Study on the Multiphysics Modeling of Molten Salt Reactor Using Adjoint-based Sensitivity Analysis Method

Department of Nuclear EngineeringTo pursue the nuclear energy as future energy resources, several reactor types of the nuclear power plant has been developed to achieve the advances in sustainability, reduction of nuclear waste, safety and reliability, proliferation resistance and competitive economies in the framework of the Generation IV International Forum (GIF). Among them, Molten Salt Reactor (MSR) is the only reactor that adopts liquid fuel serving as a coolant as well, which is not a new concept in retrospect of the history of the nuclear reactor. Fermi???s water boiler, the first nuclear reactor fueled with uranium-235 enriched uranium, designed and operated with aqueous homogeneous fuel in liquid form. It adopts liquid fuel having lots of advantages to achieve high power density and inherent safety. However, it also has some technical limitations in maintaining homogeneous state with relatively large fuel particle at that time. With a lesson of previous experiences, it was evolved to adopt the liquid fuel as the eutectic formation of fuel material with molten salt to solve the issue on the slurry fuel, which is the current MSR concept. This was successfully demonstrated by Aircraft Reactor Experiment (ARE) and Molten Salt Reactor Experiment (MSRE) by Oak Ridge National Laboratory in the 1950s. Recently, liquid-fueled MSR is reconsidered as an alternative of a conventional nuclear power plants with aims of the development of related chemical reprocessing and molten salt technologies, taking advantages of the liquid fuel in safety and economic viewpoint as well as the radioactive waste issue. In a viewpoint of design and analysis of liquid-fueled MSR system, complex system behavior should be considered in the aspects of coupled physics; neutronics and thermal-hydraulics. Different from a solid-fueled reactor, delayed neutron precursors generated in core decay at the different location from the fuel flow, and it affects the overall neutron economy. It means a distribution of the fission source is largely dependent on the velocity field which determines the overall power profile. Moreover, it affects temperature field and varies the density of liquid fuel ultimately. Because of this, Multiphysics approach on the MSR system looks promising on the assessment of the system including important aspects of coupled physics. With aims of growing computational power, considering all physics lying under certain problem can be a feasible option nowadays. However, Multiphysics model itself for the complex system should be assessed not to misinterpret the behavior along with system analysis. In the above context, this work is aimed at developing the integrated design and analysis tool for MSR on the Multiphysics approach, which enables to perform system analysis and model sensitivity analysis simultaneously including all underlying physics based on the adjoint method and its application on the assessment of new conceptual design of MSR: nanofluidic molten salt reactor. The first part explains the adjoint-based sensitivity analysis method on the Multiphysics approach. Adjoint method is the concept to establish a relatively simple problem having duality with a primal system. The concept of the adjoint formulation is independent of the model/input parameter itself, such that it has advantages of the calculating a set of the sensitivity of the certain physical system to the numerous parameters with less computational efforts, compared to traditional way of sensitivity analysis, i.e. recalculating perturbed state. To evaluate adjoint-based sensitivity method for Multiphysics problem, a one-dimensional steady-state model of the circulating liquid fuel system and its sensitivity system is established, which consists of one group neutron diffusion equation, balance equations of 6 groups of neutron precursors and 3 groups of decay heat groups, and energy conservation equation. For the condition of Molten Salt Fast Reactor (MSFR) developed by European project SAMOFAR as a representative of liquid-fueled MSR, physical interpretation of the model sensitivity considering coupled effect of two physics are discussed in terms of modeling option and importance of parameter. The second part includes the development of integrated solver within open source Multiphysics toolkit, OpenFOAM, called msrAdjointFoam. It consists of neutronics and thermal-hydraulics coupled in the same environment (i.e. internal coupling) and model sensitivity analysis solver based on the adjoint formulation of the local sensitivity of system variable to all input/model parameters. Adjoint sensitivity solver is implemented based on the mathematical derivation of model equations of the system. Validation and verification of the solver are conducted with several benchmark cases and compared with the analytic solution. The last part describes the application of the integrated design and analysis tool for developing a new conceptual design of MSR; Nanofluidic Molten Salt Reactor. The concept of nanofluid itself is for enhancement of the convection heat transfer with the adoption of excellent thermal properties with the nanoparticle. To evaluate the conceptual design of the nanofluidic molten salt reactor, msrAdjointFoam was extended to nanoMsrAdjointFoam by implementing nanofluid characteristic; dispersion model suggested by Y. Buongiorno based on the concentration of nanoparticle, and its influences on the coupled neutronics and thermal-hydraulics. Using the integrated analysis tool, several design options of the nanofluidic molten salt reactor including decay heat removal system for drain tank are assessed in terms of system performance and safety. According to the mathematical background of the concept of adjoint sensitivity system, it can be extended to the model sensitivity analysis of any engineering system that can represent in a PDE form. In addition, the sensitivity analysis method on the Multiphysics approach can give a physical insight in economic and straightforward way. Integrated Multiphysics tool developed can help to understand and evaluate the complex system such as a nuclear reactor in a more realistic way without any exaggeration of the prediction of overall system behavior considering all coupled phenomena. In the end, from the practical point of view, the concept of nanofluidic molten salt reactor is expected to be the most feasible reactor option with enhanced safety, reduction of nuclear waste, high proliferation resistance as a future nuclear power.clos

Oxygen Partial Pressure during Pulsed Laser Deposition: Deterministic Role on Thermodynamic Stability of Atomic Termination Sequence at SrRuO3/BaTiO3 Interface

With recent trends on miniaturizing oxide-based devices, the need for atomic-scale control of surface/interface structures by pulsed laser deposition (PLD) has increased. In particular, realizing uniform atomic termination at the surface/interface is highly desirable. However, a lack of understanding on the surface formation mechanism in PLD has limited a deliberate control of surface/interface atomic stacking sequences. Here, taking the prototypical SrRuO3/BaTiO3/SrRuO3 (SRO/BTO/SRO) heterostructure as a model system, we investigated the formation of different interfacial termination sequences (BaO-RuO2 or TiO2-SrO) with oxygen partial pressure (PO2) during PLD. We found that a uniform SrO-TiO2 termination sequence at the SRO/BTO interface can be achieved by lowering the PO2 to 5 mTorr, regardless of the total background gas pressure (Ptotal), growth mode, or growth rate. Our results indicate that the thermodynamic stability of the BTO surface at the low-energy kinetics stage of PLD can play an important role in surface/interface termination formation. This work paves the way for realizing termination engineering in functional oxide heterostructures.Comment: 27 pages, 6 figures, Supporting Informatio

Development of a Novel Gas-Sensing Platform Based on a Network of Metal Oxide Nanowire Junctions Formed on a Suspended Carbon Nanomesh Backbone

Junction networks made of longitudinally connected metal oxide nanowires (MOx NWs) have been widely utilized in resistive-type gas sensors because the potential barrier at the NW junctions leads to improved gas sensing performances. However, conventional MOx-NW-based gas sensors exhibit limited gas access to the sensing sites and reduced utilization of the entire NW surfaces because the NW networks are grown on the substrate. This study presents a novel gas sensor platform facilitating the formation of ZnO NW junction networks in a suspended architecture by growing ZnO NWs radially on a suspended carbon mesh backbone consisting of sub-micrometer-sized wires. NW networks were densely formed in the lateral and longitudinal directions of the ZnO NWs, forming additional longitudinally connected junctions in the voids of the carbon mesh. Therefore, target gases could efficiently access the sensing sites, including the junctions and the entire surface of the ZnO NWs. Thus, the present sensor, based on a suspended network of longitudinally connected NW junctions, exhibited enhanced gas response, sensitivity, and lower limit of detection compared to sensors consisting of only laterally connected NWs. In addition, complete sensor structures consisting of a suspended carbon mesh backbone and ZnO NWs could be prepared using only batch fabrication processes such as carbon microelectromechanical systems and hydrothermal synthesis, allowing cost-effective sensor fabrication

Characteristics and clinical course of patients referred to the NST

Background and aimsThe nutrition support team (NST) comprises doctors, nutritionists, pharmacists, and nurses who provide intensive nutritional treatment designed for each patient by evaluating their nutritional status of hospitalized patients. This study aimed to identify the clinical characteristics of patients referred to the NST among those admitted to a tertiary hospital and to understand the factors affecting their clinical course and changes in pressure sore grades.MethodsThis study included 1,171 adult patients aged 18 years or older referred to the NST at a tertiary hospital in a metropolitan city between 1 January 2019 and 31 December 2020. Patients were divided into five age groups, neuro department and non-neuro department, those treated in the intensive care unit (ICU), and those not treated in the ICU. Patients were also compared based on the presence of pressure sores at the time of NST referral and changes in pressure sore grades at the first time of NST referral and discharge (improved pressure sores, no change in pressure sores, and aggravated pressure sores). In addition, this study examined the factors affecting changes in pressure sore grades.ResultsAs age increased, the proportion of both low albumin levels and pressure sores significantly increased (p < 0.001), and the neuro department showed a significantly lower proportion of low albumin levels and pressure sores (p < 0.001). The proportion of patients with pressure sores was higher (64.9%), and this patient group showed significantly higher rates of low albumin levels (p < 0.001) and treatment in the ICU (p < 0.001). The group with aggravated pressure sore grades had a significantly higher proportion of patients in the surgery department (p = 0.009) and those treated in the ICU (p < 0.001). Admission to the surgery department was a factor that aggravated the grade of pressure sores [adjusted odds ratio (aOR) = 1.985, 95% confidence interval (CI) = 1.168–3.371]. When patients were not treated in the ICU, the grade of the pressure sores was less likely to worsen (aOR = 0.364, 95% CI = 0.217–0.609).ConclusionPressure sores and low albumin levels are closely related, and the risk of developing and aggravating pressure sores is particularly high in patients in the surgery department and those receiving ICU treatment. Therefore, it is necessary to actively implement NST referral to ensure that overall nutrition, including albumin, is well supplied, especially for patients in the surgery department and treated in the ICU, as they are at high risk of pressure sore development and aggravation. Moreover, since low albumin levels frequently occur in elderly patients, it is necessary to consider including the elderly in the indications for referral to the NST

Recent Progress on Polymeric Binders for Silicon Anodes in Lithium-Ion Batteries

Advanced polymeric binders with unique functions such as improvements in the electronic conduction network, mechanical adhesion, and mechanical durability during cycling have recently gained an increasing amount of attention as a promising means of creating high-performance silicon (Si) anodes in lithium-ion batteries with high energy density levels. In this review, we describe the key challenges of Si anodes, particularly highlighting the recent progress in the area of polymeric binders for Si anodes in cellsopen

Outer membrane protein a of Salmonella enterica serovar Typhimurium activates dendritic cells and enhances Th1 polarization

<p>Abstract</p> <p>Background</p> <p>Typhoid, which is caused by <it>Salmonella enterica </it>serovar Typhimurium, remains a major health concern worldwide. Multidrug-resistant strains of <it>Salmonella </it>have emerged which exhibit increased survivability and virulence, thus leading to increased morbidity. However, little is known about the protective immune response against this microorganism. The outer membrane protein (Omp)A of bacteria plays an important role in pathogenesis.</p> <p>Results</p> <p>We purified OmpA from <it>S. enterica </it>serovar Typhimurium (OmpA-sal) and characterized the role of OmpA-sal in promoting adaptive and innate immune responses. OmpA-sal functionally activated bone marrow-derived dendritic cells by augmenting expression of CD80, CD86, and major histocompatibility complex classes I and II. Interestingly, OmpA-sal induced production of interferon-γ from T cells in mixed lymphocyte reactions, thus indicating Th1-polarizing capacity. The expression of surface markers and cytokine production in dendritic cells was mediated by the TLR4 signaling pathway in a TLR4 Knock-out system.</p> <p>Conclusions</p> <p>Our findings suggest that OmpA-sal modulates the adaptive immune responses to <it>S. enterica </it>serovar Typhimurium by activating dendritic cells and driving Th1 polarization, which are important properties to consider in the development of effective <it>S. enterica </it>serovar Typhimurium vaccines and immunotherapy adjuvant.</p