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
Seismic behavior of an overhead crane
Overhead cranes are part of the equipment in industrial installations to which special attention must be paid. They are generally located in the upper part of buildings and are potentially subject to significant levels of acceleration in the event of an earthquake, due to the amplification induced by the supporting structure. Consequently, they are potentially subjected to significant forces and can be the source of significant forces on the supporting structure. This study is a continuation of two previous test campaigns carried out on the Azalée shaking table of the EMSI laboratory, on a mock-up of an overhead crane. It aims to provide validated numerical models of this kind of equipment. Two lines of research are considered. The first axis aims to complement the “historical” test campaigns with static tests to justify the adjustment of the numerical models. The second axis consists of exploiting, by comparison tests/calculations, all of the tests that were carried out as part of a previous test campaign for statistical analysis purposes.
Earthquake effect on underground facilities
The Industrial Centre for Geological Disposal (Cigeo) is a project for a deep geological disposal facility for radioactive waste to be built in France. These wastes will be put in sealed packages in tunnels designed at 500 meters depth. The seals are made of a bentonite/sand mixture which has a high swelling capacity and a low water permeability. As a part of the long-term safety demonstration of the repository, it must be demonstrated that the sealing structures can fulfill their functions under seismic loads over their entire lifetime. In order to guarantee this future nuclear waste repository, CEA and Andra are collaborating to work on the potential scientific and engineering challenges involved.
The responses of underground repository to earthquake events are complex due to the spatially and temporally evolving hydro-mechanical properties of the surrounding media and the structure itself. Accurate modeling of the behavior, therefore, requires a coupled multiphysics numerical code to efficiently model the seismic responses for these underground repositories within their estimated lifespan of 100 thousand years.
The research will therefore, propose a performance assessment for sequential and parallel finite element numerical modeling for earthquake analysis of deep underground facilities. Then perform a synthetic data sampling to account for material uncertainties and based on the obtained results in the previous assessment, run a sensitivity analysis using a FEM or a metamodeling process. Finally, the results and knowledge gained within the span of this project will be processed and interpreted to provide responses for industrial needs.
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.
ACCELERATING a DSN SWEEP KERNEL ALGORITHM FOR NEUTRONICS BY PORTING ON GPU.
In the framework of the Programmes Transversaux de Compétences (PTC or literally Cross-XXX Programme), the DES/ISAS/DM2S/SERMA/LLPR and the CEA-DIF are both working on the porting of deterministic neutron transport codes on GPU.
The DM2S within the Energies Direction (DES) is responsible for research and development activities on the numerical methods and codes for reactor physics, amongst which the APOLLO3® code. The neutronics laboratory of CEA-DIF is responsible for developing tools for deterministic methods in neutronics for the Simulation programme.
These two laboratories are actively preparing for the advent of new generation of supercomputers where GPU (Graphical Processing Units) will be predominant. Indeed, the underlying numerical problems to be solved along with the working methodology as well as the conclusions and experience which will be obtained from such studies may be rationalised between both laboratories. Thus, this work has given rise to this postdoctoral position which will be common to both teams. The postdoctoral researcher will be formally based at SERMA at CEA Saclay, with nevertheless regular meetings with the CEA-DIF scientists.
The postdoctoral research work is to study the acceleration of a toy model of a 3D discrete ordinates diamond-differencing sweep kernel (DSN) by porting the code on GPU. This work hinges on porting experiments which have previously been carried by both teams following two different approaches: a ‘’high-level’’ one based on the Kokkos framework for DES and a ‘’low-level’’ approach based on Cuda for CEA-DIF.
Robust path-following solvers for the simulation of reinforced concrete structures
Path-following procedures are generally employed for describing unstable structural responses characterized by ``snap-backs'' and/or ``snap-troughs''. In these formulations, the evolution of the external actions (forces/displacements) is updated throughout the deformation process to fulfill a given criterion. Adapting the external loading during the calculation to control the evolution of the material non-linearities is helpful to obtain a solution and/or to reduce the number of iterations to convergence. This second aspect is of paramount importance, especially for large calculations (at the structural scale). Different path-following formulations were proposed in the literature. Unfortunately, an objective criterion for choosing one formulation over another for the simulation of reinforced concrete (RC) structures (in the presence of different and complex dissipation mechanisms) still needs to be made available. The proposed work will focus on the formulation of path-following algorithms adapted to simulate RC structures.
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).
Development and application of Inverse Uncertainty Quantification methods in thermal-hydraulics within the new OECD/NEA activity ATRIUM
Within the Best Estimate Plus Uncertainty methodologies (BEPU) for the safety analysis of the Nuclear Power Plants (NPPs), one of the crucial issue is to quantify the input uncertainties associated to the physical models in the code. Such a quantification consists of assessing the probability distribution of the input parameters needed for the uncertainty propagation through a comparison between simulations and experimental data. It is usually referred to as Inverse Uncertainty Quantification (IUQ).
In this framework, the Service of Thermal-hydraulics and Fluid dynamics (STMF) at CEA-Saclay has proposed a new international project within the OECD/NEA WGAMA working group. It is called ATRIUM (Application Tests for Realization of Inverse Uncertainty quantification and validation Methodologies in thermal-hydraulics). Its main objectives are to perform a benchmark on relevant Inverse Uncertainty Quantification (IUQ) exercises, to prove the applicability of the SAPIUM guideline and to promote best practices for IUQ in thermal-hydraulics. It is proposed to quantify the uncertainties associated to some physical phenomena relevant during a Loss Of Coolant Accident (LOCA) in a nuclear reactor. Two main IUQ exercises with increasing complexity are planned. The first one is about the critical flow at the break and the second one is related to the post-CHF heat transfer phenomena. A particular attention will be dedicated to the evaluation of the adequacy of the experimental databases for extrapolation to the study of a LOCA in a full-scale reactor. Finally, the obtained input model uncertainties will be propagated on a suitable Integral Effect Test (IET) to validate their application in experiments at a larger scale and possibly justify the extrapolation to reactor scale.