The NILUS reactor for the co-production of electricity and potable water

The NILUS-1000 reactor, an innovative PWR with integrated layout and full natural circulation, is proposed for the adoption in those countries where the production of potable water is a major concern for the population, and where the nuclear culture could not be so developed and firmly established as the complexity of the nuclear industry would require. The NILUS concept is briefly depicted, together with the reference desalination process and plant size selected for the coupling with the 1000MWth nuclear reactor. The safety systems and the “hybrid” containment, a compact steel pressure containment with a pressure suppression pool, are described. The results of the preliminary safety analysis are reported for an ATWS accident, showing the validity of the concept design and the large grace period achieved in this beyond DBA transient

Monte Carlo Approach to Dynamic PSA: Neural Solution of Equations Describing Core Transients

The PSA analysis of a real plant represent a formidable com-putational task usually afforded either with an analytical approach based on the theory of the Markov chains or with a Monte Carlo simulation. In our opinion this latter methodology, thanks to its unique flexibility features, represents the only viable approach to the problem when time dependencies have impacts on the analy-sis: examples are time dependent transition rates (ageing), timing of the protection, control and safety systems, operator actions etc. Moreover the PSA analysis of a real plant demands taking into account the process variable dynamics when the evolution of the underlying physical process interacts with the system hardware configuration, e.g. when the process variables influence the failure rates or activate the protection systems. The inclusion of these dy-namic aspects dramatically burdens the analysis: a solution could be presently attempted only through short cuts to the solution of the deterministic equations governing the evolution of the process variables. In the present paper we consider the application of a multi-layered neural network for the solution of the mathematical mod-els related to the core behaviour of a PWR under varying thermal-hydraulic conditions. Since the neural network works very rapid-ly, this approach seems to be a good candidate for being included in a Monte Carlo dynamic PSA code which requires solving thou-sands of times the model equations relating to the different hard-ware plant configurations. Possible approximations thereby intro-duced could be tolerated if comparable with those following from the uncertainties of the stochastic parameters. The time reduction advantage is expected to increase when the future parallel com-puters become widely available

Plutonia-Thoria Fuel Cycle as Starting Solution for a wider Thorium Use

This paper is focused on a description of thoria fuel option. Our opinion is that this option, beyond being a valuable way to exploit the energy content of plutonium without further breeding it, may be a starting point for introducing an Uranium-Thorium fuel cycle, based on a different strategic context with respect to past proposals. The option is based on the adoption of current or advanced PWRs, the latter characterised by a reduced fuel power density, always adopting conventional fuel rods and assemblies. A three-batches full core loading scheme is assumed. The thoria-plutonia composition is determined by the constraints to obtain at Beginning Of Life (BOL) a non positive void coefficient, and to reach a burnup as high as possible. Different fuel compositions and pellet radius are considered. The plutonium content is in the range of 4.5÷15%, mainly depending on the plutonium quality, namely Weapon Grade (WG) or Reactor Grade (RG). The results are in terms of dynamic coefficients, life duration, plutonium consumption and final isotopic compositions. These fuels show the capability to destroy about 40÷60% of total plutonium for RG, while this figure rises to 65÷70% for WG. These values are well above those obtained by MOX option. A variant to eliminate any proliferation concern foresees the addition of small quantities of 238U at the expenses of a reduction of the fuel burnup and its capacity in burning RG plutonium, while the opposite occurs for WG. The low boron worth is not different from the MOX one, being related mainly to the plutonium content, and much less to the chosen fertile isotope. Therefore, modifications of control devices for a full core strategy is not expected to be different in the two cases. The results confirm the viability of this proposal, apt to future variants, including those connected to accelerator actinide burning solution. An irradiation experiment, expe-cted to take place at Halden HWBR in the context of the ENEA participation to the Halden Project, is the main part of the Inert Matrix – Thoria fuel R&D activity presently underway as a Polytechnic of Milan–ENEA co-operation

Why Are Radio-Galaxies Prolific Producers of Type Ia Supernovae?

An analysis of SNIa events in early type galaxies from the Cappellaro et al (1999) database provides conclusive evidence that the rate of type Ia Supernovae (SNe) in radio-loud galaxies is about 4 times higher than the rate measured in radio-quiet galaxies, i.e. SNIa-rate$(radio-loud galaxies) = 0.43^{+0.19}_{-0.14}h^2_{75}$ SNu as compared to SNIa-rate$(radio-quiet galaxies) = 0.11^{+0.06}_{-0.03}h^2_{75}$ SNu. The actual value of the enhancement is likely to be in the range $\sim 2-7$ (P$\sim 10^{-4}$). This finding puts on robust empirical grounds the results obtained by Della Valle & Panagia (2003) on the basis of a smaller sample of SNe. We analyse the possible causes of this result and conclude that the enhancement of SNIa explosion rate in radio-loud galaxies has the same origin as their being strong radio sources, but there is no causality link between the two phenomena. We argue that repeated episodes of interaction and/or mergers of early type galaxies with dwarf companions, on times-scale of about 1 Gyr, are responsible for inducing both strong radio activity observed in $\sim$14% of early type galaxies and to supply an adequate number of SNIa progenitors to the stellar population of ellipticals.Comment: 26 pages+6 figures, ApJ, in pres

A Feasibility Study of an Integral PWR for Space Applications

Fission space power systems are well suited to provide safe, reliable, economic and robust energy sources, in the order of 100 KWe. A preliminary feasibility study of a nuclear fission reactor is here presented with the following requirements: i) high reliability, ii) R&D program of moderate cost, iii) to be deployed within a reasonable period of time (e.g. 2015), iv) to be operated and controlled for a long time (10 years) without human intervention, v) possibly to be also used as a byproduct for some particular terrestrial application (or at least to share common technologies), vi) to start with stationary application. The driving idea is to extend as much as possible the PWR technology, by recurring to an integral type reactor. Two options are evaluated for the electricity production: a Rankine steam cycle and a Rankine organic fluid cycle. The neutronics calculation is based on WIMS code benchmarked with MCNP code. The reactivity control is envisaged by changing the core geometry. The resulting system appears viable and of reasonable size, well fit to the present space vector capabilities. Finally, a set of R&D needs has been identified: cold well, small steam turbines, fluid leakage control, pumps, shielding, steam generator in low-gravity conditions, self pressurizer, control system. A R&D program of reasonable extent may yield the needed answers, and some demanding researches are of interest for the new generation Light Water Reactors

Headache: Prevalence and relationship with office or ambulatory blood pressure in a general population sample (the Vobarno Study).

The association of headache and arterial hypertension is still controversial, although headache is usually considered a symptom of hypertension. The aim of this study is to evaluate the prevalence of headache in a general population sample and the relationship with arterial hypertension, as diagnosed by office measurements and ambulatory monitoring of blood pressure (BP).In the randomized sample of the Vobarno population, 301 subjects (126 males, 175 females, age range 35-50 years) underwent a structured standardized headache questionnaire, office and 24-h ambulatory BP monitoring.Prevalence of lifetime headache and of migraine was greater in females than in males. Office and 24-h BP values did not differ between subjects without headache and subjects with headache. No differences in headache prevalence (58% vs 55%), migraine prevalence (32% vs 28%) and use of analgesic drugs in the presence of headache (82% vs 78%) were observed between hypertensive patients (93.5% newly diagnosed, 6.5% treated) and normotensive subjects.In a general population sample, hypertension (diagnosed by office and/or 24-h BP) is not associated with headache

Occipital atrophy signature in prodromal Lewy bodies disease

Introduction: Dementia with Lewy bodies (DLB) is typically characterized by parietal, temporal, and occipital atrophy, but less is known about the newly defined prodromal phases. The objective of this study was to evaluate structural brain alterations in prodromal DLB (p-DLB) as compared to healthy controls (HC) and full-blown dementia (DLB-DEM). Methods: The study included 42 DLB patients (n = 20 p-DLB; n = 22 DLB-DEM) and 27 HC with a standardized neurological assessment and 3-tesla magnetic resonance imaging. Voxel-wise analyses on gray-matter and cortical thickness were implemented to evaluate differences between p-DLB, DLB-DEM, and HC. Results: p-DLB and DLB-DEM exhibited reduced occipital and posterior parieto-temporal volume and thickness, extending from prodromal to dementia stages. Occipital atrophy was more sensitive than insular atrophy in differentiating p-DLB and HC. Occipital atrophy correlated to frontotemporal structural damage increasing from p-DLB to DLB-DEM. Discussion: Occipital and posterior-temporal structural alterations are an early signature of the DLB continuum and correlate with a long-distance pattern of atrophy

Cortical Inhibitory Imbalance in functional paralysis

Background: Functional neurological disorders are characterized by neurological symptoms that have no identifiable pathology and little is known about their underlying pathophysiology. Objectives: To analyze motor cortex excitability and intracortical inhibitory and excitatory circuits' imbalance in patients with flaccid functional weakness. Methods: Twenty-one consecutive patients with acute onset of flaccid functional weakness were recruited. Single and paired-pulse transcranial magnetic stimulation (TMS) protocols were used to analyze resting motor thresholds (RMT) and intracortical inhibitory (short interval intracortical inhibition - SICI) and excitatory (intracortical facilitation - ICF) circuits' imbalance between the affected and non-affected motor cortices. Results: We observed a significant increase in RMT and SICI in the affected motor cortex (p < 0.001), but not for ICF, compared to the contralateral unaffected side. Conclusion: This study extends current knowledge of functional weakness, arguing for a specific central nervous system abnormality which may be involved in the symptoms' pathophysiology

The colours of BL Lac objects: a new approach to their classification

We selected a sample of 437 BL Lac objects, taken from the RomaBZCat catalogue, for which spectroscopic information and SDSS photometry is available. We propose a new classification of BL Lacs in which the sources' type is not defined only on the basis of the peak frequency of the synchrotron component in their Spectral Energy Distribution (types L and H), but also on the relevance of this component with respect to the brightness of the host galaxy (types N and G, for nuclear or galaxy dominated sources). We found that the SDSS colour index u-r=1.4 is a good separator between these two types. We used multiband colour-colour plots to study the properties of the BL Lac classes and found that in the X-ray to radio flux ratio vs u-r plot most of the N (blue) sources are located in a rather narrow strip, while the G-sources (red) are spread in a large area, and most of them are located in galaxy clusters or interacting systems, suggesting that their X-ray emission is not from a genuine BL Lac nucleus but it is related to their environment. Of the about 135 sources detected in the gamma-rays by Fermi-GST, nearly all belong to the N-type, indicating that only this type of sources should be considered as genuine BL Lac nuclei. The J-H, H-K plot of sources detected in the 2MASS catalogue is consistent with that of the "bona fide" BL Lac objects, independently of their N or G classification from the optical indices, indicating the existence in G-type sources of a K-band excess possibly due to a steep, low frequency peaked emission which deserves further investigations. We propose to use these colour plots as a further tool for searching candidate counterparts of newly discovered high-energy sources.Comment: 11 pages, 7 figures. Submitted 29/08/2011 to MNRAS, first referee report received 31/10/2011, accepted 21/02/201

Brain Connectivity and Information-Flow Breakdown Revealed by a Minimum Spanning Tree-Based Analysis of MRI Data in Behavioral Variant Frontotemporal Dementia

Brain functional disruption and cognitive shortfalls as consequences of neurodegeneration are among the most investigated aspects in current clinical research. Traditionally, specific anatomical and behavioral traits have been associated with neurodegeneration, thus directly translatable in clinical terms. However, these qualitative traits, do not account for the extensive information flow breakdown within the functional brain network that deeply affect cognitive skills. Behavioural variant Frontotemporal Dementia (bvFTD) is a neurodegenerative disorder characterized by behavioral and executive functions disturbances. Deviations from the physiological cognitive functioning can be accurately inferred and modeled from functional connectivity alterations. Although the need for unbiased metrics is still an open issue in imaging studies, the graph-theory approach applied to neuroimaging techniques is becoming popular in the study of brain dysfunction. In this work, we assessed the global connectivity and topological alterations among brain regions in bvFTD patients using a minimum spanning tree (MST) based analysis of resting state functional MRI (rs-fMRI) data. Whilst several graph theoretical methods require arbitrary criteria (including the choice of network construction thresholds and weight normalization methods), MST is an unambiguous modeling solution, ensuring accuracy, robustness, and reproducibility. MST networks of 116 regions of interest (ROIs) were built on wavelet correlation matrices, extracted from 41 bvFTD patients and 39 healthy controls (HC). We observed a global fragmentation of the functional network backbone with severe disruption of information-flow highways. Frontotemporal areas were less compact, more isolated, and concentrated in less integrated structures, respect to healthy subjects. Our results reflected such complex breakdown of the frontal and temporal areas at both intra-regional and long-range connections. Our findings highlighted that MST, in conjunction with rs-fMRI data, was an effective method for quantifying and detecting functional brain network impairments, leading to characteristic bvFTD cognitive, social, and executive functions disorders