Numerical simulation of radionuclides migration in the far field of a geological repository

Safety conditions associated with geological repositories must be guaranteed also in the case of radionuclides migrating from the near field to the far field of a geological repository and to the external environment. For this reason the migration process of radionuclides and the factors affecting the process patterns have a crucial importance. In the present article, in order to simulate the migration process of radionuclides in the far-field of a geological repository, the groundwater simulation code PMWIN (Processing Modflow) is used, following a methodology applied by the same authors in a previous work. The present case study refers to a non-uniform groundwater flow field and shows the influence of two important parameters, the distribution coefficient and the hydraulic gradient. The results are compared with the ones previously obtained for the uniform flow case and the different scenarios are discussed

Exergy analysis of a PWR nuclear steam supply system – Part I, general theoretical model

The paper provides an alternative, novel methodology to perform the exergetic analysis of a Pressurized Nuclear Reactor (PWR) based on the strictest definition of fission temperature to get to a careful evaluation of Exergy Destruction and exergetic Efficiency of the component. Up today, the exegetic analyses of Nuclear Power Plants (NPP) have been based on the assumption that Fission Exergy and Fission Energy are almost the same having assumed Carnot Factor almost equal to 1 as Tfiss >>T0. This assumption is based on some simplified hypotheses concerning fission temperature as applied in the definition of the Fission Exergy itself, whose value, to the best knowledge of the authors, was never modeled. On the contrary, in the first part of the paper, the authors present the results of an ongoing research, just aimed at evaluating the Exergy efficiency of the heat exchange in a PWR reactor, whose first results were already presented in [1], based on the most detailed modeling of Tfiss. The modeling, referring to a steady-state operational mode of the Reactor, takes into account all heat transfer phenomena between nuclear fuel UO2, its Zircaloy clad, cooling water, vessel material and the external environment. In the second part of the paper, the Exergy analysis is extended to all main Reactor Cooling System components (Vertical recirculating type Steam Generator, primary coolant pump and piping) with the aim to compare the Exergy Destructions and exergetic Efficiencies of the RPV with those of the other components of the Nuclear Steam Supply System, NSSS. In the Part II of the same paper,, "Exergy Analysis of a PWR Nuclear Steam Supply System - II part: a case study ", a test case is exemplified with the aim to compare the results obtained applying the methodology in question with those obtained applying the most established methodology adopted by other authors

Exergy analysis of a PWR nuclear steam supply system - II part: a case study

The paper shows the results of the exergetic analysis of the Nuclear Steam Supply System (NSSS) of the MARS Pressurized Light Water Reactor using the theoretical methodology described in the authors’ previous works [1] and [2]. The analysis firstly aims at a novel assessment of the irreversibilities occurred in the nuclear reactor vessel to compare the results, in terms of Exergy Destruction and exergetic Efficiency, with those obtained adopting one of the most employed methodology as reference. The comparison showed that a detailed exergetic analysis, mainly aimed to strictly assess the fission temperature, can lead to a higher estimate of the PWR exergetic Efficiency values

Exergy analysis of a PWR core heat transfer

The exergetic analysis, a methodology of thermodynamics that quantifies of energy losses associated with irreversibility, allows to optimize the efficiencies of the various stages of a transformation process and thus its overall efficiency. In this contribution, a novel approach to the exergetic analysis is applied to the energy transformations taking place within the core of a nuclear reactor. To perform such analysis, reference was made to a pressurized light-water reactor (PWR), modeling the heat exchanges between the fuel assemblies and the coolant fluid in the core through the balance of incoming and outgoing mass and energy flows, incoming and outgoing the reactor. The results of the analysis are validated through a comparison with the actual reactor operating parameters. The main goals of the work –part of a wider ongoing research effort- are to develop the thermo-economic analysis of a PWR nuclear power plant (NPP) to assess the actual cost of the products obtainable downstream of the NPP (electric energy and thermal energy for industrial and civil users, very different products in terms of exergy contents), and to compare with the costs of similar products obtained from conventional thermal power plants

Numerical analysis of temperature stratification in the CIRCE pool facility

In the framework of Heavy Liquid Metal (HLM) GEN IV Nuclear reactor development, the focus is in the combination of security and performance. Numerical simulations with Computational Fluid Dynamics (CFD) or system codes are useful tools to predict the main steady-state phenomena and how transitional accidents could unfold in GEN IV reactors. In this paper, to support the validation of CFD as a valid tool for the design, the capability of ANSYS CFX v15.0 to simulate and reproduce mixed natural convection and thermal stratification phenomena inside a pool is investigated. The 3D numerical model is based on the CIRCE facility, located in C.R. ENEA Brasimone. It is a pool facility, structured with all the components necessary to simulate the behavior of an HLM reactor, where LBE flows into the primary circuit. For the analysis, the LBE physical properties are implemented in CFX by using recent NEA equations [2]. Previously published RELAP5-3D© results [1] are employed to derive accurate boundary conditions for the simulation of the steady-state conditions in the pool and for CFX validation. The analysis focuses on the pool natural circulation with the presence of thermal structures in contact with LBE, considered as constant temperature sources. The development of thermal stratification in the pool is observed and evaluated with a mesh sensitivity analysis

LE VARIETÀ LINGUISTICHE IN CONTESTO INFORMALE: UNO STUDIO DI CASO DI UNA FAMIGLIA ITALIANA IN BRASILE

L’obiettivo di questa indagine è di documentare le varietà linguistiche in uso in un contesto intrafamiliare di tipo informale. Lo studio di caso che presentiamo ha come protagonisti i membri di una famiglia veneta con un livello di qualificazione medio-alta che in seguito all’ultima grande crisi economica mondiale del 2008 si sono trasferiti in Brasile. Questa indagine si inserisce all’interno degli studi sull’ecologia linguistica in contesti familiari e si è basata sull’analisi di una videoregistrazione avvenuta nel corso della consumazione del pranzo e di un questionario. L’analisi mostra che anche se l’italiano rimane il codice prevalente per tutti i membri della famiglia si nota una disinvoltura da un codice ad un altro (italiano, veneto e portoghese) che apre spazi a riflessioni metalinguistiche a livello lessicale. I codici del repertorio acquistano uno spazio di sovrapposizione ma al tempo stesso di demarcazione dei confini identitari laddove si voglia sottolineare la propria distanza dalla cultura ospite, ma anche in questo caso la commutazione avviene a seguito di una precisa volontà comunicativa. Il caso studio osservato permette di far emergere come nel caso di un plurilinguismo vissuto in termini di arricchimento tra le varietà del repertorio italiano/dialetto di cui dispongono i parlanti, l’inserimento della lingua del paese ospite si inserisce come ulteriore elemento di ricchezza accanto alla lingua di origine.   Language varieties in an informal context: a case study of an italian family in Brazil The aim of this survey is to document the language varieties used in an informal intra-family context. The case study focuses on a family with a medium-high level of education from the Veneto Region who, following the last major world economic crisis of 2008, moved to Brazil. This survey falls within studies on linguistic ecology in family contexts and is based on the analysis of a video recording made during a lunch and a questionnaire. The analysis shows that even if Italian remains the prevailing code for all family members, there is a casualness from one code to another (Italian, Venetian dialect and Portuguese) that creates space for metalinguistic reflections at the lexical level. The codes of the repertory overlap but at the same time there are clear boundaries that emphasize the distance from the host culture, although the switching takes place following a precise communicative will. The case study observed highlights how in the case of multilingualism experienced in terms of enrichment among the varieties of the Italian repertoire / dialect available to the speakers, the inclusion of the language of the host country becomes a further element of wealth in addition to the language of origin

Determination of the number of light neutrino species from single photon production at LEP

A determination of the number of light neutrino families performed by measuring the cross section of single photon production in \ee\ collision near the \Zo\ resonance is reported. From an integrated luminosity of $100~\mathrm{pb^{-1}}$, collected during the years 1991--94, we have observed 2091 single photon candidates with an energy above 1~\GeV\ in the polar angular region $45^\circ < \theta_\gamma < 135^\circ$. From a maximum likelihood fit to the single photon cross section, the \Zo\ decay width into invisible particles is measured to be \Ginv = 498 \pm 12 \mathrm{(stat)} \pm 12 \mathrm{(sys)~MeV}. Using the Standard Model couplings of neutrinos to the \Zo, the number of light neutrino species is determined to be $N_\nu = 2.98 \pm 0.07 (\mathrm{stat}) \pm 0.07 (\mathrm{sys}).

Search for R-Parity Breaking Sneutrino Exchange at LEP

We report on a search for R--parity breaking effects due to supersymmetric tau--sneutrino exchange in the reactions e+e- to e+e- and e+e- to mu+mu- at centre--of--mass energies from 91~{\GeV} to 172~{\GeV}, using the L3 detector at LEP. No evidence for deviations from the Standard Model expectations of the measured cross sections and forward--backward asymmetries for these reactions is found. Upper limits for the couplings $\lambda_{131}$ and $\lambda_{232}$ for sneutrino masses up to m_{\SNT} \leq 190~\GeV are determined from an analysis of the expected effects due to tau sneutrino exchange

Search for charged Higgs bosons in e+e−e^+ e^- collisions at centre-of-mass energies between 130 and 183 GeV

A search for pair-produced charged Higgs bosons is performed with the L3 detector at LEP using data collected at centre-of-mass energies from \mbox{130 to 183 \GeV{}}, corresponding to an integrated luminosity of 88.3 \pb. The Higgs decays into a charm and a strange quark or into a tau lepton and its associated neutrino are considered. The observed candidates are consistent with the expectations from Standard Model background processes. A lower limit of 57.5 \GeV{} on the charged Higgs mass is derived at 95\% CL, independent of the decay branching ratio \mathrm{Br(H^\pm\ra \tau\nu)}

Heavy Quarkonium Production in Z Decays

We report measurements of the inclusive production of heavy quarkonium states in $\mathrm {Z}$ decays based on the analysis of 3.6 million hadronic events collected by the L3 detector at LEP. The measurement of inclusive J production and an improved $95\%$ confidence level upper limit on $\Upsilon$ production are presented. In addition, two independent measurements of the ratio, $f_{\mathrm{p}}$, of prompt J mesons to those from B decay are made using two different isolation cuts to separate prompt J mesons from J mesons produced in the decays of b hadrons. The results are: % \begin{eqnarray} \mathrm{Br}(\mathrm{Z} \rightarrow \mathrm{J} + \mathrm{X}) & = & (3.21 \pm 0.21 \; \mathrm{(stat.)} \; ^{+ 0.19}_{- 0.28} \; \mathrm{(sys.)} ) \times 10^{-3} \; , \nonumber \\ \mathrm{Br}(\mathrm {Z} \rightarrow \Upsilon(\mathrm{1S} + X) & < & 4.4 \times 10^{-5} \; , \nonumber \\ %% f_{\mathrm{p}} & = & (7.1 \pm 2.1 \; \mathrm{(stat.)} \; \pm 1.2 \; \mathrm{(sys.)} \; ^{+1.5}_{-0.8} \;\mathrm{(theo.)} ) \times 10^{-2} \; . \nonumbe