Marijke Jacobs

Fabry Perot sensor for in-pile nuclear reactor metrology

Optical fibre sensors are attractive devices that can bring substantial advantages over conventional sensing approaches for fission Material Testing Reactors (MTRs), such as high accuracy capabilities with limited intrusiveness and the ability to withstand high temperature. In the framework of the Joint Instrumentation laboratory (JIL), CEA and SCK CEN have joined their resources to develop, in particular, an OFS prototype with the aim to measure dimensional changes on nuclear materials irradiated in MTRs. We briefly present the objectives and the workplan of that project, in which the first phase addressed an analysis of the different measurement systems considered towards the specific environmental conditions encountered in a fission reactor. Among them, radiation is responsible for the biggest error source through the density change of silica glass due to neutron-induced compaction. The analysis has leaded us to focus mainly on an Extrinsic Fabry Perot design based on low coherence interferometry. As part of the current development, we present the results of table top experiments that allow appreciating the variation with different parameters of the response, especially the modulation of the signal returned. That permits to set partially the design and brings some tolerances data. A home made signal conditioning allows to extract the cavity length and then the change in the dimension of the sample to test.

Chemical Looping Combustion: an Emerging Carbon Capture Technology

Chemical looping combustion (CLC) is a promising technology for energy production with inherent capture of carbon dioxide at minimal energy penalty. In CLC, oxygen is transferred from an air reactor to a fuel reactor by means of a solid oxygen carrier. Direct contact between air and fuel is avoided, resulting in an undiluted CO2 exhaust stream. As such, CLC was picked up recently as a high potential carbon capture and storage (CCS) technology. While initial focus was on storage projects, CO2 is more and more considered as a valuable chemical substance for enhanced oil/gas recovery projects as well as for the production of chemicals, polymers or building materials. A critical aspect of the CLC technology is the oxygen carrier performance which has a very strong impact on the economic viability. Parameters such as particle size, density, porosity, strength, attrition resistance, reactivity, environmental aspects and cost, define the performance of the oxygen carrier. The first generation oxygen carriers was Ni-based. However, due to cost of nickel and toxicity, a search for Ni-free oxygen carriers was conducted with similar or superior performance in CLC. This lead to the development of Cu-, Fe and Mn-based oxygen carriers, that demonstrate the beneficial oxygen uncoupling effect, with complete fuel conversion as a result. In this contribution it is shown that the industrial spray-drying technique is a very versatile and scalable technique for the fabrication of oxygen carriers. New and promising oxygen carriers with varying compositions, good fluidisability, high sphericity, high attrition resistance, and homogeneity on the micro-scale have been synthesized. Different materials such as perovskite type materials based on calcium-manganate, magnesium manganates, copper based materials, and iron manganates have been investigated for their performance with promising results towards complete combustion and high attrition resistance.

Testing and modeling of diffusion bonded prototype optical windows under ITER conditions

Glass-metal joints are a part of ITER optical diagnostics windows. These joints must be leak tight for the safety (presence of tritium in ITER) and to preserve the vacuum. They must also withstand the ITER environment: temperatures up to 220 °C and fast neutron fluxes of ∼3·109 n/cm2·s. At the moment, little information is available about glass-metal joints suitable for ITER. Therefore, we performed mechanical and thermal tests on some prototypes of an aluminium diffusion bonded optical window. Finite element modeling with Abaqus code was used to understand the experimental results. The prototypes were helium leaking probably due to very tiny cracks in the interaction layer between the steel and the aluminium. However, they were all able to withstand a thermal cycling test up to 200 °C; no damage could be seen after the tests by visual inspection. The prototypes successfully passed push-out test with a 500 N load. During the destructive push-out tests the prototypes broke at a 6–12 kN load between the aluminium layer and the steel or the glass, depending on the surface quality of the glass. The microanalysis of the joints has also been performed. The finite element modeling of the push-out tests is in a reasonable agreement with the experiments. According to the model, the highest thermal stress is created in the aluminium layer. Thus, the aluminium joint seems to be the weakest part of the prototypes. If this layer is improved, it will probably make the prototype helium leak tight and as such, a good ITER window candidate.

Finite Element Modeling of Thermal Stress in ITER Prototype Optical Windows and its Influencing Parameters

Glass-metal joints are needed for the optical windows in ITER to perform diagnostics. These joints must be leak tight for the safety (presence of tritium in ITER) and to preserve the vacuum. They must also withstand the ITER environment: temperatures around 250 °C and neutron fluxes of 109 n/cm2.s. At the moment, little information is available about glass-metal joints suitable for ITER. Therefore, we set-up a 2D elastic model of prototype Al diffusion bonded optical windows using Abaqus code to model temperature effects on the windows. With this model we analyzed the influence of different parameters like the joint area and the braze thickness on the mechanical properties of the joint. Calculations of the thermal stress created by a temperature field of 150 °C (normal ITER temperature) showed that the Al-bond is the weakest part of the window. To find a way of reducing the thermal stress, the influence of some parameters has been studied. In particular, a specific thickness of the Al layer can result in a minimum of stress in the Al bond while the joint area and the thickness of the glass have only a small influence on the stress in the windows. The calculations allowed to propose an optimized design for the windows prototypes.