solver module and simplified thermomechanical models for fuel pins. In addition to the core, the depressurization circuit is modeled, providing access to 3He density in the transient rods.
The second model, at the pin-scale level, is based on a APOLLO3®/THEDI coupling via the C3PO platform. APOLLO3® solves the simplified transport equation. THEDI is used to model an unsteady 1D two-phase hydraulics flow in the core. It also solves the 1D heat equation for fuel thermics. For the simulation of each power transient in CABRI, PALANTIR provides the 3He density evolution versus time; these data are imposed as boundary condition in the APOLLO3®/THEDI coupling.

Development, metrological validation and outdoor testing of a multitrack Raman/FO measurement unit dedicated to the safety of future cryogenic liquid hydrogen dispensing stations

Context: The domestic and industrial use of liquid hydrogen as the fuel of the future requires the definition of a suitable safety code. At present, tank separation criteria have been defined by anticipation using a conservative approach. It is therefore necessary to carry out full-scale experiments ("pool spreading") in order to provide input for calculation codes and build relevant standards. These experiments require the implementation of instrumentation adapted to the measurement of all gases present in free space (O2, N2, H2O, H2) in order to establish a measurement of partial pressures during each test, correlated with the other means of measurement in place (thermometry, catharometry, PIV, BOS, etc.).

Mission: In the context of an ANR-PEPR project (ESKHYMO) managed by CEA Liten, a Raman/FO Multitrack spectrometric measurement unit will be developed jointly by CEA List and CEA DES on the basis of an existing device. Raman measurement is multi-elemental, multi-track (a single measurement unit for several probes), non-explosive, and delivers a self-standardized measurement to a reference species (usually nitrogen at atmospheric pressure). The Raman/FO measurement unit comprises a laser, a spectrometer associated with a scientific CCD camera, and a fiber-optic circuit for remote measurement. The design of the Raman/FO probes will also be based on an existing CEA product, which will be miniaturized for deployment in field conditions. Four Raman/FO probes will be produced and then calibrated in air (climatic chamber) and hydrogen (shock tube or vacuum chamber) at CEA DES DM2S in Saclay. Finally, the final device will be deployed on the test site for multi-gas measurements during spraying experiments, in partnership with Air Liquide and accrediting bodies (INERIS).

Skills: Optics, laser, fiber optics, spectrometry

Experimental and technological developments of a process for the mineralization of organic liquid waste by plasma

The ELIPSE process developed at the CEA allows the destruction of organic liquids by injection into a high-power plasma.
If the feasibility of destroying different organic components at flow rates of a few liters per hour has now been demonstrated, tests must now be further developed for reference organic liquids appropriately chosen according to existing deposits.
These studies, based on the characterization data of the chosen LORs, will aim to provide detailed process results obtained with the most representative operating conditions, to allow a complete and quantitative evaluation of the process. This will make it possible to establish operating, robustness and endurance data for the process.
This work will include the study of the behavior of radioelements in the process, which will be essential for the nuclearization study: this will involve studying the physico-chemical behavior of actinides during their processing via the use of inactive simulants.

Innovative strategies for minor actinides using molten salt reactors

Within the framework of the ISAC (Innovative System for Actinides Conversion) project of the France Relance initiative, preliminary concepts of molten salt reactor capable of incinerating minor actinides have to be proposed in connection with prospective évolutions of the French nuclear fleet (stabilisation or reduction of the plutonium and americium inventory, minimization of the deep storage footprint, …) and contraints linked to the nuclear fuel cycle (plutonium and minor actinides inventories). The specificities of molten salt reactors will be exploited to design innovative transmutation strategies.
The postdoctoral fellow will be based in the reactor and fuel cycle physics unit of the IRESNE R&D institute at CEA Cadarache. He/she will develop expertise in neutronics, fuel physics, and in the design of Generation-IV reactors of the molten salt type.

Design of innovative nuclear systems cooled by heat pipes

The combined goals of CO2 emission reduction and energy self-sufficiency, in the current geopolitical context, open up new perspectives for nuclear applications (cogenerations, hydrogen production, etc.). In particular, the MNR concepts (Micro Nuclear Reactors), with a thermal power of 2 to 50 MW, bear the promise of flexibility, while providing much reliability and accrued safety.
Among the MNR technologies, the particular concept in which the core is cooled by heat pipes strongly improves the inherent safety of the design, in normal and in accidental conditions as well.
In order to demonstrate the feasibility of such an MNR technology, a predesign of a single high temperature heat pipe should be performed for different selected technologies. Then, the overall heat pipe cooling system should be evaluated. Finally, after having modelled the core cooling system, an integration study including a predesign of the core itself should be done with the two subsystems coupled.

Simulation of PEMFC flooding phenomena

The proton exchange membrane fuel cell (PEMFC) is now considered as a relevant solution for carbon-free electrical energy production, for both transport and stationary applications. The management of the fluids inside these cells has a significant impact on their performance and their durability. Flooding phenomena due to the accumulation of liquid water are known to impact the operation of the cells, causing performance drops and also damages that can be irreversible. With the use of thinner channels in ever more compact stacks, these phenomena are becoming more and more frequent. The objective of this post-doc is to progress in the understanding of flooding in PEMFCs. The work will consist in analyzing the link between the operating conditions, the design of the channels and the materials used in the cell. It will be based on a two-phase flow modeling approach at different scales, from the local scale at the channel-rib level, up to, via an upscaling approach, the level of the complete cell. The study will also be based on numerous experimental results obtained at the CEA or in the literature.

Large-scale depletion calculations with Monte Carlo neutron transport code

One of the main goals of modern reactor physics is to perform accurate multi-physics simulations of the behaviour of a nuclear reactor core, with a detailed description of the geometry at the fuel pin level. Multi-physics calculations in nominal conditions imply a coupling between a transport equation solver for the neutron and precursor populations, thermal and thermal-hydraulics solvers for heat transfer, and a Bateman solver for computing the isotopic depletion of the nuclear fuel during a reactor cycle. The purpose of this post-doc is to carry out such a fully-coupled calculation using the PATMOS Monte Carlo neutron-transport mini-app and the C3PO coupling platform, both developed at CEA. The target system is core of the size of a commercial reactor.

Cascade of circulicity in compressible turbulence

In this post-doctorate, we propose to study the properties of the small scales of forced compressible homogeneous turbulence. More precisely, exact statistical relations similar to the Monin-Yaglom relation will be investigated. The idea, detailed in reference [1], is to understand how the transfer of circulicity is organized in the inertial range. Circulicity is a quantity associated with angular momentum and, by extension, with vortex motions. The analysis of its inertial properties allows to complete the description of the energy cascade already highlighted in previous works [2,3].

The objective of the post-doctorate is to carry out and exploit direct simulations of compressible homogeneous turbulence with forcing, in order to highlight the inertial properties of circulicity .

To this end, the post-doctoral student will be given access to the very large computing center (TGCC) as well as a code, Triclade, solving the compressible Navier-Stokes equations [4]. This code does not have a forcing mechanism and the first task will therefore be to add this functionality. Once this task has been accomplished, simulations will be carried out by varying the nature of the forcing and in particular the ratio between its solenoidal and dilatational components. These simulations will then be exploited by analyzing the transfer terms of circulicity.

[1] Soulard and Briard. Submitted to Phys. Rev. Fluids. Preprint at arXviv:2207.03761v1
[2] Aluie. Phys. Rev. Lett. 106(17):174502, 2011.
[3] Eyink and Drivas.Phys. Rev. X 8(1):011022, 2018.
[4] Thornber et al. Phys. Fluids 29:105107, 2017.

Decentralized Solar Charging System for Sustainable Mobility in rural Africa

A novel stand-alone solar charging station (SASCS) will be deployed of in Ethiopia. Seeing as 45% of Sub-Saharian Africa’s population lacks direct access to electricity grids and seeing as the the infrastructure necessary to reliably harness other energy sources is largely non-existent for many such populations in Ethiopia, introducing the SASCS among some of the country’s rural communities is a necessary effort. It could ostensibly invigorate communities’ agricultural sector and support those whose employment is rooted in farming. A SASCS could also serve to integrate renewable energy within the country’s existing electricity mix. CEA INES will act as a consulting Partner for the design and implementation of the solution (second life batteries, solar will be investigated). In addition, because of CEA INES’s established expertise in the installation of solar tools within various communities, the initiative will also provide know-how for the installation of the SolChargE in Ethiopia as well as cooperate on workshops for students and technicians employed by the project.

Natural convection at high Ra numbers for nuclear safety: 2nd year

Thermal exchanges at very high Rayleigh numbers (Ra) exist on geophysical scale, at civil engineering scale and increasingly in industrial applications and here particularly in the energy sector. At this point, we mention the cooling of solar panels or the heat removal from nuclear power plants under accidental conditions. In fact, the passive safety concept of Small Modular Reactors (SMR) is based on the transfer of residual heat from the reactor to a water pool in which the reactor is placed. Since the outer reactor vessel is very high, heat exchange occurs by natural convection at Rayleigh numbers (Ra) between 1010 and 1016. Reliable heat transfer correlations exist to date only up to about Ra < 1012 with very high uncertainties in the extrapolation to higher Ra. Understanding the heat transfer at very high Ra is thus of fundamental and practical interest. The associated challenges are twofold:
• Numerical challenges: CFD codes cannot model turbulent heat transfer at very high Ra with sufficient accuracy and appropriate calculation time. Improved physical and numerical models are required, which use high performance computing (HPC) capabilities.
• Experimental challenges: Detailed experiments are essential for code validation. Since experiments in water require impractical huge dimensions, cryogenic experiments with helium are planned at CEA, based on the interesting physical properties of this fluid in the range of 5 K (high thermal expansion associated to low viscosity and thermal conduction).