1,721,648 research outputs found
Reoperations After First Lumbar Disk Herniation Surgery with or without Implantation of Mechanical Annular Closure Device
No full textLumbar diskectomy is a widely performed surgical procedure in patients affected by lumbar disk herniation (LDH). Such a surgical procedure is considered to be safe and able to provide a consistent symptomatic relief in most patients. However, perioperative complications have been reported, ranging from 13% to 15%, and pose a considerable financial burden among patients, hospitals, and national health care agencies. The most common perioperative complication following lumbar diskectomy for disk herniation is the recurrence. Although the recurrence rate of LDH has been reported to be 5%−15%, its exact incidence may be underestimated. Recurrent lumbar disk herniation (rLDH) is defined as disk herniation at the same level, regardless of ipsilateral or contralateral herniation, in a patient who has experienced a pain-free interval of at least 6 months after surgery. In this regard, a great deal of controversy exists about the risk factors for rLDH because many clinical and complicated biomechanical parameters can be taken into account. There have been many studies aimed at assessing the recurrence of LDH and the related risk factors suggesting the possible role of disk degeneration, trauma, age, smoking, gender, and obesity. Furthermore, radiologic factors, such as disk degeneration, disk height, and sagittal range of motion have been shown to be related to spinal instability and consequently to rLDH
Stress-testing the ALFRED design - Part III: Safety margins evaluation
No full textThe advancement of the design of the Advanced Lead-cooled Fast Reactor European Demonstrator (ALFRED) beyond the conceptual phase, passes through the analysis of the impact of uncertainties, notably to what concerns safety-related conditions. Compliancy of plant safety to Design Extension Conditions is, according to IAEA and in line with the meaning itself of these beyond-design conditions, usually investigated by best estimates only. Due however to the demonstration nature of ALFRED, it was decided to assess the actual safety performances of this system even in ultimate conditions. To this regard, the emphasis was put on unprotected events like the UTOP (unprotected transient of over-power) and ULOOP (unprotected loss of offsite power, resulting from the combination of a loss of flow and loss of heat sink under unprotected conditions), pinpointed as the most challenging situations sought for the plant. The purpose of the present work, which has been divided in three parts, was then to assess the ultimate ALFRED safety margins against failure of the key core components and systems (Part III). To target this objective, the evaluation of uncertainties coming, on one hand, from nuclear data was performed at first, to retrieve their impact on the reactivity coefficients, thereby on the transient behavior driven by the latter (Part I); then, uncertainties from material properties, fabrication procedures, operation and measurement, and computational tools were propagated to assess their influence on the thermal-hydraulics of the system (Part II). In this work the efforts of Parts I and II are merged together and the effect of uncertainties on safety margins and salient parameters assessed. The retrieved uncertainties are propagated to the expected number of pins experiencing fuel melting during an UTOP and to the clad time-to-failure during an ULOOP. The former has been found to be quite affected by uncertainties, but still under limits not directly posing hazards to the people and the environment, even when extremely conservative assumptions are put forward; the latter shows a milder response to uncertainties, but always guaranteeing more than an order of magnitude of safety margin relative to WENRA recommendations. © 2018 Elsevier Lt
LEADER Work Package 2 Work Program
No full textThis report describes the generai objectives and the related activities to be performed by the Work Package 2 within the LEADER project. It also organizes the work assigning specific activities (and the related man-months budget) to every Task, according to the generai objectives of the Work Package. The technical documents to be produced by the Work Package are also listed, and briefly commented to provide generai guidelines to the Task leaders. Finally, a preliminary organization of the work to be performed by every Task is briefly proposed by defining the preliminary index of every technical documen
Extension of the sub-channel code ANTEO+ to the mixed convection regime
No full textLiquid Metal cooled Fast Reactors, and notably Heavy Liquid Metal cooled systems, are promising options for achieving, in a relatively short term, the various advantages brought about by Small Modular Reactors (SMRs). To increase safety, natural circulation in the primary circuit to cool the core, even at rated power, is also considered, possibly bringing the core thermal exchange dynamics inside the mixed convection regime. To address, at the outset of the design process, thermal-hydraulics aspects, suitable tools must be employed, like the sub-channel code ANTEO+. ANTEO+ was, however, specifically built for the forced convection regime, trying to maximize modeling efficiency inside that regime; to make it applicable also for these SMRs concepts, its validity domain has been extended to the mixed convection regime. In this work, such extension process is outlined, presenting the new code structure, including the solved set of equations and models in the new anticipated application domain. A thorough validation for sub-channel and clad outer temperatures is also presented, confirming the ability of ANTEO+ in reproducing experimental data, homogeneously, in its new anticipated validity domain, with a relatively high degree of accuracy when compared to a reference tool like COBRA-IV-I-MIT. The need for Heavy Liquid Metal-cooled experiments dedicated to validation for sub-channel tools has also been highlighted so to greatly enhance confidence in the final code accuracy assessment, ultimately easing its use in the design phase. © 2017 Elsevier B.V
Efficacy of Zero-Profile Device versus Plate and Cage Implant for Treatment of Symptomatic Adjacent Segment Disease After Anterior Cervical Diskectomy and Fusion
No full text
Stress-testing the ALFRED design - Part II: Quantification of uncertainties on the fuel assembly temperature field
No full textThe advancement of the design of the Advanced Lead-cooled Fast Reactor European Demonstrator (ALFRED) beyond the conceptual phase, passes through the analysis of the impact of uncertainties, notably to what concerns safety-related conditions. Compliancy of plant safety to Design Extension Conditions is, according to IAEA and in line with the meaning itself of these beyond-design conditions, usually investigated by best estimates only. Due however to the demonstration nature of ALFRED, it was decided to assess the actual safety performances of this system even in ultimate conditions. To this regard, the emphasis was put on unprotected events like the UTOP (unprotected transient of over-power) and ULOOP (unprotected loss of offsite power, resulting from the combination of a loss of flow and loss of heat sink under unprotected conditions), pinpointed as the most challenging situations sought for the plant. The purpose of the present work, which has been divided in three parts, was then to assess the ultimate ALFRED safety margins against failure of the key core components and systems (Part III). To target this objective, the evaluation of uncertainties coming, on one hand, from nuclear data was performed at first, to retrieve their impact on the reactivity coefficients, thereby on the transient behavior driven by the latter (Part I); then, uncertainties from material properties, fabrication procedures, operation and computational tools were propagated to assess their influence on the thermal-hydraulics of the system (Part II). In this work the focus is on the latter uncertainties. The adopted methodology is presented at first, namely the semi-statistical vertical approach – characterized by an optimal degree of conservatism among the classical approaches – targeting a 3σ confidence interval. Then, the identification and propagation of each effect are shown, by means of the heat equations, so to retrieve the actual uncertainties on the parameters of interest (the temperatures themselves). Finally, a hot spot analysis to quantify the uncertainty-distorted temperature field is elaborated and presented. The performed analysis has revealed the great impact of fabrication tolerances for the coolant, film and clad temperature rises, particularly affecting safety margins during an ULOOP, while models and material properties uncertainties seem to dominate for the gap and fuel rises, which concur notably in challenging the respect of the fuel melting limit in an UTOP. © 2018 Elsevier Lt
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