ITER cryostat accidental scenario: fluid dynamics analysis of Ingress of Coolant Event Accident

ITER (International Thermonuclear Experimental Reactor) is an experimental reactor aimed at demonstrating the technological and scientific feasibility of fusion technology. A future fusion power plant producing large amounts of energy power will be required to breed all of its own Tritium. ITER will demonstrate this essential concept of Tritium self-sustainment. Among the most important components of that reactor there is the cryostat that is, specifically, a large stainless steel structure surrounding the vacuum vessel and the superconducting magnets, providing a super-cool vacuum environment. The aim of this paper is to evaluate the effects caused by a suddenly rupture of one of the cryogenic lines with release of helium inside the cryostat, event known as CrICE: Ingress of Coolant Event in Cryostat. The CrICE accident scenario has been simulated by ANSYS©CFX. To the purpose, a suitable model representing a 20° sector of the overall ITER structures, vacuum vessel, magnets, thermal shield, ports and cryostat was set up and implemented, in order to characterize and define the free volume to be filled by the gas that would be released eventually as well as the air inside the bioshield. The numerical model, the geometrical characteristics and the materials properties used as input in the simulation of the accidental scenario have been presented and discussed. The results obtained indicated that the cryostat is capable to sustain the pressure and the thermal loads generated by the accident conditions. It is also worthy to remark that these results (raw outcomes) will be used for a further detailed investigation of the structural performances of cryostat itself

experimental investigation of functional performance of a vacuum vessel pressure suppression system of iter

Abstract Important challenges for fusion technology deal with the design of safety systems aimed to protect the Vacuum Vessel (VV) from pressurizing accidents like the Loss Of Coolant Accident (LOCA). To prevent or mitigate structural damages, the solution proposed is a safety system able to quickly condense released steam in cold water at sub-atmospheric conditions. This water suppression tank (VVPSS) is so aiming at limiting the maximum pressure in the VV to 0.2 MPa during in-vessel coolant leak events and at maintaining the VV long-term pressure below atmospheric pressure during air or incondensable gases ingress, through the Direct Contact Condensation (DCC). The novelty of this study resides especially in the working condition of VVPSS, which operates precisely to sub-atmospheric pressure: up to date no explicit experimental data or investigation of DCC are in fact available in literature. To overcome this lack an extensive experimental work has been done at DICI – University of Pisa, where numerous condensation tests (more than 300) were performed. The operation condition investigated took into account downstream pressure between 30 and 117 kPa and water pool temperature from 30 up to 85 °C. The experimental measurements allow to study the influence of steam mass flux, water temperature and pool pressure on the steam condensation phenomenon (and in turn, based on the stable condensation regime, correctly analyze the design parameter of VVPSS). The results obtained are presented and discussed. Innovative condensation regime maps are in addition provided

experimental investigation of steam condensation in water tank at sub atmospheric pressure

Abstract The International Thermonuclear Experimental Reactor (ITER) Vacuum Vessel Pressure Suppression System (VVPSS) limits the Vacuum Vessel (VV) internal pressure, in case of loss of coolant (LOCA) or other pressurizing accidents from the in-vessel components, to 150 kPa (abs). This is key safety function because a large internal pressure could lead to a breach of the primary confinement barrier. Safety is ensured by discharging the steam evolved during the accident event to the VVPSS suppression tanks where it is condensed. Steam condensation occurs at sub-atmospheric pressure condition. Moreover, being this latter not standard for traditional nuclear systems, this investigation is quite new (not studied in detail before) and deals with an experimental investigation of the direct contact condensation at VVPSS prototypical thermal-hydraulic conditions. To the purpose, a small-scale experimental rig was properly designed and built at Lab. B. Guerrini of DICI-University of Pisa as well as different temperature, pressure and steam mass (flow rate per hole) conditions and sparger patterns have been investigated. The experimental test matrix is also presented in this study. The obtained results show high efficiency of condensation for all examined conditions. The main condensation regimes at sub-atmospheric pressure conditions were identified. In addition, a comparison was done between the condensation regimes experimentally determined and those available in the literature, which were obtained at atmospheric pressure. Finally, results demonstrated to be representative of the real configuration at ITER reactor

Mechanisms underlying activity of antiretroviral drugs in HIV-1-infected macrophages: New therapeutic strategies

Monocyte-derived macrophages (M/M) are considered the second cellular target of HIV-1 and a crucial virus reservoir. M/M are widely distributed in all tissues and organs, including the CNS, where they represent the most common HIV-infected cells. Differently from activated CD4+ T lymphocytes, M/M are resistant to the cytopathic effect of HIV and survive HIV infection for a long lime. Moreover, HIV-1 replication in M/M is a key pathogenetic event during the course of HIV-1 infection. Overall findings strongly support the clinical relevance of anti-HIV drugs in M/M. Nucleoside RT inhibitors (NRTIs) are more active against HIV in M/M than in CD4+ T lymphocytes. Their activity is further boosted by the presence of an additional monophosphate group (i.e., a phosphonate group, as in the case of Tenofovir), thus overcoming the bottleneck of the low phosphorylation ability of M/M. In contrast, the antiviral activity of non-NRTIs (not affecting the DNA chain elongation) in M/M is similar to that in CD4+ T lymphocytes. Protease inhibitors are the only clinically approved drugs acting at a late stage of the HIV lifecycle. They are able to interfere with HIV replication in HIV-1 chronically infected M/M, even if at concentrations greater than those observed in HIV-1 chronically infected CD4+ T lymphocytes. Finally, several new drugs have been shown to interfere efficiently with HIV replication in M/M, including entry inhibitors. A better understanding of the activity of the anti-HIV drugs in M/M may represent a key element for the design of effective anti-HIV chemotherapy. © Society for Leukocyte Biology

Sloshing effects in innovative nuclear reactor pressure vessels

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.The reactor pressure vessel is a cylindrical shell structure which contains a rather large amount of liquid and many structures. Therefore, the fluid-structure interaction problems and the free oscillation of an incompressible liquid have attracted the attention because during a postulated earthquake (e.g. Design Basis Earthquake) the primary coolant surrounding the internals is accelerated and a significant fluid-structure hydrodynamic interaction is induced: in particular, the so called coolant “sloshing” influence on the stress level in the RPV. This effect is mainly important in the case of liquid metal primary coolant case and its coupling with the reactor vessel and its internals are considered. Numerical modelling proved to be very useful for the foreseen structures analysis because neither linear nor second-order potential theory is directly applicable when steep waves are present and high-order effects are significant. In what follow numerical results are presented and discussed highlighting the importance of the fluid-structure interaction effects in terms of stress intensity and were also used in order to obtain a preliminary validation of the numerical approach/models in comparison with experimental data.cs201

Numerical-experimental analyses by Hot-Wire method of an alumina cylinder for future studies on thermal conductivity of the fusion breeder materials

The determination of the thermal conductivity of breeder materials is one of the main goal in order to find the best candidate material for the fusion reactor technology. Experimental tests have been and will be carried out with a dedicated experimental devices, built at the Department of Civil and Industrial Engineering of the University of Pisa. The methodological approach used in doing that is characterized by two main phases strictly interrelated each other: the first one focused on the experimental evaluation of thermal conductivity of a ceramic material, by means of hot wire method, to be subsequently used in the second phase, based on the test rig method, to determine the thermal conductivity of pebble bed material. To the purpose, two different experimental devices have been designed and built. This paper deals with the first phase of the methodology. In this framework, the equipment set up and built to perform Hot wire tests, the ceramic material (a cylinder of alumina), the experimental procedure and the measured results obtained varying the temperature, are presented and discussed. The experimental campaign has been lead from 50°C up to 400°C. The thermal conductivity of the ceramic material at different bulk temperatures has been obtained in stationary conditions (detected on the basis of the temperature values measured during the experiment). Numerical analyses have been also performed by means of FEM code Ansys©. The numerical results were in quite good agreement with the experimental one, confirming also the reliability of code in reproducing heat transfer phenomena

Multidrug Resistance (MDR): A Widespread Phenomenon in Pharmacological Therapies

Multidrug resistance is a leading concern in public health. It describes a complex phenotype whose predominant feature is resistance to a wide range of structurally unrelated cytotoxic compounds, many of which are anticancer agents. Multidrug resistance may be also related to antimicrobial drugs, and is known to be one of the most serious global public health threats of this century. Indeed, this phenomenon has increased both mortality and morbidity as a consequence of treatment failures and its incidence in healthcare costs. The large amounts of antibiotics used in human therapies, as well as for farm animals and even for fishes in aquaculture, resulted in the selection of pathogenic bacteria resistant to multiple drugs. It is not negligible that the ongoing COVID‐19 pandemic may further contribute to antimicrobial resistance. In this paper, multidrug resistance and antimicrobial resistance are underlined, focusing on the therapeutic options to overcome these obstacles in drug treatments. Lastly, some recent studies on nanodrug delivery systems have been reviewed since they may represent a significant approach for overcoming resistance

Functional magnetic resonance imaging in the evaluation of the elastic properties of ascending aortic aneurysm

Objective: To evaluate the aortic wall elasticity using the maximal rate of systolic distension (MRSD) and maximal rate of diastolic recoil (MRDR) and their correlation with the aortic size index (ASI). Methods: Forty-eight patients with thoracic aortic aneurysm were enrolled in this study. A standard magnetic resonance imaging (MRI) protocol was used to calculate MRSD and MRDR. Both MRSD and MRDR were expressed as percentile of maximal area/10-3 sec. ASI (maximal aortic diameter/body surface area) was calculated. A correlation between MRSD, MRDR, ASI, and the patient’s age was performed using regression plot. Results: A significant correlation between MRSD (t=-4,36; r2=0.29; P≤0.0001), MRDR (t=3.92; r2=0.25; P=0.0003), and ASI (25±4.33 mm/m2; range 15,48-35,14 mm/m2) is observed. As ASI increases, aortic MRSD and MRDR decrease. Such inverse correlation between MRSD, MRDR, and ASI indicates increased stiffness of the ascending aorta. A significant correlation between the patient’s age and the decrease in MRSD and MRDR is observed. Conclusion: MRSD and MRDR are significantly correlated with ASI and the patient’s age. They seem to describe properly the increasing stiffness of aortas. These two new indexes provide a promising, accessible, and reproducible approach to evaluate the