Analisi CFD del miscelamento di refrigerante nel vessel di un reattore nucleare VVER-1000

Analisi con il codice CFD ANSYS CFX 10.0 dei fenomeni di miscelamento di refrigerante nel vessel di un reattore nucleare VVER-100

Wideband SATCOM Model: Evaluation of Numerical Accuracy and Efficiency

The spectral method is typically applied as a simple and efficient method to solve the parabolic wave equation in phase screen scintillation models. The critical factors that can greatly affect the spectral method accuracy is the uniformity and smoothness of the input function. This paper observes these effects on the accuracy of the finite difference and the spectral methods applied to a wideband SATCOM signal propagation model simulated in the ultra-high frequency (UHF) band. The finite difference method uses local pointwise approximations to calculate a derivative. The spectral method uses global trigonometric interpolants that achieve remarkable accuracy for continuously differentiable functions. The differences in accuracy are presented for a Gaussian lens and Kolmogorov phase screen. The results demonstrate loss of accuracy in each method when a phase screen is applied, despite the spectral method\u27s computational efficiency over the finite difference method. These results provide meaningful insights when discretizing an interior domain and solving the parabolic wave equation to obtain amplitude and phase of a signal perturbation

High discharge rate characteristics of nickel-cadmium batteries for pulse load filtering

Several tests of specially fabricated nickel-cadmium batteries having circular disk type electrodes were considered. These batteries were evaluated as filter elements between a constant current power supply and a five hertz pulsed load demanding approximately twice the power supply current during the load on portion of the cycle. Short tests lasting 10,000 cycles were conducted at up to a 21 C rate and an equivalent energy density of over 40 Joules per pound. In addition, two batteries were subjected to 10 to the 7 charge/discharge cycles, one at a 6.5 C rate and the other at a 13 C rate. Assuming an electrode to battery weight ratio of 0.5, these tests represent an energy density of about 7 and 14 Joules per pound respectively. Energy density, efficiency, capacitance, average voltage, and available capacity were tracked during these tests. After 10 to the 7 cycles, capacity degradation was negligible for one battery and about 20% for the other. Cadmium electrode failure may be the factor limiting lifetime at extremely low depth of discharge cycling. The output was examined and a simple equivalent circuit was proposed

Application of a Finite-Volume Time-Domain Technique to Three-Dimensional Objects

Concurrent engineering approaches for the disciplines of computational fluid dynamics (CFD) and electromagnetics (CEM) are necessary for designing future high-performance aircraft. A characteristic-based finite-volume time-domain (FVTD) computational algorithm, used by CFD and now applied toCEM, is implemented to analyze the radar cross section (RCS) of the ogive and cone-sphere. The technique utilizes a scattered-field formulation of the time-dependent Maxwell equations. The FVTD formulation implements a monotone upstream-centered scheme for conservation laws for the flux evaluation and a Runge-Kutta multi-stage scheme for the time integration. The results are obtained from the electromagnetic fields via a Fourier transform and a near-to-far field transformation

Role of CFD Analysis in Nuclear Reactor Licensing and Design

Computational Fluid Dynamics (CFD) is a well-established industrial design tool for non-nuclear applications, helping to reduce design time scales and to improve processes throughout the engineering world, providing a cost-effective and accurate alternative to scale model testing. Within the Nuclear Reactor Safety (NRS) framework, the traditionally adopted tools for safety analysis evaluation (i.e. integral thermal-hydraulic codes) are not capable of predicting the effect of inherently three-dimensional flow fields and mixing phenomena in complex geometries, therefore the application of is considered to potentially bring real benefits in terms of deeper understanding of involved phenomena and of increased safety. However, CFD tools are considered not yet fully mature to be applied to nuclear safety related problems since further code assessment is still necessary. Nevertheless, the intensive code development and assessment work carried out in recent years and the dramatic increase in computing power are quite promising, and CFD already plays an important role as a support tool for NRS analysis. In this framework, the present thesis provides a contribution to the definition of the possible current role and the future perspectives of the application of CFD tools to NRS problems within both a licensing and a design framework. In particular, the present research activity focused on the implementation of CFD techniques within a best estimate methodology to address the licensing analysis of a Nuclear Power Plant (NPP), namely the analysis of the Double Ended Guillotine Break Loss Of Coolant Accident (DEGB-LOCA or 2A-LOCA) scenario of the Atucha-II NPP (CNA-2), which is included into the Chapter 15 of its Final Safety Analysis Report (FSAR). The adopted methodology implies the coupled application of best estimate thermal-hydraulic, neutron physics and fuel pin performance computer codes, together with the evaluation of the related uncertainties. A systematic and integrated application of CFD techniques to NRS analysis for licensing purposes is presented, able to go beyond state-of-the-art approaches in this field of application. The present research is also contributing to the assessment of CFD codes in their application to problems related to nuclear safety and technology

CFD Code Validation against Stratified Air-Water Flow Experimental Data

Pressurized thermal shock (PTS) modelling has been identified as one of the most important industrial needs related to nuclear reactor safety. A severe PTS scenario limiting the reactor pressure vessel (RPV) lifetime is the cold water emergency core cooling (ECC) injection into the cold leg during a loss of coolant accident (LOCA). Since it represents a big challenge for numerical simulations, this scenario was selected within the European Platform for Nuclear Reactor Simulations (NURESIM) Integrated Project as a reference two-phase problem for computational fluid dynamics (CFDs) code validation. This paper presents a CFD analysis of a stratified air-water flow experimental investigation performed at the Institut de Mécanique des Fluides de Toulouse in 1985, which shares some common physical features with the ECC injection in PWR cold leg. Numerical simulations have been carried out with two commercial codes (Fluent and Ansys CFX), and a research code (NEPTUNE CFD). The aim of this work, carried out at the University of Pisa within the NURESIM IP, is to validate the free surface flow model implemented in the codes against experimental data, and to perform code-to-code benchmarking. Obtained results suggest the relevance of three-dimensional effects and stress the importance of a suitable interface drag modelling

Instrumenting Full scale Boron Injection Test Facility to support Atucha-2 NPP licensing

The Atucha-2 Pressurized Heavy Water Reactor is equipped with a back-up shutdown system based on the fast injection of boron into the moderator tank. Such system had initially been designed to cope with a 10%-area (0.1A) break Loss Of Coolant Accident (LOCA) scenario, but based on upgraded licensing requirements the design had to be revised and possibly improved against a double-ended guillotine (2A) break LOCA. In particular, the boron injection had to be proven fast enough to allow a timely shutdown of the reactor, even in the case of a failure of the primary shutdown system (control rods). A full-scale test facility was built for such “design validation” purpose, in the framework of a cooperation program between the University of Pisa – San Piero a Grado Nuclear Research Group (GRNSPG) and the utility Nucleoeléctrica Argentina S.A. (NA-SA). A special instrumentation system, based on conductivity probes designed on purpose by the Helmholtz Zentrum Dresden-Rossendorf (HZDR), was adopted for the measurement of the injection delay, as well as for the monitoring of pressure at several key locations. Care was taken to reproduce the relevant NPP conditions as closely as possible to those expected on the basis of extensive safety analyses performed adopting a Best Estimate Plus Uncertainty (BEPU) approach. In this respect, not only the test facility is full-scale, but also the key components (such as the fast opening air valves, the boric acid tanks, the rupture device, the injection lance) were directly borrowed from the Atucha-2 NPP. The experimental campaign carried out by NA-SA on such test facility allowed to improve the design of the boron injection system (especially as to some fluid-structure interaction issues) and finally to achieve the main goal, i.e. the demonstration that the system’s performance is fast enough to assure a timely and safe shutdown of the reactor. This was a key contribution to the successful completion of the NPP licensing process

Inhibition of cell cycle progression by the hydroxytyrosol-cetuximab combination yields enhanced chemotherapeutic efficacy in colon cancer cells

Hydroxytyrosol (HT), a polyphenol of olive oil, downregulates epidermal growth factor (EGFR) expression and inhibits cell proliferation in colon cancer (CC) cells, with mechanisms similar to that activated by the EGFR inhibitor, cetuximab. Here, we studied whether HT treatment would enhance the cetuximab inhibitory effects on cell growth in CC cells. HT-cetuximab combination showed greater efficacy in reducing cell growth in HT- 29 and WiDr cells at concentrations 10 times lower than when used as single agents. This reduction was clearly linked to cell cycle blockade, occurring at G2/M phase. The cell cycle arrest in response to combination treatment is related to cyclins B, D1, and E, and cyclin-dependent kinase (CDK) 2, CDK4, and CDK6 down-regulation, and to the concomitant over-expression of CDK inhibitors p21 and p27. HT and cetuximab stimulated a caspase-independent cell death cascade, promotedtranslocation of apoptosis-inducing factor (AIF) from mitochondria to nucleus and activated the autophagy process. Notably, normal colon cells and keratinocytes were less susceptible to comboinduced cell death and EGFR downregulation. These results suggest a potential role of diet, containing olive oil, during cetuximab chemotherapy of colon tumor. HT may be a competent therapeutic agent in CC enhancing the effects of EGFR inhibitors

Involvement of bradykinin B2 receptor in pathological vascularization in oxygen-induced retinopathy in mice and rabbit cornea

The identification of components of the kallikrein-kinin system in the vitreous from patients with microvascular retinal diseases suggests that bradykinin (BK) signaling may contribute to pathogenesis of retinal vascular complications. BK receptor 2 (B2R) signaling has been implicated in both pro-inflammatory and pro-angiogenic effects promoted by BK. Here, we investigated the role of BK/B2R signaling in the retinal neovascularization in the oxygen-induced retinopathy (OIR) model. Blockade of B2R signaling by the antagonist fasitibant delayed retinal vascularization in mouse pups, indicating that the retinal endothelium is a target of the BK/B2R system. In the rabbit cornea assay, a model of pathological neoangiogenesis, the B2 agonist kallidin induced vessel sprouting and promoted cornea opacity, a sign of edema and tissue inflammation. In agreement with these results, in the OIR model, a blockade of B2R signaling significantly reduced retinal neovascularization, as determined by the area of retinal tufts, and, in the retinal vessel, it also reduced vascular endothelial growth factor and fibroblast growth factor-2 expression. All together, these findings show that B2R blockade reduces retinal neovascularization and inhibits the expression of proangiogenic and pro-inflammatory cytokines, suggesting that targeting B2R signaling may be an effective strategy for treating ischemic retinopathy

Enhanced Nuclear Engineering Simulators

Engineering simulation is a sophisticated multi-purpose technology allowing the users of simulators to run a variety of engineering activities due to the possibility of modifying the simulated plant architecture and components, to adjust parameters, to test alternative solutions. Engineering Simulators (ES) have been built and used worldwide for a variety of purposes: - Development and refinement of the plant design or plant modifications - Safety analyses focused on the overall system behaviour - Verification and Validation (V&V) of systems and components - Development of Operational and Emergency Procedures - Pre-Training of operators and supervisors - High level education and Communication activities - Human Factor Engineering Analysis - Adaptive Control System training Engineering Simulators also play a role in developing and maintaining key nuclear skills, as knowledge repositories and tools for training at various levels of expertise